2026 Mid-Atlantic Severe Storm General Discussion

[vortex95]

17 minutes ago, batmanbrad said:

CSU-MLP latest still painting the maximum TOR possibilities right over the general DC area:

That's a solid sign.  One thing that can misleading -- cool, dreary, and stable-looking can make ppl think, "how can this 'go away' so fast and big svr occur?"  Well, it does and can be quite dramatic.  Wichita Falls TX was socked in stable ahead of the warm front on 4/10/1979, and then an F4 cut directly through the city for the costliest tor up to this time.

Same thing in Windsor CO on 5/22/2008.  This was an odd one b/c it occurred the late morning, moved NNW, and the storm formed in a very narrow sweet spot of instability/shear ahead of a sfc low.  See here:
https://www.weather.gov/bou/TornadoMay22nd2008

Mean-looking!
https://www.youtube.com/watch?v=GfYuT0oalXQ
 

 

[wxmeddler]

2 minutes ago, vortex95 said:

It loves to make giant convective blobs on its composite reflectivity fcst.  Once it goes operational, and ppl use it more, I bet that will be a sig complaint, and they will address it.

A big issue w/ mesoscale models now is that the more hires they get and more directly simulate the atmosphere processes, the challenge to get everything in balance goes up in a non-linear fashion.  In other words, any small tweak to fix one issue can have big impacts to another part of the model.
 

The over-convection and "big blobs" on the RRFS is a known bias or "bug" with the FV3 Dynamical Core. This was explored recently by Lou Wicker at OU (See: https://doi.org/10.1175/MWR-D-25-0230.1). In short, it can't really be fixed without significant changes to the core. OMD hasn't said it outright publicly but the original plan was to turn off the HRRR and RAP at the same time as the RRFS Operationalization. But they've scrapped that specifically because of the FV3 core issues. Now the plan is to turn off the HRRR and RAP when the RRFS transitions to the MPAS Core in ~2028. (https://www.weather.gov/media/wrn/calendar/RRFS_webinar_20260625.pdf)

 

[vortex95]

30 minutes ago, Kmlwx said:

Good demonstration of how more resolution is not always automatically "better." 

There's probably a "happy medium" where errors can be smoothed while still having good resolution...but I imagine if we had like 0.25km resolution models it would be chaotic at best. Until better computing comes along I guess. 

Here is the best line I have seen that tempers the idea that the models are so good, they are better all the time by default, and by extension, human input is not needed.

"Models now can give very precise-looking forecasts/output that can be *precisely* wrong!
 

And going one step further:

"Precision does not mean accuracy!"

[Rhino16]

23 minutes ago, wxmeddler said:

The over-convection and "big blobs" on the RRFS is a known bias or "bug" with the FV3 Dynamical Core. This was explored recently by Lou Wicker at OU (See: https://doi.org/10.1175/MWR-D-25-0230.1). In short, it can't really be fixed without significant changes to the core. OMD hasn't said it outright publicly but the original plan was to turn off the HRRR and RAP at the same time as the RRFS Operationalization. But they've scrapped that specifically because of the FV3 core issues. Now the plan is to turn off the HRRR and RAP when the RRFS transitions to the MPAS Core in ~2028. (https://www.weather.gov/media/wrn/calendar/RRFS_webinar_20260625.pdf)

 

The part about the RAP is interesting to me because it seems like SPC Mesoanalysis is created using the RAP. I wonder how much work it is to change all that over unless something else replaces it like WoFS.

Edit: I guess they did it in 2012 with the RUC

[yoda]

Any idea why 1630z OTLK from SPC is late?  I'm checking kamala and SPC... I don't see it

[vortex95]

18 minutes ago, wxmeddler said:

The over-convection and "big blobs" on the RRFS is a known bias or "bug" with the FV3 Dynamical Core. This was explored recently by Lou Wicker at OU (See: https://doi.org/10.1175/MWR-D-25-0230.1). In short, it can't really be fixed without significant changes to the core. OMD hasn't said it outright publicly but the original plan was to turn off the HRRR and RAP at the same time as the RRFS Operationalization. But they've scrapped that specifically because of the FV3 core issues. Now the plan is to turn off the HRRR and RAP when the RRFS transitions to the MPAS Core in ~2028. (https://www.weather.gov/media/wrn/calendar/RRFS_webinar_20260625.pdf)

 

Thanks!  Great to know and I will pass along.

Turning off the NAM I have no issue w/, but when you roll out a new model, you should always keep its predecessor for a time for comparison.  The NAM is severely outdated, but the HRRR is not and still does a solid job, so kept it UFN!

