FOUS30 KWBC 021955
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Fri Oct 02 2020

Day 1
Valid 16Z Fri Oct 02 2020 - 12Z Sat Oct 03 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
FAR SOUTHERN FLORIDA...

...Southern Florida...
16Z Update: No significant changes were made to the outlook at
this time. A combination of deep, tropical moisture (PW over 2
inches), moderate instability with a tall, narrow CAPE profile,
and deep layer mean wind around 5 knots should support rain rates
in excess of 2 inches per hour if strong convection redevelops.
One potential issue could be a canopy of mid-high level cloud
cover from a cluster of convection about 70mi NW of Key West (at
1530Z) over the Gulf of Mexico. That could restrict instability
more than models are projecting and limit convective intensity
today. Nevertheless, the overall environment is sufficiently
supportive of very heavy rain rates that the Slight Risk area is
maintained.

Previous Discussion: A deep upper level longwave trough positioned
across the eastern two-thirds of the CONUS will remain anchored
through the forecast period as a series of shortwaves help to
sharpen a jet across the Southeast coast. As a result, upper
level divergence will strengthen atop of a quasi-stationary
surface front draped over southern Florida. The tropical airmass,
along and south of this boundary, is clearly depicted by
precipitable water values ranging between 2-2.25 inches and
MUCAPE values around 500-1000 J/kg. With sufficient large scale
lift, confluent low level flow, moisture and instability in place,
anticipate efficient rain rates, similar to what has been observed
over the past 24 hours. With steering flow out of the southwest
and boundary layer easterly winds, anticipate storms to be slow
moving, potentially backbuilding, along/south of the
aforementioned boundary. This will inevitably exacerbate hourly
rainfall totals.

According to the latest 00Z high resolution model guidance, hourly
rain rates may reach 2-3 inches per hour which is supported by the
above thermodynamics and the latest HREF neighborhood
probabilities. And based on the position of the surface front,
expect the highest rainfall totals through early Saturday to occur
across portions of far southern and southeastern FL. Areal
average precipitation will range between 1-3 inches with locally
higher amounts anticipated. Given the wet antecedent conditions
and the latest uptick in WPC QPF across portions of southern FL,
the Slight Risk was extended south and west with the Marginal Risk
expanded as well. Therefore, anticipate localized to scattered
flash flooding, especially across locations that have already
observed quite a bit of rain through the past 24 hours (along
portions of the east-central FL coast) and over urban corridors.

Pagano


Day 2
Valid 12Z Sat Oct 03 2020 - 12Z Sun Oct 04 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE
ATLANTIC COAST OF FLORIDA...


...Florida...

20 UTC update...

Only minor adjustments were needed for this update to the day 2
excessive rainfall outlook based on the latest guidance. Previous
setup and thoughts as described below still stand. A slight risk
remains along the Florida Atlantic Coast from roughly Miami to
north of Daytona Beach, with a marginal risk covering the
remainder of the southern two thirds of the Peninsula.

Santorelli

Previous discussion issued at 0754 UTC...

A favorable setup for periods of heavy rainfall will continue
Saturday as a stationary boundary lingers across the Florida
Peninsula. During Saturday, this front will likely begin to lift
northward as a warm front, spreading better instability and
moisture northward as far as the First Coast. This front will
retreat to the northwest both in response to increased low-level
ridging off the Southeast Coast, and the approach of an amplifying
longwave trough which should dig into the TN Valley by Sunday
morning. The NW displacement of this front will drive instability
as high as 1500 J/kg MUCape across much of the southern half of
the Peninsula and along most of the Atlantic Coast, with PWs also
surging above 2.25", approaching +3 standard deviations above the
climo mean, and near or above daily records according to the SPC
sounding climatology. These favorable thermodynamics will be acted
upon by a strengthening upper jet streak leaving the favorable
diffluent RRQ and an upper divergence maxima across the state,
with 850mb S/SE inflow increasing to 20-30 kts to drive deep layer
ascent progged by omega maxima spreading northward. A lack of bulk
shear indicates that storms may be of the pulse variety Saturday,
however, training along the front and parallel to the upper jet
streak suggests training will be of concern, with some
backbuilding possible along the Atlantic Coast as the front lifts
northward. Parts of the east coast of FL have received excessive
rainfall in the past 24 hours, with additional heavy rain likely
on Friday. Depending on where the heavy rain occurs on D1, an
expansion of the SLGT risk may be needed, but at this time the
greatest threat for flash flooding appears to be confined to the
east coast where antecedent rainfall has been greatest and
ensemble probabilities for 3" are the highest. The MRGL risk
covers much of the rest of the peninsula where periods of heavy
rainfall are possible.

