AWUS01 KWNH 091505
FFGMPD
TNZ000-ALZ000-MSZ000-ARZ000-092102-

Mesoscale Precipitation Discussion 0312
NWS Weather Prediction Center College Park MD
1104 AM EDT Wed Jun 09 2021

Areas affected...northern Mississippi, eastern/southeastern
Arkansas, northwestern Alabama

Concerning...Heavy rainfall...Flash flooding likely

Valid 091502Z - 092102Z

Summary...Areas of flash flooding remain likely across the
discussion area through at least 21Z. Significant impacts are
expected given extreme antecedent rainfall over the past 24 hours.

Discussion...Recent radar mosaic imagery indicates several bands
of slow-moving/propagating convection across the discussion area -
particularly in eastern Arkansas, northern Mississippi (near
Oxford), and northern Alabama (northwest of Birmingham). The location/orientation of these bands isn't particularly surprising
given broadly confluent westerly/southwesterly 850mb flow
partially orthogonal to a weak low-level boundary from near Little
Rock to near Tupelo. The low-level flow was maintaining a moist,
destabilizing pre-convective airmass across the region
(characterized by 2-inch PW values, nearly 2000 J/kg MUCAPE, and
minimal convective inhibition). The moisture and instability was
promoting rainfall rates of up to 3 inches per hour beneath
heavier thunderstorm cores which easily exceed FFG thresholds in
the region - especially in eastern Arkansas and northern
Mississippi where widespread areas of 3-10 inches of rainfall were
observed yesterday. Impressive MRMS Flash responses have already
been noted this morning in east-central Arkansas and near Oxford,
Mississippi.

Though the general axes of convergence are less focused compared
to yesterday, models/observations generally suggest that bands of
heavy rainfall will continue to propagate slowly
eastward/east-southeastward resulting in very heavy rainfall and
additional accumulations of at least 2-4 inches (locally higher)
through 2030Z. Models also indicate initiation of convection
south of these bands, which isn't surprising given the strong
destabilization occurring there. Localized training of convection
is expected in this regime (which may already be materializing in
east-central Arkansas). Convective mergers may also allow for a
slow, more southward component to MCS motions during the period as
well, allowing for heavier precipitation to eventually shift
toward the US82 corridor in Mississippi. Each of the
aforementioned factors point to locally significant flash flooding
especially beneath heavier/training convection.

Cook

ATTN...WFO...BMX...HUN...JAN...LZK...MEG...OHX...

ATTN...RFC...ABRFC...LMRFC...SERFC...NWC...

LAT...LON 35068996 35018783 34828659 34608618 34118614
33568659 33268805 33139020 33109190 33399234
34059232 34689205 34949122
$$
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AWUS01 KWNH 091732
FFGMPD
NYZ000-PAZ000-WVZ000-OHZ000-092331-

Mesoscale Precipitation Discussion 0314
NWS Weather Prediction Center College Park MD
132 PM EDT Wed Jun 09 2021

Areas affected...Virginia, northern North Carolina

Concerning...Heavy rainfall...Flash flooding possible

Valid 091731Z - 092331Z

Summary...Convection drifting slowly southward across the
discussion area could pose a very localized/isolated flash flood
risk through peak-heating hours..

Discussion...Satellite/lightning imagery indicates scattered
thunderstorms across the discussion area that were moving slowly south-southwestward. The cells were in an environment
characterized by very weak vertical wind shear (with northerly
flow around 10 knots or so from the surface to 300mb), moderate
instability (around 2000 J/kg MLCAPE), and PW values ranging from
1.3-1.7 inch. These conditions are conducive for brief heavy
downpours with as much as 1 inch per hour of rainfall in a few
spots. FFG values of around 1.5 inch-per-hour rainfall rates
(slightly lower in southern New York State and southwestern
Pennsylvania) suggest that a brief/isolated flash flood risk will
exist - particularly in areas where heavier rainfall occurs over
flood-prone or hydrophobic surfaces (i.e., urban areas and hilly
terrain). This risk should be mainly dirunally driven and lessen
after sunset.

Cook

ATTN...WFO...BGM...BUF...CLE...CTP...PBZ...

ATTN...RFC...MARFC...NERFC...OHRFC...NWC...

LAT...LON 42317939 42297756 41927676 41567661 40907664
40347684 39847756 39977979 40688129 41208142
41688113
$$
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AWUS01 KWNH 091739
FFGMPD
NYZ000-PAZ000-WVZ000-OHZ000-092337-

Mesoscale Precipitation Discussion 0314...Corrected
NWS Weather Prediction Center College Park MD
138 PM EDT Wed Jun 09 2021

Corrected for Areas Affected Header

Areas affected...northeastern Ohio, Pennsylvania, and far southern
New York State.