They were supposed to stop the HWRF and HMON last year, as the HAFS has shown marked improvement overall (I was sold when it nailed MIlton's RI, then weakening, then another RI, and then its rapid weakening leading to landfall).  The HMON?. recall when that was first rolled out in 2017 I think.  It was showing crazy intense TCs, so much the model fields would "turn inside-out" b/c the intensity was nuts.  But the HWRF and HMON continue.

I prefer avoid the notion "more is better."  Yes, second options and consensus have value, but only to a point.  It can easily become TMI and hurt the fcst process.  Also, you have those that always look for the one model that shows the worst case scenario, and they run w/ that for clicks/likes on social media, when it is well known X model is terrible or has bias for Y phenomena.  It's like the GFS for spinning up bogus TCs beyond day 7 or the ICON in just how it handles TCs (much too intense forecasts for current TCs).

[yoda]

1630z OTLK from SPC disco for our area

   While storms have weakened, showers/cloud cover remain prevalent
   near/east of the Appalachians at midday across the Mid-Atlantic
   region. This will tend to limit/delay destabilization in many areas
   (especially with north-northeastward extent). That said, air mass
   recovery/advection is expected from the west, with ample upstream
   clearing per visible satellite imagery across the Cumberland Plateau
   into parts of the Allegheny Plateau. Pending the timing/location of
   destabilization, some terrain/lee trough-related development may
   diurnally occur, although the most prevalent/more certain scenario
   may be for potentially severe storms to spread into the region this
   evening. Damaging winds will be the most common hazard regionally,
   although a tornado could occur, attributable to MCV-enhanced flow
   and/or with any storms interacting with the effective warm front
   across the Mid-Atlantic region.

[vortex95]

52 minutes ago, wxmeddler said:

The over-convection and "big blobs" on the RRFS is a known bias or "bug" with the FV3 Dynamical Core. This was explored recently by Lou Wicker at OU (See: https://doi.org/10.1175/MWR-D-25-0230.1). In short, it can't really be fixed without significant changes to the core. OMD hasn't said it outright publicly but the original plan was to turn off the HRRR and RAP at the same time as the RRFS Operationalization. But they've scrapped that specifically because of the FV3 core issues. Now the plan is to turn off the HRRR and RAP when the RRFS transitions to the MPAS Core in ~2028. (https://www.weather.gov/media/wrn/calendar/RRFS_webinar_20260625.pdf)

 

Along the same lines, how does the RRFS do w/ TCs?  And for that matter, the HRRR?  We know the NAM (3 and 12 km) is terrible and was never designed for TCs, but the newer CAMs?

[midatlanticweather]

76/76 now but breezes from the south have been more steady and the lower foggy haze is lifting. Also seing very bright patches as the clouds seem to want to break up. Little patches of thinner clouds are showing up on satellite. We shall see if this enhances anything. Air is thick 

 

[jewell2188]

Seems as though on visible, clearing should progress west to east very shortly!

[Eskimo Joe]

Latest HRRR puts a legit bow through Frederick/Loudoun/Montgomery/Carroll counties right at sunset.

[SnowenOutThere]

1 hour ago, vortex95 said:

Turning off the NAM I have no issue w/, but when you roll out a new model, you should always keep its predecessor for a time for comparison.  The NAM is severely outdated, but the HRRR is not and still does a solid job, so kept it UFN!

Not the thread for this question, but is the conversation for it. I understand turning the NAM off for convective season, however, I don’t understand turning it off for winter short term stuff. I would love to know why, I assume it’s something in how it handles thermodynamics and WAA, but the NAM is almost always the most correct model when it comes to refining the mixing line in synoptic scale winter storms. It just seems odd to turn off a model which has a very useful edge on all others, even if it sucks at a lot of other aspects; could at least compromise and run it before major storms on the east coast. Would love to know your thoughts on both why it surpasses the other mesoscale models in the mixing line placement and how to compensate for its disappearance come winter time. 

[vortex95]

1 minute ago, SnowenOutThere said:

Not the thread for this question, but is the conversation for it. I understand turning the NAM off for convective season, however, I don’t understand turning it off for winter short term stuff. I would love to know why, I assume it’s something in how it handles thermodynamics and WAA, but the NAM is almost always the most correct model when it comes to refining the mixing line in synoptic scale winter storms. It just seems odd to turn off a model which has a very useful edge on all others, even if it sucks at a lot of other aspects; could at least compromise and run it before major storms on the east coast. Would love to know your thoughts on both why it surpasses the other mesoscale models in the mixing line placement and how to compensate for its disappearance come winter time. 