Weiss



Day 3
Valid 12Z Sun Oct 04 2020 - 12Z Mon Oct 05 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN AND CENTRAL FLORIDA...

20 UTC update...

Only notable change to the previous day 3 excessive rainfall
outlook was to expand the slight risk a bit to the southwest to
include the Tampa Bay region. This is due to slight model
increases in QPF for that region, likely associated with moisture
ahead of newly upgraded T.D. Twenty-Five located near the Yucatan
Peninsula. See previous discussion for more details regarding both
Florida and the marginal risk along coastal North Carolina.

Santorelli


Previous Discussion issued at 0755 UTC...

...Florida...
A continuation of heavy rainfall from Saturday is likely on
Sunday, but with a northern displacement and potential enhancement
across parts of Northern Florida.

Nearly stalled warm front will linger across the central or
northern part of the Florida Peninsula Sunday. This boundary will
serve as a focus for thunderstorms, with a sharp moisture and
instability gradient developing along it. At the same time, a
sharpening longwave trough will be pushing eastward into the
Southern Appalachians, with a downstream jet streak becoming more
significantly poleward oriented and strengthening to a core of
150+ kts across ME, above the 97th percentile for wind speed for
early October. This leaves a robust diffluent RRQ atop Florida,
with a divergence maxima lingering in place across the Southeast.
The lift associated with this RRQ will likely drive stronger
frontogenesis along the baroclinic zone, enhancing low-level
convergence to drive robust deep layer ascent. Additionally, the
overlap of upper ventilation and low-level convergence may lead to
surface low development to further enhance rainfall potential.
While all of this is occurring, a tropical disturbance near the
Yucatan Peninsula of Mexico will spread high PWs in excess of
2.25" northward, and there is potential for a Predecessor Rain
Event (PRE) from late D2 into D3 across parts of N FL along the
western edge of a 925mb theta-e ridge >340K.

Favorable thermodynamics noted by MUCape approaching 1500 J/kg and
anomalously high PWs in an environment with warm cloud depths
exceeding 16,000 ft will drive rain rates which at times will
likely exceed 2"/hr. Generally slow storm motions to the northeast
should train, which with these rain rates could cause flash
flooding across parts of the region. While there remains some
spread into the amplitude and placement of the heaviest rainfall,
mostly due to differences in the frontal placement and amplitude
of the longwave trough, the SLGT risk was drawn to match the
highest ensemble probabilities for 3" of rainfall, with higher
amounts certainly possible, if not likely. While FFG across the
SLGT risk area is generally 3-4"/3hrs, some of this will likely be
compromised by heavy rainfall on D2, and exceedance of these
thresholds is becoming more likely. A MRGL risk surrounds the SLGT
risk area from far SE GA into central FL where heavy rain is also
possible, but the signal for flash flooding is less robust.


...Coast of North Carolina...
Guidance has trended upward with rain along the immediate coast of
NC from Cape Fear into the Outer Banks. A plume of tropical
moisture with PWs above 2" is likely to stream northeast from a
tropical disturbance near the Yucatan Peninsula. This moisture
lifting northeast will interact with a complex surface pattern,
including a stationary front/coastal front, and a powerful upper
jet streak placing favorable diffluence for ascent along the
coast. The heaviest rainfall may remain just offshore depending on
the speed and amplitude of an approaching longwave trough from the
west, but guidance has trended slightly more amplified and slower,
pulling heavy rainfall back onto the coast on Sunday. Despite
generally high FFG of 2.5-3.5"/3hrs, training of rainfall rates
greater than 1"/hr are possible which could lead to flash
flooding.


Weiss



Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt


$$
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FOUS30 KWBC 030816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sat Oct 03 2020

Day 1
Valid 12Z Sat Oct 03 2020 - 12Z Sun Oct 04 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE EAST
COAST OF FLORIDA...

