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2020 Mid-Atlantic Severe Weather - General Thread


Kmlwx
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LWX goes big for today and tomorrow in their morning AFD

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
406 AM EDT Wed Sep 2 2020

.SYNOPSIS...

A warm front will lift north of the area this afternoon. A
surface trough will linger across the area through Thursday,
before a strong cold front crosses the area Friday afternoon
with cooler and dry high pressure for the Labor Day weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...

Latest surface analysis shows our area is still wedged under high
pressure while a stationary front is stalled across North Carolina
and to our west. Tropical Storm Omar is sitting east of the Mid-
Atlantic region. East to southeasterly flow remains over our area. A
quasi zonal pattern remains across the Mid-Atlantic region aloft
with WSW flow along with pulses of shortwave energy.

Isolated to scattered rain showers continue to move across our CWA
from S to N this morning with low clouds. This is expected to
continue through this morning as the stationary boundary remains SW
of our area. This boundary will lift north as a warm front around
mid-day while SW flow develops and clouds begin to break. A surface
trough will develop east of the Blue Ridge and a cold front will be
approaching from the west. These along with shortwave energy aloft,
dew points in the mid 70s, and increasing instability, could result
in the development of scattered to numerous thunderstorms across our
area, especially between the late afternoon and evening. Shear will
be modest and there is the potential for damaging wind gusts with
any storms that develop. Tornadoes cannot be ruled out. There is
still a level of uncertainty with this forecast as the forcing is
just to our north and also how quick the cloud cover breaks behind
the warm front.

Tonight any break in the clouds could result in the development of
patchy fog, with low temperatures in the 60s and 70s. Drier
conditions, mainly after midnight. Cold front will be stalled just
north of our area.

&&

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

On Thursday, weakening cold front will be lingering just to our
north while a secondary cold front quickly approaches from the NW.
Pulses of shortwave energy along with a wave of low pressure through
this front, SW flow, upper jet streak just to our north, modest
shear, and dew points in the mid 70s again will allow for the
development of showers and thunderstorms. Convection may remain
closed to the frontal position, so this will determine our local
impacts. The main threats are damaging wind gusts, while hail and
tornado threats remain more conditional.

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I know it's not a great product to use - but UH tracks for both today and tomorrow are very respectable for this area...

That's some nice language from SPC regarding tomorrow's outlook...especially because the TOR risk is already at 5%. September can be a good tor month around here...

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10 minutes ago, Eskimo Joe said:

Always Really Wet

I dunno - I know it had that rep before. This season it's been pretty gun shy on predicting big storms for us. ARW is actually less enthused than the ARW2. HRRR looks passable for this afternoon even. A tiny UH track over MoCo too :lol: 

It's REALLY dreary out right now, though. So we could fail on the instability side of things today. Pretty unusual for same areas to get it two times in two days. So I'm going to assume we either fail today or tomorrow. Tempted to put all my eggs in the tomorrow basket after reading the SPC disco and looking at the guidance. Even the GFS paints a decent amount of parameter space over the DC area tomorrow PM. 

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I completely get that SPC doesn't want to issue a huge SLGT on a day like today from TN to the northern NY border, but I would still argue for a SLGT in our area.   The CAMs still really like DC metro later today, and that's reflected in HREF probabilities.    Both the ops (left) and para (right) indicate high probabilities of updraft helicity exceeding 25.   (That's a low end threshold, but it still reflects that there is strong agreement in intense cells with at least weak rotation.   And the probabilities of higher UH thresholds are not terrible either....)href_mxuphlprob25_MIDATL_f24_CONUSPROBPARACOMP.gif.e7d87d0f757a5183d889ac26b3786421.gif

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9 minutes ago, high risk said:

I completely get that SPC doesn't want to issue a huge SLGT on a day like today from TN to the northern NY border, but I would still argue for a SLGT in our area.   The CAMs still really like DC metro later today, and that's reflected in HREF probabilities.    Both the ops (left) and para (right) indicate high probabilities of updraft helicity exceeding 25.   (That's a low end threshold, but it still reflects that there is strong agreement in intense cells with at least weak rotation.   And the probabilities of higher UH thresholds are not terrible either....)href_mxuphlprob25_MIDATL_f24_CONUSPROBPARACOMP.gif.e7d87d0f757a5183d889ac26b3786421.gif

And going back to the discussion we've all been having the last few days - a slight is so common around here there's little bust potential. Still pretty dreary here...so maybe that plays a role. 

