[CALV-ARES] [New post] ALERT: Severe weather possible today

[Calvert County Auxiliary Communications Services via CALV-ARES]

Post       : ALERT: Severe weather possible today
URL        : https://ares.k3cal.org/2015/04/20/alert-severe-weather-possible-today/
Posted     : April 20, 2015 at 9:22 am
Author     : Eric Christensen
Categories : ALERT, Weather

http://www.spc.noaa.gov/products/activity_loop.gif?1429535984028 The Storm Prediction Center ( http://www.spc.noaa.gov/ )  has placed Calvert County (and surrounding areas) in an enhanced risk for severe weather, today.  The primary threat is damaging winds and large hail.

The timing for these storms seem to be centered around late this afternoon into the evening although a few storms could start popping up in the area around 2PM.

From the SPC (edited to show only our area):
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT MON APR 20 2015

VALID 201300Z - 211200Z

...THERE IS AN ENH RISK OF SVR TSTMS PORTIONS CENTRAL/SERN PA TO
DELMARVA AND NERN NC...

...SUMMARY...
ISOLATED TO SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED DURING THE
AFTERNOON AND EVENING ACROSS PORTIONS OF THE CORRIDOR FROM THE
MID-ATLANTIC TO THE CAROLINAS.  OTHER SEVERE THUNDERSTORMS MAY MOVE
EASTWARD OFF THE GULF AND AFFECT PARTS OF NORTHERN AND CENTRAL
FLORIDA AND SOUTHERN GEORGIA.

...SYNOPSIS...
UPPER-AIR PATTERN THIS PERIOD WILL BE CHARACTERIZED BY TWO
PRIMARY/SYNOPTIC-SCALE FEATURES...
1. SPLIT FLOW AROUND REX BLOCK LOCATED OVER WRN NORTH AMERICA...WITH
HIGH-AMPLITUDE RIDGING OVER NWRN STATES AND BROAD/WEAK CYCLONE
OFFSHORE CA.
2. LARGE CYCLONE NOW CENTERED OVER MB/ONT BORDER WITH TROUGH SSEWD
OVER MS VALLEY.  THIS CYCLONE SHOULD SHIFT SLOWLY SEWD OVER LS
THROUGH PERIOD...WHILE SEVERAL SHORTWAVES PIVOT THROUGH SRN
SEMICIRCLE OF ITS ACCOMPANYING CYCLONIC-FLOW FIELD.

STG SHORTWAVE TROUGH -- CURRENTLY LOCATED OVER LOWER OH VALLEY --
WILL LIFT NNEWD ACROSS LOWER MI TO ERN LS AREA BY 00Z THEN NWD
ACROSS NWRN ONT.  IN ITS WAKE...WEAK SHORTWAVE TROUGH -- EVIDENT IN
MOISTURE-CHANNEL IMAGERY OVER AR/LA -- WILL EJECT ENEWD ACROSS
CENTRAL APPALACHIANS.

AT SFC...11Z ANALYSIS SHOWED DEEP/985-MB LOW OVER NWRN LOWER
MI...COLD FRONT FROM THERE ACROSS INDIANA...SERN LA...AND DEEP S
TX...AND WARM FRONT SEWD ACROSS NERN OH...SWRN PA...WEAK THROUGH
WEAK LOW IN NRN MD...AND ACROSS SRN CHESAPEAKE BAY.  WARM FRONT IS
FCST TO MOVE NEWD SLOWLY TO NERN PA AND NJ BY 00Z....WHEN SFC LOW
SHOULD BE LOCATED OVER ONT NE OF LS.  BY 00Z COLD FRONT WILL ARC
SEWD FROM OCCLUSION TRIPLE POINT OVER PA SWWD ACROSS WRN
NC...GA...AND FL PANHANDLE...TO N-CENTRAL GULF.  BY
12Z...TRIPLE-POINT LOW SHOULD DEVELOP AND MOVE TO ERN MA...WITH COLD
FRONT SWWD ACROSS NRN FL TO WRN GULF.