Periods of heavy rainfall will continue across the FL Peninsula
associated with a stationary surface boundary. As this front lifts
north as a warm front, better instability and moisture will also
spread north through the afternoon. By late Saturday this front
will begin to retreat to the northwest in response to increased
low-level ridging off the Southeast Coast, and the approach of an
amplifying longwave trough which will dig into the TN Valley. The
displacement of this front will drive instability as high as 3000
J/kg MUCape across portions of the southern half of the Peninsula.
Precipitable water values will also surge above 2.25", approaching
+3 standard deviations above the climo mean, and near or above
daily records according to the SPC sounding climatology. These
favorable thermodynamics will be aided by a strengthening upper
jet streak leaving the favorable diffluent right entrance region
across the state. With boundary layer southerly/southeasterly
20-30 knot flow and deep layer steering flow out of the southwest,
convection should be fairly progressive south of the front, though
training may occur. Closer to the surface boundary, anti-parallel
corfidi vectors may help produce more slow moving/backbuilding
storms.

Given the potential for training, slow/back building storms and
the resurgence of better instability and confluent flow,
especially as the front lifts north, anticipate the heaviest rain
to focus along the east coast. Areal average precipitation through
the forecast period will range between 1-3+ inches along and just
inland of the coastline with hourly rain rates exceeding 2 inches
per hour at times which is supported by the latest HREF
neighborhood probabilities. Given parts of this region has
received over 400% of normal precipitation over the past several
days, felt any additional heavy rain could lead to flash flooding
concerns, especially across the urban corridors. Therefore, the
Slight Risk area was modified to account for this potential which
was based on the latest WPC QPF. Across the rest of the peninsula,
expect scattered convection to produce between 0.25-1+ inches of
rain with localized flash flooding possible.

Pagano


Day 2
Valid 12Z Sun Oct 04 2020 - 12Z Mon Oct 05 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN AND CENTRAL FLORIDA...

...Florida...
Heavy rainfall from Day 1 /Saturday/ is likely to continue into
Day 2 /Sunday/ as a warm front stalls across the Florida Peninsula
before drifting back to the south as a cold front late Sunday.

This warm front will lift slowly northward early Sunday before
stalling and pushing back south as a cold front in response to a
wave of low pressure developing off the Southeast coast. This
surface low will develop due to an intensifying jet streak
pivoting northward into New England, leaving strong upper
ventilation within the robust diffluent RRQ overhead. This jet
streak combined with the low-level baroclinic zone will drive
surface low development, and as this low lifts northeast the
latter half of D2, the boundary will likely sink back to the
south. While guidance has backed off somewhat on QPF, there is
still a strong potential for training heavy rainfall which may
lead to flash flooding, so the SLGT risk continues with only minor
adjustments.

PWs across the Florida Peninsula will remain anomalously high,
2.25+", as moisture associated with tropical storm Gamma gets
drawn northeastward from the Yucatan Peninsula. This high PW will
combine with MUCape reaching 1500 J/kg and warm cloud depths
nearing 16,000 ft to provide favorable thermodynamics for heavy
rainfall. Rain rates are likely to reach 2"/hr at times, and
despite 0-6km mean winds of 10-15kts suggesting fast individual
cell motions, training along the boundary is likely as evidenced
by parallel propagation vectors. This indicates that some areas
may receive several rounds of heavy rainfall Sunday, and this
could occur on top of areas that have received in excess of 300%
of normal rainfall the past 14 days. As the front sags southward
again late in the period, the low-level convergence along it will
become increasingly disconnected from the upper diffluence to
slowly cause waning of the deep layer ascent. However, the
anomalous thermodynamics will persist, so any convection could
still produce heavy rainfall. After coordination with WFO JAX and
MLB, the SLGT and surrounding MRGL risk were pulled southward just
slightly to better encompass areas that have received excessive
rainfall and flooding this week.

...Coast of North Carolina...
The MRGL risk was trimmed away from SE North Carolina and now only
includes extreme coastal eastern NC from Cape Lookout to near Nags
Head. This change is due to an eastward shift in QPF among the
guidance, likely due to a more progressive mid-level trough
leading to further east placement of the diffluent RRQ of the
downstream upper jet streak, as well as the surface low. Despite
the lowered QPF, maintained the MRGL for extreme eastern NC where
at least modest instability may lift onshore ahead of the surface
low, allowing for rain rates to exceed 1"/hr. This is where the
ECENS and GEFS ensembles still indicate a low-chance for 3+" of
rainfall which could locally exceed the FFG.

