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2022 Mid-Atlantic Severe Wx Thread (General Discussion Etc)


Kmlwx
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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
139 PM EDT Sun Sep 25 2022

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Southeastern Washington County in north central Maryland...
  Northwestern Montgomery County in central Maryland...
  Southwestern Frederick County in north central Maryland...
  Loudoun County in northern Virginia...
  Southeastern Frederick County in northwestern Virginia...
  Northeastern Warren County in northwestern Virginia...
  Clarke County in northwestern Virginia...
  North central Fauquier County in northern Virginia...
  The eastern City of Winchester in northwestern Virginia...
  Jefferson County in the Panhandle of West Virginia...
  South central Berkeley County in the Panhandle of West Virginia...

* Until 230 PM EDT.

* At 139 PM EDT, severe thunderstorms were located along a line
  extending from near Inwood to near Millwood Pike to near Stephens
  City, moving east at 55 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...
  Germantown, Leesburg, Winchester, Herndon, Broadlands, Lansdowne,
  Lowes Island, Brambleton, Charles Town, Poolesville, Millwood Pike,
  Dulles International Airport, Ashburn, Sterling, Ballenger Creek,
  Countryside, Purcellville, Brunswick, Ranson and Berryville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 3924 7727 3905 7734 3893 7745 3901 7830
      3917 7816 3933 7822 3939 7739
TIME...MOT...LOC 1739Z 264DEG 50KT 3933 7816 3918 7808 3902 7820

TORNADO...POSSIBLE
THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...1.00 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...70 MPH
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Severe Weather Statement
National Weather Service Baltimore MD/Washington DC
138 PM EDT Sun Sep 25 2022

VAC069-251800-
/O.CON.KLWX.TO.W.0039.000000T0000Z-220925T1800Z/
Frederick VA-
138 PM EDT Sun Sep 25 2022

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 200 PM EDT FOR EAST
CENTRAL FREDERICK COUNTY IN NORTHWESTERN VIRGINIA...

At 138 PM EDT, a severe thunderstorm capable of producing a tornado
was located near Winchester, moving east at 40 mph.

HAZARD...Tornado and quarter size hail.

SOURCE...Radar indicated rotation.

IMPACT...For those in the direct path of a tornado touchdown, flying
         debris will be dangerous to those caught without shelter.
         Damage to roofs, siding, and windows may occur. Mobile
         homes may be damaged or destroyed. Tree damage is likely.

Locations impacted include...
Stephenson, Clear Brook, Albin, Cedar Hill and Cedar Grove.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

This cluster of thunderstorms is capable of producing tornadoes and
widespread significant wind damage. Do not wait to see or hear the
tornado. For your protection move to an interior room on the lowest
floor of a building.

&&

LAT...LON 3921 7820 3926 7821 3932 7812 3921 7807
TIME...MOT...LOC 1738Z 264DEG 34KT 3924 7814

TORNADO...RADAR INDICATED
MAX HAIL SIZE...1.00 IN

$$
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  • 2 weeks later...
 ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 090805
   SPC AC 090805

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0305 AM CDT Sun Oct 09 2022

   Valid 121200Z - 171200Z

   ...DISCUSSION...
   ...Wednesday/Day 4 and Thursday/Day 5...
   A cold front is forecast to move quickly eastward across the western
   Great Lakes and mid Mississippi Valley on Wednesday. This will occur
   ahead of a substantial upper-level trough that is forecast to deepen
   during the day. Due to strong forcing associated with the
   upper-level trough and cold front, a line of thunderstorms will
   likely develop Wednesday afternoon. This line of storms should move
   eastward across the southern Great Lakes and Ohio Valley Wednesday
   afternoon. Although a wind-damage threat will be possible along the
   leading edge of this line, limited moisture return and weak
   instability will be problematic for a more widespread threat. An
   isolated wind-damage threat could continue into the evening as the
   cold front and line of storms moves into the central Appalachians.
   The cold front is forecast to move through the Northeast on
   Thursday, and could reintensify by midday from parts of New York and
   Pennsylvania southward into the Mid Atlantic. The wind-damage threat
   could affect areas as far north as New England Thursday afternoon. A
   15 percent contour could be needed in either Day 4 or Day 5, once
   the details become more clear in model runs that come out over the
   next day or two.
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17 minutes ago, Kmlwx said:

As is common in these out-of-season events...the NAM and NAM nest favor south and east of the metros for any enhanced activity. 

meh. 

Very true and unlike coastal snow, severe events, particularly large-scale ones tend to trend south and east.  This looks no different as earlier times are now favored. However, large scale off season high shear low cape events which normally fail to gusty showers end up being our most impressive outbreaks when they do perform.  Probably won't happen this time as the period from early October to early November have never really seen much.

