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2017 Severe Thread


mappy

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Morning AFD from LWX

arm air advection precipitation to the north of the warm front
expected to begin across the SW areas by this evening and then
spread across much of the area overnight. Current timing of
initial precipitation shield brings it into KCHO 6-8 PM,
KDCA/KIAD 9-11 pm, and KBWI 10 PM-12 AM. Elevated instability to
the north of the warm front suggest a slight chance for non-
severe thunderstorms with this initial activity.

Upper-level trough with 100 kt jet max becomes negatively tilted
late tonight inducing cyclogenesis on the lee of the Appalachians.
Rapid deepening expected by early morning with wind field increasing
substantially over the area. Further...while only modest instability
is expected (~500 to perhaps 1000 J/kg MLCAPE across north Central
VA)...impressive shear profiles suggest the potential for strong-to-
severe thunderstorms despite poor timing.

Some questions remain with regard to whether heightened threats can
materialize...since it is unclear when/if/where convection can become
surface-based over our area (best chance for surface-based
convection and significant severe continues to be just to our south).
Forecast soundings continue to indicate a stable layer...which keeps
convection slightly elevated...especially near the Chesapeake Bay
where water temperatures are relatively cool. Having said
that...rapid deepening of surface low and strength of wind field
suggest the potential is certainly there for severe storms along and
east of the Blue Ridge from early morning through early/mid-
afternoon Thursday...before surface low lifts to the northeast.

If convection can become surface based...all threats would be
possible...including tornadoes...as backed low-level flow near warm
front produces strong low-level shear.

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17 minutes ago, nw baltimore wx said:

Is Ian chasing this spring?  His photos are always amazing.

Myself, Ian, and James (wxmeddler) will be out chasing this year. Planning on being on the road May 20-June 4, which gives us the possible chase days of May 21-June 3.

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2 hours ago, Kmlwx said:

The 6z 3km NAM takes the best activity to our south and east (of DC). Looks to really slam areas from like Charles County, MD down to the NC/VA border. It does however show some trailing convection after that line passes. That follow-up activity goes over the DC area - I'd assume that would be weaker or elevated convection tho. Parameters still aren't very good at all locally. 

We seem to just missing this one. If nothing else I'll hope this is a good sign for our later season severe wx chances. 

It is a trippy run.  You have the leftovers from the storms in the OV/SE going through or near us in the early morning, then storms fire again around 11am but just miss DC to the south, and then another line fires in mid-afternoon in the DC area.

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Euro now shows a precip max stripe just west of 95 now between 12-18z. Much lower amounts in SoMD than previous runs. Probably a couple taining lines setting up somewhere during the strong southerly flow before winds veer westerly. 

Wind field associated with the sub 990 LP in PA is more impressive. Widespread 35-45mph gusts from the citites/burbs and east around 18z (westerly). 

Friday should howl pretty good too. 

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7 minutes ago, yoda said:

12z 3km NAM has some fun around 3 am with a broken line of storms moving in (sup in northern Fauquier county?)

 

 

 

The 12z is much more aggressive than 6z.  The unstable air surges much further north this time, and the mid-morning line is correspondingly further north.  Best parameters still a bit south of DC, but we are much closer to the game.

 

edit for images (top is 6z, bottom 12z), not the same hour, but the same period in the evolution of the storm

6z.PNG.5899d7974d0b8d656178d419cb1e26b2.PNG

 

12z.PNG.52d8ee2fb970e8819a00e104f2c02b44.PNG

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I know its not for our area... but we might as well keep our eye to our S and SW for this afternoon... and look what we have here :yikes:

mcd0440.gif

 

 Mesoscale Discussion 0440
   NWS Storm Prediction Center Norman OK
   0943 AM CDT Wed Apr 05 2017

   Areas affected...Portions of AL/GA/SC

   Concerning...Outlook upgrade 

   Valid 051443Z - 051645Z

   SUMMARY...Portions of the states of AL/GA/SC are being considered
   for an Outlook upgrade -- though the details are still being
   analyzed.  A very notable dry bias is apparent in the latest model
   guidance, and observational data and previous model runs are being
   heavily referenced in Outlook preparation.

   DISCUSSION...GPS PW data are exhibiting a low bias by at least 0.5
   inch from parts of AL into GA, which has influenced initialization
   of the latest numerical weather prediction guidance.  Per
   coordination with the Weather Prediction Center, it appears that
   related initialization is causing substantial dry biases in model
   guidance -- extended through the Day 1 forecast period.  With an
   inland influx of rich moisture feeding ongoing intense supercells in
   southern AL (with dewpoints into the middle 70s), and the
   around-16.6-g/kg mean mixing ratio per LIX 12Z sounding, and around
   1.5-inch PW per Atlanta and Birmingham 12Z soundings, it is evident
   that rich moisture and related strong buoyancy does indeed extend
   inland. As such, observational data and previous model runs will
   play a major role in the consideration for a High Risk upgrade, as
   the dry bias has influenced the latest model guidance. While an
   Outlook upgrade is possible, it is not certain.

   ..Cohen/Marsh/Hart.. 04/05/2017


   ATTN...WFO...ILM...CHS...CAE...GSP...JAX...FFC...TAE...BMX...
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1 hour ago, nw baltimore wx said:

Is Ian chasing this spring?  His photos are always amazing.

Mark beat me to the answer. yes. 

1 hour ago, Ellinwood said:

Myself, Ian, and James (wxmeddler) will be out chasing this year. Planning on being on the road May 20-June 4, which gives us the possible chase days of May 21-June 3.

 

27 minutes ago, yoda said:

 

horrible graphic. very misleading. SPC clearly says possible. Brad's tweet suggests otherwise. 

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1 hour ago, Ellinwood said:

Myself, Ian, and James (wxmeddler) will be out chasing this year. Planning on being on the road May 20-June 4, which gives us the possible chase days of May 21-June 3.

I'll catch both ends of your trip, heading to CO on May 22 and returning June 4 haha.

Hoping to see/find something, although won't be technically 'chasing'.

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From 1630 OTLK disco :yikes:

Furthermore, confidence has increased that substantial severe risk
   including tornado potential will develop through parts of the
   Mid-Atlantic region into the overnight hours amid strong low-level
   and deep shear, and a moistening boundary layer. As a result, severe
   probabilities have been increased across parts of the Mid-Atlantic.

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8 minutes ago, Bob Chill said:

Man, I just love the new GOES images. Should look cool around here tomorrow AM. 

 

southeast_02_20170405141718.jpg

the infrared layer is pretty sweet, you can see where the more intense cells are going

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