Weiss


Day 3
Valid 12Z Mon Oct 05 2020 - 12Z Tue Oct 06 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Weiss

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt

$$
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FOUS30 KWBC 080733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
233 AM EST Sat Feb 8 2025

Day 1
Valid 12Z Sat Feb 08 2025 - 12Z Sun Feb 09 2025

...West Virginia...

Strong N-S quasi-zonal mid and upper level flow will be perturbed
a bit during Day 1 (12Z Sat-12Z Sun) as a 150+ kt upper level jet
streak traverses the Upper Midwest and Ohio Valley, while a flat
500 mb vort lobe pushes across the Lower Great Lakes. Broad-scale
exit region forcing associated with the upper jet axis will surge
southwesterly low-level inflow ahead of the surface frontal wave,
with 850 mb moisture flux anomalies peaking between 4-5 standard
deviations above normal later this afternoon into Sat night, while
TPW values peak around 1". Robust synoptic-scale support and low-
level moisture transport will be offset somewhat by the weak
elevated instability, with MUCAPEs generally less than 500 J/Kg.
Nevertheless, even though not advertised on the latest (00Z Sat)
HREF, the aforementioned dynamic and thermodynamic ingredients will
be sufficient for spotty hourly rain rates of 0.5"+ and 3-hourly
rates of 1.0"+, with localized event totals between 1.5-2.0"+.

Current 3-hr flash flood guidance values remain quite low (1" or
less) across the outlook area, which includes much of WV. Despite
the lack of instability, the low FFG values could be exceeded over
isolated areas with 2 consecutive hours of 0.5"+/hr rainfall rates.
Since the soils in these areas are saturated, and the terrain is
rugged, we have maintained the Marginal Risk area for much of WV
(outside of its northern or eastern Panhandles).

Hurley/Roth


Day 2 Valid 12Z Sun Feb 09 2025 - 12Z Mon Feb 10 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley

$$
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FOUS30 KWBC 090808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Sun Feb 9 2025

Day 1
Valid 12Z Sun Feb 09 2025 - 12Z Mon Feb 10 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 2
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
Strong NW-SE upper level jet streak will dive southeast into CA
late on Day 3 (Tue night) -- on the western periphery of the
longwave trough towards the base. As this occurs, the broad western
U.S. trough will amplify, thereby enhancing the deep-layer ascent
and southwesterly flow/moisture transport within a maturing Warm
Conveyor Belt (WCB) downstream across the Mid South-Lower MS Valley
and TN Valley. 850-700 mb moisture flux anomalies increase to 2-3
standard deviations above normal Tue-Tue night, while TPW values
climb to 1.5-1.75" (around +2 standard deviation above normal). The strengthening dynamical and thermodynamical support will make for
efficient rainfall rates despite the lack of deep-layer
instability. Much of the guidance, non-CAM at this point being a
Day 3 forecast, depicts a widespread swath of 1.5-2.5" of rain
within the outlook areas, with more stripes of >3" within the
Slight Risk area. Storm motions nearly parallel to the WSW-ENE
oriented surface boundary will boost the potential for training,
and even though currently the non-CAM guidance is advertising
meager deep-layer elevated instability (MUCAPEs generally 250-500
J/Kg), believe these values will be amplified somewhat as the event
gets within the high-res CAM windows, again given the dynamic and
thermodynamic response to the broad-scale upper trough amplification.

2.00"+/3hr rainfall rates are anticipated where the cells do
train, again most likely within the Slight Risk area, which could
lead to localized-scattered instances of flash flooding.

Hurley

$$
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FOUS30 KWBC 100829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Mon Feb 10 2025

Day 1
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Beginning Monday afternoon, an increase of convergence on the nose
of 850mb flow extending from Texas into Tennessee will support an
increase in light to moderate rain and a few rumbles of thunder
from eastern Oklahoma through Kentucky/Tennessee. Rain rates are
expected to be modest (around 0.25-0.5 inch/3-hour period),
although some of this rainfall will eventually reach areas of
southeastern Kentucky where soils are moist and sensitive from
antecedent rainfall. The relatively short duration of light to
moderate rainfall in this area precludes an introduction of
Marginal/5% risk probabilities, although one may be needed in later
outlook updates if a longer duration of rainfall (greater than 3-6
hours) becomes apparent across southeastern Kentucky.