Yes, the NAM has some uses.  It handles CAD much better than the GFS, as one example and its MOS reflects that.  But the HRRR handles CAD well, so no loss there.

Since it has more vertical levels than all the global models, its should handle mix zone better and we are used to that.  But again, the HRRR and now RRFS should effectively replace that skill (eventually).

Losing some for other gain happens.   I recall NHC objected to an upgrade of the GFS some years ago b/c it was clearly shown that the upgrade made TC skill less for the EPAC basin.  The upgrade was done regardless.  So it's hard to please everyone!

 

[Eskimo Joe]

1 minute ago, vortex95 said:

Yes, the NAM has some uses.  It handles CAD much better than the GFS, as one example and its MOS reflects that.  But the HRRR handles CAD well, so no loss there.

Since it has more vertical levels than all the global models, its should handle mix zone better and we are used to that.  But again, the HRRR and now RRFS should effectively replace that skill (eventually).

Losing some for other gain happens.   I recall NHC objected to an upgrade of the GFS some years ago b/c it was clearly shown that the upgrade made TC skill less for the EPAC basin.  The upgrade was done regardless.  So it's hard to please everyone!

 

Use NAM MOS and HRRR together and you knew when the flip from SN -> IP -> RA would occur 90% of the time. That combination consistently schooled the GFS and Euro inside 30 hrs.

[vortex95]

1 hour ago, midatlanticweather said:

76/76 now but breezes from the south have been more steady and the lower foggy haze is lifting. Also seing very bright patches as the clouds seem to want to break up. Little patches of thinner clouds are showing up on satellite. We shall see if this enhances anything. Air is thick 

 

In tropical situations, it can be useful to use the virtual temp at the sfc instead of the dry bulb temp.  Using it can represent CAPE better in such environments (virtual temp decreases CIN  and increases CAPE).

76 dew point is nothing to shake a stick at!  Don't need too much heating for things to go and go well w/ that kind of juice.

[Eskimo Joe]

Per SPC mesoanalysis, there's a pretty solid are of instability cresting the Allegheny Front.

[vortex95]

41 minutes ago, Eskimo Joe said:

Latest HRRR puts a legit bow through Frederick/Loudoun/Montgomery/Carroll counties right at sunset.

The line is already there in ern OH (looks like a LEWP), so the HRRR is not creating the mini-bow echo from nowhere.

HRRR has a couple of cells before the bow, and then clusters after it!  My kind of tstm day!

[yoda]

Watch coming shortly... looks like for i95 corridor westward

https://www.spc.noaa.gov/products/md/md2000.html

 

[yoda]

1 minute ago, yoda said:

Watch coming shortly... looks like for i95 corridor westward

https://www.spc.noaa.gov/products/md/md2000.html

 

 

Mesoscale Discussion 2000
   NWS Storm Prediction Center Norman OK
   0228 PM CDT Sun Aug 16 2026

   Areas affected...south-central Pennsylvania...the Maryland and West
   Virginia Panhandles...and northern Virginia

   Concerning...Severe potential...Watch likely 

   Valid 161928Z - 162130Z

   Probability of Watch Issuance...80 percent

   SUMMARY...The threat for severe storms capable of mainly damaging
   wind gusts is expected to increase late this afternoon into evening.
   A severe thunderstorm watch is likely.

   DISCUSSION...In the wake of an MCV moving from south-central into
   southeast PA, clouds are gradually clearing, allowing for increased
   diabatic heating this afternoon. When coupled with a moist boundary
   layer characterized by boundary-layer dewpoints in the upper 60s to
   mid 70s F, latest objective analysis indicates MLCAPE of 1000-1500
   J/kg with decreasing convective inhibition. Additional air mass
   destabilization is expected through the remainder of the afternoon,
   allowing ongoing QLCSs to spread east into the discussion area.
   Damaging wind gusts will be the primary hazard with the most intense
   storms, especially in the vicinity of any embedded bowing structures
   that may persist. A brief tornado or two is possible in areas that
   can maintain more of a southerly wind component, where low-level
   shear is locally enhanced.

   ..Mead/Guyer.. 08/16/2026

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

   ATTN...WFO...AKQ...CTP...LWX...RNK...PBZ...

