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Kmlwx

2020 Mid-Atlantic Severe Weather - General Thread

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I'd gladly sacrifice today's activity to make tomorrow a sure thing especially if it meant Frederick/Carroll would get the bullseye.

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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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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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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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25 minutes ago, Kmlwx said:

WOOF

12z ARW, ARW2, NMM, HRDRPS, RGEM all look great for tomorrow in the SPC enhanced area.

Yeah pretty much all the CAMs are onboard for tomorrow. Might be legit.

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Because we love to predict the prediction (guess what SPC will do) around here - my guess is minimal changes (if any) at the 2am update. Probably the same for the 1300z unless something is very apparent. 

18z NAM twins will run in the next hour. 

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46 minutes ago, Kmlwx said:

WOOF

12z ARW, ARW2, NMM, HRDRPS, RGEM all look great for tomorrow in the SPC enhanced area.

Longgg range Hrrr also sees the significant threat tomorrow :weenie:

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

Quote

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.

 

Quote

***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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20 minutes ago, Kmlwx said:

NAM nest parameter space for tomorrow looks great - reflectivity not so much. 

Looked great at 12z for I-95 and points east.

 

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Are we going to use this thread for both days?  Or should we risk getting denied by posting a separate thread lol

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I’m keeping an eye on stuff out west, as EJ said. Hasn’t been too sunny here today, 82/75 currently. I dunno maybe the storms will get more robust?

 Tomorrow looks legit, from what I’ve read here. Thanks @andyhb for chiming in. 

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2 minutes ago, Kmlwx said:

Today is looking super lame at least at the current moment. More eggs into the tomorrow basket perhaps. 

Crapvection galore

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3 minutes ago, Kmlwx said:

Today is looking super lame at least at the current moment. More eggs into the tomorrow basket perhaps. 

     Yeah, I'm a bit surprised, and I think that SPC is too.    Latest HRRR still suggests that the convection firing near the I-81 corridor will still become a bigger deal further east in a few hours.

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3 minutes ago, high risk said:

     Yeah, I'm a bit surprised, and I think that SPC is too.    Latest HRRR still suggests that the convection firing near the I-81 corridor will still become a bigger deal further east in a few hours.

There's probably enough moisture to support a threat for storms (some strong maybe) past sunset. For the superstitious/non-scientific side of us - this could bode well for our odds to see stronger storms tomorrow. We just can't seem to string multiple days together - the area of focus always shifts a little bit day to day - even when it seems like we'll be bullseyed for days on days. 

I personally thought that earlier mesoscale discussion was VERY high probs for something that had not even developed yet - and didn't look insanely good on modeling. 

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10 minutes ago, Kmlwx said:

There's probably enough moisture to support a threat for storms (some strong maybe) past sunset. For the superstitious/non-scientific side of us - this could bode well for our odds to see stronger storms tomorrow. We just can't seem to string multiple days together - the area of focus always shifts a little bit day to day - even when it seems like we'll be bullseyed for days on days. 

I personally thought that earlier mesoscale discussion was VERY high probs for something that had not even developed yet - and didn't look insanely good on modeling. 

      SPC Mesoanalysis shows the supercell composite here increasing to 8 here over the next couple of hours.     Given that and most of the CAMs showing convection developing by now, I'm assuming that's why they went with such high watch probs.      I'd think that the convection to the west should do better as it moves east into the better environment, but we'll see.

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