ACUS48 KWNS 040854
SWOD48
SPC AC 040852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Tue May 04 2021

Valid 071200Z - 121200Z

...DISCUSSION...
Models indicate that blocking mid-level ridging may linger, but it
may redevelop east of the Labrador Sea into the southern Greenland
vicinity during this period. Coincidingly, a deep mid-level closed
low appears likely to redevelop eastward, from near James Bay into
areas near/north of the Canadian Maritmes, with initially amplified
large-scale troughing to its south de-amplifying and while shifting northeastward out of the eastern U.S. As this occurs, a belt of
westerlies emanating from the northern mid-latitude Pacific may
become more prominent across and east of the Rockies.

Latest medium-range guidance now appears much lower in amplitude
with mid-level troughing developing across the Intermountain West
this weekend, before progressing east of the Rockies, as well as
with ridging building north of a subtropical high center developing
near the Yucatan peninsula. However, in association with the
progression of the troughing, there remains at least some potential
for severe thunderstorm development this coming weekend into early
next week across parts of the central and southern Great Plains into
the lower Mississippi Valley and Gulf Coast states.

This may be focused near the intersection of a developing frontal
cyclone and dryline across the central Great Plains on Saturday,
when lapse rates will be steep, but CAPE may still be a bit modest. Boundary-layer moisture return off the Gulf may become supportive of
more substantive CAPE on Sunday, when the focus for strongest
convection begins to become a bit more unclear. It is possible that
this may become confined to portions of central Texas into the Red
River vicinity, before spreading into portions of the western and
central Gulf states on Monday, ahead of the southward advancing
front. Due to sizable uncertainties, severe weather probabilities
are maintained at below 15 percent.

..Kerr.. 05/04/2021
$$
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ACUS48 KWNS 050858
SWOD48
SPC AC 050857

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0357 AM CDT Wed May 05 2021

Valid 081200Z - 131200Z

...DISCUSSION...
The medium-range models continue to indicate that a blocking
mid-level high may shift/redevelop east of the Labrador Sea, across
and perhaps just east of southern Greenland through this period.
Upstream, developments remain more unclear, but a mid-level high
developing this weekend across the Canadian Prairies, within the
northern branch of a splitting flow, may be relatively short-lived.
It appears that mid-level troughing developing within the southern
branch, inland of the Pacific coast through the southern Rockies,
probably will progress east of the Rockies as a series of emerging smaller-scale perturbations this weekend into early next week.

In association with the first emerging short wave impulse, a
developing cyclone, frontal zone and dryline across the central
Great Plains may become a focus for organized severe storm
development on Saturday. Beneath steep mid-level lapse rates, it
appears that low-level moisture return from the Gulf of Mexico may
become sufficient to contribute to moderate CAPE by late afternoon.
In the presence of strong deep-layer shear, a few supercells are
possible along the dryline and near a warm front across parts of
central Kansas, before convection grows upscale into an organizing
cluster Saturday evening. This may be accompanied by the risk for
large hail and a couple of tornadoes initially, before strong wind
gusts become the more prominent hazard.

It appears that surface frontal wave development will weaken and
remain weak, while quickly migrating eastward across the Mid South
into the Mid Atlantic by early next week, with a southward
advancement of the trailing surface front into the Florida
peninsula, northern Gulf of Mexico and lower Rio Grande Valley. As
it does, continuing severe weather potential becomes more unclear,
but it appears that it may remain relatively limited.

..Kerr.. 05/05/2021
$$
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ACUS48 KWNS 070841
SWOD48
SPC AC 070840

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0340 AM CDT Fri May 07 2021

Valid 101200Z - 151200Z

...DISCUSSION...
Generally zonal flow is forecast across the southern Plains and
Southeast on Day 4/Monday where greater low-level moisture should
reside. Steep mid-level lapse rates should be present across parts
of the southern Plains, and moderate to potentially strong
instability may exist along/near a front. However, the lack of an
obvious large-scale forcing mechanism aloft lends uncertainty
regarding storm coverage and placement on Monday. Somewhat better
severe potential may exist on Day 5/Tuesday across parts of TX as a
shortwave trough ejects eastward across the southern/central Plains.
Still, there does not appear to be a robust low-level mass response
ahead of this feature, and there is some uncertainty with the
evolution and placement of the upper trough.

This upper trough should move eastward from the Plains to the MS
Valley and OH Valley from Day 6/Wednesday into Day 7/Thursday. Rich
low-level moisture may remain confined to coastal portions of TX and
the Southeast in this time frame, with a fairly muted threat for
organized severe storms. Large differences in medium-range guidance
regarding the synoptic-scale pattern across the CONUS by late next
week suggest limited predictability.

..Gleason.. 05/07/2021
$$
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ACUS48 KWNS 090832
SWOD48
SPC AC 090831

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0331 AM CDT Wed Jun 09 2021

Valid 121200Z - 171200Z

...DISCUSSION...
An upper high is forecast to retrograde from the southern High
Plains on Sat/D4 across the Four Corners states through the
remainder of the period, resulting in hot conditions and weak shear.
Meanwhile, a low-amplitude shortwave trough is forecast to round the
ridge and turn southeastward across the upper MS Valley and Great
Lakes beginning on Sunday/D5. A relatively stable air mass will
already be in place across this region, minimizing thunderstorm
chances with this trough.

