000
FXUS61 KRNK 041503
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1003 AM EST SAT FEB 4 2012

.SYNOPSIS...
LOW PRESSURE WILL TRACK EAST ACROSS THE MID MISSISSIPPI VALLEY
TODAY...REACHING THE CENTRAL APPALACHIANS TONIGHT BEFORE PASSING
TO NEAR THE CAROLINA COAST ON SUNDAY. ANOTHER AREA OF UPPER LEVEL
LOW PRESSURE MAY AFFECT THE REGION ON MONDAY. HIGH PRESSURE BUILDS
NORTH OF THE REGION BEHIND THIS SYSTEM BRINGING A RETURN TO DRIER
WEATHER ON TUESDAY.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
AS OF 948 AM EST SATURDAY...

ALTHOUGH LLVLS ARE DRY ACROSS MUCH OF THE REGION...SHIELD OF RAIN
IS DENSE ENOUGH TO MOISTEN THE ATMOS ENOUGH SUCH THAT SHOWERS HIT
THE GROUND WEST OF THE BLUE RIDGE OVER THE NEXT FEW HOURS. PROFILE
IS COLD AND DRY ENOUGH SO A SLT CHC THERE COULD BE VERY BRIEF
INCONSEQUENTIAL SLEET NE GREENBRIER AND SOUTHERN SHENANDOAH FOR AN
HOUR. SHOULD BE A VERY LIGHT QPF BUT HIGH POPS SCENARIO UNTIL LATE
THIS AFTERNOON OR EARLY EVENING. JFZ/GEV/TNB/MKJ RAINING RIGHT
NOW...BUT MAY SEE A BREAK AS WARM FRONT BARELY NUDGES NORTH THIS PM.
COULD BE A SITUATION WHERE BLF IS MUCH WARMER THAN NEARBY JFZ/MKJ
AS THE WARM AIR ONLY MAKES NORTHERN PROGRESS JUST WEST OF THE
RIDGES IN SW VA. SOUTHERLY COMPONENT ONLY MAKES A BRIEF APPEARANCE IF
ANY SOUTHERN SHENANDOAH...SO LOWERED MAX T THERE A BIT.

AS OF 255 AM EST SATURDAY...

SHORTWAVE RIDGING ACROSS THE REGION WILL BEGIN TO FLATTEN INTO A
MORE CONFLUENT UPPER FLOW REGIME OVER THE NEXT 24 HOURS IN ADVANCE
OF THE SLOW MOVING CENTRAL STATES UPPER LOW. THIS WILL ALLOW DEEPER
MOISTURE AHEAD OF THE ASSOCIATED SURFACE LOW TO SHEAR EAST RESULTING
IN INCREASING PRECIP CHANCES ESPCLY THIS AFTERNOON INTO TONIGHT AS
THE WAVE RIDES IN FROM THE WEST. MAIN QUESTIONS REMAIN WITH TIMING
OF ONSET OF MORE STEADIER -RA INTO DRY AIR TODAY AND THEN HOW FAR
SOUTH CAN COLDER AIR TO THE NORTH MAKE IT LATER TONIGHT WHEN THE
MAIN AXIS OF LIFT/PRECIP WILL BE ONGOING.

