2021 Mid-Atlantic Severe Weather - General Discussion

[WxUSAF]

3 minutes ago, high risk said:

big-time outflow boundary passage here in southern Howard County.    Gusts definitely exceeding 30 mph.     Not sure if I'm going to cash in on some rain.

Yeah, outflow was respectable. Rain starting.

[frd]

38 minutes ago, Kmlwx said:

I like how SPC issued a mesoscale discussion that is almost entirely offshore  

[mappy]

2 hours ago, toolsheds said:

I think @mappy is on the eastern shore today.  She should be prime though for storms down in Salisbury though......:-) 

Thanks, storm incoming now 

[WxUSAF]

42 minutes ago, WxUSAF said:

Yeah, outflow was respectable. Rain starting.

Only about 0.1”. Meh. Take what I can get I guess.

[frd]

Another bust, whats new this year. 

[CAPE]

Nice outflow/gust front from that cluster to my SW. Major T&L with that. Power went off briefly. Might be something forming on the north edge of that. Getting some rain now.

[CAPE]

Pouring now. Maybe some hail in that cell just to my west.

[SnowenOutThere]

No what this misses, right? 

[NoVaWx]

That weakened right as it got here. 

[yoda]

Sunday then midweek maybe?

[high risk]

15 hours ago, yoda said:

Sunday then midweek maybe?

      I'm modestly intrigued by Sunday.      It's clear unclear how much instability will be available, but deep layer shear looks respectable.   There isn't much agreement on how intense storms will be or what the coverage will look like, but the CAMs have overall trended towards at least scattered storms in the area later Sunday.     At this point, I'd just be happy with some rain.

[Kmlwx]

Not in terms of setup - but purely the SPC map itself - the day 2 outlook reminds me of Jun 2012

[George BM]

18 hours ago, Kmlwx said:

Not in terms of setup - but purely the SPC map itself - the day 2 outlook reminds me of Jun 2012

PDS STW or bust! 

 

 

My two amateur pennies:

With a WNW to ESE boundary nearby (just to our northeast) tomorrow a few storms could pop. While shear looks fairly modest, low-level lapse rates look to be very steep with mid-level lapse rates around 6+C/km. Any storms that do pop will have a good environment for downburst winds. A potential limiting factor would be slightly lower low-level moisture content (PW 1.25"+, MeanW: 10g/kg or so). But slightly cooler mid-level temps may offset that a bit. 

Thursday is more dependent on what happens upstream late Wednesday/early Thursday. But flow/shear look to be stronger at least.

[yoda]

Thursday... hmm... nice SPC map.  I know it's i66 north for now... but can see it coming south some... some beefy wording in the morning day 2 disco too

[CAPE]

Interesting discussion from Mount Holly. Plenty of potential, lots of uncertainty.

One of the more difficult warm season forecasts in recent memory for Thursday, with reasonable outcomes ranging from a largely uneventful day to a fairly high end severe weather event. Synoptically, northwest flow aloft continues. Surface low pressure is expected to track eastward through the Great Lakes in response to a southeastward digging shortwave propagating through the 50 to 60 kt 500 mb flow. Meanwhile, a convectively enhanced wave will likely dive southwest of us on Thursday. This wave will result from explosive convective development and likely derecho formation over the Midwest on Wednesday. This MCS/derecho will probably not be much of a factor for our region, either tracking southwest of us and/or not surviving this far in severe form. The SPC SWODY1 does extend a Marginal Risk into our Delmarva zones on the off chance it does make it all the way to the coast. This feature may also serve to deposit convective debris over our region, which would limit instability for new convection on Thursday. However, anvil level storm relative winds suggest this is unlikely, and that much of the convective debris will probably be shunted south of us. But the evolution of Wednesday`s convection and potential lingering debris and/or outflow boundaries will no doubt have some impact on Thursday. Another complicating factor is much of the guidance indicating fairly widespread but likely non-severe convection over our region on Thursday morning and early afternoon. This is likely in response to retreating high pressure, combined with surface convergence and increased low level moisture in response to a shift to southeasterly flow. This type of weakly forced convection is common in these regimes, and is a common failure mode for severe weather events. If early day convection is as widespread as much of the guidance indicates, I would be doubtful of the afternoon severe potential, especially in eastern portions of the area, even as the better forcing from the approaching mid-level jet and vorticity max arrives. With those caveats mentioned, the dynamics on Thursday are no doubt impressive, unlike any we`ve seen this year in terms of the potential overlap of instability, shear, and forcing if everything comes together right. 28.0z CAM guidance largely clobbers the region with severe convection Thursday afternoon and evening, but run-to- run consistency has been poor. Should several of those 0z CAM solutions (i.e. 3km NAM, ARW) and their associated forecast soundings come to pass, then a significant severe weather event with all severe hazards would be likely. The Storm Prediction Center has added a Slight Risk of severe weather over much of the region.

[mappy]

lot of derecho mentions on twitter this AM for Wisconsin and points southeast. 

for us:

 ...Mid-Atlantic Vicinity...

   Modest deep-layer northwesterly flow will be in place today as an
   upper trough pivots eastward off the Atlantic coast. A very moist
   airmass is in place with dewpoints generally from the upper 60s to 
   mid 70s F. Strong heating will result in strong destabilization
   during the afternoon. Nebulous large-scale ascent is forecast, and
   should limit coverage, with isolated thunderstorm development
   expected during the afternoon/evening. While low-level winds will be
   light, southerly flow beneath northwesterly winds aloft will result
   in moderate effective shear magnitudes, aiding in at least briefly
   organized cells/clusters. Steep low-level lapse rates and high PW
   values will support isolated damaging gusts through early evening.

