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2020 Mid-Atlantic Severe Weather - General Thread

Kmlwx

By Kmlwx,
in Mid Atlantic

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andyhb

andyhb

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CONFIDENCE HAS INCREASED THAT AT LEAST SCATTERED STORMS WILL FORM   OVER THE HIGHER TERRAIN OF THE CENTRAL APPALACHIANS AND/OR BLUE   RIDGE MOUNTAINS BY PEAK AFTERNOON HEATING ON THURSDAY AS LARGE-SCALE   ASCENT ASSOCIATED WITH THE SHORTWAVE TROUGH OVERSPREADS THIS AREA.   RATHER POOR MID-LEVEL LAPSE RATES WILL PERSIST, BUT STRONG HEATING   OF THE MOIST LOW-LEVEL AIRMASS SHOULD STILL YIELD MLCAPE OF   1500-2500 J/KG, STRONGER WITH SOUTHWARD EXTENT INTO VA AND THE   DELMARVA. THE ENHANCED (40-50 KT) MID-LEVEL FLOW ATTENDANT TO THE   SHORTWAVE TROUGH WILL FOSTER SIMILAR VALUES OF DEEP-LAYER SHEAR, AND   ORGANIZED STORMS APPEAR LIKELY, WITH BOTH SUPERCELLS AND BOWING LINE   SEGMENTS POSSIBLE. THIS CONVECTION IS EXPECTED TO SPREAD EASTWARD   ACROSS THE MID-ATLANTIC LATE THURSDAY AFTERNOON AND INTO THE   EVENING.    

A FEW TORNADOES MAY OCCUR WITH ANY INITIALLY DISCRETE SUPERCELLS, AS   A 30-40 KT SOUTHWESTERLY LOW-LEVEL JET SHOULD PROVIDE SUFFICIENT   VEERING/STRENGTHENING OF THE LOW-LEVEL WINDS. THIS TORNADO POTENTIAL   APPEARS TO BE MAXIMIZED THURSDAY AFTERNOON ALONG/EAST OF THE BLUE   RIDGE MOUNTAINS INTO THE I-95 CORRIDOR OF MD/DC/NORTHERN VA. AT   LEAST SCATTERED DAMAGING WINDS ALSO APPEAR LIKELY LATER INTO THE   AFTERNOON AND EARLY THURSDAY EVENING ACROSS THIS REGION AND INTO THE   DELMARVA, AS SOME CLUSTERING OF STORMS SHOULD OCCUR WITH EASTWARD   EXTENT. CONFIDENCE IN THIS SCENARIO OCCURRING HAS INCREASED ENOUGH   TO INCLUDE GREATER SEVERE PROBABILITIES FOR BOTH TORNADOES AND   DAMAGING WINDS. A CORRESPONDING ENHANCED RISK HAS BEEN INTRODUCED   ACROSS NORTHERN VA, DC, CENTRAL/EASTERN MD, DE, AND FAR SOUTHERN NJ   TO ACCOUNT FOR THESE THREATS.

That's a pretty stout discussion on the SWOD2.

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Kmlwx
Kmlwx

My camera looking north from the apartment back in Columbia got something - looks like a lowering. 

mappy
mappy

so pretty

high risk
high risk

Had a glorious view of that York cell from southern Howard County.     Could see a fair amount of lightning within it too.

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Kmlwx

Kmlwx

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22 minutes ago, andyhb said:

That's a pretty stout discussion on the SWOD2.

You know it's real when @andyhb pops into our subforum. Do you think we perform or bust tomorrow? 

Just now, Eskimo Joe said:

Tomorrow is an okay setup for N Central MD. I'm just glad we didn't get a DY2 MOD...that's the kiss of death in these parts.

I doubt this goes to even a D1 moderate. It seems like the kind of scenario that is exactly the reason they mad the "enhanced" category. I'll eat my words if I'm wrong. Further, assume they'd wait for 1630z tomorrow to do it. I just don't think the coverage is going to be wide enough - it's already a tiny 10% area to begin with - and no derecho type setup. 

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Eskimo Joe

Eskimo Joe

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Just now, Kmlwx said:

You know it's real when @andyhb pops into our subforum. Do you think we perform or bust tomorrow? 

I doubt this goes to even a D1 moderate. It seems like the kind of scenario that is exactly the reason they mad the "enhanced" category. I'll eat my words if I'm wrong. Further, assume they'd wait for 1630z tomorrow to do it. I just don't think the coverage is going to be wide enough - it's already a tiny 10% area to begin with - and no derecho type setup. 

DY1 MOD Risk for tornado is now 15% w/ SIG Severe. There's almost no chance we get that. https://www.spc.noaa.gov/misc/SPC_probotlk_info.html

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Kmlwx

Kmlwx

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Just now, Eskimo Joe said:

DY1 MOD Risk for tornado is now 15% w/ SIG Severe. There's almost no chance we get that. https://www.spc.noaa.gov/misc/SPC_probotlk_info.html

For the heck of it - I took a look at the H5 maps for September 24, 2001 - didn't realize how amplified H5 was for that. Nothing at all like that setup. I think a lot of people like to sleep on September for us. But September might as well be May/June. I think the outlook is about as robust as it is going to get. The most I could see is a non-hatched 15% showing up. I don't think the ingredients are quite there for hatching of EITHER wind or tornado. 

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Eskimo Joe

Eskimo Joe

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Just now, Kmlwx said:

For the heck of it - I took a look at the H5 maps for September 24, 2001 - didn't realize how amplified H5 was for that. Nothing at all like that setup. I think a lot of people like to sleep on September for us. But September might as well be May/June. I think the outlook is about as robust as it is going to get. The most I could see is a non-hatched 15% showing up. I don't think the ingredients are quite there for hatching of EITHER wind or tornado. 