LATEST MODELS HAVE AGAIN TRENDED SLOWER IN ONSET OF WARM FRONTAL
PRECIP TODAY...WITH INITIAL AREA OF SPOTTY ISENTROPIC DRIVEN -RA
PUSHING IN FROM THE SW THIS MORNING MOSTLY GOING TO MOISTEN THE
COLUMN. IN FACT MOST GUIDANCE ONLY BRINGING MEASURABLE PRECIP TO
THE FAR SW THRU MIDDAY...THEN OVERSPREADING A MORE SOLID SHIELD OF
-RA BY MID/LATE AFTERNOON WHEN FCST RAOBS SHOW RATHER RAPID
SATURATION FROM WEST TO EAST AS BETTER UVV GETS FOCUSED IN AHEAD
OF THE SFC WAVE. SINCE FLOW ALOFT QUITE FAST AND TRENDS ALWAYS
SEEM FASTER WITH THIS WARM ADVECTION SCENARIO...KEPT DECENT CHANCE
POPS WEST THRU LATE MORNING AND THEN ACCELERATED LIKELY TO CAT
POPS ACROSS THE REGION BY LATE AFTERNOON FOR AT LEAST SOME LIGHT
QPF TYPE COVERAGE. WITH SO MUCH LOW LEVEL DRY AIR...LIKELY TO SEE
SOME SLEET MIX IN AT THE ONSET IN SPOTS IF PRECIP IS FAST ENOUGH
BEFORE THINGS GET TOO WARM WEST. OTRW WITH WARMING ALOFT KEEPING
PRECIP MOSTLY LIQUID EXCEPT FAR NORTH WHERE COULD EVAPORATIVE COOL
ENOUGH FOR A BRIEF MIX TO SNOW HIGHLANDS REGION. HIGH TEMPS TRICKY
WITH WEDGE NOT REALLY DEVELOPING UNTIL OVERNIGHT AND 85H VALUES
QUITE WARM OVERTOP WEAK S/SW FLOW BUT DECENT WET BULB COOLING
SETUP EARLY ON. GIVEN SLOWER PRECIP TRENDS HAVE ADJUSTED HIGHS UP
A BIT BUT STILL BELOW THE WARM MET MOS VALUES OF 50S TO NEAR 60
SOUTH/EAST WHICH COULD HAPPEN IN SPOTS IF CLOUDS THIN THIS
MORNING.

SFC WAVE TRACKS INTO THE SW OVERNIGHT WITH THE 85-9H LOW A BIT
FARTHER NORTH THAN EARLIER RUNS. THIS IN COMBO WITH THE TIGHT 850 MB
TEMP GRADIENT SINKING SOUTH LATE SHOULD CAUSE LIFT TO FOCUS OVER THE
CWA AS A SQUEEZE PLAY BETWEEN THE BAROCLINIC ZONE JUST NORTH AND
WARM ADVECTION PLAYS OUT. ALSO RIGHT REAR OF THE UPPER JET MAY
ENHANCE PRECIP INTO MORE BANDED NATURE WITH A GOOD SWATH OF A
QUARTER TO HALF INCH QPF LIKELY WITH PERHAPS MORE NW SLOPES NEAR THE
THETA-E GRADIENT AND LESS SW. DEEPER COLD AIR MAY CATCH THE NRN
PERIPHERY OF THE PRECIP IN TIME FOR A MIX TO WET SNOW AT ELEVATION
SO INCLUDED A MENTION IN BATH/ROCKBRIDGE REGION ALTHO IFFY GIVEN
WARMER SREF SOLNS. OTRW RUNNING WITH OVERALL CAT POPS THRU MUCH OF
THE NIGHT...THEN TAPERING BEST COVERAGE TO MAINLY THE FAR EAST AND
WEST LATE AS THE FLOW ALOFT TURNS MORE WESTERLY AFTER MIDNIGHT.
TEMPS SHOULD STEADY DURING THE EVENING AND THEN SLOWLY FALL INTO THE
UPR 30S/LOW 40S EAST LATE PER NE FLOW/COLD ADVECTION UNDER THE
WEDGE WHILE LINGERING IN THE LOW/MID 40S ELSW.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH TUESDAY NIGHT/...
AS OF 330 AM EST SATURDAY...

