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2017 Severe Thread

mappy

By mappy,
in Mid Atlantic

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Kmlwx

Kmlwx

Posted
Posted

I am personally not sure the upgrade was warranted in our area. To our west and north sure...but the modeling just doesn't seem to support a robust threat for DC area locally. Robust wording in the SPC outlook though...they even mention the potential for strong tornadoes...

A lot of the hi-res guidance has stuff weakening before it gets here or the dreaded DC split. I'm having trouble finding modeling that brings robust activity through DC. We'll see if the trend is for something more on the short range models...I'm out unless you're well west...for now. 

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Eskimo Joe

Eskimo Joe

Posted
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SPC likely included the cities as a cover-your-a$$ and they've been off recently.  LWX is weenie as heck and if they're pretty 'meh' then it doesn't encourage me.  Still, we're 72 in Gaithersburg at 8am and the cloud deck is racing NE.  Probably good for a gusty thunderstorm or something today.

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mappy

mappy

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I don't want to knock SPC, but they haven't had the best record with this system as it moved across the country. With that said, today is worth keeping an eye on. Really going to depend on how fast the backdoor front can move north and out of the area and clearing. Much like yesterday, north of that boundary that was near DC, it was much too stable and anything that popped up was meet with a quick death. Today could be the same if clouds hang around. 

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Kmlwx

Kmlwx

Posted
Posted
1 minute ago, mappy said:

I don't want to knock SPC, but they haven't had the best record with this system as it moved across the country. With that said, today is worth keeping an eye on. Really going to depend on how fast the backdoor front can move north and out of the area and clearing. Much like yesterday, north of that boundary that was near DC, it was much too stable and anything that popped up was meet with a quick death. Today could be the same if clouds hang around. 

We love our clouds on severe days here in the DC area ;)

I'm out for now on today. Pending instability - a lot of the models are very meager with instability for our area. 

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Eskimo Joe

Eskimo Joe

Posted
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One thing we have going for us is that large area of clearing from I-95 west.  The broad SW flow should aid the eroding of any low level wedge.  It was 51 in Reisterstown and overcast when I left, 63 in Lisbon and it's 72 with partly sunny skies in Gaithersburg.  Impressive boundary.  http://weather.cod.edu/satrad/exper/?parms=dcarea-02-48-0 

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JoJo

JoJo

Posted
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2 minutes ago, Kmlwx said:

We love our clouds on severe days here in the DC area ;)

I'm out for now on today. Pending instability - a lot of the models are very meager with instability for our area. 

Today looks like it could be a day where the shear takes advantage of any instability between 500 j/kg and 1000 j/kg. The enhanced risk large and somewhere in it will get an upgrade based one the trends

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mappy

mappy

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2 minutes ago, JoJo said:

Today looks like it could be a day where the shear takes advantage of any instability between 500 j/kg and 1000 j/kg. The enhanced risk large and somewhere in it will get an upgrade based one the trends

Agreed. Shear is about the only real good thing we have going for us, as of now. 

ETA: disregard HRRR comment, was from an earlier run. 

 

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high risk

high risk

Posted
Posted

Cheers to WW007!      This case is a great example of the evolution of severe weather forecasting from basing it off of forecasted parameters to forecasting it off of details in hi-res guidance.     It has previously been the latter, and we're moving towards the former - kind of in the dreaded "in between" zone now, figuring out how much to trust when the models show "meh" when the parameters scream "woohoo!" (or vice versa).     We saw this on the FL/GA high risk bust earlier this year:   the parameters were insane, yet the models showed weak updraft helicity signatures.    The models were correct.     But it would be unwise to say that we can always trust the hi-res forecasts.

So today, the parameters here look good, but the reflectivity forecasts are uninspiring until you go further north and northwest.     It *may* be related to the models mixing out some of the low-level moisture.    If you look at NAM nest or HRRR forecast soundings, the dew points drop from the upper 60s this morning to the lower 60s by the end of the day.    If that's right, a big event here won't happen.    If the mixing is overdone, then it could be game on.

