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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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I took a deeper look at the NAM twins for tomorrow. They clear out Virginia south of I-66 and up into northern Carroll / Baltimore counties which causes some better surface instability. No surprise that's where the better sim radar returns are progged for tomorrow. Hopefully it's wrong and we all get a repeat of last week.

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Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1220 PM CDT Wed Jun 02 2021

   Valid 031200Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
   MID-ATLANTIC...

   ...SUMMARY...
   Strong to severe storms are possible over a portion of the Middle
   Atlantic Thursday with locally strong to damaging gusts the primary
   threat. Other strong to severe storms with locally strong to
   damaging wind gusts will be possible over a portion of the Tennessee
   and Ohio Valleys as well as eastern Oregon.

   ...Synopsis...
   A shortwave trough will move from portions of the Mid-South into the
   Mid-Atlantic on Thursday. A weak frontal boundary will push through
   the Ohio Valley into the Appalachians. Ahead of the boundary,
   moisture return is expected to continue through the day into the
   Mid-Atlantic and parts of the Northeast. In the Pacific Northwest
   into the northern Rockies, a shortwave trough will impact the region
   by late afternoon into the evening.

   ...Mid-Atlantic...
   Widely-scattered to scattered convection is expected to develop both
   ahead of the weak boundary and within areas of pre-frontal
   confluence from northern Virginia into southeastern New York. There
   remain uncertainties as to where the greatest boundary layer
   destabilization will occur given cloud cover within the warm
   conveyor belt as well as warm advection precipitation in North
   Carolina/southern Virginia. Forecast soundings indicate a greater
   potential for cloud breaks from northern Virginia into southeastern
   New York. This area will also see a modest increase in 850 mb flow
   by afternoon/evening which will increase the threat for damaging
   gusts and perhaps an isolated tornado. Father north into eastern New
   York/Vermont, there is less certainty on the degree of
   destabilization, but relatively strong mid-level forcing should
   promote scattered storms with some attendant threat for wind damage.
   Mid-level lapse rates will not be overly steep, but where greater
   buoyancy develops isolated large hail will be possible.
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Afternoon AFD has no mention of anything for Friday at all... but interesting tidbit about tonight into early tomorrow in there...

@high risk @Kmlwx @Eskimo Joe

Quote

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
255 PM EDT Wed Jun 2 2021

.SYNOPSIS...

High pressure will remain offshore through this weekend and into
early next week. An upper level trough will reside to our west
through Thursday, before progressing off to our east by later Friday
into Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...

I continue to remain doubtful about convective potential this
afternoon after looking at recent 1749Z NUCAPS soundings across
the fcst area. Soundings still show a strong capping inversion
with substantial dry air between 850-500 mb. However, things are
expected to change rapidly this evening as moisture and
instability surge northward with an advancing warm front.
Expecting nmrs showers and possible thunderstorms to develop
this evening and move northeast overnight before exiting to
the east after daybreak Thu. While SPC does not have area under
any risk of severe wx, shear will be increasing tonight, and as
we saw during the May 3rd Ranson WV tornado, isolated tornadoes
can occur when sfc features like a warm front move through an
area.

&&

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

Low and high dense overcast after early morning showers
especially east of the Blue Ridge puts some doubt about how much
destabilization can occur Thu afternoon. It does appear that
for areas west of the Blue Ridge, any cloud cover should be thin
enough to allow substantial breaks to develop and for air mass
to destabilize rapidly. Anticipating that storms will develop
early in the afternoon east of the Appalachians and move
generally ENE with a risk of damaging winds given strengthening
low-mid level flow and moderate instability (i.e ML CAPE around
1000 J/kg). While storms should tend to move at a relatively
fast pace, the mid-level flow will become nearly parallel to
the sfc flow and likely result in some training of storms which
may pose a risk of flash flooding given storms should be highly
efficient rainfall producing (i.e. high PWATs and high 1000-500
mb RHs). Anticipating a convective type watch for much if not
the entire area tomorrow afternoon. Convection should begin to
wind down mid evening, but may linger well into the night across
southern MD.

Conditions improve somewhat Fri as upper trough shifts east and
light NW flow dry things out a bit. Drying conditions expected
Fri night.
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1 hour ago, Eskimo Joe said:

Sterling seems pretty bullish about tomorrow. Curious as to what they are seeing to make them so.

