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2017 Severe Thread


mappy

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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
237 PM EDT MON AUG 21 2017

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  North central Stafford County in northern Virginia...
  Southeastern Prince William County in northern Virginia...

* Until 330 PM EDT

* At 237 PM EDT, a severe thunderstorm was located 8 miles west of
  Dale City, moving east at 10 mph.

  HAZARD...60 mph wind gusts and quarter size hail.

  SOURCE...Radar indicated.

  IMPACT...Damaging winds will cause some trees and large branches
           to fall. This could injure those outdoors, as well as
           damage homes and vehicles. Roadways may become blocked by
           downed trees. Localized power outages are possible.
           Unsecured light objects may become projectiles.

* Locations impacted include...
  Dale City, Woodbridge, Lake Ridge, Montclair, Triangle, Dumfries,
  Cherry Hill, Independent Hill, Nokesville, Occoquan and Aden.
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1 minute ago, Eskimo Joe said:

Won't see this everyday

12Z regional soundings sampled poor mid-level
   lapse rates, somewhat tempering convective vigor. Additionally,
   visible satellite and radar data suggest a loss of insolation from
   the ongoing solar eclipse is stunting destabilization of the
   boundary layer.

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1 minute ago, North Balti Zen said:

Pretty good lightning show over that way too.

Flash Flood Warning now too:

Quote

The National Weather Service in Sterling Virginia has issued a

* Flash Flood Warning for...
  East central Baltimore City in northern Maryland...
  Southeastern Baltimore County in northern Maryland...

* Until 730 PM EDT

* At 330 PM EDT, Doppler radar indicated thunderstorms producing
  heavy rain across the area. Up to two inches of rain have already
  fallen. Flash flooding is expected to begin shortly.

* Some locations that may experience flooding include...
  Baltimore, Middle River, North Point State Park, Sparrows Point,
  Back River, Millers Island, Dundalk, Essex, Rosedale, Rossville,
  Bowleys Quarters, Edgemere, Fort Howard, Chase, Eastpoint, Martin
  State Airport and Turners Station.
 

 

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4 hours ago, yoda said:

Possible tornado threat tomorrow evening?  00z NAM soundings don't have huge hodographs, but there's enough there (200+ 1km SRH) for a tor threat IMO between 21z and 03z across the region

I don't think we'll get storms to pop south of 40N in that time frame. I did however notice the same thing further north into eastern PA. Even southeastern PA could have initiation problems, though.

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5 hours ago, Ellinwood said:

I don't think we'll get storms to pop south of 40N in that time frame. I did however notice the same thing further north into eastern PA. Even southeastern PA could have initiation problems, though.

          yeah, the shear is respectable later today, but the mid-level temps are warm, and the forecast soundings have that tall, skinny cape which is never good for parcel accelerations. The HRRR parallel, however, does pop a few decent looking cells in northern MD just after dark.

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Hmmm

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
225 PM EDT Tue Aug 22 2017

.NEAR TERM /TONIGHT/...

Temperatures in the lower 90s and dewpoints in the low 70s have
led to another day with CAPEs of 1000-2000. It is a different
synoptic situation from yesterday as we have our eyes on a
front/line of storms stretching from Ontario to southern IL.
Watches are in effect to our west and north. Aside from any
isolated cells that fire ahead of the line the main possibility
of convection looks to be from around 9 pm over the mountains to
after midnight by the Bay. Models have consistent in weakening
the cells once these move east of the Blue Ridge. Yes heating
will be over/CAPE will be diminishing but think given the
amount of energy in the atmosphere still believe severe storms
could be possible through midnight.

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New Mesoscale Discussion from SPC shows the certain issuance of a box to our north shortly, but the discussion area includes the northern most row of counties in Maryland.  I would think that the southern boundary of the new watch would be the Mason-Dixon line, but it will be interesting to see if they go further south (although I'm not sold on a svr threat south of the PA/MD border.)

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  • 2 weeks later...

I mentioned this in the regular September discussion last night, but it belongs here too:     [ But the evening hours (Saturday) may have sneaky potential, especially in southern MD.    A warm front will be lifting into the area, and the NAM nest has a convective line along the cold front.     Enough low-level warm air could get into southern MD to make things interesting, given the decent wind field that will be in place. ]       SPC does have a marginal risk not too far southeast of our area and some interesting discussion.

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13 hours ago, high risk said:

I mentioned this in the regular September discussion last night, but it belongs here too:     [ But the evening hours (Saturday) may have sneaky potential, especially in southern MD.    A warm front will be lifting into the area, and the NAM nest has a convective line along the cold front.     Enough low-level warm air could get into southern MD to make things interesting, given the decent wind field that will be in place. ]       SPC does have a marginal risk not too far southeast of our area and some interesting discussion.

Is this one of those rare situations where we could get those cool inversion thunder rumbles?

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7 hours ago, Kmlwx said:

NAM nest looks actually okay for tomorrow PM on the sim radar. 

   agreed, and the shear is decent too.   The only thing lacking is more instability, as low-level moisture is only modest, so the cape is tall and skinny.   if we had 70's dew points, this would be an enhanced day.

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From this morning's AFD:

.NEAR TERM /TODAY/...

An upper level trough will descend towards the Mid-Atlantic,
buckling as it collides with a building ridge over the
northwestern Atlantic. This will cause a strengthening mid/upper
jet through the day. At the surface, a cold front will slowly
approach from the west, and increasing low-level convergence
will increase by afternoon. Although mid-level lapse rates are
not all that spectacular, increasing low-level moisture combined
with daytime heating will result in roughly 1000-2000 J/kg of
CAPE. The increasing upper jet will result in 30-40 kts of
effective shear by mid-afternoon into the early evening, highest
across the northern parts of the CWA. Showers and scattered
thunderstorms appear likely, some of which may contain gusty
winds along with a marginal flash flood risk. There will be
potential for training, but storm motion will be fast.

The main storm mode should be linear segments and multicell
clusters, though semi-discrete/transient supercell structures cannot
be ruled out given the magnitude of the shear. The best coverage of
stronger storms should be mainly north of I-66 where the best
convergence/shear is. Gusty winds would be the primary hazard, with
hail or an isolated tornado a secondary (though non-zero) threat.

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