2023 Mid-Atlantic Severe Wx Thread (General Discussion)

[Kevin Reilly]

23 minutes ago, TSSN+ said:

Confirmed one in PA 

To repeat, a tornado is on the ground. TAKE COVER NOW! Move to a
basement or an interior room on the lowest floor of a sturdy
building. Avoid windows. If you are outdoors, in a mobile home, or in
a vehicle, move to the closest substantial shelter and protect
yourself from flying debris.

This is incredible how many confirmed tornadoes have we had in the northern Mid Atlantic VA, MD, PA, NJ, DE.  This has been a repeating theme all the way back to April.

[TSSN+]

5 minutes ago, Kevin Reilly said:

This is incredible how many confirmed tornadoes have we had in the northern Mid Atlantic VA, MD, PA, NJ, DE.  This has been a repeating theme all the way back to April.

That cell in northern Cambria looks nasty 

[yoda]

SLGT risk nudged southward into N VA to include BR and to the NW on 01z SPC OTLK

[TSSN+]

Pretty crazy how weather works sometimes. We had a moderate risk and 10% tornado and didn’t get basically any tornado warnings or tornadoes around here yet the area in 2% today is getting waxed 

[Kevin Reilly]

4 minutes ago, TSSN+ said:

Pretty crazy how weather works sometimes. We had a moderate risk and 10% tornado and didn’t get basically any tornado warnings or tornadoes around here yet the area in 2% today is getting waxed 

The storm south of Pittsburgh looks rough and the one moving quickly towards Altoona, PA 

[nj2va]

Moving from obs to here. 

Amazing light show (“heat lightning”) on the deck from the storms just north of here in PA.  Flashes every minute or so. 
 

That line heading towards here looks pretty potent. 

[yoda]

925pm AFD from LWX about tonight

.NEAR TERM /THROUGH SUNDAY/...
The Storms Prediction Center has issued a Severe Thunderstorm
Watch for western and portions of central Maryland and much of
eastern West Virginia, including the Eastern Panhandle with
exception to Jefferson County, until 2am tonight. A broad area
of heavy showers and strong to severe thunderstorms are moving
northwest to southeast across southwestern Pennsylvania and
northern West Virginia. The embedded severe thunderstorms have
been capable of producing tornadoes in our neighboring CWA
offices. Otherwise, heavy rainfall, frequent lightning, damaging
winds and large hail are all possible or will be common with
this intense thunderstorm activity.

Shortly before 10pm, Garrett County could be the first zone to
get intense storms. These storms have a lot of lightning and are
capable of wrapping up into tornadoes based on radar indication.
Be cautious about late evening activities outdoors. Additional
zones to the east and south will likely be affected through
midnight to 1am. Some decrease in thunderstorm intensity and
coverage is possible and could occur shortly after midnight
along and just east of the mountains, but just be aware that the
Severe Thunderstorm Watch is in effect until 2am tonight.

Beyond 2am, there is some uncertainty as to where and how much
of this convection could persist and remain potent into the
overnight hours. Therefore, we are glossily monitoring the
activity in case additional watches or warnings may be needed
into the overnight. Model guidance seems to indicate that the
trend will be decreasing around and beyond 2am. We are
cautiously optimistic on this due to the CAPE and wind shear
available at such a late evening hour. Once convection wains
some or most, temperatures will drop back into the upper 60s to
lower 70s.

[yoda]

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
949 PM EDT Sat Aug 12 2023

The National Weather Service in Sterling Virginia has issued a

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

* Until 1030 PM EDT.

