Mesoscale Discussion 2052
NWS Storm Prediction Center Norman OK
1253 PM CDT Thu Aug 20 2026

Areas affected...parts of southeastern Pennsylvania...central and
southern New Jersey...north central and eastern Virginia...much of
Delaware and Maryland.

Concerning...Severe potential...Watch likely 

Valid 201753Z - 202000Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms are likely to develop and intensify through
4-6 PM EDT, accompanied by the risk for a couple of tornadoes
initially and increasing potential for strong to severe gusts
spreading toward coastal areas into early evening.

DISCUSSION...Moderate to strong boundary-layer destabilization is
ongoing across much of the northern Mid Atlantic, particularly
within seasonably high moisture content air advecting northward
through the coastal plain, to the east of deepening (albeit weak)
surface troughing to the lee of the Blue Ridge.  This is occurring
downstream of mid-level troughing, with at least a couple of
convectively generated perturbations and belt of augmented westerly
flow (30-50 kt in the 700-500 mb layer).

It appears that associated forcing for ascent may increasingly begin
to impact a corridor from central Maryland through southeastern
Pennsylvania by 20-22Z, if not a bit earlier, supporting the
initiation of intensifying thunderstorm development.  At least
initially, this may include a few evolving supercell structures in
the presence of strong deep-layer shear.  

Downstream of a developing wave along a weak low-level baroclinic
zone strengthened by differential heating, low-level hodographs are
forecast to remain modest to weak.  However, they may still be
sufficient to contribute to potential for a couple of tornadoes,
aided by appreciable near-surface buoyancy developing in associated
with insolation, warm advection and dew point increases into the
lower 70s F.

Otherwise, at least some upscale growth of initial storms will
contribute to increasing potential for damaging surface gusts, with
additional thunderstorm development southward along and east of the
deeper lee surface troughing.

..Kerr/Smith.. 08/20/2026

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

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

LAT...LON   39437731 40007709 40347561 40497448 39637445 38797545
            38047655 37317704 37667808 38897776 39437731 

MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1133 AM CDT Thu Aug 20 2026

Valid 201630Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID-ATLANTIC...PARTS OF THE SOUTHEAST...AND FROM THE CENTRAL
PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Scattered severe storms are possible this afternoon into this
evening across parts of the Mid Atlantic, posing a risk for a couple
of tornadoes and damaging wind gusts.  Large hail and isolated wind
damage will be possible late today into tonight with severe storms
from Nebraska into northwest Wisconsin.  Scattered damaging gusts
are possible over parts of the Deep South this afternoon into the
early evening.

...Central Appalachians into the Mid-Atlantic...
Radar mosaic late this morning showed a couple of weak convectively
related vorticity maxima moving east across the central and southern
Appalachians (i.e., southwest PA, eastern KY).  One of these lead
disturbances was sampled by the WSR-88D VAD at Jackson, KY, with an
upstream shortwave trough over the OH Valley moving towards the
Mid-Atlantic states.  

The airmass across the Mid-Atlantic into the Carolinas will continue
to heat amid patchy but thinning cloud cover.  Model guidance shows
moderate buoyancy developing by early to mid afternoon from the
southern Appalachians northward into the northern Mid-Atlantic
region.  A belt of stronger 700-500 mb westerly flow (30-45 kt) will
overspread the northern half of VA northward into PA/NJ.  Beneath
this stronger flow, southerly low-level flow veering and
strengthening with height will support hodographs favorable for
organized severe storms, including supercells and organized line
segments.  The latest model guidance shows a few simulated
supercells developing in the area centered over MD and the upper
Chesapeake Bay vicinity during the 20-00z timeframe.  This scenario
seems plausible given some low-level enlargement to the hodograph
and effective shear around 40 kt.  A tendency for upscale growth
into a line segment is expected as this activity moves east towards
the coast during the evening.  A couple of supercell tornadoes are
possible with this activity, in addition to a line-embedded
mesovortex and scattered damaging gusts.  

...Carolinas into the TN Valley and lower MS Valley...
Ample low-level moisture and strong heating will result in an
unstable airmass from the Carolinas into much of the Southeast.
Low-level convergence along a cold front that will extend from the
western Carolinas into AR this afternoon will result in scattered
thunderstorm coverage as 2500-4000 J/kg MLCAPE develops by mid
afternoon.  High PW (in excess of 2 inches) and steep 0-3 km lapse
rates and modest westerly to west-northwesterly flow will favor
damaging downbursts with the stronger southeast-moving clusters.  

...Central Plains into the Upper MS Valley...
A tongue of relatively rich low-level moisture (mainly 60s F surface
dewpoints) will extend from the central Great Plains northward ahead
of a cold front, which is forecast to be draped from western MN into
western NE this afternoon.  Thunderstorm initiation is anticipated
first across the Upper MS Valley before expanding southwestward. 