The aforementioned shortwave trough will eventually phase with a
deep upper low that is forecast to drop south out of James Bay,
resulting in a large area of cyclonic flow aloft over Great Lakes
and Northeast for the D6/Mon through D8/Wed period. As a result of
this pattern, high pressure will spread south across the northern
Plains, Great Lakes and Northeast, shunting any appreciable moisture
and instability south. While daily thunderstorms are expected along
the southward-moving cold front, this setup would not favor
organized severe storms.

Strong instability and robust low-level moisture will remain across
the southern Plains, lower MS Valley and across the Gulf Coast
states through Tuesday/D7. However, shear will remain weak, with
only sporadic areas of daytime thunderstorms with attendant low
predictability.

..Jewell.. 06/09/2021
$$
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ACUS48 KWNS 100857
SWOD48
SPC AC 100855

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CDT Thu Jun 10 2021

Valid 131200Z - 181200Z

...DISCUSSION...
For the D4/Sunday to D8/Thursday period, the large-scale pattern
will feature an upper high building over the Four Corners states,
with ridge extending north across the Rockies and High Plains. To
the east, an upper low is forecast to drop south out of Hudson Bay,
with increasing cyclonic flow aloft from the Great Lakes into the
Northeast. The result will generally be hot temperatures across the
West, with stabilizing high pressure from the Midwest into the
Northeast. Over the Plains, southerly winds will maintain a warm
moist air mass, with only isolated diurnal activity anticipated.

Around D6/Tuesday, some overlap of strong flow aloft and instability
may develop over parts of the Carolinas, on the southern periphery
of the deepening upper trough over the Northeast. Models are not in particularly good agreement with the airmass quality in this region
on D6/Tuesday, thus predictability is low.

For the D6/Tuesday to D7/Wednesday time frame, several models
indicate a shortwave trough moving across the Pacific Northwest, and
perhaps skirting parts of MT and the northern Plains as the upper
ridge flattens. If this occurs, at least a minimal severe risk could
develop, mainly over MT, but predictability is low.

..Jewell.. 06/10/2021
$$
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ACUS48 KWNS 150854
SWOD48
SPC AC 150852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Thu Oct 15 2020

Valid 181200Z - 231200Z

...DISCUSSION...
An upper trough embedded within the mid-level westerlies is forecast
to move from the north-central states into the Northeast and Canada
on Day 4/Sunday. Although low-level moisture return may occur to the
south of this feature across the southern Plains vicinity, the
potential for organized severe storms appears low. Medium-range
guidance has come into somewhat better agreement regarding the
evolution of the mid/upper-level jet across the northern/central
CONUS in the early to middle portion of next week. Still,
differences remain in both the northward extent and quality of the
low-level moisture return across the central CONUS. Some guidance
suggests potential for isolated severe storms across parts of the southern/central Plains into the mid MS Valley and perhaps the
Midwest from Day 5/Monday into at least the middle of next week.
However, too much uncertainty exists regarding this severe potential
to include any probabilities at this time.

..Gleason.. 10/15/2020
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ACUS48 KWNS 020743
SWOD48
SPC AC 020741

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0241 AM CDT Fri Oct 02 2020

Valid 051200Z - 101200Z

...DISCUSSION...
Large-scale mid-level ridging appears likely to persist within the
westerlies across the northern mid-latitude eastern Pacific into
western North America through the middle of next week, with broad
downstream troughing east of the Rockies into the western Atlantic.
Toward the middle of next week, there could be some re-amplification
of the ridging along an axis near the Canadian/U.S. Rockies, ahead
of a large developing mid-level trough approaching the Pacific
Coast. As this occurs, the large-scale downstream troughing may
amplify along a negatively tilted axis from Hudson Bay into western
Atlantic.

While embedded short wave developments remain much more uncertain,
this regime appears likely to maintain a west-northwesterly to
northwesterly mid-level flow across much of the nation. The
development of a southerly return flow of moisture off the Gulf of
Mexico appears unlikely, maintaining generally dry and/or stable
conditions with low convective potential.

..Kerr.. 10/02/2020
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ACUS48 KWNS 030803
SWOD48
SPC AC 030802

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0302 AM CDT Sat Oct 03 2020

Valid 061200Z - 111200Z

...DISCUSSION...
Medium-range models continue to indicate that initially broad
large-scale ridging, across the northern mid-latitude eastern
Pacific into western Northern America, may undergo amplification
while shifting eastward during the early to middle portion of the
coming work week. As this occurs, a significant short wave impulse,
digging within increasingly northwesterly flow to its east, appears
likely to contribute to substantive trough amplification along a
negatively tilted axis from the Hudson Bay vicinity into the western
Atlantic by late next week. This probably will be accompanied by
another substantive cold intrusion across the Great Lakes into the
Northeast, and a building surface ridge beneath increasingly
confluent mid-level flow, east of the Mississippi Valley and across
much of the Gulf Coast states. This should maintain/reinforce
generally dry and stable boundary-layer conditions across all but
the Florida Peninsula. Even if trends depicted in the latest
(03/00Z) ECMWF (which include the faster inland progression of a
significant mid-level trough on the leading edge of a strong zonal
flow emanating from the mid-latitude Pacific, and deeper surface
troughing across the higher plains by early next weekend) are
correct, convective potential appears low through this period.

..Kerr.. 10/03/2020
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