HAMweather.com Area Forecast Discussion for County Warning Area RNK

Thu, 16 Feb 2012 13:10:45 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
623 AM EST THU FEB 16 2012

.SYNOPSIS...
LOW PRESSURE WILL PASS TO THE NORTH TODAY WITH THE ASSOCIATED
TRAILING COLD FRONT CROSSING THE REGION FROM THE WEST THIS
AFTERNOON AND EVENING. HIGH PRESSURE WILL BUILD BACK ACROSS THE
REGION FROM THE WEST LATER TONIGHT INTO FRIDAY BEFORE PASSING
OFFSHORE ON SATURDAY. A STRONG AREA OF LOW PRESSURE WILL RIDE
NORTHEAST FROM THE GULF COAST AND AFFECT THE AREA SATURDAY NIGHT
AND SUNDAY.

.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 AM EST THURSDAY...

RATHER DISJOINTED FRONTAL SYSTEM WILL PUSH EAST CROSSING THE
REGION LATER TODAY BEFORE PASSING OFFSHORE THIS EVENING. EXPECT SE
FLOW TO GET SHRA GOING A BIT FASTER THAN FORECAST THIS MORNING
WITH FOLLOWING ISENTROPIC LIFT LEADING TO AT LEAST A SWATH OR TWO
OF SHOWERS CROSSING THE REGION THRU EARLY OR MID AFTERNOON. COULD
STILL SEE ONGOING CONVECTION TO THE SOUTH ROB PRECIP ACROSS THE
SOUTH THIS MORNING...WITH BEST LIFT LOOKING TO AFFECT THE
WEST/NORTH EARLY ON BEFORE ANOTHER WEAK WAVE DEVELOPS ALONG THE
FRONTAL TRIPLE POINT OVER NC THIS AFTERNOON. THEREFORE HAVE SPED
UP ARRIVAL OF HIGHER POPS OVER THE MOUNTAINS THIS MORNING...WITH A
PERIOD OF CAT POPS OVERSPREADING THE REGION BY MID OR LATE
MORNING. SFC COLD FRONT CROSSES THE FAR WEST THIS AFTERNOON WHICH
SHOULD START TO DECREASE SHRA WEST BY MID AFTERNOON AND OVER THE
EAST BY EVENING. STILL LOOKS LIKE A RATHER LIGHT QPF EVENT WITH A
QUARTER TO A THIRD OF AN INCH ON AVERAGE BUT PERHAPS MORE SOUTH IF
THE SECONDARY WAVE DOES HOLD UP AND ENHANCE SHRA MORE DESPITE LACK
OF INSTAB. SOUTHERLY WINDS REMAIN GUSTY ACROSS THE FAR WEST AS
HAVE BEEN NEAR ADVISORY LEVELS AROUND BLF FOR THE PAST HOUR OR SO.
THINK ONCE THE FLOW TURNS MORE SW AND SHRA ARRIVES WILL SEE SPEEDS
DIMINISH UNDER THE INVERSION SO HOLDING OFF ON NPW ISSUANCE FOR
NOW. HIGH TEMPS AGAIN IFFY WITH READINGS CURRENTLY AROUND 50 AHEAD
OF THE ONSET OF PRECIP WHICH WILL EVAPORATIVE COOL THINGS BACK
SOME THIS MORNING AND CREATE A WEAK WEDGE NORTH OF THE WARM FRONT
TO THE SOUTH. SINCE LATEST MAV VALUES CLOSE TO THE GOING FCST AND
ENSEMBLES VALUES...NOT MAKING TOO MANY CHANGES TO HIGHS WITH MOST
UPR 40S TO LOW 50S.

WEAK UPPER TROF WILL PASS EAST OF THE REGION THIS EVENING CAUSING A 
QUICK DECREASE IN MOISTURE DEPTH EARLY ON WITH ONLY SOME UPSLOPE 
RAIN/SNOW SHOWERS LINGERING SE WVA REGION AS NW FLOW KICKS IN. 
HOWEVER MODEL SOUNDINGS AGAIN SHOW VERY SHALLOW MOISTURE BANKED UP 
AGAINST THE NW SLOPES WITH JUST ENOUGH TO PRODUCE A PERIOD OF 
-DZ OR EVEN -FZDZ IF TEMPS EVER DO GET BELOW FREEZING. ELSW LEAVING 
IT DRY WITH DOWNSLOPE CLEARING EAST ALTHO MAY SEE A PERIOD OF DENSE 
FOG PIEDMONT GIVEN THE RATHER WEAK NW FLOW THAT WILL LIKELY BE 
SLOWER THAN FORECAST WITH THE LAGGING 85H COOL ADVECTION. LOW TEMPS 
WILL BE SLOW TO FALL ESPCLY WEST WHERE WILL HAVE MORE CLOUDS/MIXING 
WITH COLDER VALUES POSSIBLE EAST PER PERIODS OF BETTER RAD COOLING 
UNDER CLEARING.

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
AS OF 233 AM EST THURSDAY...

HIGH PRESSURE IN THE OHIO VALLEY WILL DRIFT SLOWLY EAST AND OFF
THE MID ATLANTIC COAST SATURDAY MORNING. THIS HIGH AND ZONAL FLOW
ALOFT WILL KEEP THE AREA DRY THROUGH AT LEAST SATURDAY MORNING.