* At 949 PM EDT, a severe thunderstorm was located 7 miles south of
  Farmington, or 15 miles southeast of Uniontown, moving southeast 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, Bittinger, Grantsville, Loch Lynn
  Heights, Friendsville, Deer Park, Accident, Merrill, Keysers Ridge,
  Jennings, Mineral Spring, Deep Creek Lake State Park, Swallow Falls
  State Park, McHenry, Selbysport, Big Run State Park, New Germany,
  Piney Grove, and McComas Beach.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.
PBZ: Great to hear.
&&

LAT...LON 3972 7893 3948 7907 3948 7910 3943 7911
      3943 7913 3941 7914 3942 7916 3939 7916
      3939 7919 3936 7922 3936 7925 3934 7926
      3931 7928 3945 7948 3972 7948
TIME...MOT...LOC 0149Z 295DEG 37KT 3971 7955

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

[nj2va]

Tons of lightning as these storms roll in. 
 

Looks like daytime for a few seconds when the flashes are most intense. 

[yoda]

Severe Weather Statement
National Weather Service Baltimore MD/Washington DC
1004 PM EDT Sat Aug 12 2023

MDC023-130230-
/O.CON.KLWX.SV.W.0280.000000T0000Z-230813T0230Z/
Garrett MD-
1004 PM EDT Sat Aug 12 2023

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1030 PM EDT
FOR GARRETT COUNTY...

At 1004 PM EDT, a severe thunderstorm was located over Friendsville,
or 9 miles west of Bittinger, moving southeast at 45 mph.

HAZARD...70 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, Bittinger, Grantsville, Loch Lynn
Heights, Friendsville, Deer Park, Accident, Merrill, Keysers Ridge,
Jennings, Mineral Spring, Deep Creek Lake State Park, Swallow Falls
State Park, McHenry, Selbysport, Big Run State Park, New Germany,
Piney Grove, and McComas Beach.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3972 7893 3948 7907 3948 7910 3943 7911
      3943 7913 3941 7914 3942 7916 3939 7916
      3939 7919 3936 7922 3936 7925 3934 7926
      3931 7928 3945 7948 3972 7948
TIME...MOT...LOC 0204Z 295DEG 37KT 3965 7939

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...70 MPH

$$

[nj2va]

The wind and lightning are insane. 8 trees came down from the storms earlier this week. Hopefully we don’t lose more. 

[yoda]

Mesoscale Discussion 1978
   NWS Storm Prediction Center Norman OK
   0912 PM CDT Sat Aug 12 2023

   Areas affected...northern WV...western MD and southern PA

   Concerning...Severe Thunderstorm Watch 639...

   Valid 130212Z - 130345Z

   The severe weather threat for Severe Thunderstorm Watch 639
   continues.

   SUMMARY...Strong to severe storms should continue for a few more
   hours with a risk for damaging gusts and isolated hail.

   DISCUSSION...Across WW639, several clusters of strong to severe
   storms are expected to persist for a few more hours tonight. The
   environment remains broadly favorable for severe weather as storms
   track to the southeast across far southern PA, northern WV and
   western MD. Storms have taken on a general linear mode, suggesting
   damaging gusts are the primary risk for the remainder of tonight.
   However, isolated hail is also possible, but more uncertain given
   the trend away from supercell structures over the last couple of
   hours. Given recent HRRR and radar trends, the highest confidence in
   severe potential is expected over northern WV and the MD Panhandle
   for the next couple of hours.

   ..Lyons.. 08/13/2023

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

   ATTN...WFO...CTP...LWX...PBZ...RLX...

 

https://www.spc.noaa.gov/products/md/md1978.html

[yoda]

Severe Thunderstorm Warning
MDC001-023-WVC023-057-130300-
/O.NEW.KLWX.SV.W.0281.230813T0229Z-230813T0300Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
1029 PM EDT Sat Aug 12 2023

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Southwestern Allegany County in western Maryland...
  Central Garrett County in western Maryland...
  Northern Grant County in eastern West Virginia...
  Southwestern Mineral County in eastern West Virginia...

* Until 1100 PM EDT.

* At 1029 PM EDT, a severe thunderstorm was located near Piedmont, or
  near Westernport, moving southeast at 30 mph.