Concerning...Heavy rainfall...Flash flooding possible

Valid 091737Z - 092337Z

Summary...Convection drifting slowly southward across the
discussion area could pose a very localized/isolated flash flood
risk through peak-heating hours..

Discussion...Satellite/lightning imagery indicates scattered
thunderstorms across the discussion area that were moving slowly south-southwestward. The cells were in an environment
characterized by very weak vertical wind shear (with northerly
flow around 10 knots or so from the surface to 300mb), moderate
instability (around 2000 J/kg MLCAPE), and PW values ranging from
1.3-1.7 inch. These conditions are conducive for brief heavy
downpours with as much as 1 inch per hour of rainfall in a few
spots. FFG values of around 1.5 inch-per-hour rainfall rates
(slightly lower in southern New York State and southwestern
Pennsylvania) suggest that a brief/isolated flash flood risk will
exist - particularly in areas where heavier rainfall occurs over
flood-prone or hydrophobic surfaces (i.e., urban areas and hilly
terrain). This risk should be mainly dirunally driven and lessen
after sunset.

Cook

ATTN...WFO...BGM...BUF...CLE...CTP...PBZ...

ATTN...RFC...MARFC...NERFC...OHRFC...NWC...

LAT...LON 42317939 42297756 41927676 41567661 40907664
40347684 39847756 39977979 40688129 41208142
41688113
$$
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AWUS01 KWNH 101620
FFGMPD
NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-102215-

Mesoscale Precipitation Discussion 0321
NWS Weather Prediction Center College Park MD
1219 PM EDT Thu Jun 10 2021

Areas affected...portions of the northern Mid-Atlantic region

Concerning...Heavy rainfall...Flash flooding likely

Valid 101616Z - 102215Z

SUMMARY...Slow moving thunderstorms are expected to increase in
coverage across the northern Mid-Atlantic region this afternoon.
Rainfall rates of 1-2 in/hr will be common, but locally higher
rates can not be ruled out.

DISCUSSION...Visible satellite imagery through 1545Z showed an
expanding cumulus field within an otherwise mostly clear
environment across the Delmarva Peninsula into MD and southeastern
PA. A few showers and thunderstorms have also popped up on
regional radar imagery over northern Delaware Bay and along the
Catocin Mountains of northern MD into the Appalachian chain of
southern PA. PWATs within the pre-convective environment are 1.7
to 2.0 inches and 850-200 mb mean-layer flow is very weak across
the entire region at less than 10 kt, which will support slow
storm motions. Little CIN on the 12Z soundings from WAL and IAD
suggest storm coverage will continue to increase with daytime
heating with the front and local terrain acting as sources for
lift. In addition, locally stronger easterly flow just behind the
cold front may help to support near-stationary convection along
the terrain of northern VA into northwestern MD and southern PA.

Given the lack of speed shear with height, storms should not be
organized in nature or long-lasting, but they should be rather
efficient with rainfall production given high wet bulb zero
heights of roughly 13 kft. Rainfall rates of 1-2 in/hr are very
likely with localized rainfall rates up to 3 in/hr possible. In
fact, rainfall rates from the HRRR support 1-2 inches of rain in
15 to 30 minutes which seems reasonable given the moist
environment. Portions of the Delmarva into southern MD and
southeastern PA received heavy rainfall yesterday and will be more
susceptible to localized flash flooding today. While flash
flooding is not expected to be widespread across the entire
region, scattered to numerous slow moving thunderstorms will
produce heavy rainfall with several areas at risk for flash
flooding, including the urban I-95 corridor from south of D.C.
into northern DE with 2-4 inches expected through 22Z.

Otto

ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...

ATTN...RFC...MARFC...OHRFC...NWC...

LAT...LON 40587854 40517767 40357679 40047594 39547543
38187496 37767548 37877657 39167880 39907971
40507942
$$
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AWUS01 KWNH 101727
FFGMPD
MSZ000-LAZ000-ARZ000-102315-

Mesoscale Precipitation Discussion 0322
NWS Weather Prediction Center College Park MD
127 PM EDT Thu Jun 10 2021

Areas affected...central AR into northeastern LA and central MS

Concerning...Heavy rainfall...Flash flooding likely

Valid 101722Z - 102315Z

SUMMARY...Backbuilding and training convection is expected to
continue areas of flash flooding for central MS and northeastern
LA, expanding northwestward into central AR through early evening.
Peak rainfall rates of 2-3 in/hr should continue and the overlap
with recent areas of heavy rain will exacerbate ongoing flooding.
An additional 3-5 inches is forecast through 23Z.