Cook


Day 2
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
Increasing coverage of showers and thunderstorms along and ahead of
a well defined cold front trailing a developing area of low
pressure taking shape over the Tennessee Valley will lead to an
increasing threat of excessive rainfall Wednesday into early
Thursday from easter Texas and parts of Arkansas and Louisiana
into the west aspect of the Appalachians of Tennessee and southeast
Kentucky. At the synoptic scale, a broad trough over the western
U.S. will amplify, thereby enhancing the deep-layer ascent and
southwesterly flow/moisture transport over this part of the country
due to a increasing low level flow. 850-700 mb moisture flux
anomalies still look to increase to 2-3 standard deviations above
normal Tuesday/Tuesday night while Precipitable Water values climb
to 1.5-1.75" (around +2 standard deviation above normal). The
strengthening dynamical and thermodynamical support will make for
efficient rainfall rates despite the lack of deep- layer
instability and the exit region of a 125 to 150 kt upper level jet
should aid deep layer vertical ascent. Much of the guidance
generally depicts a widespread swath of 1.5-3" of rain within the
outlook areas, with the most aggressive model being the ECMWF with
maximum values exceeding 4 inches. Storm motions nearly parallel
to the WSW-ENE oriented surface boundary will boost the potential
for training despite meager deep- layer elevated instability
(MUCAPEs generally 250-500 J/Kg). With 2.00"+/3hr rainfall rates
still being anticipated where the cells do train, again most
likely within the Slight Risk area, which could lead to localized-
scattered instances of flash flooding.

Bann


Day 3
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
TENNESSEE VALLEY INTO THE MID-SOUTH,,,

...Tennessee Valley into the Mid-South...
The threat of excessive rainfall will continue on Wednesday and
early Thursday ahead of the same system which brought the
excessive rainfall potential on Tuesday into early Wednesday as a
cold front makes its way eastward. Broad scale ascent will continue
to aided by the southern entrance region of a 135 to 155 kt upper
level jet...while moisture convergence is maximized along a well
defined surface cold front which intercepts a plume of moisture
being pulled northward by a 40 to 50 knot low level jet. There is
still spread in the guidance about placement of where the heaviest
rainfall will occur but amounts generally in the 1 to 3 inch
range...with locally higher amount where any enhanced rainfall
rates set up due to banding/training. Given antecedent
conditions...feel that a Slight risk should suffice.

...California Coast...
The plume of moisture from the Pacific Ocean towards the end of Day
2 will start to bring rain to the coastal areas during the Day 3 period...beginning in northern and central portions of California
on Wednesday that propagates southward during Wednesday night and
Thursday. Present indications are that the heaviest amounts remain
off shore...but a general uptick in amounts was noted over the past
24 hours in this area.

Bann

$$
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FOUS30 KWBC 110836
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 AM EST Tue Feb 11 2025

Day 1
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

Few changes needed to the old Day 2 ERO as it propagates into the
Day1 period. Main focus for heavy rainfall and the potential for
excessive rainfall will be along and ahead of a cold front
associated with a developing synoptic scale low pressure system
within a broad/fairly flat flow pattern. Inclusion of more CAM
guidance supports the idea of higher intensity rainfall extending
as far west as eastern Texas...a tendency we often see convection
get organized farther southwest than expected in events like this,
and there is growing QPF signal in the 12z ECMWF, UKMET and Gem Reg
over this area. The Slight risk area extended northeastward where
there is a bit of instability that develops later in the period but
looks to be lacking initially. At expect the flash flood risk to
pick up more over this area as we head into day 2.

Bann


Day 2
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
TENNESSEE VALLEY INTO THE MID-SOUTH...

...Tennessee Valley into the Mid-South...

The prolonged heavy rainfall event will continue om Wednesday into
Wednesday night over the Southeast. The extended duration of this
event will lead to storm total rainfall into the 3-5" range, with
locally higher totals possible. As stronger forcing ejects eastward
on Wednesday, an increase in the low level jet should aid in both
increasing moisture convergence and advecting instability
northward. The best overlap of ingredients that has the potential
for excessive rainfall looks to be over parts of AL/GA into far
southwest Tennessee. This is approximately the same area as the
previous Day 3 outlook...and given no major shifts in the synoptic
pattern saw little reason to make too many changes.

...California Coast...
The plume of moisture from the Pacific Ocean towards the end of Day
2 will start to bring rain to the coastal areas during the Day 3 period...beginning in northern and central portions of California
on Wednesday that propagates southward on Wednesday night and
early Thursday. Present indications are that the axis of the
Atmospheric River and the associated heaviest amounts remain off
shore or right along the coastal terrain...but a general uptick in
amounts was noted over the past 24 hours in this area.