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2 minutes ago, 2010 extreme said:

Very true and unlike coastal snow, severe events, particularly large-scale ones tend to trend south and east.  This looks no different as earlier times are now favored. However, large scale off season high shear low cape events which normally fail to gusty showers end up being our most impressive outbreaks when they do perform.  Probably won't happen this time as the period from early October to early November have never really seen much.

This is true - especially if it's very dynamic at 500mb (negative tilted trough, well timed, and with some overlap in whatever CAPE is available and the shear and forcing). 

November 2006 had a very dynamic event. 

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3 hours ago, Kmlwx said:

As is common in these out-of-season events...the NAM and NAM nest favor south and east of the metros for any enhanced activity. 

meh. 

          Yeah, definitely looks better south and east of here, where the better instability will reside.    A slightly slower system could, however, change things a bit.

          Pros:  good wind fields including some favorable hodographs, good surge of low-level moisture

          Cons:  limited heating leading to crappy lapse rates and very limited CAPE,  no real height falls of note (the trough lifts to the northeast, which also explains why it won't be very cold behind the front)

 

 

 

 

 

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I'm a little more in today and less meh - but still pretty meh. 

The latest (06z) NAM nest looked decent. CIPS had a bit of a signal as well...at least as much as you could expect off-peak season. SREF even paints some sigtor ingredients in our region tomorrow on the 21z frame. 

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4 hours ago, Kmlwx said:

I'm a little more in today and less meh - but still pretty meh. 

The latest (06z) NAM nest looked decent. CIPS had a bit of a signal as well...at least as much as you could expect off-peak season. SREF even paints some sigtor ingredients in our region tomorrow on the 21z frame. 

          Yeah, the timing is better, and instability therefore looks ever-so-slightly better.    There will pretty clearly be a line of strong convection just ahead of the front.    Whether it will contain lightning or be surfaced-based is unclear.    Some of the CAMs even suggest some discrete cells in advance of the line.    The shear is very strong, and some of the models even suggest some healthy low-level shear, so this event certainly warrants some watching.

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4 minutes ago, high risk said:

          Yeah, the timing is better, and instability therefore looks ever-so-slightly better.    There will pretty clearly be a line of strong convection just ahead of the front.    Whether it will contain lightning or be surfaced-based is unclear.    Some of the CAMs even suggest some discrete cells in advance of the line.    The shear is very strong, and some of the models even suggest some healthy low-level shear, so this event certainly warrants some watching.

Seems like the kind of day where a bunch of cells with little or no lightning and tops under 35kft will all seem to take on mini-supercell characteristics and perhaps put down a brief tornado. Chaotic kind of days. 

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LWX afternoon AFD sounds interesting for tomorrow 

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As the main upper level trough of low pressure progresses slowly
to the east across the Midwest and Great Lakes, a strong surface
cold front will push into western Pennsylvania and northwest
West Virginia shortly after daybreak Thursday morning. During
the course of the morning, additional showers are expected to
develop almost anywhere in the CWA with the primary focus in the
Appalachians, Virginia Piedmont, and to the I-81 corridor.
These developing showers will be scattered, but a more develop
line of heavy showers and thunderstorms could develop across
western Maryland and northern West Virginia around Noon or
shortly before Noon just ahead of the strong surface cold front.
This activity could take on such a linear alignment that we may
be noting this as a QLCS. This QLCS like others, take shape
when there is a strong and persistent southerly flow at the
surface and a few thousand feet above ground. Hence, this type
of flow allows for increased moisture and brings a component of
wind shear to the table with developing convection. Such
alignment of showers and thunderstorms brings the main threat
of damaging winds. Also sometimes QLCS can produce embedded
tornadoes. Hail cannot be ruled out either, but doesn`t seem the
higher ranked component as CAPE or instability will be small or
marginal.

Timing of the heavy showers and strong to severe thunderstorms
or QLCS factor seems to be 11am to 1pm in western MD and
northern WV, 2pm to 4pm the I-81 corridor, and 5pm to 8pm the
metropolitan areas and into southern Maryland. As the cold front
clears the respective areas, so does the convection. Once the
front passes, a sharp wind shirt is anticipated from west to
east. Temperatures Thursday will top out middle 60s to lower
70s, then fall rapidly Thursday evening and night into the
upper 30s to lower 40s. As previously mentioned, the airmass
filling in behind the front will be Pacific and not Arctic, so
Thursday night temperatures may not be as uncomfortable as could
be with the airmass discrepancy.
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