BY SUNRISE SUNDAY MORNING...THE COLD FRONT WILL HAVE MOVED SOUTH OF
OUR AREA...BUT RAINFALL IS EXPECTED TO STILL BE WIDESPREAD AS FAR
NORTH AS INTERSTATE 81. FURTHER NORTH...WILL BEGIN TO SEE RAIN...
POSSIBLY BECOMING MIXED WITH SNOW IN HIGHER ELEVATIONS OF GREENBRIER
COUNTY AND THE ALLEGHANY HIGHLANDS...TAPER OFF AS NORTHERLY WINDS
BRING DRIER AIR INTO THE REGION. RAINFALL WILL CONTINUE TO DIMINISH
THROUGH THE AFTERNOON AS HIGH PRESSURE BUILDS DOWN THE EASTERN FACE
OF THE APPALACHIANS...WITH RESIDUAL SHOWERS TAPERING OFF IN THE
NORTH CAROLINA PIEDMONT BY EVENING.

DUE TO THE SLOW MOVEMENT OF THIS FRONTAL BOUNDARY...HIGH
TEMPERATURES FOR SUNDAY WILL BE A CHALLENGE...ESPECIALLY IN THE
FOOTHILLS OF NORTH CAROLINA. SEVERAL FORECAST MODELS ARE CALLING FOR
TEMPERATURES TO SPIKE TO NEAR 60 DEGREES IN THE FOOTHILLS AS HOLES
DEVELOP IN THE CLOUD COVER AND WINDS BECOME NORTHWESTERLY...WARMING
ADIABATICALLY AS THE AIR BLOWS DOWNSLOPE OFF THE BLUE RIDGE...
SIMILAR TO A CHINOOK WIND. AT ANY RATE...BELIEVE THIS SCENARIO IS A
LITTLE TOO OPTIMISTIC CONSIDERING RESIDUAL SHOWER ACTIVITY WILL
STILL BE IN THE AREA...AND WENT WITH WHAT IS BELIEVED TO BE MORE
REASONABLE LOW TO MID 50S IN THE FOOTHILLS. ELSEWHERE...HIGH
TEMPERATURES WILL RANGE FROM THE UPPER 30S ACROSS THE ALLEGHANY
HIGHLANDS...TO THE LOW 50S ACROSS THE NORTH CAROLINA PIEDMONT.

THE ONLY OTHER CONCERN FOR THE SHORT TERM PERIOD WILL BE MONDAY
NIGHT AND EARLY TUESDAY...AS AN UPPER LEVEL TROUGH PUSHES QUICKLY
ACROSS OUR AREA. MOISTURE ACROSS OUR AREA WILL BE LIMITED...BUT
BELIEVE THERE WILL BE JUST ENOUGH TO SQUEEZE OUT A FEW RAIN SHOWERS
LATE MONDAY EVENING FOR THE MOUNTAINS...WITH THESE SHOWERS BECOMING
MIXED WITH SNOW EARLY TUESDAY MORNING AS THE COLDER AIR ASSOCIATED
WITH THE TROUGH MOVES IN. BY SUNRISE...PRECIPITATION IS EXPECTED TO
END AS THE TROUGH PASSES EASTWARD...AND HIGH PRESSURE AGAIN BECOMES
THE DOMINANT INFLUENCE HEADING INTO WEDNESDAY.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 330 AM EST SATURDAY...

BY LATE WEDNESDAY THROUGH FRIDAY MODEL GUIDANCE VARIES DRAMATICALLY
REGARDING THE SYNOPTIC WEATHER PATTERN ACROSS THE EASTERN U.S. THE
ECMWF TRENDS TOWARD HAVING A PROGRESSIVELY AMPLIFIED POSITIVELY
TILTED TROUGH FROM QUEBEC PROVINCE CANADA SOUTH THROUGH THE EAST
COAST WHICH TEAMS UP WITH A SOUTHERN JET SHORTWAVE TROUGH. THE
RESULT IS A GENEROUS SWATH OF MOISTURE EXITING THE GULF OF
MEXICO...AND HEADING NORTHEAST ACROSS FLORIDA AND OFF THE EAST
COAST.

