SPC MD 1881

SPC MD 1881

MD 1881 Image

Mesoscale Discussion 1881
NWS Storm Prediction Center Norman OK
0425 PM CDT Thu Oct 21 2021

Areas affected...northeast OH...far western PA

Concerning...Severe potential...Watch unlikely 

Valid 212125Z - 212330Z

Probability of Watch Issuance...20 percent

SUMMARY...The tornado risk will likely continue for another hour or
so (thru 600-630 pm EDT) and decrease towards sunset and likely be
very limited after sunset.

DISCUSSION...Radar imagery from Cleveland's 88D shows a broken band
of supercells immediately ahead of a strong mid-level vorticity
maximum moving east across the southern Great Lakes.  Surface
temperatures have warmed into the low-mid 60s with dewpoints near 60
F.  RAP forecast soundings indicate 100-250 J/kg MLCAPE with a
relatively straight hodograph yielding 150-225 m2/s2 0-1 km SRH. 
The current expectation is for a continuation of the tornado risk
for the next hour or so given the sufficient buoyancy in place
across northeast OH.  However, as the boundary layer begins to cool
this evening towards sunset and temperatures fall into the 60-62 deg
range, storm-scale rotation will gradually become more intermittent
and less intense.  The tornado risk will correspondingly lessen as
supercell rotation weakens.  The tornado risk will further diminish
after sunset as cooling further increases convective inhibition and
supercell rotation becomes more marginalized.

..Smith/Dial.. 10/21/2021

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


LAT...LON   40878149 41618112 41758020 41168008 40248090 40088214

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SPC MD 1880

SPC MD 1880

MD 1880 Image

Mesoscale Discussion 1880
NWS Storm Prediction Center Norman OK
0324 PM CDT Thu Oct 21 2021

Areas affected...Portions of far west TX

Concerning...Severe potential...Watch unlikely 

Valid 212024Z - 212300Z

Probability of Watch Issuance...5 percent

SUMMARY...Isolated storms capable of producing occasional gusty
winds and hail should continue through the rest of the afternoon.
Watch issuance is not expected.

DISCUSSION...A few storms have developed this afternoon over the
Davis Mountains and vicinity in far west TX. This region remains
displaced to the south of stronger mid-level flow across the
northern/central CONUS. Still, there is modest veering/strengthening
of the wind field with height through mid levels per recent VWPs
from KMAF. Around 20-25 kt of deep-layer shear should help foster
occasional storm organization. The presence of steep mid-level lapse
rates observed on the 12Z MAF sounding suggests some threat for
isolated marginally severe hail with the strongest storms. Diurnal
heating of the boundary layer has also steepened low-level lapse
rates, and occasional strong to severe downdraft winds may also
occur as the cores collapse. With a lack of stronger flow aloft,
storm motions should remain rather slow, with the overall severe
threat likely remaining quite isolated this afternoon. Therefore,
watch issuance is not expected.

..Gleason/Bunting.. 10/21/2021

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


LAT...LON   30520459 30910411 31050357 30590277 30060280 29600321
            29640398 29870444 30150464 30520459 

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SPC Oct 21, 2021 2000 UTC Day 1 Convective Outlook

SPC Oct 21, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0240 PM CDT Thu Oct 21 2021

Valid 212000Z - 221200Z


Thunderstorms associated with isolated strong wind gusts will be
possible this afternoon across parts of the southern and central
Appalachians into the Upper Ohio River Valley. Isolated storms
capable of marginally severe hail and strong gusts may also occur
over far West Texas.

...20z Update...

No appreciable changes are warranted to the 1630z outlook; however,
a small 2 percent tornado probability has been introduced over the
upper Ohio Valley region.

Latest satellite imagery suggests large-scale forcing is spreading
across OH toward western PA. Convection is gradually responding to
the approaching short-wave trough with a strengthening band of
convection along the surging cold front. Additionally, a narrow
corridor of scattered convection extends along the OH River into
western PA. Warm advection appears to be partly contributing to this
activity and wind profiles do support organized rotating updrafts.
While the tornado threat is low with these storms, it is non zero
and have opted to introduce a 2 percent probability to reflect this

..Darrow.. 10/21/2021

.PREV DISCUSSION... /ISSUED 1125 AM CDT Thu Oct 21 2021/

Upper-level low pressure near the southern tip of Lake MI will move
east today while gradually evolving into an open wave. An associated
surface low and cold front will move east in tandem with the upper
low across the Ohio Valley, with the trailing portion of the cold
front moving east through the central/southern Appalachians. An
upper-level ridge will be in place over much of the western U.S. as
a strong upper trough approaches the Pacific Northwest.

...Upper Ohio Valley and central and southern Appalachians...
Buoyancy will remain modest across the OH Valley portion of the
Marginal Risk area today owing to 50s dew points and generally poor
lapse rates, with afternoon MLCAPE values averaging 500 to locally
1000 J/kg. Moderately strong southwest mid-level flow will result in
45-55 kts of effective shear, more than sufficient to support
fast-moving clusters of storms and perhaps supercell structures
capable of producing strong/damaging gusts. Expect an increase in
thunderstorm coverage this afternoon near the eastward-moving cold
front as ascent with the upper trough develops over the region.

Farther south from southeast KY into northeast AL buoyancy will be
greater, averaging 1000 to 2000 J/kg, while effective shear will
only average 25-30 kts. Nevertheless, isolated stronger storms
within this environment along and in advance of the cold front will
be capable of producing strong wind gusts this afternoon and early

...Far West Texas...
A relatively moist air mass in conjunction with orographic
influences should contribute to at least isolated thunderstorm
development in vicinity of the Davis Mountains this afternoon.
Relatively steep mid-level lapse rates, moderate buoyancy, and
effective shear on the order of 25-30 kt may support some locally
severe storms capable of hail and strong wind gusts through early

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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook Image
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1257 PM CDT Thu Oct 21 2021

Valid 221200Z - 231200Z


The previous forecast remains on track. Latest fuel guidance
continues to show poor to modest fuel dryness across much of the
southern Great Basin, which will negate fire weather concerns
despite areas of elevated wind/RH conditions.

..Moore.. 10/21/2021

.PREV DISCUSSION... /ISSUED 1150 PM CDT Wed Oct 20 2021/

Upper-level ridging across the central CONUS will lose some
amplitude on Friday. Cyclonic flow will increase to the east and
west of the upper ridge. At the surface, a cold front will move into
the central Great Basin by the end of the period. A slightly
better-defined surface lee trough in the Plains will allow some
breezy conditions to develop along with increased moisture. While
dry and windy conditions are likely ahead of the cold front in the
southern Great Basin, poorly receptive fuels will keep fire concerns
low. A narrow zone of dry westerly winds in eastern New Mexico may
develop to the west of better low-level moisture. However, winds
still appear likely to remain at or below 15 mph and peak for a
short duration.

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

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