2026 Mid-Atlantic Severe Storm General Discussion

[mappy]

Morning clouds and rain always bodes well for severe later 

[H2O]

13 minutes ago, mappy said:

Morning clouds and rain always bodes well for severe later 

It will clear off at 12:52pm and be sunny for exactly one hour and 22 min. That will give enough time for one cell to form near Winchester to miss east coast npz and give a severe warning to leesburgtownville up to Frederick. Then a dc split will happen with one red box over laurel for broad rotation on radar 

[midatlanticweather]

2 minutes ago, H2O said:

It will clear off at 12:52pm and be sunny for exactly one hour and 22 min. That will give enough time for one cell to form near Winchester to miss east coast npz and give a severe warning to leesburgtownville up to Frederick. Then a dc split will happen with one red box over laurel for broad rotation on radar 

Well here in Purcellville we may get a warning... and have it dropped as downslope of the Blue Ridge/Mount Weather (probably some Government experiment, but keep that a secret) splits it and then reforms exactly like you said!

 

[JenkinsJinkies]

13 minutes ago, H2O said:

It will clear off at 12:52pm and be sunny for exactly one hour and 22 min. That will give enough time for one cell to form near Winchester to miss east coast npz and give a severe warning to leesburgtownville up to Frederick. Then a dc split will happen with one red box over laurel for broad rotation on radar 

Translation you have a flight at 1:14.

[mappy]

47 minutes ago, H2O said:

It will clear off at 12:52pm and be sunny for exactly one hour and 22 min. That will give enough time for one cell to form near Winchester to miss east coast npz and give a severe warning to leesburgtownville up to Frederick. Then a dc split will happen with one red box over laurel for broad rotation on radar 

lol sounds about right. 

[TSSN+]

1 hour ago, mappy said:

Morning clouds and rain always bodes well for severe later 

Suns coming out in Charlestown so let’s see how this goes. HRRR been getting more robust each run. 

[batmanbrad]

SPC quite late with their 9AM D1 outlook update, wondering if they've been waiting on some additional model data?

[yoda]

4 minutes ago, batmanbrad said:

SPC quite late with their 9AM D1 outlook update, wondering if they've been waiting on some additional model data?

It shows up here - https://kamala.cod.edu/SPC/

Well, the discussion does

 

[SnowenOutThere]

2 hours ago, yoda said:

Morning discussion from LWX 

DISCUSSION...
KEY MESSAGE 1...Severe weather is possible, mainly east of the
Blue Ridge this afternoon into early evening.

A slow-moving cold front arcs down the Saint Lawrence River
Valley to the lower Great Lakes back into the central Great
Plains. To the south, a largely stationary front was attempting
to lift slowly northward as a warm front, and stretched from the
Carolinas back to Oklahoma. Showers and thunderstorms were
persistently trekking west to east along the northern front,
with a weak surface low and MCV/shortwave crossing Illinois.
This shortwave will be the impetus for convective development
across the Mid-Atlantic later today as the local area sits in
between the two aforementioned fronts.

Most instability this morning is rather weak and elevated in
nature, but is expected to increase rapidly in the I-95 corridor
from south to north as higher moisture air advects into the
area, as well as near the Appalachians ahead of an approaching
shortwave, both by late this morning. For now, weak lift and CAPE is
keeping things limited to a few WAA showers near the metros.

Additional development, perhaps even deeper convective cores,
is possible by as early as late morning given the anticipated
rapid increase in CAPE and lift.

Flow aloft is seasonably strong by late August standards, with a
100+ knot 300 hPa jet streak expected to pivot over the Saint
Lawrence River Valley into northern New England by evening. The
tail of this upper jet may actually strengthen and persist near
the Mason-Dixon Line early this evening, which could briefly
enhance large scale ascent locally via RRQ dynamics.

In the mid levels, the previously mentioned shortwave has
trended notably deeper and a bit slower over the last 12-24
hours. This brings the axis of the shortwave, its enhanced flow,
and PVA across the Appalachians around midday, then across
areas near and east of the Blue Ridge/Catoctin Mountains east to
I-95 and the Chesapeake Bay during peak heating. In addition to
bringing large scale ascent, this pushes effective deep layer
bulk shear into the 35- to 50-knot range later today (highest
north/northeast). Shear of this magnitude is favorable for
sustained, organized updrafts, including line segments and
supercells (discrete or line-embedded).

Thermodynamically, the atmosphere will be very moist, especially
further east. Strong low-level theta-e advection is expected to
persist through early evening ahead of the approaching shortwave
and cold front. Widespread clouds will limit heating somewhat,
especially west of the Blue Ridge where the storm threat is
notably less, but with the strong low-level moisture advection
and slow-but-steady cooling aloft, the net result should be
about 1000-2000 J/kg MLCAPE in the moist plume east of the Blue
Ridge heading into this afternoon, possibly as early as late
morning. The moist low-level advection beneath cooling aloft
may also result in re-generative CAPE and multiple rounds of
thunderstorms in any one location. This would be most likely
from near the DC metro north and east where large scale ascent
is strongest, with the added component of enhanced low-level
convergence along bay or river breezes (and eventually composite
outflow boundaries).