THE WEATHER BEGINS TO DETERIORATE SATURDAY AFTERNOON AND INTO THE 
DAY SUNDAY. LOW PRESSURE IS EXPECTED TO TRACK ALONG THE GULF 
SATURDAY...THEN TURN NORTHEAST SATURDAY NIGHT AS IT MOVES OVER THE 
SOUTHEASTERN USA. PRECIPITATION ASSOCIATED WITH THIS FEATURE WILL BE 
ALL LIQUID. A DEFORMATION ZONE WILL DEVELOP TO THE NORTHWEST OF THIS 
SURFACE LOW EARLY SUNDAY MORNING. THIS ZONE MAY BE COLD ENOUGH FOR 
MOSTLY SNOW TO FALL...ESPECIALLY IF THE LOCATION IS OVER THE 
APPALACHIAN MOUNTAINS. EVEN THOUGH THERE IS A GOOD CHANCE SNOW WILL 
FALL IN THIS DEFORMATION ZONE...BULK OF THE PRECIPITATION AND ENERGY 
WILL BE OFF THE COAST. THEREFORE ACCUMULATIONS SHOULD REMAIN ON THE 
LIGHT SIDE.

THE 00Z GFS/ECMWF ARE IN AGREEMENT WITH THE SCENARIO STATED ABOVE. 
PREVIOUS RUNS OF THE GFS HAD THE TRACK FARTHER TO THE NORTH WHILE 
THE ECMWF HAD THE LOW TRACKING ACROSS THE FLORIDA PANHANDLE. IF THE 
LATEST 00Z MODELS VERIFY...THE SURFACE LOW WILL TRACK OFF THE NC/VA 
COAST SUNDAY. THIS WOULD PLACE THE DEFORMATION ZONE OVER RNK CWA. 
STILL WOULD LIKE TO HAVE MORE CONTINUITY IN THE MODELS BEFORE 
INCREASING POPS TO CATEGORICAL. ALSO WITH LOW CONFIDENCE...WILL KEEP 
P-TYPE AS A RAIN/SNOW MIX.

ABUNDANT SUNSHINE AND DRY AIR WILL ALLOW TEMPERATURES TO RUN 5F-10F 
ABOVE NORMAL ON FRIDAY. SATURDAY TEMPERATURES DEPENDENT ON TIMING 
AND PLACEMENT OF THE GULF LOW AND TIMING OF ONSET PRECIPITATION. LOW 
LEVEL FLOW OVER THE REGION WILL BE EASTERLY...THEREFORE HAVE COOLER 
TEMPERATURES ALONG AND EAST OF THE BLUE RIDGE. DOWNSLOPE FLOW ON 
WESTERN SLOPES SHOULD BUMP TEMPERATURES UP ABOVE NORMAL ONCE AGAIN 
SATURDAY. SUNDAY TEMPERATURES ARE VERY DEPENDENT ON THE TRACK OF THE 
SURFACE LOW AND ASSOCIATED DEFORMATION ZONE. FOR NOW...I HAVE 
TEMPERATURES IN THE EAST AROUND NORMAL WHILE THE MOUNTAINS ARE ABOUT 
5F BELOW NORMAL.

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 245 AM EST THURSDAY...

ONCE THIS WEATHER MAKER GOES OFFSHORE...SURFACE HIGH PRESSURE BUILDS 
IN FOR MONDAY AND TUESDAY. SPLIT UPPER FLOW CONTINUES THROUGH DAY 7. 
THE NEXT SHORT WAVE AND ASSOCIATED SURFACE LOW COMING OUT OF THE 
SOUTHERN UNITED STATES WILL REACH THE FORECAST AREA ON WEDNESDAY OR 
THURSDAY.

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AS OF 600 AM EST THURSDAY...

CIGS WILL CONTINUE TO LOWER FROM WEST TO EAST AS SWATHS OF SHOWERS
SPREAD EAST ACROSS THE REGION THIS MORNING. EXPECTING A QUICK
DOWNTURN TO MVFR AT KBLF/KLWB BY MID MORNING AND ALONG THE BLUE
RIDGE BEFORE MIDDAY AND OUT EAST DURING THE AFTERNOON. COULD SEE
POCKETS OF IFR DEVELOP BETWEEN THE INITIAL BATCH OF SHRA AND THE
NEXT AS THE COLUMN MOISTENS. WITH SOUTHEAST FLOW CIGS WILL BE
MUCH LOWER NEAR BLUE RDG AND EVEN DOWN ON THE RIDGE AT TIMES WITH
FOG...UNTIL WINDS SHIFT WESTERLY LATE AFTERNOON. FOG SHOULD NOT BE
AN ISSUE AT THE AIRPORTS AND VSBYS WILL MOSTLY BE MVFR RANGE...BUT
AGAIN COULD BRIEFLY GO IFR INTO EARLY OR MID AFTERNOON AS SHRA
BANDS WORK THROUGH.

SHOWERS EXIT THE REGION BY LATE MID AFTERNOON WEST AND LATE
AFTERNOON EAST...WITH A FEW LINGERING SHOWERS POSSIBLE FAR WESTERN
SLOPES INTO EVENING...BUT KEPT OUT OF KBLF TAF FOR NOW. MVFR OR
IFR CIGS THOUGH SHOULD LINGER AT KBLF OVERNIGHT WITH MVFR/VFR CIGS
AT KLWB AND PERHAPS KBCB/KROA. AN IMPROVEMENT TO VFR CONDITIONS
UNDER HIGH PRESSURE IS EXPECTED BY THURSDAY NIGHT IN PIEDMONT AND
FOR ALL LOCATIONS ON FOR FRIDAY.

ANOTHER COMPLEX STORM SYSTEM WILL AFFECT THE AREA OVER THE
WEEKEND... WITH MVFR CEILINGS POSSIBLE IN RAIN LATE SATURDAY INTO
SATURDAY NIGHT AND SNOW MOUNTAINS AND RAIN WEST INTO SUNDAY. DRIER
WEATHER AND A RETURN TO VFR IS EXPECTED FOR MONDAY.

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.