I seem to remember a few sporadic severe days in our area over the years that had them really using ominous language for a rather "standard" event. 

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I was just playing around with the SPC Severe Event Archive. Something I did not realize is that if you put in MD as the selected state. The September 24th 2001 event (College Park TOR) is the event immediately before April 28th 2002 in the archive. Not terribly impressive since September is a fair timeframe for our last severe event of the season, and April for the first. But to have two such memorable events right next to each other in the archive stood out to me. 

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6 hours ago, yoda said:

Afternoon AFD has no mention of anything for Friday at all... but interesting tidbit about tonight into early tomorrow in there...

@high risk @Kmlwx @Eskimo Joe

           Yeah, shear will be increasing later tonight, but there just isn't any instability to get a decent updraft.   Even west of the Blue Ridge where "instability will be surging north", sfc-based CAPE values by early morning will be only a couple hundred J/kg at best.

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4 hours ago, Eskimo Joe said:

Sterling seems pretty bullish about tomorrow. Curious as to what they are seeing to make them so.

      I mean, it's not to going to be a day that we all talk about for years, but in a very tame severe weather season, it has the potential to be one of the better days so far.    Looks like sfc-based CAPE in the 1500 range with modest shear, and if you throw out the anemic NAM nest solutions, most CAMs do bring storms into the area later tomorrow afternoon into an environment that will support some wind reports and maybe an isolated brief TOR.

      For now, I'm less excited about Friday due to downsloping, but the inverted-V soundings do support wind potential if storms can organize.

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Today's SPC morning outlook disco 

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Thu Jun 03 2021

   Valid 031200Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE MID ATLANTIC AND NORTHEAST...

   ...SUMMARY...
   Strong to severe storms are possible across parts of the Mid
   Atlantic and Northeast, mainly this afternoon and evening. Damaging
   wind gusts are expected to be the primary threat, though isolated
   hail and a tornado or two will also be possible.

   ...Synopsis...
   A positively tilted upper trough extending from the Great Lakes into
   the lower MS Valley this morning is forecast to move slowly eastward
   through the period, as an upper ridge amplifies over the Great Basin
   vicinity. A warm front will move northward through portions of New
   England during the day, while a weak surface trough will move
   eastward from the Ohio Valley into the Appalachians. 

   ...Mid Atlantic into Western New England...
   Scattered clusters of convection are expected through the day along
   and east of the weak surface trough moving out of the Ohio Valley,
   within a plume of moist southwesterly flow ahead of the upper
   trough. The area most likely to see some diurnal heating and at
   least modest destabilization prior to the onset of convection is the
   Mid Atlantic into portions of western New England. In this area,
   MLCAPE potentially exceeding 1000 J/kg in conjunction with effective
   shear of 35-45 kt will favor organized convection by mid afternoon.
   Locally damaging wind is expected to be the primary hazard, given
   the anticipated cluster mode, but some hail cannot be ruled out
   despite generally weak midlevel lapse rates. If any supercells
   (either discrete or cluster-embedded) can be sustained, low-level
   flow/shear will also be sufficient to support a tornado or two.

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The last couple of frames of the visible satellite leaves some room for optimism for those of us in the slight risk area. The 12z RAOB from Sterling indicated a convective temp of 79° and we're starting to see a few 80°+ values pop up. If we can get into the lows 80s then perhaps things can work out better for us.

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1 minute ago, Eskimo Joe said:

The last couple of frames of the visible satellite leaves some room for optimism for those of us in the slight risk area. The 12z RAOB from Sterling indicated a convective temp of 79° and we're starting to see a few 80°+ values pop up. If we can get into the lows 80s then perhaps things can work out better for us.

IAD is currently at 82/67.

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2 minutes ago, Eskimo Joe said:

The last couple of frames of the visible satellite leaves some room for optimism for those of us in the slight risk area. The 12z RAOB from Sterling indicated a convective temp of 79° and we're starting to see a few 80°+ values pop up. If we can get into the lows 80s then perhaps things can work out better for us.

Everything south of I-70 looks to be at least 80 by now.  I don't suspect we'll have much problem with bouyancy.  HRRR has liked that I-70 line for several runs now so maybe a thermal boundary setting up there that we'll see some additional focus along

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