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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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26 minutes ago, Kmlwx said:

The parent NAM is really going gung-ho on Tuesday afternoon. Even the sim reflectivity looks good on the NAM nest but for mainly Virginia. There are some hefty SARS analogs showing up on the parent NAM as well. 

Really crossing my fingers that we don't get our infamous morning convection to muck things up and ruin the steep MLLRs. If any early morning convection immediately to our west and/or over us is sparse enough or, preferably, nonexistent then later in the day Tuesday could be fun for at least some (Decent CAPE and MLLRs, etc.) 

Oddly though the SPC doesn't even have DC proper within the general thunder risk for Tuesday (Day 3)! :lol:

I wonder if we get a rare Day 3 update this afternoon? I mean surely you'd think we'd at least be in a MRGL risk for Tuesday now all things considered.

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1 hour ago, George BM said:

Really crossing my fingers that we don't get our infamous morning convection to muck things up and ruin the steep MLLRs. If any early morning convection immediately to our west and/or over us is sparse enough or, preferably, nonexistent then later in the day Tuesday could be fun for at least some (Decent CAPE and MLLRs, etc.) 

Oddly though the SPC doesn't even have DC proper within the general thunder risk for Tuesday (Day 3)! :lol:

I wonder if we get a rare Day 3 update this afternoon? I mean surely you'd think we'd at least be in a MRGL risk for Tuesday now all things considered.

Our best events come when SPC plays catchup ;) 

Remember...we were only in a 5% area for most of the day on the 2012 derecho day. 

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The 12z parent NAM giveth, the 00z taketh away....

Not very excited about Tuesday now, based on what I've seen in the evening runs.     I'm on board with the MRGL for Monday - looks like some stronger convection later in the day (especially north of DC), in an environment that isn't great but isn't awful either.

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8 hours ago, high risk said:

The 12z parent NAM giveth, the 00z taketh away....

Not very excited about Tuesday now, based on what I've seen in the evening runs.     I'm on board with the MRGL for Monday - looks like some stronger convection later in the day (especially north of DC), in an environment that isn't great but isn't awful either.

Best Well That Sucked GIFs | Gfycat

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2 hours ago, Kmlwx said:

There have been some decent sim reflectivity panels for this afternoon and evening. But yeah - tomorrow looks kind of cooked. 

Getting some clearing and sun now... lets see how this afternoon unfolds.  Some storms would be nice

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Not totally cooked tomorrow -- yet. There will be subsidence aloft for a good portion of the day and a remnant EML, so it will remain capped to convection for most of the day. Most likely evolution, if it happens, would be initiation over higher terrain and on the leading edge of height falls on the backside of the shortwave ridge.  An old MCV from overnight convection to the west couldn't hurt either. There's ample instability and moderate low-to-mid level shear, so we're just looking for a suitable trigger.

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Definitely a lot of bouncing around going on with the NAM and NAM nest. The sim reflectivity looks decent for tomorrow on the NAM nest now - even looks okay for Wednesday. Could we pull the rare 3 in a row for storms?

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13 minutes ago, Kmlwx said:

Definitely a lot of bouncing around going on with the NAM and NAM nest. The sim reflectivity looks decent for tomorrow on the NAM nest now - even looks okay for Wednesday. Could we pull the rare 3 in a row for storms?

Gotta actually rain on Day 1 first.

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Hmmm

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1222 PM CDT Mon May 03 2021

   Valid 041200Z - 051200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   FAR SOUTHEAST
   ARKANSAS...LOUISIANA...MISSISSIPPI...TENNESSEE...ALABAMA AND
   NORTHWEST GEORGIA...

   ...SUMMARY...
   Widespread strong to severe thunderstorm development is possible
   Tuesday from the lower Mississippi and Ohio Valleys into the
   Allegheny and Cumberland Plateau regions.  This will include a risk
   for large hail, damaging wind gusts and a few tornadoes.

   ...Synopsis...

   The severe weather forecast for Tuesday remains complex with
   lingering uncertainty. Most of the forecast changes for this cycle
   are peripheral/modest for the Slight and Enhanced risk areas. The
   Marginal risk area has been expanded quite a bit to the east, from
   the South Carolina to Delmarva coast. 

   On a broader scale, an upper trough extending from the Upper Midwest
   to southwest TX/northeast Mexico will migrate eastward, becoming
   oriented from the upper Great Lakes to GA by Wednesday morning.
   Several smaller shortwave perturbations are forecast to eject
   northeastward across parts of the lower MS Valley to the lower Great
   Lakes vicinity as well as portions of the central
   Appalachians/Mid-Atlantic vicinity. At the surface, a seasonally
   moist airmass will be in place, with mid 60s to low 70s dewpoints as
   far north as the TN Valley and into the Carolinas/Chesapeake Bay
   vicinity. Low to mid 60s dewpoints will spread further north into
   the lower Great Lakes eastward toward the I-95 corridor from
   Philadelphia into southern NJ. Meanwhile, an EML characterized by
   steep 700-500 mb lapse rates around 7-8 C/km will advect eastward
   across the lower MS Valley into the TN Valley, aiding in strong
   destabilization with MLCAPE values forecast around 2000-3000 J/kg.
   Weaker, but still sufficient lapse rates will exist across parts of
   the Ohio Valley eastward to the mid-Atlantic coast. A belt of
   increasing southwesterly midlevel flow will overspread much of the
   lower MS Valley into the Mid-Atlantic ahead of the main upper
   trough, providing further support for organized convection. As a
   result, a broad area of strong to severe thunderstorms are expected
   across a large part of the southeastern US into the Mid-Atlantic.

