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Sept. 28-30 Rainfest Obs/Disc


Ellinwood

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Ohey

day1probotlk_20160928_1300_torn_prt.gif

day1probotlk_20160928_1300_wind_prt.gif

 

...NRN NC TO DC AREA...
   WIDELY SCATTERED TO SCATTERED TSTMS ARE EXPECTED THROUGH AFTN...SOME
   OF WHICH SHOULD BE SUPERCELLS.  MAIN CONCERN HAS BECOME TORNADO
   POTENTIAL...WITH DAMAGING GUSTS AND ISOLATED SVR HAIL ALSO POSSIBLE.

   BASED ON FRONTAL MORPHOLOGY DISCUSSED ABOVE...AND LIKELY PATCHWORK
   RETREAT OF CONVECTIVELY STABILIZED AIR MASS AMIDST INCREASING
   LOW-LEVEL WAA...NRN RIM OF WARM SECTOR SHOULD SPREAD ACROSS VA
   PORTION OF OUTLOOK AREA TODAY.  THIS WILL RESULT IN SWATH OF RICH
   LOW-LEVEL MOISTURE AND HIGH THETAE FROM PREFRONTAL CAROLINAS NNEWD
   ACROSS AT LEAST ERN/CENTRAL VA...PERHAPS INTO ADJOINING PARTS OF MD.
   SFC DEW POINTS COMMONLY UPPER 60S TO NEAR 70 F WILL CHARACTERIZE
   THAT AIR MASS...ALONG WITH 1.5-1.75-INCH PW AND LOW LCL.  BEHIND
   MORNING ACTIVITY...AREAS OF SUSTAINED DIABATIC SFC HEATING ALSO ARE
   EXPECTED OVER OUTLOOK AREA THROUGH AFTN...BASED ON TRENDS IN IR
   IMAGERY...RESULTING IN WEAK CINH.  MLCAPE IS EXPECTED TO RISE INTO
   1500-2500 J/KG RANGE IN MUCH OF WARM SECTOR...DECREASING IN FRONTAL/
   TRANSITION ZONE NWD OVER NRN VA/CENTRAL MD/DC REGION.

   RELATIVELY BACKED NEAR-SFC WINDS SHOULD BE MAINTAINED INVOF ARCHING
   FRONTAL ZONE...BENEATH RIBBON OF INCREASING/SSWLY 850-MB FLOW. 
   RESULT WILL BE ENLARGED LOW-LEVEL HODOGRAPHS AND RELATED
   ENHANCEMENTS TO LOW-LEVEL SHEAR...DEEP SHEAR...BOUNDARY-LAYER
   CONVERGENCE...AND STORM-RELATIVE INFLOW.  MODIFIED FCST SOUNDINGS
   FROM SEVERAL MODELS SHOW BOTH EFFECTIVE AND FIXED/0-1-KM SRH IN
   200-250 J/KG RANGE THIS AFTN.  STRENGTHENING HEIGHT GRADIENT ALOFT
   RELATED TO SWD SHIFT OF CYCLONE WILL BOOST EFFECTIVE-SHEAR
   MAGNITUDES INTO 40-45-KT RANGE.  THESE CONDITIONS SHOULD SUPPORT
   POTENTIAL FOR MIXTURE OF SUPERCELLS AND CLUSTERED CONVECTION...AND A
   FEW DISCRETE/SEMI-DISCRETE AND CYCLIC SUPERCELLS MAY OCCUR.  OVERALL
   SVR THREAT SHOULD DIMINISH GRADUALLY THROUGH EVENING/OVERNIGHT AS 
   1.  CONVECTIVE MODE BECOMES MORE MESSY AND
   2.  SFC LAYER STABILIZES FROM COMBINATION OF SLOW DIABATIC COOLING
   AND AREAL SPREAD OF OUTFLOW. 
   VERTICAL SHEAR AND LIFT EACH SHOULD WEAKEN WITH SWD EXTENT THROUGH
   CAROLINAS...RENDERING SVR POTENTIAL MORE ISOLATED/DISORGANIZED.
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FLOOD WARNING
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
923 AM EDT WED SEP 28 2016

MDC009-037-281715-
/O.NEW.KLWX.FA.W.0063.160928T1323Z-160928T1715Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
ST. MARYS MD-CALVERT MD-
923 AM EDT WED SEP 28 2016

THE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA HAS ISSUED A

* FLOOD WARNING FOR URBAN AREAS AND SMALL STREAMS IN...
  ST. MARYS COUNTY IN SOUTHERN MARYLAND...
  CALVERT COUNTY IN SOUTHERN MARYLAND...