   LAT...LON   38357955 38947931 39407927 40267895 40477848 40397801
               39307761 38237782 37877812 37537857 37497918 37897993
               38357955 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH

[Eskimo Joe]

Definitely looking like a non zero tornado threat west of US 15 this evening. Mesoanalysis and mesonet data showing some nice backing of winds and surge in dews.

[Eskimo Joe]

Also a heavy precip disco for our far western posters:

Quote

Mesoscale Precipitation Discussion 1070
NWS Weather Prediction Center College Park MD
139 PM EDT Sun Aug 16 2026

Areas affected...Northeastern Ohio and Western Pennsylvania to
Potomac Highlands

Concerning...Heavy rainfall...Flash flooding possible

Valid 161737Z - 162230Z

SUMMARY...Organized thunderstorms over northeast Ohio will progress east through western Pennsylvania into this evening. 
Cell-training is possible with a localized flash flooding concern rest of the afternoon.

DISCUSSION...As of 1730Z, an MCS over northeast Ohio is ahead of an MCV over western Lake Erie. Sufficient instability is downstream with SBCAPE of 2000-3000 J/kg. 
Abundant moisture is present with 2.2" PW over eastern OH that will advect east with the line. Deep layer westerly flow will keep the system progressive overall, 
though development ahead will locally train with a general 1-2 local 3" rainfall in the forecast into this evening. 1hr FFG downstream is generally 1 to 1.5", so 
flash flooding should be localized to areas with repeating activity.

Unlike areas farther west and south, recent HRRR and RRFS runs have a decent handle on this convective line with potential for another round development 
still ahead of the MCV later. The 15Z RRFS is hotter than the HRRR with QPF per usual with a risk for 4" along an axis that does not seem reasonable since 
the RRFS depiction is confined too far north compared to reality from NEXRAD. Flash flooding is considered possible and should remain localized. This area 
is rather flood prone, so this area will continue to be monitored and should a second line develop this evening, a subsequent discussion would be needed.

Jackson

 

[yoda]

Interesting...

Special Weather Statement
National Weather Service Baltimore MD/Washington DC
410 PM EDT Sun Aug 16 2026

MDZ509-510-162130-
Eastern Garrett-Western Garrett-
410 PM EDT Sun Aug 16 2026

...A LINE OF SEVERE THUNDERSTORMS IS APPROACHING GARRETT COUNTY...

At 405 PM EDT, radar indicated severe thunderstorms were located
along a line extending from near Jefferson Boro to near Cassville to
Monongah to near Enterprise. Movement was east at 50 mph.

Locations impacted include...
Mountain Lake Park, Oakland, Bayard, Bittinger, Grantsville, Loch
Lynn Heights, Friendsville, Deer Park, Accident, Redhouse, Hutton,
Gorman, Jennings, Crellin, Deep Creek Lake State Park, Swallow Falls
State Park, McHenry, Big Run State Park, Piney Grove, and McComas
Beach.

This includes Interstate 68 in Maryland between mile markers 1 and
30.

Frequent cloud to ground lightning is occurring with this line of
storms. Lightning can strike 10 miles away from a thunderstorm. Seek
a safe shelter inside a building or vehicle.

If you are on or near Deep Creek Lake, be preapred to take swift
action to get out of the water and move indoors or inside a vehicle
as storms approach. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning.

[yoda]

Updated afternoon AFD from LWX 

DISCUSSION...
KEY MESSAGE 1...Severe weather and flash flooding are possible
through tonight.

Very active weather is expected over the next 12 hours, with
the threat for flash flooding, damaging wind gusts, and a few
tornadoes.

As of 330 PM, regional radar shows two developing MCSs across
western Pennsylvania and West Virginia, both with a history of
producing damaging winds. These MCSs are expected to continue
eastward into our area over the next few hours. Skies have
cleared out ahead of the storms, so strong daytime heating is
underway and conditions are destabilizing. MLCAPE values are
forecast to increase to around 1500-2000 J/kg ahead of the line,
with effective bulk shear increasing to around 30-35 knots. This
parameter space should allow these storms to continue across
much of the forecast area, leading to a threat for primarily
damaging winds. With around 30 knots of 0-3 km shear oriented
roughly perpendicular to the lines, a brief QLCS tornado also
can`t be ruled out. This threat could be locally maximized as
the line encounters a warm front oriented from north to south
extending from near Frederick to Fredericksburg. The storms
should tend to weaken later tonight as they move east of this
boundary into a lower instability airmass.