   ...Lower MS Valley/Southeast...

   The greatest/most concentrated severe threat on Tuesday appears to
   extend parts of AR/LA eastward into TN/AL/GA. Some uncertainty
   continues across this region as ongoing convection is expected over
   parts of the area during the morning hours as an MCS spreads
   eastward across the Ohio Valley and perhaps parts of the TN Valley.
   How this system from the Day 1/Monday period evolves will have some
   impact on how further convection develops later in the
   morning/afternoon as the airmass recovers ahead of the main surface
   cold front spreading southeast through the afternoon. Little capping
   is expected across the area and pockets of stronger heating will
   likely result in early development of thunderstorm clusters across
   parts of MS/AL/GA. While effective shear will initially be modest,
   this should rapidly increase through the morning. This initial
   activity will pose a threat for all severe hazards, including hail,
   damaging gusts and a couple of tornadoes.

   By late morning/early afternoon, convection is expected to develop
   along the surface cold front from parts of AR into far east TX. Some
   of this activity will likely remain cellular initially amid
   supercell wind profiles. With midlevel lapse rates around 7.5-8 C/km
   this activity could produce significant hail, in addition to
   damaging gusts and a couple of tornadoes. With time, stronger
   forcing and boundary-parallel deep layer flow should result in
   upscale growth into bowing/linear segments as convection shifts
   eastward across MS/LA and into AL during the afternoon/evening. This
   will increase the potential for more widespread damaging gusts, and
   favorable low level speed shear should continue to support
   mesovortex tornado potential along the line. 

   ...Ohio Valley to the Mid-Atlantic...

   A moist boundary layer (low to mid 60s F dewpoints) beneath modest
   midlevel lapse rates will be in place on Tuesday amid 35-50 kt
   850-700 mb west/southeasterly flow. MLCAPE values around 1500-2500
   J/kg are forecast as pockets of strong heating result in steepening
   low level lapse rates. Low level flow will remain weak, but marginal
   supercell wind profiles should support isolated to scattered
   organized thunderstorm development during the afternoon. A
   well-mixed boundary layer, with inverted-v low level thermodynamic
   profiles indicate potential for locally damaging gusts. Some of the
   stronger cells also could produce marginally sever hail. 

   Some guidance suggests that the morning MCS over parts of OH/TN
   Valley may continue eastward and spread into parts of VA/NC/SC. If
   an organized convective system can be maintained, this could
   increase damaging wind potential during the afternoon/evening and an
   upgrade to Slight risk could be needed in later outlooks.

   ..Leitman.. 05/03/2021
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yay pity MD to our west lol

https://www.spc.noaa.gov/products/md/md0494.html

mcd0494.gif

Mesoscale Discussion 0494
   NWS Storm Prediction Center Norman OK
   0147 PM CDT Mon May 03 2021

   Areas affected...portions of southern and eastern Ohio into West
   Virginia and southwestern Pennsylvania

   Concerning...Severe potential...Watch unlikely 

   Valid 031847Z - 032045Z

   Probability of Watch Issuance...5 percent

   SUMMARY...A couple of the stronger storms may pose a localized
   severe risk through the afternoon hours. A damaging gust or two are
   possible and a brief tornado cannot be completely ruled out. Given
   the sparse nature of the severe threat, a WW issuance is not
   anticipated.

   DISCUSSION...Convection has gradually deepened and become more
   widespread across portions of the Ohio Valley as a mid-level vort
   max traverses the region. Pockets of insolation have allowed for
   marginal destabilization of the boundary layer, with around 250-400
   J/kg MLCAPE currently realized (per latest Mesoanalysis). 18Z PBZ
   and RLX VWPs depict considerable veering of the sfc-500 m winds,
   with modest 0-3km speed shear all contributing to 150-300 m2/s2
   0-3km SRH, with 0-1km SRH values occasionally exceeding 200 m2/s2.
   Nonetheless, upper support is expected to remain modest, with low
   and mid-level lapse rates likely to remain below 6.5 C/km across
   most locations. While the favorable shear environment would support
   a damaging gust or a brief tornado with a stronger storm, the
   marginal instability is expected to limit the severe threat. Given
   the very sparse and brief nature of any severe threat that can
   materialize, a WW issuance is not expected.

