SPC - No watches are valid as of Tue Sep 21 22:16:02 UTC 2021

No watches are valid as of Tue Sep 21 22:16:02 UTC 2021.

SPC - No MDs are in effect as of Tue Sep 21 22:16:02 UTC 2021

No Mesoscale Discussions are in effect as of Tue Sep 21 22:16:02 UTC 2021.

SPC Sep 21, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
      
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0249 PM CDT Tue Sep 21 2021

Valid 212000Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
EASTERN TEXAS INTO NORTHWEST MISSISSIPPI...

...SUMMARY...
Isolated damaging wind gusts remain possible this afternoon into
early evening over portions of far southeast Arkansas into northern
Louisiana, east Texas, and western Mississippi.

...20Z Update...
Only minor changes were made to the latest forecast. The
northernmost portions of the Marginal risk across central AR were
trimmed given convective overturning over this area. Cold pool
mergers have supported a modest consolidation of pulse-cellular
storms into line segments, and these will pose the greatest risk for
a damaging gust or two through the remainder of the afternoon into
early evening, before nocturnal cooling sets in. Please refer to MCD
1774 for more details.

..Squitieri.. 09/21/2021

.PREV DISCUSSION... /ISSUED 1108 AM CDT Tue Sep 21 2021/

A large upper trough extends from the western Great Lakes region
into the southern Plains today, with a strong cold front stretching
from IN to TX.  This front will continue to sag southward into the
Arklatex region, where a very moist and unstable air mass is
present.  Scattered thunderstorms have already begun to develop
along the front in AR, with further development expected through the
afternoon into northern LA and east TX.  Hot and humid surface
conditions, coupled with strengthening mid-level winds and
increasing large scale forcing, may result in a few intense cells
this afternoon.  Locally damaging wind gusts will be the main
threat.  A few CAM solutions suggest a more organized cluster of
storms will persist across southern AR into northern MS this
evening, with a continued threat of isolated damaging wind gusts.


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SPC Sep 21, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook
      
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1230 PM CDT Tue Sep 21 2021

Valid 221200Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF THE OHIO VALLEY INTO THE SOUTHERN AND CENTRAL APPALACHIANS AND
MIDDLE ATLANTIC REGIONS...

...SUMMARY...
A few strong to severe storms with a risk for mainly damaging wind
gusts and a couple of tornadoes will exist Wednesday from a part of
the Ohio Valley, the central and southern Appalachians to a portion
of the Middle Atlantic region.

...Ohio Valley into the central and southern Appalachians and Middle
Atlantic regions...

High-amplitude upper trough now approaching the upper MS Valley will
continue east, evolving into a closed circulation over the TN and OH
Valleys Wednesday. The attendant surface low initially over southern
OH tomorrow morning will move northeast, reaching the lower Great
Lakes Wednesday evening. Trailing cold front will move east through
the OH and TN Valleys, reaching the Middle Atlantic region tomorrow
evening. A moist boundary layer will reside in the warm sector with
dewpoints ranging from the low to mid 60s F across eastern parts of
the OH Valley to upper 60s F over the Middle Atlantic. However,
widespread clouds should limit overall destabilization potential.

Scattered showers and thunderstorms will be ongoing along the front
from the OH Valley into the TN Valley. A separate area of scattered
showers and a few thunderstorms is forecast to be in progress across
the Middle Atlantic. Between these two regimes, some potential will
exist for pockets of limited diabatic warming to occur, which will
result in modest destabilization of the boundary layer. Storms
developing along and ahead of the front may subsequently undergo
some intensification. The low-level is forecast to remain somewhat
displaced to the east of stronger winds aloft, but the best
combination of low-level and deep shear will probably occur from a
portion of VA into northeast OH and PA. Some storms may evolve into
bowing segments, and some supercells structures are also possible.
The potential limiting factors imposed by an expected marginal
thermodynamic environment precludes more than a MRGL risk category
at this time.

..Dial.. 09/21/2021


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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0249 PM CDT Tue Sep 21 2021

Valid 221200Z - 231200Z

No changes. See previous discussion below.

..Bentley.. 09/21/2021

.PREV DISCUSSION... /ISSUED 0135 AM CDT Tue Sep 21 2021/

...Synopsis...
A progressive upper-level trough is expected to move through the
Pacific Northwest on Wednesday, resulting in increasing low and
mid-level winds. Despite recent rainfall over the western CONUS,
parts of the northern Sierra/northwest Great Basin and northern
Rockies/High Plains remain dry and may see elevated fire weather
conditions evolve as winds increase through the day.

...Northwest Nevada...
Zonal mid-level flow is forecast to increase with the approach and
passage of a progressive shortwave trough. This will result in
strengthening downslope flow off the northern Sierra into northwest
NV. High-res and ensemble guidance suggests winds between 15-20 mph
are probable and will be coincident with RH reductions into the
teens. Although ERC values have fallen in recent days, many
locations report values above the 50th percentile, which will
support at least a low-end fire weather concern. Elevated conditions
may extend as far east as northeast NV, but confidence in this
scenario is low.

...Northern Montana...
A deepening surface low over the Canadian Prairies will augment west
to southwesterly pressure-gradient winds over northern MT through
the day. Sustained winds in the upper teens are expected, and some
degree of downslope warming/drying will support RH values in the
15-25% range. While some locations have seen recent rainfall, fuels
remain dry within the precipitation gaps, and may be receptive to
fire spread given the expected wind/RH combinations. Locally
critical conditions are possible in the immediate lee of the terrain
of western MT, but widespread critical conditions are not
anticipated.

...Please see www.spc.noaa.gov/fire for graphic product...


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