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2020 Mid-Atlantic Severe Weather - General Thread


Kmlwx
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Well.. they are being issued per spotters... but interesting warnings... @high risk

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
1026 PM EST Tue Mar 3 2020

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Washington County in north central Maryland...
  East central Allegany County in western Maryland...
  Northwestern Frederick County in north central Maryland...
  North central Loudoun County in northern Virginia...
  Central Frederick County in northwestern Virginia...
  Northern Clarke County in northwestern Virginia...
  The City of Winchester in northwestern Virginia...
  Jefferson County in the Panhandle of West Virginia...
  Morgan County in the Panhandle of West Virginia...
  Berkeley County in the Panhandle of West Virginia...
  Northern Hampshire County in eastern West Virginia...

* Until 1100 PM EST.

* At 1026 PM EST, severe thunderstorms were located along a line
  extending from 6 miles southwest of Claylick to 11 miles southeast
  of Romney, moving east at 75 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Emergency management.

  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...
  Hagerstown, Winchester, Martinsburg, Thurmont, Charles Town,
  Emmitsburg, Romney, Shepherdstown, Hancock, Paw Paw, Municipal
  Stadium, Robinwood, Brunswick, Fountainhead-Orchard Hills, Ranson,
  Berryville, Boonsboro, Smithsburg, Inwood and Paramount-Long
  Meadow.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.
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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
1028 PM EST Tue Mar 3 2020

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Shenandoah County in northwestern Virginia...
  Southern Frederick County in northwestern Virginia...
  Northwestern Rockingham County in western Virginia...
  Southern Clarke County in northwestern Virginia...
  Northwestern Warren County in northwestern Virginia...
  North central Page County in northwestern Virginia...
  The southwestern City of Winchester in northwestern Virginia...
  Northeastern Pendleton County in eastern West Virginia...
  Southeastern Grant County in eastern West Virginia...
  Hardy County in eastern West Virginia...
  Southern Hampshire County in eastern West Virginia...

* Until 1115 PM EST.

* At 1028 PM EST, severe thunderstorms were located along a line
  extending from 11 miles southwest of Romney to 6 miles north of
  Upper Tract, moving southeast at 45 mph.

  HAZARD...60 mph wind gusts.

  SOURCE...Trained weather spotters.

  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...
  Winchester, Front Royal, Strasburg, Woodstock, Moorefield,
  Petersburg, Millwood Pike, Rough Run, Berryville, Broadway,
  Timberville, Mount Jackson, Stephens City, Wardensville,
  Basye-Bryce Mountain, Upper Tract, Mathias, Star Tannery, New
  Market and Middletown.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.
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3 minutes ago, high risk said:

This line is producing.     I've seen a few events like this over the years, with a fast-moving line of low-topped showers requiring warnings.    Will be interesting to see how far southeast they survive.

Doesn't look like HRRR really had this "line" looking back at the 01z/02z run... kinda intriguing though

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2 minutes ago, yoda said:

Doesn't look like HRRR really had this "line" looking back at the 01z/02z run... kinda intriguing though

 

       There are some small hints of it in the previous HRRR runs, but it's overall really tough for a model to get this, as it has to get the initial forcing and cold pool dynamics.

       Forecast soundings show a strengthening unidirectional wind profile and some downdraft cape......

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1 minute ago, Mrs.J said:

Line is closing in on me. Reports of 68 mph wind gust in Hagerstown by NWS

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
1054 PM EST Tue Mar 3 2020

The National Weather Service in Sterling Virginia has issued a

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

* Until 1130 PM EST.

* At 1054 PM EST, severe thunderstorms were located along a line
  extending from near Carroll Valley to 6 miles west of Charles Town,
  moving east at 70 mph.

  HAZARD...70 mph wind gusts.

  SOURCE...Trained weather spotters.

  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, Damascus, Thurmont, Charles Town,
  Poolesville, Emmitsburg, Shepherdstown, Harry Grove Stadium,
  Ballenger Creek, Mount Airy, Robinwood, Taneytown, Brunswick,
  Walkersville, Manchester, Ranson, Boonsboro, Smithsburg and
  Braddock Heights.
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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1054 PM EST TUE MAR 03 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1048 PM     TSTM WND GST     HAGERSTOWN RGNL ARPT    39.71N  77.73W
03/03/2020  M68 MPH          WASHINGTON         MD   ASOS


&&

EVENT NUMBER LWX2000782
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Maybe something to look forward to next week?  From the Day 4-8 SPC OTLK:

 Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0331 AM CST Fri Mar 06 2020

   Valid 091200Z - 141200Z

   ...DISCUSSION...
   Some combination of weak large-scale forcing for ascent and lack of
   deep boundary layer moisture return inland of the Gulf coast seems
   likely to result in continuing low convective potential across much
   of the U.S. through at least the middle of next week.  Medium-range
   models generally suggest that a significant mid-level low, initially
   over the southern mid-latitude eastern Pacific, will only slowly
   progress into the Southwest next Tuesday and Wednesday, before
   accelerating across and east-northeast of the southern Rockies late
   next week.  It may undergo considerable deformation as it does, but
   at least some phasing with a northern branch perturbation appears
   possible, and models suggest that this could support significant
   surface cyclogenesis from the central Plains through the Great Lakes
   and Quebec next Thursday and Friday.  Associated large-scale forcing
   for ascent and strengthening of wind fields and shear could
   contribute to an environment conducive to organized severe
   thunderstorm potential.  However, aside from the extended time
   frame, a number of uncertainties linger, including synoptic and
   sub-synoptic developments that may impact destabilization, timing of
   the most significant thunderstorm development, and area of greatest
   impact, which could be anywhere from the southern Plains through the
   Appalachians and parts of the Northeast/Mid Atlantic Coast region.

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SPC has us mentioned in the 1730 DAY 2 OTLK for maybe some gusty winds tomorrow afternoon... no MRGL, just general FWIW

 ...Mid-Atlantic Vicinity...

   Bands of showers and isolated thunderstorms are expected to develop
   by midday along and ahead of the eastward advancing cold front. Low
   level moisture will remain modest, with surface dewpoints as high as
   the low to mid-50s possible. Surface heating also is expected to be
   limited by cloud cover, with temperatures warming into the 50s to
   low 60s. As a result, surface-based instability is expected to be
   quite limited, generally less than 250 J/kg. However, southwesterly
   wind just above the surface will be quite strong, with 40+ kt winds
   forecast as low as 925 mb. If pockets of stronger heating occur,
   resulting in areas of steeper low-level lapse rates, sporadic,
   locally strong gusts could accompany these bands of showers and
   thunderstorms during the afternoon.

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  • 3 weeks later...
55 minutes ago, yoda said:

Looks like our first chance in a while of some thunderstorms, maybe even an isolated severe threat is on Sunday afternoon

Now this is not for our region (SW of Chicago)... AND it's just one run from last night's 0z NAM at range but... it's not too often that you see 100+ knot EBWD with 1,000+ J/kg MLCAPE.

(Also, please ignore the fact that I accidentally called these files as the 3kNAM... the images below are actually from the lower-res NAM)

32620200z3kNAM.thumb.png.3692d56bfe7125d0ab01d014341ecca4.png

32620200z3kNAM2.thumb.png.e6bb8bf8adaa252f161aa3ee21ae1bab.png

 

The following is just me thinking out loud. I'm not making assumptions about the severe threat over yonder.

 

I wonder if 1,500+ J/kg mlcape and LIs of -5 to -6 would be enough instability for storms to not get ripped apart by this kind of shear verbatim (Is CAPE fat enough?). 

Yeah 1,500 J/kg mlcape is not all that weak but... that shear though... 

Of course I'm not trying to take away from the high-ceiling that storms will have should they take advantage of their environment. 

 

@high risk @csnavywx thoughts on this?

 

Also I realize now that I have a problem with using too many ellipses and parentheses. 

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53 minutes ago, yoda said:

Looks like our first chance in a while of some thunderstorms, maybe even an isolated severe threat is on Sunday afternoon

I, um, all things being equal, given how much food is in various freezers and the quarantine situation many are dealing with, really don’t want severe storms to be a thing this spring. Need power. Etc.

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13 hours ago, George BM said:

Now this is not for our region (SW of Chicago)... AND it's just one run from last night's 0z NAM at range but... it's not too often that you see 100+ knot EBWD with 1,000+ J/kg MLCAPE.

(Also, please ignore the fact that I accidentally called these files as the 3kNAM... the images below are actually from the lower-res NAM)

32620200z3kNAM.thumb.png.3692d56bfe7125d0ab01d014341ecca4.png

32620200z3kNAM2.thumb.png.e6bb8bf8adaa252f161aa3ee21ae1bab.png

 

The following is just me thinking out loud. I'm not making assumptions about the severe threat over yonder.