Finally, PWs will approach or exceed 2 inches in the moist axis
near and east of I-95 this afternoon into early evening. Deep
warm cloud layers in the high PW airmass will yield heavy to
extreme instantaneous and sub-hourly rainfall rates in the
stronger precip cores. Individual cell motion is expected to be
progressive (30-40 mph) given enhanced flow through the column
and the potential for modest cold pool development with any
persistent cells, clusters or line segments. However, the wavy
slow-moving front approaching from the north may lie close to
parallel to the mean steering flow at times, especially when
modulated by outflow from potential multiple rounds of storms.
This, coupled with the bay breeze which often takes on a similar
orientation, plus the urban footprint that has seen heavy rain
recently raises a (primarily urban/poor drainage) flash flood
risk over the I-95 corridor in northeast Maryland, including the
Baltimore area. The threat is a bit more conditional further
south and west into areas like Annapolis and the DC/Capital
Beltway region; these areas also feature urban sprawl and
inherently lower FFG, but the training potential is more
conditional based on favorable outflow or cell interactions
given slightly further displacement from the synoptic front(s)
and bay breeze.

Multiple hazards are possible today, and are outlined below.

Damaging Wind...
Straight-line/downburst winds are likely the highest threat
today, at least from an areal coverage standpoint. Tall, skinny
CAPE profiles with modest pockets of mid-level dry air yield
DCAPE of 600-800 J/kg, which would be marginally favorable for
strong to severe downdrafts. Background mid-level flow may
approach 40 knots around 700 hPa. With the high PW air and
modest DCAPE, water-loaded downdrafts via precip drag would be
possible especially with any bowing line segments or collapsing
mesocyclones/mesovorticies. The lack of steeper lapse rates
(hence modest DCAPE) should keep most wind gusts within the
strongest storms in the 55-70 mph range, with more widespread
40-55 mph potential. Given heavy precip and late summer, leafed-
up trees, would anticipate scattered to numerous instances of
tree and branch falls and subsequent power outage potential. The
risk is highest near and east of I-95 where storms are most
likely to become linear and be a bit more intense, since they`re
further east in the moist axis with a little more time to heat.
To the west, especially west of the Blue Ridge, less moisture
and heating should keep the coverage of more intense storms low.

Tornadoes...
A conditional risk for a brief spin-up is evident for most areas
east of the Blue Ridge given the magnitude of low/mid-level flow
and high PWs/lower LCLs. Relatively greater tornado potential
may exist closer to the front near the I-70 corridor east of
Frederick where surface winds will be backed and low-level SRH
will be higher, especially in close proximity to the bay breeze
along the western shore of the Chesapeake Bay into northeast MD.
Potential would be further maximized by (1) discrete supercells
occurring earlier when the synoptic low-level winds remain
backed and SRH is higher on a broad scale, and (2) with any
favorable QLCS surge/mesovortex interactions with residual
outflow or the bay breeze. Although unlikely due to a lack of
stronger 0-1 km shear/SRH and steeper lapse rates, robust 3CAPE
near the bay could result in a conditional risk for a strong
tornado if all of the above factors were to coalesce.

Flash Flooding...
We have been in a wetter pattern recently, but the majority of
the region is still in or just coming out of drought. Poor
drainage and urban areas are susceptible to heavy rain,
especially the intense sub-hourly rates possible today,
regardless. Additionally, areas near and just northeast of
Baltimore have seen multiple episodes of heavy rain over the
last few weeks. Individual storms should move pretty swiftly,
but the slowing southwest end of any lines or clusters would
orient parallel to the nearby surface front, bay breeze, and
mean steering flow. This brings a risk of flash flooding to
northeast MD in particular, with a more conditional risk further
south and west into the greater DC metro.

Hail...
Although lapse rates aloft will be modest at best given the
moist profiles, supercellular shear and modest mid-level cooling
will be favorable for at least some marginal/spotty severe hail
potential. Should mid-level shear/cooling be more potent or
cells be more discrete, the hail risk could increase, but this
seems unlikely given the otherwise tropical-esque airmass.

The threat for severe weather and flooding appears highest
between 2 PM this afternoon and 8 PM this evening, progressing west
to east in one or two rounds. However, it may start a couple hours
earlier further west (or on the bay breeze), and could linger
through late evening over southern Maryland.

By later this evening, the departure of large scale lift and the
loss of daytime heating should end the severe/flood threat.

This is one of the best read ups I’ve read in a bit! We’ll have to see how the situation evolves with our cape ml lapse rates improving. 

[yoda]

LWX will do an 18z SPEC sounding per SPC request - in updated morning AFD 

[Eskimo Joe]

29 minutes ago, yoda said:

LWX will do an 18z SPEC sounding per SPC request - in updated morning AFD 

Given the tornado risk east of I-95, this is justified. I could see a tornado watch going up east of here.

[The Dude]

1 hour ago, SnowenOutThere said:

This is one of the best read ups I’ve read in a bit! We’ll have to see how the situation evolves with our cape ml lapse rates improving. 

Agreed.  Fantastic AFD.  The team at LWX is top notch.

[Kmlwx]

Crapvection around now

[ravensrule]

15 minutes ago, Kmlwx said:

Crapvection around now

Are you at Chipotle?

[Kmlwx]

7 minutes ago, ravensrule said:

Are you at Chipotle?

 

Qdoba > Chipotle 

[yoda]

Well thats interesting... 30%wind and 5% tornado moved westward, now includes DC metro on 1630z OTLK 

 

[yoda]

Oh... um hello there CIG 1 hatching 

 

[vortex95]

14 hours ago, Eskimo Joe said:

Do you think this is an I-95 and east event, or are the western suburbs in play?

It seems just E  of I95 and just S and SE of the metro is always "in play!"  The way I approach it now is, "is the area between a line from DCA and IAD and about 15 mi to the N in play b/c this area seems most variable and gets the shaft, relatively speaking, more often that not.  Probably due to the location from things like downslope from the Appalachians, but it seems very dependent on the mean flow.  W and WNW seems to be not good often (DC split), but of course, this is just a broad view.  Subtle differences in the mesoscale can be huge.

[yoda]

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.