2026 Mid-Atlantic Severe Storm General Discussion

[high risk]

11 hours ago, vortex95 said:

Yet another solid 500 trough for July,  This time actuality cuts-off and is slow to move out, so looks like Mon-Wed tstms each day in some form, and maybe Thu if the ECMWF is right.  Tue appears the best for svr wx currently.

         The Euro is a legit severe solution for Tuesday.   The GFS screams "dying MCS moves through at 9AM and kills off the afternoon threat".

[Kmlwx]

1 hour ago, high risk said:

         The Euro is a legit severe solution for Tuesday.   The GFS screams "dying MCS moves through at 9AM and kills off the afternoon threat".

Dueling models

[Eskimo Joe]

10 hours ago, high risk said:

         The Euro is a legit severe solution for Tuesday.   The GFS screams "dying MCS moves through at 9AM and kills off the afternoon threat".

I'll still take the Euro over the GFS.

[yoda]

https://partnerservices.nws.noaa.gov/products/cache/205-2026/PNSLWX/c88b4b76421e8f7e48bd910a1aa7a19e

Didnt see this posted yet

[ravensrule]

On 7/24/2026 at 7:53 PM, CAPE said:

I am definitely skinny CAPE- relatively modest updrafts but over a vertically deep layer(quite long/tall) and with lots of juice. 

@ravensrulewill be along shortly

Unfortunately it was longly this time. I love that you have a lot of juice though. Please don’t waste it. 

[yoda]

Morning day 3 discussion from SPC 

Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0226 AM CDT Sun Jul 26 2026

   Valid 281200Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   MID-ATLANTIC INTO THE CAROLINAS AND CENTRAL AND SOUTHERN
   APPALACHIANS...

   ...SUMMARY...
   Severe thunderstorms capable of mainly damaging winds appear
   possible from the southern Mid-Atlantic into the Carolinas and
   central and southern Appalachians Tuesday into Tuesday evening.
   Isolated severe wind gusts may occur in the central High Plains.

   ...Synopsis...

   A short-wave trough initially over the lower Great Lakes Tuesday
   morning is forecast to evolve into a closed low over the
   Mid-Atlantic. Within the base of that feature, a belt of enhanced
   mid-level flow will spread from the OH Valley into VA and NC by
   afternoon.  At the surface, an area of low pressure over southwest
   ON Tuesday morning is expected to reform in the Delmarva by
   afternoon with a lee trough extending southwest along the Piedmont.
   Meanwhile, a cold front will advance southeast through the central
   and southern Appalachians, the southern Mid-Atlantic into the
   Carolinas.


   ...Mid-Atlantic into Southern Appalachians...

   Showers and thunderstorms (some potentially strong) are expected to
   be ongoing Tuesday morning from the upper OH Valley into the
   Mid-Atlantic and central Appalachians within a zone of forcing for
   ascent preceding the short-wave trough. Various 00Z model data
   indicate deep convection lingering into afternoon from the central
   Appalachians into the Delmarva and points north, leading to
   uncertainty in the degree of air mass destabilization in those
   areas. Where stronger heating can occur, the presence of a moist air
   mass will contribute to moderate instability by afternoon within a
   kinematic environment featuring anywhere from 30 to 45 kt of
   deep-layer shear.

   Thunderstorms are expected to increase in coverage and intensity
   during the afternoon preferentially along the cold front and lee
   trough where sufficient destabilization has occurred. Organized
   storm modes appear possible, including supercells and bowing
   structures, with the primary hazards being damaging wind gusts. Some
   tornado threat could materialize Tuesday afternoon in the Delmarva
   near the surface low. That threat is conditional on sufficient air
   mass destabilization and the presence of a supercell mode.

 

[Kmlwx]

CSU MLP guidance favors south of the area for Tuesday. CIPS is not enthused really. NCAR which normally is overly bullish is not terrible but given its normal...is under enthused as well. 

[high risk]

14 hours ago, Eskimo Joe said:

I'll still take the Euro over the GFS.