DISCUSSION...A long-lived complex of thunderstorms over the Lower
Mississippi Valley has shown a slow evolution over the past 6
hours toward the south and west. Low level cloud elements on
visible imagery continue to show a confluent pattern into the
tri-state region of AR/LA/MS where MRMS rainfall estimates ending
at 17Z have been near 4 in/hr in Issaquene County. A lack of
rainfall observations in the area has made it difficult to confirm
MRMS estimates, but the history of this complex and the efficient
environment make the MRMS rates seem reasonable. MLCAPE estimates
as of 17Z show 2000-3500 J/kg over northern LA into central AR
where mostly clear skies have allowed surface temperatures to
climb into the upper 80s while dewpoints are in the mid to upper
70s.

While winds at 850 mb have weakened since earlier this morning
into the 10-20 kt range, similar strength and direction of the
850-300 mb mean flow has supported backbuilding of storms into
southeastern AR. Short term forecasts from the RAP have been
consistent with maintaining the current strength and direction of
the low and mid-level flow into the early evening. Therefore, weak
to locally moderate low level confluent flow within the moist
environment and the presence of the right-entrance region of a
40-60 kt upper level jet streak to the north should continue to
support convective development over the next several hours.

Ongoing training near the LA/AR/MS junction may weaken in the next
2-3 hours in favor of increasing development into a expanding
cumulus field over central AR. The greatest confidence for an
additional 3-5 inches of rain exists across far western MS into
northeastern LA and southern AR, while convection to the north
(centarl AR) is expected to be more scattered in nature with
rainfall rates of 1-2 in/hr. Given heavy rain over the past 3
days, additional any added heavy rain will only worsen ongoing
flooding concerns.

Otto

ATTN...WFO...JAN...LZK...MEG...SHV...

ATTN...RFC...ABRFC...LMRFC...NWC...

LAT...LON 35689213 35289148 34019055 33468979 33018917
32418911 32098970 32089100 32769240 33579289
34879299 35589275
$$
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AWUS01 KWNH 101802
FFGMPD
MDZ000-VAZ000-WVZ000-OHZ000-KYZ000-102300-

Mesoscale Precipitation Discussion 0323
NWS Weather Prediction Center College Park MD
201 PM EDT Thu Jun 10 2021

Areas affected...WV...southwest OH...Western & Southwestern VA...

Concerning...Heavy rainfall...Flash flooding possible

Valid 101800Z - 102300Z

SUMMARY...Slow/Chaotic motions but ample deep warm cloud layer for
efficient rainfall through complex terrain.

DISCUSSION...GOES-E WV and Visible suite depict a vertically
sheared cyclone with 6.2um channel centered over western VA, 7.3
over central WV and IR/VIS channels showing compact center into
southwest OH. As a result, there is weak chaotic flow regimes,
though low level through 7H suggests southwesterly moist flow
across E WV into the front ranges of the Appalachians in western
VA and this is denoted well in the 850-7H Layer PW from CIRA.
Being on the western periphery of the upper-level waves has
supported some additional clearing for ample isolation and
building of instability. Mtn/Valley circulation combined with
some low level mass piling is supporting increasing agitation of
cu field both under the best mid-level cooling/upper-low but also
along the southeast quadrant of the lower circulation along/near
the Ohio River. Mid-level cloudy conditions have all but rendered
areas across far N WV into the western MD/Eastern WV panhandle
less conducive.

Deepest convective elements are forming with the better mid-level
lapse rates along the terrain of far E KY into W VA. Still, due
to deep warm cloud layer, ample moisture individual cells will be
highly efficient with up to 2"/hr rates. Cell motions will be
near zero further north and west with 5-10 kts toward the NNE
across southern portions of the MPD area. Hi-Res CAMs all suggest
best scattered 2-2.5" totals over E WV into W VA with the slightly
better 5-10 kts of inflow to help maintain updrafts more than the
"up and splat" nature further north and east,
propagating/regenerating along the outflows.

Still both modes have solid potential to exceed the low FFG in
complex terrain which is about 1"/hr though lower values of
.5-.75"/hr are nearer the low level cyclone convergence point.
Flash flooding is likely though it will be highly
scattered/locally focused to only a few watersheds...where some
neighboring watersheds may miss out totally.

Gallina

ATTN...WFO...JKL...LWX...MRX...PBZ...RLX...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC...

LAT...LON 39598200 39578099 39458008 39277949 39047903
38157928 37377979 36738086 36788232 37348272
38158231 39158235
$$
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