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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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4 minutes ago, 87storms said:

true, we certainly would expect severe during a tropical storm running under us, but something about having that stagnant air mass that we score in.  i'm mostly just basing it off experience without any science, which is why it'll probably fail lol.  definitely agree with your point for today's example.

Not to mention the plentiful other factors like how much sunshine we get, lapse rates - so many ways to fail around here. Some of it is probably anecdotal as you mention. 

I think for a day like the June 2012 derecho - you're absolutely right - that HOT, stagnant airmass fueled the maintenance of the storms as they plowed east. 

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20 minutes ago, Kmlwx said:

Not to mention the plentiful other factors like how much sunshine we get, lapse rates - so many ways to fail around here. Some of it is probably anecdotal as you mention. 

I think for a day like the June 2012 derecho - you're absolutely right - that HOT, stagnant airmass fueled the maintenance of the storms as they plowed east. 

yea, like the last couple weeks leading up to ida it was almost the same airmass everyday...humid/stagnant and afternoon storms, at least close to the mason dixon line.

i'm still annoyed that i didn't take vid of the derecho.

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Sounds like evening fun... afternoon LWX AFD 

 

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Stacked low is located well to the north in Canada while a cold
front trails through upstate NY and the Ohio and Tennessee
Valleys. An MCV is moving through southeast VA this afternoon,
and will likely represent the first "round" of thunderstorms
which will brush by the Northern Neck and Southern Maryland.

Guidance has been quite variable with where and when the next
storms will develop, although so far it appears the stable
layers in the 12Z IAD sounding are holding strong. The terrain
and/or a weak pressure trough could serve as an initiation
point later this afternoon. Additional convection could form or
strengthen as the actual cold front presses eastward this
evening. For this afternoon, moderate instability and DCAPE are
in place near and east of the Blue Ridge, though shear is still
lacking. Thus expect activity to be somewhat pulsey and
disorganized. Increasing shear will overspread the region this
evening, so storms may be able to organize into a line or
clusters. Damaging winds will be the main threat, although some
hail is possible. There may be a brief window for a tornado or
two this evening as a low level jet spreads into the region.
This jet and slow frontal motion may also result in some
training of storms which could lead to some localized flooding.

While the biggest severe weather threat will likely be this
evening, showers and some thunderstorms will likely continue
along the frontal zone through the night as it progresses
eastward, some anafrontal in nature. Some locally heavy rain
could continue during this time
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  • 2 weeks later...
4 minutes ago, yoda said:

Last chance saloon tomorrow night into Thursday?

We always seem to end up getting a squally threat - or some sort of high shear/low CAPE event later in Oct/Nov as well. Something with a very strong cold front that has a thin tongue of 50-60 dews ahead of it. 

But yeah - perhaps the last of the warm season style severe potential. 

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1 hour ago, Kmlwx said:

We always seem to end up getting a squally threat - or some sort of high shear/low CAPE event later in Oct/Nov as well. Something with a very strong cold front that has a thin tongue of 50-60 dews ahead of it. 

But yeah - perhaps the last of the warm season style severe potential. 

    Yeah, I won't assess the end of the season yet, but Thursday (maybe later tomorrow night for western areas) has some sneaky potential, particularly if the slowest solutions are correct.    I still think it's more of a flooding threat, but shear will be strengthening.     If we can get some heating ahead of the main frontal band on Thursday, at least some modest SVR potential is possible. 

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14 hours ago, Kmlwx said:

18z NAM nest was pretty aggressive with a severe threat in the metro corridor for Thur afternoon. Looks like a small window - but it's definitely there. 

       NAM nest (and other guidance) has trended much faster now for tomorrow's activity.    Still perhaps a small threat for an embedded circulation somewhere during the morning, but instability will be limited.

 

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Just now, high risk said:

       NAM nest (and other guidance) has trended much faster now for tomorrow's activity.    Still perhaps a small threat for an embedded circulation somewhere during the morning, but instability will be limited.

 

Yep - just looks rainy to me now. 

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Hmmm

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0734 PM CDT Wed Sep 22 2021

   Valid 230100Z - 231200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   CENTRAL APPALACHIANS...MID-ATLANTIC AND CAROLINAS...

   ...SUMMARY...
   Thunderstorms associated with a marginal tornado and wind-damage
   threat will be possible this evening into tonight from the central
   Appalachians into the Mid-Atlantic. A few strong wind gusts may also
   occur in the Carolinas this evening.

   ...Central Appalachians/Mid-Atlantic...
   The latest water vapor imagery shows a high-amplitude upper-level
   trough located over the Great Lakes and Ohio Valley with
   south-southwesterly mid-level flow over much of the Northeast. At
   the surface, a 1003 mb low is located in far northwestern
   Pennsylvania. A pre-frontal trough extends southeastward from the
   surface low into west-central Pennsylvania and then southward into
   central Virginia. Thunderstorms are ongoing along and near the
   pre-frontal trough. Ahead of the storms, surface dewpoints are in
   the 65 to 70 F range and weak instability is present. The strongest
   instability is located from southeast Pennsylvania southward into
   far eastern Virginia where the RAP is estimating MLCAPE to be in the
   500 to 750 J/kg range. In addition, the WSR-88D VWP near Washington
   D.C. has strong speed shear and veering winds with height in the
   lowest 1 km. This is resulting in 0-1 km shear in the 35 to 40 kt
   range suggesting that a marginal tornado threat could develop as the
   thunderstorms along the pre-frontal trough move eastward. The
   marginal tornado threat could affect much of Pennsylvania, Maryland
   and central Virginia along and near the axis of a 40 to 55 knot
   low-level jet. Any storm that rotates may also produce strong wind
   gusts.
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