Bann


Day 3
Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE
SOUTHERN CALIFORNIA COAST...

There is a Moderate Risk of excessive rainfall over portions of the
Southern California coast embedded within a broader Slight risk of
excessive rainfall covering much of the central and southern
California coast. An atmospheric river is expected to skirt the
coast as it makes its way south and east. The primary concern is
for damaging flooding and debris flow from the numerous fresh burn
scars in the region given the 24-hour QPF in the 1.5 to 3.5 inch
range...with potentially localized higher amounts. In
addition...the area is highly urbanized and an environment in which
much of the rainfall will turn immediately to runoff. Farther
north...the Slight risk was extended into portions of the
Sacramento Valley and San Joaquin Valley...where QPF is not
expected to be as great but the conditions have been wetter and
soils are more saturated than soils farther south.

Bann

$$
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FOUS30 KWBC 120741
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
241 AM EST Wed Feb 12 2025

Day 1
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE
DEEP SOUTH AND COASTAL AREAS OF CALIFORNIA...

Large Marginal and Slight Risk areas extend from Louisiana to the
central Appalachians and portions of Virginia. The Marginal and
Slight Risk areas cover multiple regimes for excessive rainfall potential:

1) Long-duration, moderate to heavy rainfall along an axis
extending from east Texas (beginning at 12Z) east-northeastward
into northern Georgia and the southern Appalachians. Much of this
axis has experienced appreciable antecedent rainfall amounts (in
the 2-3 inch range on February 11) and models are consistent in
depicting at least one more round of heavy rain across that same
axis as a thunderstorm complex organizes and moves east-
northeastward from in Texas later this morning. Another 1-3 inches
of is expected (heaviest from western in to central Mississippi).
Given the wet soils from prior rainfall, several instances of
flash flooding are expected from central Louisiana through the
southern Appalachians and northern Georgia.

2) Somewhat lighter rainfall should occur across portions of
Virginia and West Virginia through the day. Not only are soils
water-logged and streamflows above average across these areas, but
recent snow/ice could melt under persistent warm advection and
temperatures slowly rising above freezing through the forecast
period. Light to moderate rainfall could enhance excessive
runoff/ponding especially in sensitive areas and low spots.

3) CAMs are in very loose agreement in depiction of east-west
oriented outflow boundary left behind by convective complex(es)
across portions of southern MS/AL through early afternoon. Strong south-southwesterly 850mb flow and abundant moisture should result
in reignition of deep convection focused along boundaries for much
of the afternoon and early evening. The orientation of these
boundaries should focus convective development and may allow for
training and intense rainfall rates at times. This is supported in
particular by the 00Z HRRR, which depicts 5-9 inch rain amounts
across southern Alabama through 12Z Thursday. Uncertainty in the
specific placement of boundaries/heavy rainfall corridors and dry
antecedent conditions are factors that preclude a higher risk,
although some higher-end flash flood potential exists in this
scenario - especially if complexes can materialize over more
populated areas of LA/MS/AL/GA.

Cook


Day 2
Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE
SOUTHERN CALIFORNIA COAST...

...California...
The peak of the atmospheric river is expected during this period
with the initial focus on coastal central California at the start
of the period, then the best IVT shifts southward through the
period, reaching southern California by the end of the period
Thursday night. IVT values from the GFS peak at around 600-700
kg/m/s initially along the central coast then settle around 400-500
kg/m/s as the AR reaches SoCal. The greatest QPF amounts will be
confined to the coastal terrain areas as well as for the Sierra.
Total amounts for the 24-hour period look to be between 1-3" with
the favored terrain areas and peaks topping out between 4- 6"+.

The primary concern is the potential for damaging and potentially life-threatening burn scar flash flooding and debris flows,
particularly for southern California where the Moderate Risk (Level
3/4) is in place. Even outside the burn scar regions, the intense
rain rates and rainfall totals over the highly urbanized area could
bring scattered to numerous instances of flash flooding. Elsewhere,
a broad Slight Risk (Level 2/4) exists for much of the coastal
ranges as well as the Central Valley and lower elevations of the Sierra Nevada.