           I'd usually agree with you.  But as we now move into CAM range, recognizing that the U.S. CAMs all have some influence of the GFS, the solutions seem to be favoring the GFS more.   The idea of a deep sfc low over the St Lawrence Valley isn't dead in the Euro, but even its AI version likes a secondary low in the Mid-Atlantic.   Verbatim, some pretty strong forcing rolls through during the morning and midday hours, which screams flash flooding more than severe.   That said, 1) a surface low will be nearby, so you always need to watch for a tornado threat, especially if we can heat up before the forcing arrives   2) there is time to change some of the synoptic details

[frd]

3 hours ago, high risk said:

Verbatim, some pretty strong forcing rolls through during the morning and midday hours, which screams flash flooding more than severe.  

Exactly,  that statement echoes what Mount Holly has in the latest AFD.  The boundary may also stall in the Central and Northern regions leading to flash flooding. 

[frd]

Latest update NWS Storm Prediction Center Norman OK

 

 

SPC AC 261919

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0219 PM CDT Sun Jul 26 2026

   Valid 281200Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   MID ATLANTIC INTO NORTH CAROLINA AND THE SOUTHERN APPALACHIANS...

   ...SUMMARY...
   Severe thunderstorms capable of damaging winds and isolated hail are
   possible from the southern Mid-Atlantic into the Carolinas and
   central and southern Appalachians Tuesday into Tuesday evening.
   Isolated severe wind gusts may occur in the central High Plains.

   ...Southern Mid Atlantic into North Carolina and southern
   Appalachians...
   An upper trough with a 40-50 kt midlevel speed max will push
   southeastward across the Appalachians and into parts of the Mid
   Atlantic and Carolinas during the day, supporting thunderstorms
   through much of the period.

   Storms are expected to be ongoing early Tuesday from PA and WV into
   eastern KY, near a cold front. This activity should persist as it
   moves into MD/VA/NC, where a surface trough will deepen. Daytime
   heating along with ample low-level moisture will support 1500-2000
   J/kg MLCAPE, and winds will be veering with height, supporting a few
   supercells. Despite warm temperatures aloft, the 40-50 kt deep-layer
   shear may support hail in the strongest cells. In addition,
   southwesterly 850 mb winds up to 40 kt late in the day may yield an
   isolated tornado risk from southeast VA into NC. Moderately high
   PWAT along with steep low-level lapse rates during the peak heating
   hours will also support locally damaging wind gusts.

   ...Northern High Plains...
   Instability will increase over eastern WY, western SD/NE and
   northeast CO during the afternoon as a weak surface trough develops.
   Southeast surface winds will maintain 50s to lower 60s F dewpoints,
   with storms forming after 21Z near the higher terrain in WY/CO.
   South to southeast storm motions may bring multicellular storms
   across western NE and northeast CO during the evening with a few
   severe gusts possible.

   ..Jewell.. 07/26/2026

   CLICK TO GET WUUS03 PTSDY3 PRODUCT

   NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
   CURRENT UTC TIME: 1936Z (3:36PM), RELOAD THIS PAGE TO UPDATE THE TIME
        

[vortex95]

On 7/25/2026 at 8:14 AM, MN Transplant said:

There's a version I used in my graduate studies called NCAPE (Normalized CAPE).

 

Normalized CAPE (J/kg)
The NCAPE (Normalized CAPE) is CAPE that is divided by the depth of the buoyancy layer (units of m s**-2). Values near or less than .1 suggest a "tall, skinny" CAPE profile with relatively weak parcel accelerations, while values closer to .3 to .4 suggest a "fat" CAPE profile with large parcel accelerations possible. Normalized CAPE and lifted indicies are similar measures of instability.

Also, a fairly new type of CAPE, ECAPE!  It accounts for dry air entraiment.

"Substantial mixing occurs between the upward-moving air currents in thunderstorms (updrafts) and the surrounding comparatively dry environmental air, through a process called entrainment. Entrainment controls thunderstorm intensity via its diluting effect on the buoyancy of air within updrafts."