   ..Squitieri/Grams.. 05/03/2021

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

   ATTN...WFO...CTP...LWX...RNK...PBZ...RLX...ILN...
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18 minutes ago, WinterWxLuvr said:

Surprised the WV storm isn’t tornado warned with that radar presentation 

There is one now

ULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Baltimore MD/Washington DC
626 PM EDT Mon May 3 2021

The National Weather Service in Sterling Virginia has issued a

* Tornado Warning for...
  Southeastern Washington County in north central Maryland...
  Northwestern Loudoun County in northern Virginia...
  Central Jefferson County in the Panhandle of West Virginia...

* Until 700 PM EDT.

* At 626 PM EDT, a severe thunderstorm capable of producing a tornado
  was located over Corporation Of Ranson, or over Charles Town,
  moving east at 25 mph.

  HAZARD...Tornado.

  SOURCE...Radar indicated rotation.

  IMPACT...For those in the direct path of a tornado touchdown,
           flying debris will be dangerous to those caught without
           shelter. Damage to roofs, siding, and windows may occur.
           Mobile homes may be damaged or destroyed. Tree damage is
           likely.

* This dangerous storm will be near...
  Harpers Ferry around 640 PM EDT.

Other locations impacted by this tornadic thunderstorm include
Shenandoah Junction, Bolivar, Pleasantville, Neersville, Millville,
Bakerton and Halltown.
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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
626 PM EDT MON MAY 03 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0600 PM     TSTM WND DMG     RIDGEWAY                39.30N  78.07W
05/03/2021                   BERKELEY           WV   911 CALL CENTER

            REPORT OF DOWNED TREES AND A STRUCTURE COLLAPSE NEAR
            MCGLYNN LANE.
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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
645 PM EDT MON MAY 03 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0644 PM     TSTM WND DMG     1 N RANSON              39.31N  77.86W
05/03/2021                   JEFFERSON          WV   911 CALL CENTER

            *** 1 INJ *** STRUCTURE COLLAPSE ALONG THE 200 BLOCK OF
            16TH AVE. IN RANSON, WV.
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mcd0504.gif

 

Mesoscale Discussion 0504
   NWS Storm Prediction Center Norman OK
   0545 PM CDT Mon May 03 2021

   Areas affected...Portions of Maryland...Virginia...and Washington
   DC.

   Concerning...Severe potential...Watch unlikely 

   Valid 032245Z - 032345Z

   Probability of Watch Issuance...5 percent

   SUMMARY...An isolated risk of damaging winds or a brief tornado will
   be possible over the next couple of hours along a diffuse warm
   front. A weather watch is unlikely.

   DISCUSSION...Recent radar imagery and storm reports showed a small
   supeprcell over Jefferson Co. Maryland had intensified over the last
   45 minutes. SPC mesoanalysis indicates this storm is located along a
   diffuse surface warm front stretching from eastern Ohio toward the
   northern Chesapeake Bay. To the south of the front, surface
   temperatures in the mid 70s F and dewpoints in the lower to middle
   60s F are support MUCAPE of 800-1200 J/kg. Enhanced mid-level flow
   ahead of a shortwave trough across the Carolinas is contributing to
   30-40 kt of effective shear as analyzed by local VAD VWPs.
   Observational trend suggest that severe weather in the form of
   damaging wind gusts and perhaps a tornado will be possible with this
   storm as it tracks east along the front over the next 1 to 2 hours.
   Given the limited spatial area and expected longevity of any severe
   risk as the storm moves into cooler air near the bay, a weather
   watch is unlikely.

   ..Lyons/Thompson.. 05/03/2021
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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
650 PM EDT Mon May 3 2021

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Southeastern Washington County in north central Maryland...
  Southwestern Frederick County in north central Maryland...

* Until 730 PM EDT.

* At 650 PM EDT, a severe thunderstorm was located near Harpers
  Ferry, or near Shepherdstown, moving east at 25 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...
  Frederick, Harry Grove Stadium, Ballenger Creek, Brunswick,
  Walkersville, Braddock Heights, Clover Hill, Jefferson,
  Buckeystown, Rosemont, Rohrersville, Burkittsville, Gapland,
  Brownsville, Bloomfield, Clifton, Arnoldtown, Utica, Petersville
  and Bolivar.

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.
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18 minutes ago, NorthArlington101 said:

That velocity/storm presentation looks legit. Someone on a forum I follow was nerding out about this wind profile, can’t read ‘em myself but maybe others could translate.

ee0eebd8136ea612220fc67894acbb82.jpg

@high risk can explain better but you see a curved hodograph on the left indicating supercell potential and very strong helicity (SRH on the right) in the lowest levels of the atmosphere.

Looks like a nice tornado profile if you have the other ingredients (moisture, instability, so on). 

More on hodographs here: https://www.weather.gov/media/lmk/soo/Hodographs_Wind-Shear.pdf

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