A Moderate Risk of excessive rainfall continues from yesterday's Day
3 ERO across portions of the Southern California coast, and for the
new Day 2 ERO was expanded slightly on the northwest side to
encompass the Lake Burn Scar (2024), while also eastward to include
the southwest San Bernardino Mountains, including the Line Burn Scar
(also 2024). Again, the primary concern is for damaging flooding and
debris flow from the numerous fresh burn scars in the region given
the 24-hour QPF in the 1.5 to 3.5 inch range (with localized higher
amounts). In addition, the area is highly urbanized and an
environment in which much of the rainfall will turn immediately to runoff.

Farther inland, given the QPF trends and snow levels, the Slight
Risk was extended into eastern portions of the San Joaquin Valley
and southern Sierra/adjacent foothills. This expansion includes the
Borel burn scar (2024).

...Florida Panhandle and Southern Georgia...
Lingering heavy rainfall will continue Thursday across portions of
the Florida Panhandle and southern Georgia, ahead of the approaching
cold front. Rainfall amounts look to be generally in the 1-3"
range, with some potential for localized rain rates sufficiently
high enough to cause some urban/localized flooding concerns.

Hurley/Taylor


Day 3
Valid 12Z Fri Feb 14 2025 - 12Z Sat Feb 15 2025

...Southern California...
IVT plume weakens while pushing southward across SoCal to begin
the Day 3 Period. While the bulk of the event (Slight-Moderate
excessive rainfall risk) is expected on Day 2 or through Thursday
night, will maintain a Marginal Risk into the early part of Day 3
(Friday morning), especially if the southward AR progression slows down a bit.

...Mid South...
Amplifying longwave trough across the Southwest-4 Corners Region
Fri-Fri night will lead to backing mid/upper layer flow and
deepening WAA/moistening downstream within a maturing Warm Conveyor
Belt (WCB). Thermodynamic profiles will respond appreciably as a
result, especially late in the period (Fri night) as the low- level
flow backs SSW and increases (to 50+ kts at 850 mb). This leads to
robust low-level moisture transport late Friday night into early
Saturday morning, with 850-700 mb moisture flux anomalies ramping
up to 4-5 standard deviations above normal per the ensembles. There
will also be a corresponding uptick in elevated instability as
well, to the tune of 500-1000 J/Kg towards 12Z Sat. While the main
event will be on Saturday (see Day 4 ERO), will maintain the
Marginal Risk inherited from yesterday's Day 4 ERO given the
anticipation of the ingredients ramping up fairly quickly Friday
night, which given the probabilistic QPF along with the latest CSU UFVS-verified ERO first-guess fields, could lead to localized
runoff issues across portions of the Mid South. by the pre-dawn hours Saturday.

Hurley
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FOUS30 KWBC 130812
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
312 AM EST Thu Feb 13 2025

Day 1
Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN CALIFORNIA...

...California...
Overall, not much change to the previous forecast, with the
unfolding atmospheric river expected to peak near the start of the
period. A long warm front currently extending along the coast is
expected to press inland this morning, with IVTs climbing to around
700-800 kg/m/s near the upstream cold front as it approaches the
coast later this morning. The strongest moisture flux is expected
to center near SF Bay at the start of the period, before steadily
shifting south along the coast today. Models continue to show IVTs
decreasing as the axis moves south, dropping to around 400-500
kg/m/s as the AR reaches Southern California later this afternoon
into the evening. Guidance has remained fairly consistent,
indicating precipitation amounts of 4-6 inches along the central to
southern coastal ranges and the Sierra Nevada, falling mostly as
rain below 6000 ft.

A Moderate Risk (level 3/4) remains in place across portions
Southern California, from Santa Barbara County southeastward into
the San Gabriel and San Bernadino mountains, where damaging and
potentially life-threatening burn scar flash flooding and debris
flows remain a primary concern. Even outside of the burn scar areas,
intense rain rates over complex terrain and urban areas may produce
scattered to numerous instances of flash flooding. Elsewhere, a
broad Slight Risk (Level 2/4) exists for much of the remaining
coastal ranges as well as parts of the Central Valley and the lower
elevations of the Sierra Nevada.

...Florida Panhandle and Southern Georgia...

Lingering heavy rainfall will continue this morning across
portions of the Florida Panhandle and southern Georgia ahead of an
approaching cold front. HREF neighborhood probabilities indicate
that additional rainfall amounts of 1-2 inches are likely within
the highlighted area, with some potential for localized rain rates
high enough to cause some urban/localized flooding concerns.

Pereira


Day 2
Valid 12Z Fri Feb 14 2025 - 12Z Sat Feb 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-SOUTH...