CAPE values we see plotted are almost never full realized due to dry air entrainment.  How much entrainment occurs varies greatly.

https://journals.ametsoc.org/view/journals/mwre/147/3/mwr-d-18-0137.1.xml
 

AMS24poster.pdf

[vortex95]

Some overnight action in NW flow.  Supercell split here w/ the right most one an anticyclonic supercell (nice flared and sheared appearance)  A left split, even though it does not look like that for movement, but you have to remember the frame of reference.  In NW flow you have to rotate your frame reference 90 deg from typical SW flow.

As is commonl, the anticyclonic storm moves faster than its cyclonic counterpart.

Hail cores aloft (loop is from DOX).
 

[yoda]

There were quite a lot of hail cores and "large hail" last night... I saw numerous statements and warnings for ping pong to baseball sized hail

[Kmlwx]

I still would generally favor south of DC for tomorrow. But the NAM nest and HRRR do get activity (some seemingly severe?) into all areas tomorrow. After shrinking the 15% contour to the south of us yesterday, CSU guidance has it back north of the M/D line. So that's good. 

We'll see (as always!)

[Eskimo Joe]

25 minutes ago, Kmlwx said:

I still would generally favor south of DC for tomorrow. But the NAM nest and HRRR do get activity (some seemingly severe?) into all areas tomorrow. After shrinking the 15% contour to the south of us yesterday, CSU guidance has it back north of the M/D line. So that's good. 

We'll see (as always!)

At this point, I would just be happy with a regionwide 1.5" - 2.5" of rain. We are seriously in need of a recharge of the aquifers and water ways.

[SolidIcewx]

12 minutes ago, Eskimo Joe said:

At this point, I would just be happy with a regionwide 1.5" - 2.5" of rain. We are seriously in need of a recharge of the aquifers and water ways.

A repeat of last tuesday would be nice

[high risk]

4 hours ago, Kmlwx said:

I still would generally favor south of DC for tomorrow. But the NAM nest and HRRR do get activity (some seemingly severe?) into all areas tomorrow. After shrinking the 15% contour to the south of us yesterday, CSU guidance has it back north of the M/D line. So that's good. 

We'll see (as always!)

   I think so too, but this is still really complicated, and the 12Z suite hasn't locked in on anything yet.   It *does* seem like while the main MCS will be west of here in the morning hours, some piece of it will approach and probably strengthen a bit.  If it arrives around commute time, it will probably be sub-severe, but if it's mid-morning, severe is possible.   Guidance then differs sharply on how much heating will occur behind any morning activity, but how much will it matter.   Steepening lapse and strong forcing might compensate for limited surface heating.   At least scattered storms are likely by mid-afternoon, and some solutions are widespread.   All hazards would be possible; the low-level winds are probably too weak for tornadoes, but the directional shear will be there, so it wouldn't take much to increase the tornado threat.

[frd]

Here we go again 

Flood Watch
National Weather Service Mount Holly NJ
215 PM EDT Mon Jul 27 2026

DEZ001-NJZ001-007>010-012>020-026-027-PAZ054-055-060>062-070-071-
101>106-280615-
/O.NEW.KPHI.FA.A.0006.260728T1200Z-260729T1800Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
New Castle-Sussex-Warren-Morris-Hunterdon-Somerset-Middlesex-
Western Monmouth-Eastern Monmouth-Mercer-Salem-Gloucester-Camden-
Northwestern Burlington-Ocean-Coastal Ocean-Southeastern
Burlington-Carbon-Monroe-Berks-Lehigh-Northampton-Delaware-
Philadelphia-Western Chester-Eastern Chester-Western Montgomery-
Eastern Montgomery-Upper Bucks-Lower Bucks-
Including the cities of Honey Brook, West Chester, Norristown,
Lansdale, Jim Thorpe, Wilmington, Easton, Jackson, Sandy Hook,
Allentown, Kennett Square, Chalfont, Washington, Philadelphia,
Freehold, Pottstown, Moorestown, Reading, Media, Wharton State
Forest, Oxford, Morristown, Cherry Hill, Pennsville, Perkasie,
Doylestown, Camden, New Brunswick, Stroudsburg, Flemington,
Glassboro, Trenton, Collegeville, Somerville, Morrisville, Long
Beach Island, Newton, Mount Holly, and Bethlehem
215 PM EDT Mon Jul 27 2026

...FLOOD WATCH IN EFFECT FROM TUESDAY MORNING THROUGH WEDNESDAY
AFTERNOON...

