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2017 Severe Thread


mappy

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Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
912 PM EDT Fri Jun 23 2017

.SYNOPSIS...
Tropical air will envelop the area today. A cold front will
cross the area late tonight into Saturday. High pressure will
return Sunday and persist through early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Besides a few showers across the region late this afternoon and
early this evening...the LWX CWA has been quiet especially compared
to our neighbors to the west and north. This will change tonight
as remnants of TD Cindy and a cold front will move into the
Mid- Atlantic region. Showers will spread across the region
tonight with embedded heavy showers and gusty winds. The
atmosphere is moist with an observed PWAT from KLWX of 1.9 at
00z. Sfc dewpts in the 70s will give to moderate instability
across the region tonight. Shear is also moderate with near
50kts of 0-6km bulk shear. Thunderstorms are possible as the
cold front crosses the region overnight. Hi-res guidance depicts
some line segments that may produce stronger winds and severe
thunderstorm warnings can not be ruled out overnight. Seems like
the best chance will be across the northern half of the outlook
area. Rainfall amounts of 0.75- 1 in are expected across the
northern half and will taper off to around 0.25 in across the
Central Foothills/southern MD overnight with higher amounts in
heavier bands/thunderstorms.

Elsewhere...a strong LLJ will be on top of the region tonight
and widespread showers will likely bring down gusty winds.
Gusts 35-45 mph can not be ruled out across the region into
early Saturday morning. The cold front should cross the region
by 8AM Saturday morning and drying will occur behind it.
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So, we had wondered the about the possibility of a spinup or two Friday night in the strongly sheared environment with low LCLs.    it obviously didn't work out here, but the same concept of a favorable environment did come together better in eastern NJ early Saturday.     This video captures one of the short-lived EFOs  (warning: language)     

 

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We can haz meso discussion:

Mesoscale Discussion 1211
   NWS Storm Prediction Center Norman OK
   1154 AM CDT Sat Jul 01 2017

   Areas affected...portions of central/eastern
   Pennslyvania...central/western Maryland...West Virginia
   Panhandle...and northern Virginia

   Concerning...Severe potential...Severe Thunderstorm Watch likely 

   Valid 011654Z - 011800Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorms are expected to increase in
   coverage/intensity this afternoon with a risk for damaging winds and
   perhaps large hail.  Trends will be monitored and a Severe
   Thunderstorm Watch is likely prior to 19Z.

   DISCUSSION...Thunderstorms have been slowly intensifying across
   portions of southern New York and western/central Pennsylvania in
   the vicinity of a surface trough of low pressure as of 1645Z. 
   Downstream, diurnal heating of a moist air mass with dew points in
   the lower 70s continues, and surface-based instability by early/mid
   afternoon should range between 1000-locally 2000 J/kg.  Increasing
   large-scale ascent will develop over the area this afternoon as a
   mid-level impulse moves northeast from the lower Great Lakes/Ohio
   Valley, contributing to a continued increase in thunderstorm
   coverage/intensity.  Deep-layer southwesterly shear of 30-40 kts
   will promote multicell clusters/line segments with a threat for
   damaging winds this afternoon.  Some potential exists for a
   supercell with mid-level rotation, especially with more discrete
   cells across the discussion area, resulting in the potential for
   isolated large hail.

   A Severe Thunderstorm Watch will likely be needed prior to 19Z for
   much of the area.

   ..Bunting/Grams.. 07/01/2017
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Severe Thunderstorm Warning

Severe Thunderstorm Warning
DCC001-MDC031-033-VAC013-059-610-011945-
/O.NEW.KLWX.SV.W.0113.170701T1900Z-170701T1945Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
300 PM EDT SAT JUL 1 2017

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  The District of Columbia...
  Southeastern Montgomery County in central Maryland...
  Northwestern Prince Georges County in central Maryland...
  Arlington County in northern Virginia...
  The City of Falls Church in northern Virginia...
  Northeastern Fairfax County in northern Virginia...

* Until 345 PM EDT

* At 259 PM EDT, a severe thunderstorm was located over Reston,
  moving east at 35 mph.

  HAZARD...60 mph wind gusts.

  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...
  Arlington, Rockville, Bethesda, Reston, College Park, Greenbelt,
  Langley Park, Beltsville, Vienna, Forestville, Falls Church, Coral
  Hills, Bladensburg, Pimmit Hills, Mclean, Byrd Stadium, American
  Legion Bridge, Fort Totten, Rosslyn and Crystal City.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Get indoors to protect yourself from wind and lightning. Trees around
you may be downed from damaging winds, so if you are near large
trees, move to an interior room on the lowest floor. Don`t drive
underneath trees or in wooded areas until the threat has passed.
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Pretty surprised to get home and see we received .96"  Radar didn't look that impressive...I was visiting family just east of frederick and had a pretty good storm.  Extended period of very heavy rain, gusty winds and plenty of T&L.  Nothing that reached severe levels but the best storm I've witnessed this season.

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On 7/7/2017 at 5:41 PM, BTRWx said:

I wonder what was D.C.'s coldest derecho-like MCS on record to survive over the Apps...

In order for an MCS or Derecho to survive the loss of daytime heating and downsloping, they typically need a stout Elevation Mixing Layer (EML) and about 4,000 j/kg of SBCAPE ahead of them.  The 2012 and 2008 derechoes had just that.

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35 minutes ago, Eskimo Joe said:

In order for an MCS or Derecho to survive the loss of daytime heating and downsloping, they typically need a stout Elevation Mixing Layer (EML) and about 4,000 j/kg of SBCAPE ahead of them.  The 2012 and 2008 derechoes had just that.

Was yesterday an anomaly?

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