...Mid-South...

Although most of the convective activity, and thus heavy rainfall
threat, in the region should be concentrated in the Day 3 period
(after 12Z Saturday), model guidance does indicate that convection
is likely to begin blossoming late Friday Night. Conditions will
become increasingly favorable after 06Z Saturday with a strong 55-65
knot low-level jet expanding east from the Plains, and significant
northward moisture transport leading to rapid moistening of the
boundary layer. MUCAPE values of around 500-1000 j/kg should support
organized convection with the potential for rainfall rates in excess
of 1 inch per hour at times. Although there is a lack of a
significant front or boundary to help organize a band of convection,
the strength of the LLJ may support backbuilding within a broad zone
of developing convective clusters. This may be enough for some brief
training and a ramp-up in flash flood potential prior to 12Z
Saturday. The 00Z runs of the NAM Nest and FV3 show more widespread
convection than other models; if this trend persists as additional
hi-res guidance becomes available, an expansion of the Marginal Risk
and/or the addition of a Slight Risk area may become warranted with time.

...Southern California...

The Marginal Risk was removed for southern California given a more
limited QPF signal on the latest guidance, and hi-res models in
excellent agreement on a lack of organized convection. The bulk of
the threat should be in the Day 1 period.

Lamers


Day 3
Valid 12Z Sat Feb 15 2025 - 12Z Sun Feb 16 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE TENNESSEE AND OHIO VALLEYS AND THE CENTRAL APPALACHIANS...

...Ohio and Tennessee Valleys...

Confidence remains high in significant rainfall-related impacts on
Saturday and Saturday Night with model guidance in excellent
agreement depicting a swath of 3-6 inches of rainfall in the 24-hour
period across the region. Although models vary slightly with the
placement, they almost unanimously depict a corridor of heavy rain
about 750mi long centered somewhere in TN/KY. This same region has
generally seen above average precipitation in recent weeks, with the
14-day precip in much of KY, N TN, WV, and W VA at least double the
normal values. The confluence of these factors should make the
region especially vulnerable to flooding from the predicted
rainfall. For additional context on the current hydrologic picture
across the region, refer to the National Hydrologic Discussion from
the National Water Center at water.noaa.gov.

Convection may be ongoing at the beginning of the forecast period
and should become increasingly focused along a developing warm front
to the east of a surface low that will be emerging out of the Plains
on Saturday. The front will be positioned on the nose of very strong
SW, or even WSW, inflow, which should favor backbuilding and
training and a corridor of very heavy rainfall. The environment will
be atypical of mid-February with PWATs reaching around 1.5 inches
and MUCAPE of 500-1000 j/kg. For example, the Nashville sounding
archive exists back to 1948 and they've only ever reached 1000 j/kg
MUCAPE once in February, and 1.5 inch PWATs a few times. The
environment will support rainfall rates in excess of 1 inch per
hour, and given the potential for training and backbuilding, these
rates may be sustained for several hours in some locations. These
would be the areas of greatest concern for flash flooding -- not
only in terms of likelihood but severity -- particularly if the
higher rain rates are sustained over urban areas or vulnerable
terrain for extended periods of time.

The inherited Moderate Risk was mostly maintained as-is with a
slight expansion to the southwest in the vicinity of Memphis, TN;
and a more significant expansion eastward into S WV and W VA. The WV-
VA border region just received some significant snowfall, and model
guidance indicates a fairly high probability of warm, moist air (dew
points in excess of 45 degrees) accompanying the rainfall into this
area, which may lead to a combination of runoff from rain and snow melt.

It's worth noting a couple additional things. First, the amount of
rain forecast from E KY into S WV and W VA in particular is quite
unusual for the heart of the winter season. Calendar day precip
records across that area for January and February are generally in
the 2-3 inch range, and NBM probabilities indicate it is likely (60+
percent chance) we will see these types of 24-hour rainfall totals
in those areas. Second, this relatively rare winter rain event would
be delivered to an area that has been quite wet recently, and in
some areas has snow on the ground. And third, the high-end scenarios
in much of the Moderate Risk area would be significant by historical
standards. The NBM 90th percentile from N TN into S/E KY and S WV is
on par with the top several wettest days (for any season!) in the
station records in the area. This corridor is where the greatest
concern for severe impacts exists, and it's possible an upgrade to
High Risk may be needed for portions of the area in subsequent updates.

Lamers
$$
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