* WHAT...Flash flooding caused by excessive rainfall is possible.

* WHERE...Northern Delaware, New Jersey and eastern Pennsylvania
  including the Southern Poconos, Lehigh Valley and metro
  Philadelphia.

* WHEN...From Tuesday morning through Wednesday afternoon.

* IMPACTS...Excessive runoff may result in flooding of rivers,
  creeks, streams, and other low-lying and flood-prone locations.
  Creeks and streams may rise out of their banks. Flooding may occur
  in poor drainage and urban areas.

* ADDITIONAL DETAILS...
  - Showers and thunderstorms will increase over the area Tuesday
    morning and afternoon. Rainfall rates of 1 to 2 inches per
    hour are possible. Total rainfall of 2 to 4 inches could
    occur into Tuesday night.
  - http://www.weather.gov/safety/flood

PRECAUTIONARY/PREPAREDNESS ACTIONS...

You should monitor later forecasts and be prepared to take action
should Flash Flood Warnings be issued.

&&

 

[yoda]

Damage videos coming out of SE WI/NE IL look really bad

[yoda]

2 minutes ago, yoda said:

Damage videos coming out of SE WI/NE IL look really bad

Severe Weather Statement

National Weather Service Chicago/Romeoville
122 PM CDT Mon Jul 27 2026

ILC091-INC089-271930-
/O.CON.KLOT.SV.W.0205.000000T0000Z-260727T1930Z/
Kankakee IL-Lake IN-
122 PM CDT Mon Jul 27 2026

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 230 PM CDT
FOR NORTHEASTERN KANKAKEE AND LAKE COUNTIES...

At 122 PM CDT, a severe thunderstorm was located near St. John, or
near Cedar Lake, moving southeast at 40 mph.

THIS IS A DESTRUCTIVE STORM FOR CROWN POINT, WINFIELD, LOWELL, AND
SCHNEIDER.

HAZARD...100 mph wind gusts.

SOURCE...Radar indicated.

IMPACT...You are in a life-threatening situation. Flying debris may
         be deadly to those caught without shelter. Mobile homes
         will be destroyed. Expect considerable damage to homes and
         businesses. Expect extensive tree damage and power outages.

Locations impacted include...
Merrillville, Schererville, Hobart, Crown Point, Cedar Lake, Lowell,
Dyer, St. John, Lakes of the Four Seasons, Winfield, Lake Dalecarlia,
Grant Park, Shelby, and Schneider.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This is an EXTREMELY DANGEROUS SITUATION with tornado like wind
speeds expected. Mobile homes and high profile vehicles are
especially susceptible to winds of this magnitude and may be
overturned. For your protection move to an interior room on the
lowest floor of a building. This storm has the potential to cause
serious injury and significant property damage.

&&

LAT...LON 4124 8722 4122 8729 4119 8732 4118 8737
      4116 8739 4118 8745 4117 8746 4116 8762
      4130 8765 4130 8753 4148 8752 4147 8722
TIME...MOT...LOC 1822Z 304DEG 35KT 4140 8755

THUNDERSTORM DAMAGE THREAT...DESTRUCTIVE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...100 MPH

[Kmlwx]

That radar looks like a nuke went off....holy crap

[Eskimo Joe]

15 minutes ago, yoda said:

Damage videos coming out of SE WI/NE IL look really bad

Insane stuff dude.

 

 

[SolidIcewx]

The debris ball on that tornado was insane

[Eskimo Joe]

33 minutes ago, SolidIcewx said:

The debris ball on that tornado was insane

Without a doubt, the largest debris ball I've ever seen on radar.