* UNTIL 115 PM EDT

* AT 922 AM EDT...DOPPLER RADAR AND AUTOMATED RAIN GAUGES INDICATED
  THUNDERSTORMS WITH HEAVY RAIN OVER THE AREA. THE RAIN WILL CAUSE
  FLOODING...ESPECIALLY IN LOW-LYING AND POOR DRAINAGE AREAS...AND
  IN URBANIZED AREAS. 4 TO 5 INCHES OF RAIN ARE ESTIMATED TO HAVE
  FALLEN IN THE PRINCE FREDERICK AREA...AND MORE HEAVY RAIN IS
  OCCURRING TO THE SOUTH OF THIS OVER CALVERT AND SAINT MARYS
  COUNTIES.


* SOME LOCATIONS THAT WILL EXPERIENCE FLOODING INCLUDE...
  LEXINGTON PARK...CHESAPEAKE RANCH ESTATES...LEONARDTOWN...PRINCE
  FREDERICK...FLAG HARBOR...CALVERT CLIFFS...HALLOWING POINT...
  CUCKOLD CREEK...GREENWELL STATE PARK...BREEZY POINT...SAINT LEONARD
  CREEK...SHERIDAN POINT...SAINT CLEMENTS BAY...TOWN CREEK...WICOMICO
  RIVER...WHITE POINT BEACH...CALIFORNIA...GOLDEN BEACH...LUSBY AND
  PATUXENT RIVER NAVAL AIR STATION.

ADDITIONAL RAINFALL AMOUNTS OF 2 TO 3 INCHES ARE POSSIBLE IN THE
WARNED AREA.
 

http://forecast.weather.gov/showsigwx.php?warnzone=MDZ018&warncounty=MDC009&firewxzone=MDZ018&local_place1=Prince

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Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
954 AM EDT Wed Sep 28 2016

.SYNOPSIS...
An upper level low will impact the area through Thursday night...
bringing the potential for heavy rainfall to the Mid Atlantic.
This will gradually move away from the area this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...

Complex weather situation is unfolding across the area...as
strong upper-level low is dropping southward into the Ohio River
Valley. At the surface, frontal boundary is across southern VA...where it
will remain through much of today. Very challenging forecast over
the next couple of days. It`s interesting to see how much the
atmosphere moistened up in the 12 hours betweeen the 00Z and 12Z
IAD sounding. This increase in moisture has led to some very heavy
ranifall across Lower Southern Maryland - radar estimates of over
4" in 3 hours has led to the issuance of a flood warning for
Calvert and St. Marys Counties. Training storms could lead to some
flooding issues later today.

Another factor with the sounding/VWP is the wind field - low level
winds are from the east...turning abruptly to the southwest above
6000 feet. Turning in the atmosphere has led SPC to put the CWA
east of the Blue Ridge at a 5% tornado risk. Limiting factor would
be cloud cover..but given we had to issue severe warnings at 550
am this morning implies that there is energy in the atmosphere.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...

Heaviest rain expected later tonight into Friday morning as strong
upslope flow (up to 50 kts out of SE) and high precipitable water
transport set up over the area (axis of heaviest rainfall expected
over our area). Flash Flood watch in good shape...as repetitive
bouts of moderate-to-heavy rain could eventually saturate the dry
soils and lead to runoff concerns. Storm total QPF still greater
than 3 inches over a large area...with the potential for higher
totals in localized areas. Despite the weak instability on
Thursday...strong wind field remains...so could also be a few
stronger storms with wind/hail threats.
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