100% agree. 

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Kmlwx

Kmlwx

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FWIW - There wasn't really much of a signal on CIPS the last day or two for tomorrow either. Some enhancement but nothing to write home about. I generally like bowling ball closed upper lows better (or a very amplified pattern in general) for tor risk around here. 

I think the lack of CIPS shows us that our better severe events potentially have a different configuration at some height level. Nonetheless, ingredients are there for a fun day. Not "outbreak" status though. 

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andyhb

andyhb

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7 minutes ago, Kmlwx said:

You know it's real when @andyhb pops into our subforum. Do you think we perform or bust tomorrow? 

I'm a fan of the low level hodograph curvature I've seen on a few soundings, although I'd like to see the magnitude of the 850 mb flow increase a bit to be more sure on tornado potential. SPC mentions 30-40 kts, but most soundings I've pulled are more in the 20-30 kt range.

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Kmlwx

Kmlwx

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Very strongly worded discussion from LWX now as well.  

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...

Dry weather is expected to continue through early Thursday with 
temps in the 70s. Another higher risk day is expected Thursday 
afternoon and into early evening. The front to our north will drop 
southward through the day Thursday. This boundary coupled with warm 
and moist air advected into our region due to a southerly flow along 
with strong shortwave will lead to an enhanced risk for severe 
weather. CAPE values will increase above 2000 as temperatures and 
moisture increase during the day Thursday. Shear will be better than 
today which will lead to an increased risk for a tornadoes Thursday. 
SPC has upgraded our region to an enhanced risk for severe weather 
with a 10 percent chance for tornadoes. Thursday could be a very 
dangerous environment with more widespread threat for severe weather 
and tornadoes. We will to need monitor the changing weather 
situation to determine the timing, coverage and risk for Severe WX 
tomorrow.
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Newman

Newman

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mcd1669.gif

   SUMMARY...Thunderstorms are expected to develop from northern
   Virginia into northern Maryland and southeast Pennsylvania by
   21-22Z. A few supercells capable of damaging wind gusts and isolated
   tornadoes will be the main threats. A tornado watch will likely be
   needed prior to 21Z.

   DISCUSSION...As of mid afternoon a progressive vorticity maximum was
   situated over southwestern PA and will continue east into the Middle
   Atlantic region during the late afternoon and evening. A band of
   low-topped convection has already developed in association with this
   feature extending into northern WV where instability is limited.
   Farther downstream, a lee trough resides just east of the central
   and southern Appalachian mountains. East of this feature
   temperatures have warmed to the upper 80s F with dewpoints in the
   low to mid 70s contributing to 1500-2000 J/kg MLCAPE despite very
   weak mid-level lapse rates resulting from warm temperatures aloft.
   As the corridor of deeper ascent attending the shortwave trough
   continues east and begins to overtake the western edge of the moist
   warm sector, additional storms will likely develop from northern VA
   into southeast PA. Winds in the 850-500 mb layer will undergo a
   modest increase with approach of the impulse, resulting in 35-40 kt
   effective bulk shear and 100-200 m2/s2 storm relative helicity. This
   environment should be sufficient for some organized storm structures
   including a few supercells capable of locally strong to damaging
   gusts and a couple of tornadoes through early evening.
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CAPE

CAPE

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Mount Holly updated AFD for severe threat this evening and tomorrow-

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As we head through the late afternoon and particularly into this evening, expect showers back over western MD into west Virginia associated with a disturbance aloft to intensify into storms as they move east and conditions become more unstable with time. This should result in storms entering our western zones (SE PA into Delmarva) early this evening. Storm mode will likely be mixed but tends toward a broken line or clusters. Think there is the potential for at least some of these storms to be severe as ML CAPES will be in the neighborhood of 1000 j/kg with deep layer shear around 35 knots or so. 0-3 km shear will also be around 30 knots due to fairly strong belt of mid level winds. Best chance for severe weather looks to be in our western zones (especially MD eastern shore) with damaging winds being the main threat. However, due to good low level turning of the winds as well as shear still can not rule out the possibility of a tornado or two. LCL heights are also low. Limiting factor though will be deep layer shear being a bit less than optimal for tornadic supercells.

 

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***Severe weather possible late day Thursday***

A weak, diffuse frontal boundary will sit across the area to start the day Thursday as the area will also continue to lie just south of the jet core aloft. Through the day Thursday there will continue to be disturbances moving through aloft roughly aligned with this boundary and the strongest of these will help develop a wave along the front by late day with another round of strong to severe storms expected. The day will start dry though with even some sunshine in the morning. However mid and high clouds increase during the afternoon ahead of this developing wave. Expect that storms will develop by mid afternoon to our west over central PA and move into the area by the late afternoon / early evening time frame. Conditions look to be even more favorable for severe weather compared to today and the SPC has upgraded our Delmarva zones as well as extreme southern NJ to an enhanced risk for severe storms. ML CAPEs look to reach the 1000-2000 j/kg range with deep layer shear around 40 knots. There will also be veering low level winds with the low level warm advection profile. The upshot is the environment looks to be favorable for supercells and all severe weather threats will be on the table...damaging winds, large hail, and even the threat for tornadoes. Again, highest threat looks to be over Delmarva but the threat exists farther north as well. Storm coverage also looks to be fairly widespread. Mode looks like it will tend towards multi-cell clusters with again, embedded supercells possible.

 

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