Storms are right on the doorstep of the Alleghenies at the
moment, and should press eastward toward the I-95 corridor by
around 8-10 PM. Additional storms are also in the process of
developing across central Indiana to north central Ohio. Some
recent CAM runs hint that those storms may develop into a
secondary line that would move through a couple hours after the
first round. There are also some hints of backbuilding,
especially in the DC Metro area between those rounds as low-
level flow picks up behind the first MCS, equaling or exceeding
winds higher up in the atmosphere. This results in Corfidi
upshear vectors near zero, suggesting that backbuilding and
localized training could be possible in the vicinity of the warm
front. Thermodynamically, the environment is extremely
favorable for heavy rainfall production, with precipitable water
values well in excess of 2 inches, and forecast to potentially
near 2.5 inches this evening. That coupled with MLCAPE values
around 1000 J/kg and deep warm cloud layers will make any storms
capable of producing very heavy instantaneous rainfall rates.
That coupled with the potential for multiple rounds of storms,
and/or training/backbuilding raises concerns for flash flooding
this evening. A Flood Watch remains in effect for Garrett
County, which had a flood event a few nights ago. Another Flood
Watch may be considered for the DC Metro shortly, given the
above conditions.

Storms are expected to clear the area by around 2 or 3 AM, with
dry conditions later tonight. Additional thunderstorms may be
possible tomorrow afternoon, but coverage of storms is expected
to be much lower, and the threat for both severe thunderstorms
and flash flooding is expected to be much lower, if not zero.

 

[yoda]

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
435 PM EDT Sun Aug 16 2026

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Garrett County in western Maryland...

* Until 515 PM EDT.

* At 434 PM EDT, severe thunderstorms were located along a line
  extending from 8 miles east of Point Marion to 11 miles east of
  Brookhaven to Newburg to 7 miles east of Grafton, moving east at 40
  mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Radar indicated.

  IMPACT...Damaging winds will cause some trees and large branches
           to fall. This could injure those outdoors, as well as
           damage homes and vehicles. Roadways may become blocked by
           downed trees. Localized power outages are possible.
           Unsecured light objects may become projectiles.

* Locations impacted include...
  Mountain Lake Park, Oakland, Bayard, Bittinger, Grantsville, Loch
  Lynn Heights, Friendsville, Deer Park, Accident, Redhouse, Hutton,
  Gorman, Jennings, Keysers Ridge, Mineral Spring, Crellin, Deep
  Creek Lake State Park, Swallow Falls State Park, McHenry, and
  Selbysport.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

For your protection move to an interior room on the lowest floor of a
building.

Damaging wind, and continuous cloud to ground lightning are
occurring with these storms. Move indoors immediately. Lightning is
one of nature`s leading killers. Remember, if you can hear thunder,
you are close enough to be struck by lightning.

If on or near Deep Creek Lake, get away from the water and move
indoors or inside a vehicle. Remember, lightning can strike out to
15 miles from the parent thunderstorm. If you can hear thunder, you
are close enough to be struck by lightning. Move to safe shelter
now.

&&

LAT...LON 3972 7911 3930 7930 3930 7933 3928 7935
      3927 7937 3924 7942 3922 7943 3920 7947
      3920 7949 3972 7948
TIME...MOT...LOC 2034Z 284DEG 36KT 3975 7974 3965 7968 3940 7982 3938
7989

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

[yoda]

Severe Thunderstorm Watch up until 11pm

URGENT - IMMEDIATE BROADCAST REQUESTED
   Severe Thunderstorm Watch Number 588
   NWS Storm Prediction Center Norman OK
   435 PM EDT Sun Aug 16 2026

   The NWS Storm Prediction Center has issued a

   * Severe Thunderstorm Watch for portions of 
     District Of Columbia
     Maryland
     Central Pennsylvania
     Virginia
     Eastern West Virginia
     Coastal Waters

   * Effective this Sunday afternoon and evening from 435 PM until
     1100 PM EDT.

   * Primary threats include...
     Scattered damaging wind gusts to 65 mph likely
     A tornado or two possible

   SUMMARY...Multiple organized clusters of storms will likely cross
   the mountains and generally persist east-southeastward into the
   region, as the downstream air mass near/east of the mountains
   destabilizes in the wake of early morning storms and cloud cover.
   Damaging winds are the most common severe hazard expected, but some
   tornado potential may exist as well, particularly near an effective
   warm front.

   The severe thunderstorm watch area is approximately along and 65
   statute miles east and west of a line from 40 miles east northeast
   of Altoona PA to 50 miles south southwest of Staunton VA. For a
   complete depiction of the watch see the associated watch outline
   update (WOUS64 KWNS WOU8).

 

[yoda]