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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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39 minutes ago, Eskimo Joe said:

Tomorrow screams surprise severe

     Is it really a "surprise" when the models show discrete rotating cells 2 days in advance, and SPC puts us in an initial Day 2 MRGL with potential for a later upgrade?    B)

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14 minutes ago, high risk said:

     Is it really a "surprise" when the models show discrete rotating cells 2 days in advance, and SPC puts us in an initial Day 2 MRGL with potential for a later upgrade?    B)

someone will say it came without warning. 

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Curious to see what SPC does here with the updated day 2 outlook in 20 minutes.    I think there is enough in the 12z CAMs today to go with a SLGT (5% TOR) in roughly a Farmville, PA to Williamsport, PA corridor (~80 miles on either side), but I wouldn't be shocked if they want until tomorrow morning to upgrade either.

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54 minutes ago, high risk said:

Curious to see what SPC does here with the updated day 2 outlook in 20 minutes.    I think there is enough in the 12z CAMs today to go with a SLGT (5% TOR) in roughly a Farmville, PA to Williamsport, PA corridor (~80 miles on either side), but I wouldn't be shocked if they want until tomorrow morning to upgrade either.

Personally, I'm thinking an Intercourse to Balls Mills line, but that's probably just splitting hairs.

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15 minutes ago, high risk said:

Curious to see what SPC does here with the updated day 2 outlook in 20 minutes.    I think there is enough in the 12z CAMs today to go with a SLGT (5% TOR) in roughly a Farmville, PA to Williamsport, PA corridor (~80 miles on either side), but I wouldn't be shocked if they want until tomorrow morning to upgrade either.

     They stuck w the MRGL.....

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 Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1234 AM CDT Wed Aug 18 2021

   Valid 181200Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE MID-ATLANTIC...

   ...SUMMARY...
   A few tornadoes will be possible today across portions of the
   central Appalachians and Mid-Atlantic. Thunderstorms associated with
   strong winds and hail may also occur across parts of the
   Intermountain West, and over portions of the Mid-South/Tennessee
   Valley.

   ...Mid-Atlantic...
   The remnants of Tropical Depression Fred are forecast to move north
   across the central Appalachians and Mid-Atlantic, with the center of
   circulation located over West Virginia by the start of the period.
   Deep tropical moisture will advect northward with low to mid 70s
   surface dewpoints expected by early afternoon. Some cloud breaks and
   modest surface heating should be more than enough to support MLCAPE
   of 500-1000 J/kg through the day. High-resolution and regional
   guidance are in good agreement that surface wind fields in the
   northeastern quadrant of the remnant low will remain strong through
   much of the day. A 40 kt mid-level speed max should also enhance
   low- and mid-level shear across much of PA, MD, and northern VA,
   where model soundings show 0-1 km SRH of 200-300 m2/s2. The
   combination of sufficient buoyancy and strong low-level shear should
   support multiple supercells with the potential for a few tornadoes
   and isolated strong wind gusts through the afternoon/early evening.

 

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mcd1550.gif.b48644f75e76d3256057907baf1ee3ef.gif

 

Mesoscale Discussion 1550
   NWS Storm Prediction Center Norman OK
   0746 AM CDT Wed Aug 18 2021

   Areas affected...Parts of the eastern West Virginia
   Panhandle...northern Virginia...central Maryland and adjacent south
   central Pennsylvania

   Concerning...Severe potential...Watch possible 

   Valid 181246Z - 181445Z

   Probability of Watch Issuance...40 percent

   SUMMARY...The development of occasional isolated supercell
   structures with the potential to produce tornadoes (generally
   short-lived) may increase through 11 am-1 pm EDT, mainly west
   through northwest of the District of Columbia into the higher
   terrain around Martinsburg, WV and Hagerstown, MD.  It is not yet
   certain a watch will be needed, but trends are being monitored for
   this possibility.

   DISCUSSION...The remnant surface low of Fred has migrated northward
   into areas south/southeast of Parkersburg, WV during the past few
   hours.  As this has occurred, very moist boundary layer has advected
   northwestward across the Mid Atlantic region.  This includes dew
   points as high as the mid 70s F into the higher terrain centered
   around the Martinsburg, WV vicinity, where low-level convergence is
   becoming focused, and an area of enhanced mid/upper forcing for
   ascent is forecast to overspread through 15-17Z.  Beneath a narrow
   belt of 30+ kt southerly flow around 850 mb, this also appears
   likely to coincide with where clockwise-curved low-level hodographs
   will become maximized, with the terrain contributing to the
   maintenance of backed/southeasterly near surface flow.  As breaks in
   the overcast allow for insolation to contribute to boundary-layer
   destabilization, it appears that the environment may become
   increasingly conducive to supercell structures with the potential to
   produce relatively short-lived tornadoes.

   ..Kerr/Edwards.. 08/18/2021

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

   ATTN...WFO...CTP...LWX...
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