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Noteworthy parts of SPC

 Areas of precip and cloud cover will render a rather patchy or
   streaky planar buoyancy field today.  Still, with rich moisture over
   most of the warm sector, areas of sustained diurnal heating should
   offset modest mid/upper lapse rates enough for areas of 500-1500
   J/kg peak MLCAPE over higher terrain, and 2000-3000 J/kg over parts
   of the Mid-South and east of the Blue Ridge in VA.  Low-level and
   deep-layer shear generally should increase northward into areas of
   weaker overall instability, but may favor supercell potential as far
   south as central/southern VA.  Effective SRH of 150-300 J/kg may
   develop intermittently from there through northern NY, especially
   near and east of the prefrontal trough where surface flow is most
   backed.  Some part of that corridor may require an upgrade to
   unconditional probabilities once mesoscale  placement, coverage, and
   timing/forcing uncertainties are better resolved
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To be honest - the parameters (and I know these don't necessarily guarantee anything) for today and tomorrow look about as good as any event we've seen this year so far. If we can get decently unstable tomorrow I could see it being a 10% tor day - especially given that text from SPC in the day 2. Very doubtful they'd introduce that until D1 though. 

I think a lot of areas will see storms this PM - the question is how severe they will be.

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1 hour ago, MN Transplant said:

In EJ's world, we only hit these if they are billion-dollar disasters.  So, still due ;)

I'm always skeptical of severe in these parts of the country. We have so many things that can and do go wrong (terrain, CAD, etc.) that it's hard to get excited until the event is unfolding or right on top of you. Even the other week we had a DY1 ENH that was crapola.

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6 minutes ago, Kmlwx said:

To be honest - the parameters (and I know these don't necessarily guarantee anything) for today and tomorrow look about as good as any event we've seen this year so far. If we can get decently unstable tomorrow I could see it being a 10% tor day - especially given that text from SPC in the day 2. Very doubtful they'd introduce that until D1 though. 

I think a lot of areas will see storms this PM - the question is how severe they will be.

       Hard to argue with this.      I'm still more bullish for today than most, but I understand the question marks.    For tomorrow, the potential is real.    My only concerns are the weaker lapse rates (although they are now progged a bit better than earlier guidance) and potential weak sfc wind speeds (although the NAM nest seems to be weaker than some other models)

       I'd still prefer today's lapse rates with tomorrow's wind profiles, but good luck getting those two to align in this region.....

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3 minutes ago, high risk said:

       Hard to argue with this.      I'm still more bullish for today than most, but I understand the question marks.    For tomorrow, the potential is real.    My only concerns are the weaker lapse rates (although they are now progged a bit better than earlier guidance) and potential weak sfc wind speeds (although the NAM nest seems to be weaker than some other models)

       I'd still prefer today's lapse rates with tomorrow's wind profiles, but good luck getting those two to align in this region.....

And of course - knowing our area we will find a way to blank on both today AND tomorrow. Latest HRRR still looks good for storms this PM but with pretty garden variety intensity. 

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23 minutes ago, Kmlwx said:

There are some PDS TOR soundings showing up on the NAM nest for both today and tomorrow :lol: 

The NAM nest reflectivity looks great for DC tomorrow - less so for @mappy. Taking the NAM nest at face value would put the bigger emphasis on tomorrow. 

eh, ill take whatever we get. 

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I think social science has led to the ref on numbers. They have been in many of their graphics for a while. We tend to always mention numbers ourselves ... a level one of five, etc. 

Figures I'm in Cape Cod. Enjoy the wedges. 

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10 minutes ago, Ian said:

I think social science has led to the ref on numbers. They have been in many of their graphics for a while. We tend to always mention numbers ourselves ... a level one of five, etc. 

Figures I'm in Cape Cod. Enjoy the wedges. 

Are you endorsing tomorrow as a potential legit event?

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