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2017 Severe Thread


mappy

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13 hours ago, yoda said:

Better send those pics and stuff to LWX... LWX made no mention of rotation in their warnings

I'll send it to them today when I get a chance. I notice there was no mention from lwx but there was definitely rotation and a clear well formed wall cloud and even seemed to be a bit of a funnel cloud for a short time.  It passed right over me and things got wild for a short time. It definitely had the same feel as other close encounters I've had when chasing but this was the first time it was at my house.  Didn't come close to touching down but no doubt it had rotation.  It kind of caught me off guard. I was just thinking it was a typical thunderstorm and went out to get the umbrella down on my pool deck when the wind picked up and suddenly realized what was going on and was in the middle of it as it passed over. 

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21 hours ago, yoda said:

Better send those pics and stuff to LWX... LWX made no mention of rotation in their warnings

I did send in the photos and this was the reply from NWS. They got back very quickly btw. 

"Good (late) afternoon,

Thank you for the phone call and the pictures! We were watching this as it crossed out of Pennsylvania and had noted some weak rotation on the FAA Terminal Doppler Radar for BWI, and were wondering if there was visible rotation. It definitely organized on a storm scale, but not quite strong enough in the lowest levels to produce a tornado. A Severe Thunderstorm Warning was issued a short time later for points further east for straight line winds, which knocked down a fair number of trees (we heard of about a dozen or so) in Harford County."
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11 hours ago, mappy said:

Put the Bay City/Stevensville Tornado path on a map. Survey is still considered preliminary, but can be found here: https://nwschat.weather.gov/p.php?pid=201707242221-KPHI-NOUS41-PNSPHI

Working.jpg

 This is fantastic.     I crossed Kent Island today on my way to the beach, and it's very obvious where the tornado crossed Rt 50, with sheared-off trees on both sides of the road.

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23 minutes ago, AmericanWxFreak said:

They yanked the slight risk completely lol 

I would agree. I don't see any guidance that looks particularly robust with regards to a severe threat. Even the heavy rain threat seems a bit north on latest guidance IMO. 

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  • 2 weeks later...

So LWX... you say there is a threat on Monday... and the magical T word appears ;)

Quote

.LONG TERM /MONDAY THROUGH FRIDAY/...
A slow moving, moisture laden frontal system will drag through the
region early next week. PWATs near 2 inches combined with strong
convergence in the midst of low pressure tracking along the slow
moving front will likely lead to numerous showers and thunderstorms
with heavy rainfall. Upper level divergence aided by a 100+ knot jet
streak at 250 mb will help sustain and organize storms, as well. The
deep-layer shear could contribute to a severe weather threat
depending on instability.

There is some uncertainty with the low track Monday which will
determine finer scale details such as where the heaviest rain sets
up and where severe weather potential (wind/hail/tornadoes) is
maximized. The NAM takes the low to the north over PA which would
lead to an elevated severe threat but perhaps reduce the widespread
heavy/persistent rain potential. The GFS is further south across
central VA with a cooler boundary layer and less severe potential
for most of the area but a significant heavy rain threat due to
strong surface convergence. The ECMWF basically splits the
difference, with various ensemble members falling somewhere in
between.
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9 hours ago, yoda said:

00z NAM NEST slams DC south 23z to 01z... shows up on the UD helicity swaths as well

 

     NAM nest still looks interesting, but the 6z cycle moved the location of interest further south.    The HRRR keeps the heating zone further south as well, and it now doesn't fire any convection during those evening hours.    It seems that areas north of a line from Alexandria to Deale have little SVR threat;  areas to the south (and perhaps quite a bit to the south) have a modest chance of SVR perhaps during the main batch of precip during the early afternoon and then a conditional risk if storms fire again in the early evening.

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On 3/1/2017 at 10:23 AM, yoda said:

Any possibility that this has the resemblance of what I think was a late June day a few years ago when a line of storms moved through DC region around 3pm with wind gusts to 80 mph?  Or is this a whole different system?