  HAZARD...70 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...
  Keyser, Westernport, Bittinger, Lonaconing, Piedmont, Deer Park,
  Elk Garden, Kitzmiller, Barton, Franklin, Luke, Jennings, Deep
  Creek Lake State Park, Swallow Falls State Park, McHenry, Big Run
  State Park, McComas Beach, Merrill, New Germany, and Dogwood Flats.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

[WVclimo]

Nothing severe but some great lightning here now.  Almost continuous thunder.

[Round Hill WX]

Well aren't we special! Monday....

[high risk]

4 hours ago, Round Hill WX said:

Well aren't we special! Monday....

 

       The 5% makes sense, given the southeasterly low-level winds progged by all guidance.   What's keeping us from a higher threat is fairly weak surface wind speeds as well as lower speeds in the 900-700 mb level.    If the low-level wind fields end up stronger, we would have more significant TOR potential.  

[Interstate]

2 hours ago, high risk said:

       The 5% makes sense, given the southeasterly low-level winds progged by all guidance.   What's keeping us from a higher threat is fairly weak surface wind speeds as well as lower speeds in the 900-700 mb level.    If the low-level wind fields end up stronger, we would have more significant TOR potential.  

Thank god. I spent 9 hours cleaning up last night and today from the storms on Monday. Happy return from vacation for me. 

[high risk]

Looking at the 00Z CAMs, I'd put the Monday TOR threat as an SPC 2% area instead of 5 for the local area due to weak low-level winds and limited storm coverage.   The bigger TOR threat might be western MD and adjacent parts of WV/PA in the early evening.

There are also some timing differences for Tuesday.    HRRR would require that the SLGT area be extended back west of DC, but it seems like an outlier for now.

[yoda]

2 hours ago, high risk said:

Looking at the 00Z CAMs, I'd put the Monday TOR threat as an SPC 2% area instead of 5 for the local area due to weak low-level winds and limited storm coverage.   The bigger TOR threat might be western MD and adjacent parts of WV/PA in the early evening.

There are also some timing differences for Tuesday.    HRRR would require that the SLGT area be extended back west of DC, but it seems like an outlier for now.

5 percent tor remains on new Day 1

 

[Kmlwx]

Most of the guidance seems to be in agreement that there may be a late afternoon/evening round of showers/storms - but much of the guidance is pretty weak with that stuff. NAM and RAP seem to think best parameters may actually show up during the 3z-6z window...while it will suck for daylight, it's possible this can still perform. Wonder if the CAPE will remain surface based that late, though...may end up being elevated (admittedly I haven't looked closely at the soundings). 

I'm not very intrigued for the early round...and I do wonder if that is going to stabilize some areas too much to have the nighttime round of storms. 

Another storm day when I'm at work all day....

[high risk]

12 minutes ago, Kmlwx said:

Most of the guidance seems to be in agreement that there may be a late afternoon/evening round of showers/storms - but much of the guidance is pretty weak with that stuff. NAM and RAP seem to think best parameters may actually show up during the 3z-6z window...while it will suck for daylight, it's possible this can still perform. Wonder if the CAPE will remain surface based that late, though...may end up being elevated (admittedly I haven't looked closely at the soundings). 

I'm not very intrigued for the early round...and I do wonder if that is going to stabilize some areas too much to have the nighttime round of storms. 

Another storm day when I'm at work all day....

     That's mostly how I see it too.    I'll disagree on round 1 being "weak" - the HRRR simulated reflectivities are fine;  isolated SVR seems likely, but I question the TOR threat with the weaker low-level winds.    Shear cranks up after dark, but we'll be fighting decreasing instability.    To me, the biggest potential overlap between increasing shear and still-sufficient sfc-based instability will be northwest of the DC area.

[Eskimo Joe]

Watch some rando right moving supercell drop right down I-270 today. We're famous for those kind of set ups.

