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2018 Mid-Atlantic General Severe Discussion


Kmlwx
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.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
The warm front will lift northward into Pennsylvania by Saturday
afternoon. This places the region solely in the warm sector, 
allowing for temperatures to rise into the upper 80s to low/mid 
90s with dew points rising into the 60s. This will promote the 
development of 1000-2000 J/KG of MLCAPE, with shear values 
increasing markedly as winds at 700 mb approach 50 knots. 
Forecast soundings indicate that for the vast majority of the 
day the region will remain capped. Thus, convective evolution 
will be dependent on convection that will likely already be 
ongoing across OH/PA that may move into the region from the 
northwest on westerly flow and a southward moving frontal 
boundary. While its uncertain how far south the convection can 
progress, the atmosphere will be primed for a severe weather 
threat, provided the cap can be broken. The main threat will be 
damaging winds, with a secondary threat of large hail. The 
highest risk of severe thunderstorms will be across eastern WV 
and northern/central Maryland. The Storm Prediction Center has 
placed this region in an Enhanced Risk for severe thunderstorms,
with a Slight Risk south to near the Washington DC metropolitan
area. The threat window will be late afternoon and through the 
evening hours.

The frontal boundary will sink further southward Saturday night,
and will be bisecting the region by Sunday morning.
Southwesterly flow will continue south of the boundary, with 
northeasterly flow taking over across the cool side. Thus the
combination of ongoing convection, frontogentical forcing, 
increasing precipitable water values, and shortwaves passing 
through the flow aloft, will promote continued areas of
showers and elevated convection. The severe threat will be
dwindling during the first half of the night, however attention
will then turn to the possibility of heavy rain and a low risk
of flooding across the higher terrain of eastern WV and western
VA due to repeated convection and upslope west flow. Lows
Saturday night will range from the upper 50s to upper 60s.

Sunday will be highly dependent on the eventual frontal
position, but have shown the boundary between Charlottesville
and Dulles, with stable/cooler low levels northeast of this, and
very warm and humid air southwest. Forecast soundings and
Showalter Indices indicate the potential of elevated convection
across all areas, but there is the potential for additional 
strong to locally severe thunderstorms in the warm sector. Will 
continue to have to monitor potential for heavy rain as well. 
Highs will range from the 60s across NE MD to potentially near 
90F towards Nelson County VA. Shower chances continue into 
Sunday night as well.

 

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The first Day 1 OTLK from SPC should be interesting to see... I expect something like 5 tor/15 hail/30 wind... but with ML Lapse Rates nearing 7.0 C/KM and even higher in some areas due to an EML in the area... wouldn't be surprised to see a 30% hail tossed in.  Tor probs will probably stay at 5% until later in the day

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After being on the southern plains for a week and not even seeing lightning there, I'm ready for this!    But, I'm still totally unsure how this will evolve.   The best signals in the CAMs are still for southeast PA and far northeast MD.      Deep layer shear is terrific, and as has been noted previously in this thread, lapse rates are impressive, so the hail/wind threat is legit.  That said, low-level shear is weak, so I don't think that a good tornado threat is shaping up.

For DC metro, the CAMs are all over the place, but the most consistent signal appears to be for the late evening hours.    Maybe something will go earlier on an outflow boundary, and some guidance has some healthy storms moving through very late at night, so nailing down the time window is unusually complicated.

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I usually sit the sidelines during sever season... I know very little. Love severe but have never taken the time to dig into it.

A definite shift in the stability to my west... To my east are clear blue skies. To my west is now starting to bubble. Hoping for a good early season garden soaker... Possibly something even more interesting.

Sent from my SAMSUNG-SM-G920A using Tapatalk

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URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 85
   NWS Storm Prediction Center Norman OK
   455 PM EDT Sat May 12 2018

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Delaware
     Central and eastern Maryland
     Southern New Jersey
     Southeast Pennsylvania
     Coastal Waters

   * Effective this Saturday afternoon and Sunday morning from 455
     PM until 100 AM EDT.

   * Primary threats include...
     A couple intense tornadoes possible
     Scattered damaging winds and isolated significant gusts to 75
       mph possible
     Isolated large hail events to 1.5 inches in diameter possible

   SUMMARY...Scattered strong to severe storms will spread east towards
   the Mid-Atlantic Coast through the evening. Low-level wind profiles
   on the cool side of a quasi-stationary front will favor a few
   rotating storms with mainly a damaging wind and tornado risk.
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The Severe Thunderstorm Watch includes the District now.

WATCH COUNTY NOTIFICATION FOR WATCHES 84/85
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
504 PM EDT SAT MAY 12 2018

DCC001-MDC031-033-VAC013-059-510-600-610-130300-
/O.EXA.KLWX.SV.A.0084.000000T0000Z-180513T0300Z/

THE NATIONAL WEATHER SERVICE HAS EXTENDED SEVERE THUNDERSTORM
WATCH 84 TO INCLUDE THE FOLLOWING AREAS UNTIL 11 PM EDT THIS
EVENING

THE DISTRICT OF COLUMBIA

IN MARYLAND THIS WATCH INCLUDES 2 COUNTIES

IN CENTRAL MARYLAND

MONTGOMERY            PRINCE GEORGES

IN VIRGINIA THIS WATCH INCLUDES 5 COUNTIES

IN NORTHERN VIRGINIA

ARLINGTON             CITY OF ALEXANDRIA    CITY OF FAIRFAX
CITY OF FALLS CHURCH  FAIRFAX

THIS INCLUDES THE CITIES OF ALEXANDRIA, ARLINGTON, ASPEN HILL,
BETHESDA, BOWIE, CAMP SPRINGS, CHANTILLY, CLINTON, COLLEGE PARK,
FAIRFAX, FALLS CHURCH, GAITHERSBURG, GERMANTOWN, GREENBELT,
HERNDON, LAUREL, MCLEAN, POTOMAC, RESTON, ROCKVILLE,
SILVER SPRING, SUITLAND-SILVER HILL, AND WASHINGTON.

$$
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13 minutes ago, high risk said:

 

   uh, have you looked at the upstream radar?

 sorry about that.   I thought I was replying to a different post (that I think the poster deleted) that questioned the need for any watch.     Your question was perfectly legit.   I wasn't expecting a TOR box either, but the supercell composite values in that area are actually impressive.

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5 minutes ago, Eskimo Joe said:

Nice tongue of CAPE and helicity across the boundary for the severe t'storm and tornado watches.  Kinda psyched.

Radar trends still significantly favor that tornado watch zone. Looks like the best line will (as expected) go into NE Maryland. Let's see if outflow can trigger anything closer to the DC region.

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2 minutes ago, Kmlwx said:

Radar trends still significantly favor that tornado watch zone. Looks like the best line will (as expected) go into NE Maryland. Let's see if outflow can trigger anything closer to the DC region.

That said - mesoanalysis is bonkers in a tiny area just ENE of DC. Has very high supercell parameter values there as well as high EHI. 

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