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2017 Severe Thread

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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

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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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12z 3km NAM gets some storms into the region after dark... but they aren't as robust as they were in the NW portion of the LWX CWA

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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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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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3 minutes ago, nw baltimore wx said:

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

     Yes, I think there is some thunder potential Saturday evening, even on the cool side of the boundary.

 

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well, I talked up the Saturday evening potential, and I'm going to officially cancel it now.    warm sector will be confined way southeast of DC Metro

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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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Some fairly large tree branches snapped off here and a basketball hoop toppled.  Waiting for the rain to subside to do a more thorough check of the yard.

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Severe Weather Statement
National Weather Service Baltimore MD/Washington DC
347 PM EDT TUE SEP 5 2017

MDC021-043-WVC003-037-052000-
/O.CON.KLWX.SV.W.0253.000000T0000Z-170905T2000Z/
Washington MD-Frederick MD-Jefferson WV-Berkeley WV-
347 PM EDT TUE SEP 5 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 400 PM EDT
FOR WASHINGTON AND WESTERN FREDERICK COUNTIES IN NORTH CENTRAL
MARYLAND...NORTHERN JEFFERSON AND EASTERN BERKELEY COUNTIES IN THE
PANHANDLE OF WEST VIRGINIA...

At 347 PM EDT, severe thunderstorms were located along a line
extending from near Waynesboro to Shepherdstown, moving east at 45
mph.

HAZARD...70 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...
Frederick, Hagerstown, Thurmont, Emmitsburg, Shepherdstown, Municipal
Stadium, Harry Grove Stadium, Ballenger Creek, Robinwood, Brunswick,
Walkersville, Fountainhead-Orchard Hills, Ranson, Boonsboro,
Smithsburg, Braddock Heights, Paramount-Long Meadow,
Wilson-Conococheague, Williamsport and Mount Aetna.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
351 PM EDT TUE SEP 5 2017

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Southeastern Washington County in north central Maryland...
  Northwestern Carroll County in north central Maryland...
  Frederick County in north central Maryland...
  Northeastern Loudoun County in northern Virginia...
  Southeastern Jefferson County in the Panhandle of West Virginia...

* Until 430 PM EDT

* At 350 PM EDT, severe thunderstorms were located along a line
  extending from Rouzerville to Ranson, moving east at 45 mph.

  HAZARD...70 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...
  Frederick, Westminster, Thurmont, Charles Town, Emmitsburg, Harry
  Grove Stadium, Ballenger Creek, Taneytown, Brunswick, Walkersville,
  Boonsboro, Braddock Heights, New Market, Mount Lena, Harpers Ferry,
  Green Valley, Clover Hill, Discovery-Spring Garden, Point Of Rocks
  and Wolfsville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Remain alert for a possible tornado! Tornadoes can develop quickly
from severe thunderstorms. If you spot a tornado go at once into the
basement or small central room in a sturdy structure.

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Severe Weather Statement
National Weather Service Baltimore MD/Washington DC
356 PM EDT TUE SEP 5 2017

MDC013-021-043-VAC107-WVC037-052030-
/O.CON.KLWX.SV.W.0256.000000T0000Z-170905T2030Z/
Washington MD-Carroll MD-Frederick MD-Loudoun VA-Jefferson WV-
356 PM EDT TUE SEP 5 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 430 PM EDT
FOR SOUTHEASTERN WASHINGTON...NORTHWESTERN CARROLL AND FREDERICK
COUNTIES IN NORTH CENTRAL MARYLAND...NORTHEASTERN LOUDOUN COUNTY IN
NORTHERN VIRGINIA AND SOUTHEASTERN JEFFERSON COUNTIES IN THE
PANHANDLE OF WEST VIRGINIA...

At 356 PM EDT, severe thunderstorms were located along a line
extending from near Rouzerville to near Ranson, moving east at 45
mph.

HAZARD...70 mph wind gusts and quarter size hail.

SOURCE...Emergency management and observations.

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The squall line looked pretty intense here at 1920z( 3:20 Eastern).  Some wind reports close to Hagerstown and Martinsburg. Still has 60 dbZ for Frederick MD, so you'll get a heavy downpour there, possible hail.

bfMJJK1.png

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It's odd, because the HRRR has consistently had the line fall apart as soon as it gets dark/touches DC, despite DPs that are higher on the coastal plane.  I could see this holding together for a bit further East than the HRRR shows.

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1 hour ago, 87storms said:

the legend of the dc split continues.

Well, you may rightly think that the DC area gets missed by severe weather in most years. I have been playing a severe weather game on a different forum. Do you know how many points I have gotten from Washington DC and nearby cities this year? Tons. I hit the day when there were 3 tornadoes in Washington, plus I hit 2 or 3 or 4 other big days where the hail and wind reports came in by the dozen(s). One day I picked La Plata MD because it seems to attract (F5) severe weather. That pick worked out alright, I think I got about 10-15 hail/wind points.

Looks like some heavy rain is about to come into Leesburg VA. I see 60 dBz on composite reflectivity there at Middleburg, VA.

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23 minutes ago, Chinook said:

Well, you may rightly think that the DC area gets missed by severe weather in most years. I have been playing a severe weather game on a different forum. Do you know how many points I have gotten from Washington DC and nearby cities this year? Tons. I hit the day when there were 3 tornadoes in Washington, plus I hit 2 or 3 or 4 other big days where the hail and wind reports came in by the dozen(s). One day I picked La Plata MD because it seems to attract (F5) severe weather. That pick worked out alright, I think I got about 10-15 hail/wind points.

Looks like some heavy rain is about to come into Leesburg VA. I see 60 dBz on composite reflectivity there at Middleburg, VA.

 

in general, this is a moderate place to live.  winters are rarely extreme.  summers are rarely extreme.  storms are rarely extreme.  we're a jack of all trades here, but that's what i like about it.  pretty good mix of everything.

the leesburg stuff looks like it has potential for the dc-bmore corridor.

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Well that came out of nowhere. Loudest crack of thunder I've heard in a while just woke me and the wife up in fairfax.  Didn't even know it was supposed to storm tonight. 

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