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Kmlwx

2020 Mid-Atlantic Severe Weather - General Thread

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Mesoscale Discussion 1673
   NWS Storm Prediction Center Norman OK
   0206 PM CDT Thu Sep 03 2020

   Areas affected...the Mid-Atlantic

   Concerning...Severe potential...Tornado Watch likely 

   Valid 031906Z - 032100Z

   Probability of Watch Issuance...95 percent

   SUMMARY...A tornado watch will be needed this afternoon as a
   damaging wind and tornado threat increases.

   DISCUSSION...A broad area of shower activity extends from the Ohio
   Valley into Pennsylvania and New York amid a belt of strong
   mid-level flow. Areas south and east of this activity have slowly
   destabilized through the day with temperatures now in the upper 80s
   to low 90s in northern Virginia, eastern Maryland, and Delaware. In
   addition, the boundary layer is very moist with dewpoints in the mid
   to upper 70s. This has yielded moderate MLCAPE ranging from 1000 to
   2000 J/kg across the region despite very weak mid-level lapse rates
   (5 C/km per 18Z IAD RAOB). Expect at least a few strong storms to
   develop in the eastern periphery of the cloud shield in the next 1-2
   hours as destabilization continues and deep-layer ascent increases
   ahead of a shortwave moving out of West Virginia. 

   Once storms develop, they will likely become supercellular, at least
   initially, given 40-45 kts of effective shear (per KLWX VWP and 18Z
   IAD RAOB). 18Z IAD RAOB showed relatively weak flow in the lowest
   1.5 km, but upstream VWP from KRLX shows strong (40 kt) flow at 1km.
   Once this overspreads northern Virginia, Maryland, and Pennsylvania
   in a few hours, the damaging wind threat will increase and low-level
   shear will increase which should increase the tornado threat. The
   best tornado threat will likely be across northern Virginia,
   southern Maryland, and far southern Pennsylvania where there has
   been less mixing and surface winds remain southerly or
   south-southeasterly.  

   A tornado watch will likely be needed in the next hour or two as
   storm coverage/intensity increases.

   ..Bentley/Grams.. 09/03/2020

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

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

 

mcd1673.gif

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40 to 45kt shear per the 18z raob. Helicity favorable for anything discrete to spin.

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The WV/OH is kinda beefy...that might be the real show from DC and points south. 

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1 hour ago, juliacarolecat said:

Sorry for a silly question, I’m new to posting but a lurker for years.

Is the tornado threat for north/central Maryland and then it will switch to more of a wind threat as it becomes more linear moving East? Ik bowing line segments can produce tornadoes but always thought they were more associated with high winds.

The thinking is more linear as it moves eastward towards the coast, and reading the discussion from Mount Holly they think the most likely place for a tornado is in Cecil over into Newcastle in DE up into SE PA. Possibly some interaction with the warm front lying across that area, backing the flow some is my guess. Bigger overall  threat will be damaging straight line winds, with fairly strong winds aloft and decent Dcape. Bowing segments generally produce straight line winds but can also produce tornadoes as vorticity sometimes develops on the north/south end of the line. How far north are you?

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Just now, high risk said:

Hello, SPC?    Hello?     Time to get that box issued.

Its being processed now.

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Cell NE of Frederick has some broad rotation and is starting to get that “look”.

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Just now, Eskimo Joe said:

SPC issues Tornado Watch until 0200 UTC.

Hail to 1 inch and isolated significant gusts to 75mph

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667   
WWUS20 KWNS 031938  
SEL5    
SPC WW 031938  
DCZ000-DEZ000-MDZ000-NJZ000-PAZ000-VAZ000-WVZ000-CWZ000-040200-  
  

URGENT - IMMEDIATE BROADCAST REQUESTED  
TORNADO WATCH NUMBER 485
 
NWS STORM PREDICTION CENTER NORMAN OK  
340 PM EDT THU SEP 3 2020  
  
THE NWS STORM PREDICTION CENTER HAS ISSUED A  
  
* TORNADO WATCH FOR PORTIONS OF   
  DISTRICT OF COLUMBIA  
  DELAWARE  
  MARYLAND  
  SOUTHERN NEW JERSEY  
  SOUTHEAST PENNSYLVANIA  
  NORTHERN VIRGINIA  
  EASTERN WEST VIRGINIA PANHANDLE  
  COASTAL WATERS  
  
* EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 340 PM UNTIL  
  1000 PM EDT.  
  
* PRIMARY THREATS INCLUDE...  
  A FEW TORNADOES LIKELY  
  SCATTERED DAMAGING WINDS LIKELY WITH ISOLATED SIGNIFICANT GUSTS  
    TO 75 MPH POSSIBLE  
  
SUMMARY...MULTIPLE SUPERCELLS WILL LIKELY DEVELOP NEAR AND NORTH OF  
THE GREATER WASHINGTON D.C. AREA AND SPREAD EAST AS A CLUSTER ACROSS  
THE COASTAL PLAIN THROUGH MID-EVENING. A FEW TORNADOES AND SWATHS OF  
DAMAGING WINDS ARE LIKELY.  
  
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 85 STATUTE MILES  
EAST AND WEST OF A LINE FROM 45 MILES NORTH NORTHWEST OF WILMINGTON  
DE TO 30 MILES WEST SOUTHWEST OF PATUXENT RIVER MD. FOR A COMPLETE  
DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE  
(WOUS64 KWNS WOU5).  
  
PRECAUTIONARY/PREPAREDNESS ACTIONS...  
  
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR  
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH  
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR  
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS  
AND POSSIBLE WARNINGS.  

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Not a lot of lightning and the tops are low on the carroll cell. I'm more interested in the ones along I81.

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...A TORNADO WARNING REMAINS IN EFFECT UNTIL 415 PM EDT FOR SOUTH
CENTRAL CARROLL COUNTY IN NORTH CENTRAL MARYLAND...NORTHWESTERN
HOWARD COUNTY IN CENTRAL MARYLAND AND SOUTHEASTERN FREDERICK COUNTIES
IN NORTH CENTRAL MARYLAND...

At 354 PM EDT, a severe thunderstorm capable of producing a tornado
was located over Mount Airy, or near Damascus, 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...
  Eldersburg around 415 PM EDT.

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