[thunderbolt]

[Kmlwx]

1 hour ago, high risk said:

     That's mostly how I see it too.    I'll disagree on round 1 being "weak" - the HRRR simulated reflectivities are fine;  isolated SVR seems likely, but I question the TOR threat with the weaker low-level winds.    Shear cranks up after dark, but we'll be fighting decreasing instability.    To me, the biggest potential overlap between increasing shear and still-sufficient sfc-based instability will be northwest of the DC area.

Model soundings seem to still show a decent amount of CAPE overnight - but also have some CINH as well as can be expected. Probably if nothing else a good light show overnight. 

[Eskimo Joe]

Interesting factoid of the day.

 

[yoda]

1300z SPC OTLK seems to be tossing the HRRR and RAP... and @Kmlwx describes tonight pretty well too

 

Mid-Atlantic to TN/KY...
   Several episodes of strong-severe thunderstorms are possible across
   this corridor, with enough spatial overlap between them to warrant
   maintaining a continuous area of severe probabilities similar to
   those outlined in the previous outlook. 

   A broad area of ongoing precip with embedded thunderstorms --
   initially over portions of KY/TN -- largely should remain non-severe
   while shifting eastward into the central Appalachians today. 
   However, increasing deep-layer flow and favorable low-level moisture
   will precede the associated UVV plume, along with muted diurnal
   heating of a moist airmass with weak CINH from parts of WV across
   the nearby Blue Ridge and Piedmont of VA, eastward toward Chesapeake
   Bay and over the Delmarva Peninsula.  This may support strong-severe
   gusts and hail with thunderstorms forming during the afternoon over
   higher terrain and shifting eastward to northeastward toward the
   coast.  Of note:  progs with RAP basis -- including HRRR -- appear
   to be mixing and drying the boundary layer excessively over the
   Piedmont and coastal plain, leading to potential underproduction
   and/or muting of convection.

   After several hours of warm advection and increasing surface heating
   behind the morning activity, the best organized overall severe
   threat should develop this afternoon from parts of middle/eastern TN
   to southern OH/WV, and shift eastward over the adjoining
   Appalachians.  MLCAPE should range from around 2000-3000 J/kg across
   middle/eastern TN -- where strongest heating/recovery is probable
   but deep flow/shear somewhat weaker -- to around 500-1000 J/kg near
   the Ohio River and northern WV.  Effective-shear magnitudes around
   40-50 kt should be common over eastern KY and WV, with modest 0-1-km
   SRH but around 150-250 J/kg effective SRH.  This suggests an
   eastward-moving corridor of convection containing blend of
   supercells, multicell clusters and quasi-linear segments with
   sporadic bow/LEWP features will be possible, with accompanying
   threat for damaging to severe gusts, isolated hail, and at least
   marginal/conditional tornado potential. 

   The northern part of this convective plume may persist overnight
   into an airmass east of the mountains -- across parts of the
   Piedmont and coastal plain of the Mid-Atlantic -- supportively
   recovered via theta-e advection from any earlier activity not far to
   the south and east.  The parameter space should be favorable for
   severe well after dark, with 40-50 kt effective-shear magnitudes,
   locally enlarged hodographs with 200-300 J/kg effective SRH, and
   around 1000-2000 J/kg MLCAPE.  Convective coverage is uncertain, but
   all hazards will be possible. 

[Kmlwx]

I hope they have a fix for the HRRR over mixing in the works. It seems to do it EVERY time. 

[yoda]

1630z SPC OTLK still has the 5 percent tor probs with no change 

[Kmlwx]

12z ARW2 brings some cells/line through around 5 or 6 and then has a rogue super cellular type thing doing what @Eskimo Joe mentioned earlier lol

ETA: It shows it in the 02-04z timeframe. 

[high risk]

2 hours ago, Kmlwx said:

I hope they have a fix for the HRRR over mixing in the works. It seems to do it EVERY time. 

      There will be no upgrades to the HRRR since it's slated for retirement.