000
FXUS61 KRNK 202321
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
621 PM EST FRI NOV 20 2009

.SYNOPSIS...
HIGH PRESSURE WILL BE CENTERED OVERHEAD TONIGHT AND SATURDAY.
LOW PRESSURE DEVELOPING OVER THE NORTHWEST GULF OF MEXICO WILL
MOVE SLOWLY ACROSS THE DEEP SOUTH OVER THE WEEKEND. THE LOW
PRESSURE IS EXPECTED TO REACH THE NORTH CAROLINA COAST MONDAY
MORNING.

.NEAR TERM /THROUGH SATURDAY/...
1026 MB SFC HIGH CENTERED OVER EASTERN KY WILL DRIFT
EAST...PASSING OVERHEAD TONIGHT AND SATURDAY. THIS SHOULD ENSURE A
DRY FORECAST THROUGH THE FIRST HALF OF THE WEEKEND.

FOR TONIGHT WENT A FEW DEGREES BLO MOS FOR THE T-MINS PER NEAR
PREMIUM RADIATIONAL AFFECTS. SOME FOG STILL POSSIBLE...MAINLY
ALONG THE RIVERS...BUT NOT LOOKING FOR ANYTHING WIDESPREAD.

SATURDAY WILL FEATURE INCREASING HIGH CLOUDS...A PRECURSOR OF MORE
TO COME SATURDAY NIGHT AND SUNDAY AS GULF COAST SYSTEM INCHES
CLOSER. SATURDAYS T-MAX WILL BE DEPENDENT ON OVERALL THICKNESS OF
THE CIRRUS. ATTM THINK CIRRUS WILL BE THIN WITH SUN BLEEDING
THROUGH FOR MOST OF THE DAY...THUS MOS ADVERTISED NUMBERS LOOK
PRETTY GOOD TO ME WITH READINGS CLIMBING INTO THE 50S.

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
SIGNIFICANT PLACEMENT AND TIMING ISSUES EXIST BETWEEN THE MID-RANGE
MODELS IN HANDLING THE EJECTION OF THE SOUTHERN STREAM CLOSED
LOW...WHICH WILL EVENTUALLY LIFT AND FILL AS IT MOVES NORTHEAST OUT
OF THE GULF COAST STATES.

NAM AND GEM SLOWEST OF THE MODELS BY ALLOWING NORTHERN STREAM ENERGY
TO BYPASS BLACKSBURG AREA WELL TO THE NORTH. PASSAGE OF NORTHERN
STREAM TROF AND SUBSEQUENT BUILDING HEIGHTS IN ITS WAKE SUPPORTS
AMPLIFICATION OF NEW ENGLAND SURFACE HIGH PRESSURE WHICH WEDGES
SOUTHWEST INTO MID ATLANTIC REGION...AND RETARDS NORTHEASTWARD PUSH
OF SOUTHERN STREAM ENERGY AND ADVANCE OF DEEPER MOISTURE PROFILES.
LATEST RUN OF GFS AND PREVIOUS RUN OF ECMWF A LITTLE MORE
PROGRESSIVE WITH ADVANCE OF SOUTHERN STREAM ENERGY...BUT PERHAPS A
BIT SLOWER THAN EARLIER RUNS.

FINAL PLACEMENT AND TIMING OF THIS SYSTEM WILL HAVE A HUGE IMPACT ON
TEMPERATURES AND THREAT OF PRECIPITATION DURING THE MID RANGE
PERIOD. CONSIDERING THE EXTENT OF SURFACE RIDGING EXPECTED TO OCCUR
SOUTHWEST INTO THE MID ATLANTIC REGION IN THE WAKE OF NORTHERN
STREAM SHORT WAVE...EXPECT TO SEE AMPLE MID AND HIGH LEVEL CLOUD
CANOPY ON SATURDAY NIGHT...BUT WITH ATMOSPHERE BELOW 600 MILLIBARS
REMAINING QUITE DRY...NORTHERN EDGE OF PRECIPITATION SHIELD IN
ADVANCE OF SOUTHERN STREAM WAVE WILL LIKELY BE HARD PRESSED TO REACH
THE SURFACE WITH THE EXCEPTION OF THE EXTREME SOUTHWESTERN MOUNTAINS
BY LATE AT NIGHT. AN EARLY DROP OF TEMPERATURE IS EXPECTED DUE TO
RADIATIVE COOLING...ESPECIALLY ACROSS THE NORTHERN PORTION OF THE
FORECAST AREA WHERE CLOUD COVER WILL BE INITIALLY QUITE THIN...TO BE
FOLLOWED BY A FLATTER FALL AS CLOUDS LOWER AND THICKEN. EXCEPTION
WILL BE ACROSS THE EXTREME SOUTHERN AREAS...WHERE THICKER CLOUD
COVER WILL PREVENT RAPID INITIAL DROP IN TEMPERATURE...WITH
REDUCTION OCCURRING LATE AT NIGHT IF PRECIPITATION ARRIVES AND
DRIVES TEMPERATURES TOWARD WET BULB VALUES.

TENACIOUS SURFACE WEDGE WILL LIKELY HOLD OVER THE BLACKSBURG
FORECAST AREA THROUGHOUT SUNDAY...AND WILL LIKELY STRENGTHEN AS THE
DAY PROGRESSES AS WEAK UPSLOPING AND EVAPORATIVE COOLING DUE TO
PRECIPITATION BEGINS OVER AT LEAST PORTIONS OF THE FORECAST AREA.
WITH STRONG WEDGE IN PLACE...BEST BAROCLINIC ZONE AND ISENTROPIC
LIFT WILL REMAIN SOUTH AND EAST OF THE BLACKSBURG AREA...ALTHOUGH
UPPER DIFFLUENCE RESULTING FROM RIGHT ENTRANCE REGION OF NORTHERN
STREAM AND LEFT EXIT REGION OF SOUTHERN STREAM WILL BE IN/NEAR THE
BLACKSBURG AREA OF CONCERN.