...UPPER OH VALLEY AND PA...CENTRAL APPALACHIANS EWD TO COASTAL
CAROLINAS/MID ATLC...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP THIS AFTN INVOF
PREFRONTAL AND NEARLY FRONT-PARALLEL SFC TROUGH...WITH MORE ISOLATED
DEVELOPMENT ELSEWHERE OVER WARM SECTOR.  SOME OF THIS ACTIVITY WILL
BECOME SVR WITH LARGE HAIL...DAMAGING GUSTS AND A TORNADO OR TWO
POSSIBLE.

MIDLEVEL HEIGHT FALLS WILL OCCUR OVER THIS REGION AS PRIMARY VORTEX
ALOFT SHIFTS IN THIS DIRECTION...WHILE SMALL PERTURBATIONS TRAVERSE
ASSOCIATED SWLY FLOW ALOFT.  SOME CONCERNS LINGER ABOUT SPEED AT
WHICH AIR MASS ACROSS PA/MID ATLC CAN DESTABILIZE AND RECOVER DUE TO
LOW-LEVEL THETAE ADVECTION FOLLOWING EARLY-MORNING RAINFALL.
HOWEVER...IR/VIS IMAGERY SHOWS POTENTIAL FOR SOME LOW-CLOUD BREAKUP
AND SFC DIABATIC HEATING OVER THIS REGION AHEAD OF POTENTIAL AFTN
CONVECTIVE ARC...IN ADDITION TO ADVECTION OF MIDLEVEL AIR CONTAINING
STEEPER LAPSE RATES ACROSS THIS REGION.  SFC DEW POINTS SHOULD RISE
BACK INTO 50S ACROSS MOST OF PRECONVECTIVE PA AND 60S FARTHER S.
NET RESULT SHOULD BE GENERATION OF PLUME OF 1000-2000 J/KG
MLCAPE...WITH FURTHER SUPPORT FROM MINIMAL MLCINH.  MIXED CONVECTIVE
MODES ARE LIKELY...WITH 35-40 KT EFFECTIVE-SHEAR MAGNITUDES AND
CURVED LOW-LEVEL HODOGRAPHS INDICATING POTENTIAL FOR A FEW
SUPERCELLS AND BOWS AMIDST MULTICELL CLUSTERS AND BANDS.  AS
SUCH...SVR THREAT IS MULTI-MODAL AS WELL.

CONDITIONAL TORNADO RISK IS GREATER NEAR WARM FRONT WHERE SFC WINDS
WILL BE MOST BACKED AND LOW-LEVEL VORTICITY IS RICHEST.  INSTABILITY
TRENDS MAY LEAD TO UPGRADE IN UNCONDITIONAL PROBABILITIES LATER
TODAY.  ATTM...THERE REMAINS TOO MUCH UNCERTAINTY REGARDING
DESTABILIZATION IN WAKE OF MORNING RAIN...AND ALSO REGARDING
STRENGTH OF LOWEST-1-KM FLOW TO ENLARGE ALREADY CURVED HODOGRAPHS
AND BOOST SRH.

ALTHOUGH SOME SVR CANNOT BE RULED OUT FARTHER S ACROSS SRN SC AND
MUCH OF GA...CONCERNS REGARDING WEAKNESS OF BOTH LIFT AND FLOW IN
LOW LEVELS...WHICH MANIFEST REASONABLY IN LESSER CONVECTIVE
COVERAGE/INTENSITY IN PROGS...PRECLUDE GREATER PROBABILITIES ATTM.

..EDWARDS/PICCA.. 04/20/2015
All stations are encouraged to monitor NOAA All-Hazards Radio ( http://www.nws.noaa.gov/nwr/ )  and the CARA 146.985 repeater.  I'll try to keep everyone updated with any new information as it becomes available.

-- 


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