ANY WEATHER ACROSS OUR REGION WOULD MAINLY BE IN THE FORM OF
LIGHT WESTERN SLOPE UPSLOPE RAIN/SNOW SHOWERS AS QUICK MOVING
CLIPPER SYSTEMS IN THE NORTHERN FLOW ENTER THE DRY AIR MASS ACROSS
OUR REGION. THE GFS ON THE OTHER HAND...MAINTAINS A GENERAL BROAD
TROUGH ACROSS THE NORTH CENTRAL PART OF CONUS THAT DRIFTS EASTWARD.
THIS SCENARIO ALLOWS FOR A GREATER POTENTIAL FOR GULF MOISTURE
HAVING A FARTHER WESTERN TRACK AS IT PROGRESSES
NORTHEASTWARD...DIRECTLY ACROSS OUR AREA BY THURSDAY NIGHT INTO
FRIDAY...RATHER THAN BEING SHUNTED EASTWARD IN ADVANCE OF THE THE
SHARP EAST COAST TROUGH THE ECMWF IS DEPICTING.

PLAN TO FOLLOW CLOSELY TO THE GUIDANCE PUT FORTH BY HPC WHICH IS
MORE CLOSELY IN LINE WITH ABOVE DESCRIBED ECMWF SOLUTION. AS A
RESULT...OUR FORECAST WILL REFLECT SLIGHT CHANCE POPS DURING THE
TIME PERIODS OF WEDNESDAY AFTERNOON AND EARLY
EVENING...THURSDAY...AND THEN AGAIN ON FRIDAY TO ACCOUNT FOR
DISTINCT QUICK MOVING SHORTWAVE TROUGH PROGRESSING ACROSS THE
AREA. NONE OF THESE WILL HAVE SIGNIFICANTLY COLDER AIR BEHIND
IT...BUT THERE WILL BE A SLIGHT COOL DOWN IN THE WAKE OF THE ONE
ON WEDNESDAY.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
AS OF 600 AM EST SATURDAY...

CIGS WILL CONTINUE TO LOWER THIS MORNING WITH SPOTTY -RA AFFECTING
THE SE WVA SITES AND PERHAPS AS FAR EAST AS KBCB THRU MIDDAY.
HOWEVER APPEARS MOST SHOULD REMAIN AT VFR LEVELS WITH 4-6K FT CIGS
DEVELOPING WEST AND MAINLY MID DECK OUT EAST. INITIAL MAIN BATCH
OF RAIN SHOULD THEN AFFECT MOST LOCATIONS DURING THE AFTERNOON
WITH CLOUD BASES LOWERING TO MVFR LEVELS A FEW HOURS AFTER THE
LIGHT RAIN BEGINS. WIDESPREAD RAIN AND FOG WILL MAKE FOR POOR
FLYING CONDITIONS OVERNIGHT AS LOW PRESSURE PASSES INTO THE REGION
CAUSING CEILINGS TO LOWER TO IFR/LIFR WITH PREVAILING MVFR/IFR
VSBYS INTO SUNDAY MORNING.

EXPECTING POOR FLYING CONDITIONS INTO AT LEAST MIDDAY SUNDAY AS THE
LOW TRACKS ACROSS OR JUST SOUTH OF THE REGION. DRIER AIR BEGINS
TO MOVE INTO THE AREA BY LATE SUNDAY WITH IMPROVING CONDITIONS
FROM NORTH TO SOUTH DURING THE AFTERNOON. MVFR OR LOWER CLOUDS MAY
GET TRAPPED UNDER A WEDGE OF HIGH PRESSURE INTO MONDAY MORNING
WITH YET ANOTHER UPPER DISTURBANCE BRINGING ADDED MVFR CIGS IN
SPOTS INTO MONDAY AFTERNOON. APPEARS IMPROVEMENT TO VFR POSSIBLE
UNDER WEAK HIGH PRESSURE TUESDAY BEFORE ANOTHER WAVE BRINGS MVFR
CIGS BACK TO THE SE WVA SITES ON WEDNESDAY.

&&

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

&&

$$
SYNOPSIS...JH
NEAR TERM...JH/KM
SHORT TERM...NF
LONG TERM...DS
AVIATION...JH/RCS

NWS RNK Office Area Forecast Discussion