 

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high risk

high risk

Posted
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To see why the HRRR (and other hi-res guidance) hates our area later today, here is a forecast sounding for 6PM in south-central Montgomery Co.    The dew point was in the upper 60s earlier in the day (with cape in the 1250 range), but it mixes out the low-level moisture later in the day, dropping the sfc dew point and killing instability.     If it's wrong about this mixing, then we'll be in business.    Otherwise, meh.

hrrr_2017050112_fh10_sounding_39.11N_77.09W.png

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yoda

yoda

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17 minutes ago, high risk said:

To see why the HRRR (and other hi-res guidance) hates our area later today, here is a forecast sounding for 6PM in south-central Montgomery Co.    The dew point was in the upper 60s earlier in the day (with cape in the 1250 range), but it mixes out the low-level moisture later in the day, dropping the sfc dew point and killing instability.     If it's wrong about this mixing, then we'll be in business.    Otherwise, meh.

hrrr_2017050112_fh10_sounding_39.11N_77.09W.png

12z NAM is intriguing... it takes DP's back to the lower 60s around 21z... but back to the mid to upper 60s by 03z and 06z as the storms move in

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Kmlwx

Kmlwx

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I have decent confidence that the western panhandle of Maryland NE up into PA will do decently. Models keep delivering decent storms to those areas and fizzle for us. We can hope they will be wrong. Will be interesting to watch dewpoints later today. 

And Yoda, never bank on nocturnal severe except in rare cases. Even if dews come back up at 3z or 6z - we won't perform at that hour. They'll naturally surge before cold frontal passage. 

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yoda

yoda

Posted
Posted 
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
947 AM EDT Mon May 1 2017

.SYNOPSIS...
A strong cold front will approach from the west today before
passing through tonight. High pressure will bring cooler and
drier weather during the middle of the week. Low pressure will
move into the area late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Hazardous weather expected across the Mid-Atlantic region
later this afternoon and evening. Strong to severe
thunderstorms are likely. Interested parties should stay tuned
into the changing weather through tonight.

A strong cold front is located over the Ohio Valley this morning
and a warm front is located across northeastern Maryland. The
warm front will lift north late this morning into early this
afternoon while the cold front approaches from the west. A
strong pressure gradient between the cold front and high
pressure over the Atlantic will allow for gusty southerly winds.
Frequent gusts around 30 to 35 mph are expected. The southerly
flow will usher in warm and humid conditions for today.
Dewpoints will top off well into the 60s and max temps will be
in the lower 80s across most locations.

The warm and humid airmass will lead to some instability. The
modified 12z KIAD sounding shows around 500-1000 j/kg of mlcape
later this afternoon into this evening. This lines up with
forecast soundings as well. Shear profiles will be quite
impressive due to a strengthening jet associated with the cold
front. The combination of forcing from the cold front...the
instability and the strong shear profiles enhances the threat
for severe thunderstorms later this afternoon and evening.
Damaging winds will be the primary threat...but isolated
tornadoes and large hail are also possible in thunderstorms that
develop during this time.

The first round of convection is likely to propagate in from the
southwest well ahead of the cold front during the mid to late
afternoon hours. Severe thunderstorms are possible during this
time...but confidence is low since the strongest forcing from
the mid and upper-level jet as well as the cold front should
remain well off to the west. Those features will move into the
area from the west by early this evening. This is when
confidence for severe thunderstorms is highest. The highest
instability...shear and forcing should line up for locations
near and west of the Blue Ridge and Catoctin Mountains early
this evening...best chance between 21 and 01z. Farther
east...confidence is a bit lower for severe weather since peak
heating will have passed and the outflow may outrun some of the
stronger storms since the storm motion will be southwest to
northeast. Having that been said...the wind fields will remain
quite strong through this evening and there will still be some
instability due to the unusually warm and humid airmass in
place. Therefore...severe thunderstorms are still possible near
and east of Interstate 95 this evening...best chance between 00z
and 04z.
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