[H2O]

[yoda]

Interesting...

 

[mattie g]

33 minutes ago, yoda said:

Interesting...

 

So...we'll never see those alerts?

[mattie g]

1 hour ago, CAPE said:

Interesting discussion from Mount Holly. Plenty of potential, lots of uncertainty.

One of the more difficult warm season forecasts in recent memory for Thursday, with reasonable outcomes ranging from a largely uneventful day to a fairly high end severe weather event. Synoptically, northwest flow aloft continues. Surface low pressure is expected to track eastward through the Great Lakes in response to a southeastward digging shortwave propagating through the 50 to 60 kt 500 mb flow. Meanwhile, a convectively enhanced wave will likely dive southwest of us on Thursday. This wave will result from explosive convective development and likely derecho formation over the Midwest on Wednesday. This MCS/derecho will probably not be much of a factor for our region, either tracking southwest of us and/or not surviving this far in severe form. The SPC SWODY1 does extend a Marginal Risk into our Delmarva zones on the off chance it does make it all the way to the coast. This feature may also serve to deposit convective debris over our region, which would limit instability for new convection on Thursday. However, anvil level storm relative winds suggest this is unlikely, and that much of the convective debris will probably be shunted south of us. But the evolution of Wednesday`s convection and potential lingering debris and/or outflow boundaries will no doubt have some impact on Thursday. Another complicating factor is much of the guidance indicating fairly widespread but likely non-severe convection over our region on Thursday morning and early afternoon. This is likely in response to retreating high pressure, combined with surface convergence and increased low level moisture in response to a shift to southeasterly flow. This type of weakly forced convection is common in these regimes, and is a common failure mode for severe weather events. If early day convection is as widespread as much of the guidance indicates, I would be doubtful of the afternoon severe potential, especially in eastern portions of the area, even as the better forcing from the approaching mid-level jet and vorticity max arrives. With those caveats mentioned, the dynamics on Thursday are no doubt impressive, unlike any we`ve seen this year in terms of the potential overlap of instability, shear, and forcing if everything comes together right. 28.0z CAM guidance largely clobbers the region with severe convection Thursday afternoon and evening, but run-to- run consistency has been poor. Should several of those 0z CAM solutions (i.e. 3km NAM, ARW) and their associated forecast soundings come to pass, then a significant severe weather event with all severe hazards would be likely. The Storm Prediction Center has added a Slight Risk of severe weather over much of the region.

TL;DR

AmWx Mid-Atlantic fail tomorrow.

[H2O]

32 minutes ago, mattie g said:

TL;DR

AmWx Mid-Atlantic fail tomorrow.

Hey now. We had less of a more chance of storms on Monday and look how that worked out for EastCoastNPZ and MN Trans. 

[high risk]

We’ll see what details come out of the guidance today, but this right now feels like a setup for tomorrow in which we waste really good shear with debris from a dying Midwest MCS. 

[mappy]

2 hours ago, yoda said:

Interesting...

 

I think its good. If we send EAS alerts for flash flood warnings and tornado warnings, then we should do so for severe (80+ mph wind) thunderstorms too. The general public hardly pays attention as it is, whether its newscasts or warnings issued, so having this extra layer of communication hopefully will help curb the "it came without warning!" bullshit. 

[rclab]

1 hour ago, H2O said:

 

1 hour ago, H2O said:

The WWE and WCT ……. I’m not surprised. As always ….

[yoda]

1 hour ago, high risk said:

We’ll see what details come out of the guidance today, but this right now feels like a setup for tomorrow in which we waste really good shear with debris from a dying Midwest MCS. 

Some pretty nice soundings showing up on 12z NAM for 21z THUR and 00z FRI across the region 

Like KMRB and KHGR at 21z THUR

[yoda]

Hmmm... updated morning discussion sounds intriguing for this afternoon and evening 

 

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1035 AM EDT Wed Jul 28 2021

.SYNOPSIS...
A weak front stalled in the region today will be the focus of a
few showers and thunderstorms this afternoon. A much stronger
front later Thursday and Thursday night will result in more
widespread showers and storms. High pressure will return Friday
and linger into the weekend, with cooler and drier air taking
hold. Another system may approach early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Mid-morning update: Current visible satellite imagery shows
mostly sunny skies across the area, allowing strong daytime
heating to occur. 12z IAD sounding shows steeper than climo
mid-level lapse rates (6.5 C/km) and lots of dry air in the
mid- upper levels. With strong daytime heating occurring, low-
level lapse rates are expected to become very steep as well
(exceeding 9.5 C/km). The sounding shows 1164 J/kg of DCAPE
prior to daytime heating, and that value should only increase.
The combination of steep low-level lapse rates, better than
climo mid-level lapse rates, high DCAPE, and decent flow in the
mid- levels suggests that damaging winds could be a threat with
any storms this afternoon. Can`t rule out an instance or two of
large hail with any stronger storms either, given the better
than climo mid- level lapse rates, ample dry air in the mid-
levels, and decent shear through a deep layer. In the absence
of stronger forcing for ascent both aloft and at the surface,
the smaller details with respect to placement and timing of
storms remain a bit up in the air. We`ll continue to monitor
trends through the remainder of the day.

[Eskimo Joe]

There certainly is a risk for some wet microbursts today. Out Total Totals are pushing 50 and the low level lapse rates are pretty robust. Could see a few decent terrain based storms. 

[Eskimo Joe]

 

[yoda]

SLGT risk moved south on 1730 update... includes all of LWX CWA.  5/5/15

[Newman]

Tornado threat increased for everyone in the latest day 2 outlook