ABUNDANT CLOUD COVER...NORTHEASTERLY SURFACE SLOW...AND INCREASING
THREAT OF PRECIPITATION SHOULD HOLD TEMPERATURES DOWN TO BELOW THAT
FORECASTED BY MOS GUIDANCE...AND THIS ALREADY WELL DEPICTED IN
CURRENT SET OF GRIDS. WITH DEEPEST MOISTURE AND BEST UPWARD VERTICAL
MOTION FIELDS THOUGH INCREASINGLY SATURATED COLUMN OF ATMOSPHERE
DISPLACED TO THE SOUTH AND EAST...WILL CONTINUE TO RUN HIGHEST
THREAT OF PRECIPITATION ACROSS SOUTHERN AND EASTERN ZONES...
TRENDING DOWNWARDS FURTHER NORTHWEST TOWARD OUR WV COUNTIES.

SOUTHERN STREAM ENERGY AND RESULTING DEVELOPMENT OF COASTAL LOW
PRESSURE SHOULD LIFT NORTHEAST OF THE BLACKSBURG FORECAST AREA
SUNDAY NIGHT INTO MONDAY...TO BE FOLLOWED BY SLOWLY CLEARING SKIES
FROM THE SOUTHWEST MONDAY AFTERNOON INTO MONDAY NIGHT AS WEAK HIGH
PRESSURE BEGINS TO BUILD IN FROM THE WEST.

AS WOULD BE EXPECTED UNDER A STRONG WEDGE SITUATION...MOS GUIDANCE
LIKELY TOO WARM BY DAY AND CLOSE TO OR A BIT COOL BY NIGHT
CONSIDERING THE VERY COMPRESSED DIURNAL TEMPERATURE CURVE THAT WILL
BE REALIZED THROUGH THIS PERIOD.

.LONG TERM /TUESDAY THROUGH FRIDAY/...
ECMWF INDICATES UPPER LEVEL RIDGING APPROACHING THE AREA TUESDAY
AFTERNOON INTO EARLY WEDNESDAY MORNING...WHILE THE SURFACE WEDGE
HANGS ON THROUGH THE END OF THE WEEK. IT ALSO SUGGESTS A SURFACE AND
UPPER LOW PRESSURE SYSTEM DEVELOPING OVER THE MIDWEST AND PUSHING
TOWARD THE AREA BY MID TO LATE WEEK. HAVE AT LEAST CHANCE TO SLIGHT
CHANCE OF POPS ACROSS THE COUNTY WARNING AREA THROUGH THE EXTENDED
PERIOD. WITH THICKNESSES 1000-850MB AND 850-700MB THICKNESSES
LOWERING BY MID WEEK...THERE COULD BE SOME LIGHT SNOW MIXED WITH
RAIN IN THE HIGHER ELEVATIONS OF SOUTHEAST WEST VIRGINIA. IN THESE
SAME AREAS MAINLY ALONG THE RIDGES...SURFACE LOW TEMPERATURES COULD
ALSO REACH FREEZING OR A FEW DEGREES BELOW.

GFS HAS BEEN HAVING A HARD TIME WITH RUN TO RUN CONSISTENCY IN THE
EXTENDED. IT HAS BEEN FASTER AND MORE PROGRESSIVE WITH PUSHING THE
SYSTEMS THROUGH THE FORECAST AREA. DUE TO THIS HAVE LEANED MORE
TOWARD THE ECMWF AS IT SEEMS TO BE A BIT MORE CONSISTENT IN EACH RUN
THE PAST FEW DAYS.

.AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH SATURDAY. LATE
NIGHT FOG FORMATION IS POSSIBLE IN THE RIVER VALLEYS. HAVE KEPT
LIFR FOG IN THE LWB TAF SINCE FOG OFF THE RIVER WILL DRIFT INTO
THE AIRPORT. OTHERWISE VFR CONDITIONS AREA EXPECTED THROUGH
SATURDAY NIGHT.

THE NEXT THREAT OF WIDESPREAD IFR/MVFR CONDITIONS WILL BE
ENCOUNTERED SUNDAY INTO MONDAY AS A SLOW MOVING AREA OF LOW
PRESSURE MOVES NORTHEAST FROM THE GULF OF MEXICO. CLOUD BASES
SATURDAY AND SATURDAY NIGHT SHOULD REMAIN ABOVE 10KFT.
SUNDAY...CLOUD BASES WILL LOWER WITH CIGS FALLING BLO 3KFT SUNDAY
AFTERNOON AND INTO SUNDAY NIGHT. A 12-24 HOUR PERIOD OF -RA OR
DRIZZLE WILL ACCOMPANY THE IFR/MVFR CIGS...AND VSBYS MAY OBSCURE
THE MTN RIDGES.

TUESDAY WILL FEATURE IMPROVING CONDITIONS AS THE SFC LOW TRACKS
NORTHEAST UP THE EASTERN SEABOARD WITH HIGH PRESSURE BUILDING OVER
THE MID ATLANTIC FOR MID WEEK.

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

SYNOPSIS...PM
NEAR TERM...PM
SHORT TERM...WERT
LONG TERM...REB
AVIATION...AMS/PM