I remember LWX issuing STW swaths

You're probably thinking about the June 4, 2008 event. A severe MCS came through the region at 60-65 mph bringing widespread wind damage throughout the much of the DMV region. The line in West Virginia certainly resembles that event. The only thing is that there is no where near as much CAPE with 500-1000 J/kg mlcape expected by the afternoon. June 4, 2008 had mlcape of 2000-3000 J/kg with 40-50kt effective shear by the afternoon. However with skies clearing out nicely and 70+kt effective bulk shear ahead of this line, I'm definitely intrigued about today's threat. 

June 4, 2008:

59890db9d12ab_June42008midatlantic.gif.2164d87c9ba21084a2580db62c85755b.gif

59890eba82931_June42008midatlantic2.gif.3037423e83af987c518661fccd318d04.gif

 

Today:

59890f1a6f8a6_March12017midatlantic.gif.938e8878758b54ad33ab2a02b55f357b.gif

 

 

Is what I would have said if I was a member on March 1st at 10:23 AM EST. 

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mcd1476.gif

Mesoscale Discussion 1476
   NWS Storm Prediction Center Norman OK
   0248 PM CDT Fri Aug 11 2017

   Areas affected...portions of central and eastern PA...eastern WV
   Panhandle...MD...and northern VA

   Concerning...Severe potential...Watch unlikely 

   Valid 111948Z - 112115Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Isolated 45-60 mph gusts and marginally severe hail are
   possible with the more intense/transient supercell storms this
   afternoon.  A brief/weak tornado cannot be ruled out.

   DISCUSSION...Radar mosaic over the past hour has shown a blossoming
   of thunderstorms over central PA into the eastern WV Panhandle.  The
   discussion area resides within a belt of moderately strong
   west-southwesterly 500-mb flow (40-45 kt) per area WSR-88D VAD data.
   Surface analysis indicates temperatures have warmed into the upper
   70s degrees F over PA and warmer air with temperatures in the lower
   80s is located farther south over MD/northern VA.  A relatively
   moisture-rich airmass is in place with upper 60s north and around 70
   south.

   Despite modest low and mid-level lapse rates, around 500 J/kg MLCAPE
   has developed within a strengthening/veering wind profile with
   height.  A mid-level vorticity maximum is traversing eastward across
   the southern Great Lakes and approaching the region.  As a result, a
   couple of the stronger updrafts will probably acquire transient
   supercell structure this afternoon.  The primary hazards with this
   activity will be isolated strong to locally severe gusts capable of
   wind damage.

   ..Smith/Guyer.. 08/11/2017

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...PHI...BGM...CTP...LWX...PBZ...
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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
426 PM EDT FRI AUG 11 2017

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  East central Shenandoah County in northwestern Virginia...
  Warren County in northwestern Virginia...
  Northwestern Fauquier County in northern Virginia...
  North central Rappahannock County in northwestern Virginia...

* Until 515 PM EDT

* At 425 PM EDT, a severe thunderstorm was located near Strasburg,
  moving east at 15 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...
  Front Royal, Strasburg, Linden, Chester Gap, Flint Hill, Fort
  Valley, Huntly, Arco, Howellsville, Seven Fountains, Dilbeck,
  Riverton, Karo, Glen Echo, Bentonville, Blue Mountain, Browntown,
  Cedarville, Buckton and Riverside.
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BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
512 PM EDT FRI AUG 11 2017

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Central Warren County in northwestern Virginia...
  Northwestern Fauquier County in northern Virginia...
  Central Rappahannock County in northwestern Virginia...

* Until 600 PM EDT

* At 511 PM EDT, a severe thunderstorm was located near Front Royal,
  moving east at 25 mph.

  HAZARD...60 mph wind gusts and half dollar 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...
  Front Royal, Hume, Delaplane, Linden, Chester Gap, Flint Hill,
  Washington, Castleton, Huntly, Arco, Hackleys Crossroads, Fourway,
  Cresthill, Rectortown, Glen Echo, Five Forks, Rock Mills, Markham,
  Browntown and Ashville.
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