Moderate northwesterly flow aloft will support supercell wind
profiles, with elongated/straight hodographs, and the threat for all
severe hazards.  Large to very large hail (i.e. greater than 2 inch
diameter) will be the primary severe hazard, particularly during the
early evening as the storms move into greater instability.  Isolated
strong to severe gusts (i.e. 55 to 75 mph) are possible as well.
Given the supercellular storm mode and low-level southerly flow, a
low-probability tornado risk also exists. Some risk for isolated
damaging gusts may persist into the early overnight across southern
NE and northern KS if clustering can
occur.

...AZ...
Not much change from prior forecast thinking in that isolated to
widely scattered storms are forecast but a generally lower risk for
severe gusts is anticipated later today into this evening.  Steep
lapse rates and inverted-V profiles will support an isolated risk
for severe gusts with the more intense downdrafts.

..Smith/Wendt.. 08/20/2026

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1222 PM CDT Thu Aug 20 2026

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS...

...SUMMARY...
Scattered damaging hail (some greater than 2 inch diameter) and
severe wind gusts may occur over parts of the central Plains late
Friday afternoon and evening. Scattered storms, some with severe
wind gusts and hail, also are possible across parts of the Midwest
and Southeast.

...Central Plains...

Enhanced northwesterly flow aloft will overspread portions of the
region on Friday. Meanwhile, a plume of steep midlevel lapse rates
will shift east across the central Plains toward the Mid-MO Valley.
A corridor of rich boundary layer moisture will be in place within
east/southeast low-level flow across portions of KS/NE ahead of a
west-to-east oriented surface boundary. Moderate to strong
instability is forecast by late afternoon into evening, supporting
widely scattered thunderstorm development near the surface boundary.
Vertically veering wind profiles with elongated/straight hodographs
and 45+ kt effective shear magnitudes will support initial
supercells. Large to very large hail (some greater than 2 inches
diameter) will be possible. With time, a forward propagating cluster
could develop and move southeast across parts of NE and KS. Some
potential for severe gusts (a few near 70-80 mph) will be possible
given large instability and steep low-level lapse rates. 

It is uncertain how far south the severe risk will persist into the
overnight hours. Forecast guidance, including CAMs, vary
considerably, but some potential could spread into parts of northern
OK late Friday/early Saturday. For now, have extended the Marginal
risk southward across KS to account for conditional severe
potential. 

...IA/WI/IL...

Northwesterly flow aloft will modestly increase on Friday as an
upper trough deepens over the Midwest. Cooling aloft will also
result in areas of steepening midlevel lapse rates atop a seasonally
moist airmass ahead of a southeastward-advancing cold front. This
will aid in a corridor of moderate to strong destabilization across
portions of IA into northern IL and southern/eastern WI. Vertical
wind profiles will support supercell thunderstorms capable of large
hail and strong wind gusts. The southward extent of the risk into
central IL is a bit uncertain, but some risk could persist into late
evening.

...Southeast/Carolinas...

A very moist and strongly unstable airmass will be in place in the
vicinity of a surface trough Friday afternoon. Strong heating and
weak confluence will aid in thunderstorm development along the
surface trough and higher terrain. Sufficient storm coverage could
result in clustering/forward propagating as storms move eastward
through the afternoon/early evening. Otherwise, weak vertical shear
will limit overall organization, but sporadic severe/damaging gusts
could occur from wet microbursts within the unstable/high PW
airmass.

..Leitman.. 08/20/2026

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1029 AM CDT Thu Aug 20 2026

Valid 201700Z - 211200Z

...NO CRITICAL AREAS...

No changes to the previous forecast with no drawn areas. Hot and dry
conditions continue across the Intermountain West resulting in fair
to poor overnight RH recoveries over low elevation portions of OR
and surrounding states, where the fire weather threat increases
through the next couple of days.

..Stearns.. 08/20/2026

.PREV DISCUSSION... /ISSUED 1238 AM CDT Thu Aug 20 2026/

...Synopsis...
Upper-level troughing will persist over the northeastern CONUS
today, with an embedded mid-level shortwave yielding increased
precipitation chances over a drought-stressed environment in
northern Minnesota and Wisconsin. The established upper ridge over
the Great Basin will continue to amplify, delivering above normal
temperatures and dry conditions to the Interior West. Meanwhile, an
upper trough will deepen along the West Coast, ushering stronger
southwesterly flow into the northwestern CONUS. Only brief and
localized elevated fire environment conditions are expected over
much of the Intermountain West this afternoon.

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