 

I wonder if 1,500+ J/kg mlcape and LIs of -5 to -6 would be enough instability for storms to not get ripped apart by this kind of shear verbatim (Is CAPE fat enough?). 

Yeah 1,500 J/kg mlcape is not all that weak but... that shear though... 

Of course I'm not trying to take away from the high-ceiling that storms will have should they take advantage of their environment. 

 

@high risk @csnavywx thoughts on this?

 

Also I realize now that I have a problem with using too many ellipses and parentheses. 

              1500 is probably enough cape to handle that kind of instability, especially given that it's not "tall, skinny" cape, and there is enough low-level instability for good parcel accelerations.   The forecasted soundings keep getting better, and SPC now has a day 2 MDT which looks justified.     Still questions about evolution of elevated convection earlier in the day and resulting impact on how far north the warm front can get, but areas just south of wherever the warm front ends up look primed.

 

 

  

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for us on Sunday, right now the forecast soundings look terrible with limited instability and weak low level flow.     It's also unclear whether the cool air will erode over the northeastern half of this subforum.      Gonna need a huge improvement in the setup to give us anything of interest.

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Just now, high risk said:

              1500 is probably enough cape to handle that kind of instability, especially given that it's not "tall, skinny" cape, and there is enough low-level instability for good parcel accelerations.   The forecasted soundings keep getting better, and SPC now has a day 2 MDT which looks justified.     Still questions about evolution of elevated convection earlier in the day and resulting impact on how far north the warm front can get, but areas just south of wherever the warm front ends up look primed.

 

 

  

Thank for the reply. Yeah the latest long-range HRRR has some loltastic soundings. I mean check out this uncontaminated sounding below. I mean 3,000+ J/kg MLCAPE, LI near -10 with effective bulk-shear around 100kts. Lol!

327202012zhrrrsounding.thumb.png.88cfb4f0c8659a6ad46e35f890b4ca2e.png

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1 minute ago, George BM said:

Thank for the reply. Yeah the latest long-range HRRR has some loltastic soundings. I mean check out this uncontaminated sounding below. I mean 3,000+ J/kg MLCAPE, LI near -10 with effective bulk-shear around 100kts. Lol!

 

       wow!     low-level directional shear is lacking a bit, but the low LCLs and impressive low-level cape would make that a volatile environment.    Even if we chop off a few degrees from the T and Td, it's still scary.

 

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1730 SPC OTLK from day 2 has all of us in 2/5/5... mentions supercells with all hazards possible but conditional threat... here is the disco for our region:

...Mid-Atlantic...
   Large-scale ascent is forecast to remain fairly weak Sunday across
   the Mid-Atlantic. However, some modest mid-level height falls should
   overspread this region by Sunday afternoon. Latest model guidance
   also suggests the possibility of a weak, secondary surface low
   developing over MD and vicinity through the day. More robust diurnal
   heating is expected across this region, and weak to potentially
   moderate instability (MLCAPE 500-1500 J/kg) should develop
   along/south of a surface warm front that will likely be located
   across parts of central/eastern PA into southern/central NJ.
   Effective bulk shear of 50-70+ kt would easily support supercells,
   with all severe hazards possible. The main uncertainty is whether
   any storms will form along/ahead of the cold front. Latest guidance
   shows substantial variability regarding overall convective coverage
   across this region. For now, have opted to expand the Marginal Risk
   eastward across much of the Mid-Atlantic to account for this
   somewhat conditional potential.

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Afternoon AFD from LWX:

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Sunday will start with ample low clouds and fog attempting to
lift. How quickly it does so may be the key to the forecast.
Believe there will be a sharp inversion, with a warm nose which
could be as warm as 19C near 925 mb.

A cold front will approach during the day, and cross the region
during the afternoon, during peak heating (18-00 UTC). There
will be ample shear across the region. Instability will be the
question. If the wedge holds, then instability will be minimal
and the front would either come through dry or as a few showers
(with perhaps an elevated rumble of thunder). But, if the wedge
does manage to mix out, then MUCAPE may exceed 1000 j/kg. Given
the other ingredients in place, that would be supportive of
robust thunderstorms. There are guidance members on each side of
the fence.

After collaboration with SPC, decided that the conditional
threat great enough to at least mention somehow...hence
Marginal Risk of severe. Am maintaining a chance of precip
crossing the area in the database, with a slight chance of
thunder. It may be that both solutions are correct; ie:
cool/stable air across northern Maryland while moist/unstable
air present across central Virginia and southern Maryland. Will
be monitoring later cycles to discern these details.

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