FXUS61 KRNK 221142
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
642 AM EST TUE DEC 22 2009
.SYNOPSIS...
A SURFACE RIDGE OF HIGH PRESSURE EXTENDING FROM THE UPPER GREAT
LAKES SOUTHEAST INTO THE MID ATLANTIC REGION WILL REMAIN NEARLY
STATIONARY THROUGH THURSDAY. LOW PRESSURE WILL THEN MOVE EAST INTO
THE MID ATLANTIC STATES THURSDAY NIGHT...BRINGING ANOTHER ROUND OF
WINTRY PRECIPITATION THAT SHOULD CHANGE TO RAIN ON CHRISTMAS DAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS HAS BEEN THE CASE FOR THE PAST COUPLE OF DAYS...UPSLOPE FLOW AND
ABUNDANT LOW LEVEL MOISTURE TRAPPED BENEATH INVERSION LAYER HAS
RESULTED IN TENACIOUS CLOUD COVER...MAINLY ALONG AND WEST OF THE
FOOTHILLS AND BLUE RIDGE. THESE CLOUDS...COMBINING WITH CONTINUED
LIGHT MIXING...DEEP SNOW PACK...AND LOW SUN ANGLE...HAVE SEVERELY
COMPRESSED DIURNAL TEMPERATURE CURVE...WITH ONLY A FEW DEGREE
DEPARTURE FROM DAY TO NIGHT BEING REALIZED ACROSS THE MOUNTAINS. AS
A RESULT...MOS GUIDANCE HAS CONSISTENTLY BEEN TOO COLD FOR NIGHTTIME
TEMPERATURES SINCE NO NOTABLE RADIATIVE COOLING HAS OCCURRED DESPITE
SNOW PACK.
EAST OF THE BLUE RIDGE...DOWNSLOPING HAS BEEN SUFFICIENT TO LIMIT
EASTWARD EXTENSION OF CLOUD CANOPY...SO DIURNAL TEMPERATURE CURVE
HAS BEEN MUCH MORE PRONOUNCED...ALTHOUGH NIGHTTIME LOWS AND DAYTIME
HIGHS HAVE ALSO BEEN A BIT ABOVE MOS GUIDANCE.
LITTLE CHANGE IN WEATHER IS EXPECTED IN THE NEAR TERM PERIOD.
CONTINUED WEAK UPSLOPING SHOULD MAINTAIN AT LEAST BROKEN CEILINGS
WEST OF THE BLUE RIDGE TODAY...AGAIN INHIBITING EXTENT OF DAYTIME
HEATING...ALTHOUGH HIGHS SHOULD FINALLY EXCEED FREEZING IN MOST
AREAS AS WEAK WARM ADVECTION IN ADVANCE OF NEXT SHORT WAVE ALLOWS
LOWER ATMOSPHERE TO WARM SEVERAL DEGREES C. EAST OF THE BLUE
RIDGE...BETTER INSOLATION SHOULD AGAIN ALLOW TEMPERATURES TO REACH
OR EXCEED 40F...ESPECIALLY ACROSS SOUTHSIDE VIRGINIA INTO NORTH
CENTRAL NORTH CAROLINA.
TEMPERATURE FORECAST ACROSS THE NORTHEASTERN PORTION OF THE
BLACKSBURG FORECAST AREA WILL BE A BIT MORE PROBLEMATIC. LATEST
SATELLITE PICTURES SHOW SHORT WAVE TROF MOVING EAST INTO THE OHIO
VALLEY...AND ISENTROPIC LIFT AND ASSOCIATED MID LEVEL CLOUDS IN
ADVANCE OF THIS FEATURE WILL IMPACT AT LEAST NORTHERN AREAS THIS
AFTERNOON. ANY REDUCTION OF INSOLATION WILL AGAIN INHIBIT AMOUNT OF
DAYTIME WARMING...SO TEMPERATURES NOT LIKELY TO EXCEED THE MID OR
UPPER 30S NORTH OF HIGHWAY 460.
FOLLOWING PASSAGE OF THIS WAVE TONIGHT...SKIES ACROSS THE NORTHEAST
WILL GRADUALLY CLEAR...SUPPORTING THE POSSIBILITY OF A GOOD
RADIATIVE EVENT. HOWEVER...CLOUDS SHOULD LINGER OVER THE
MOUNTAINS...AND MAY EVEN BEGIN TO DEVELOP ALONG THE FOOTHILLS OF
SOUTHWESTERN VIRGINIA INTO NORTHWESTERN NORTH CAROLINA AS SURFACE
WINDS BECOME UPSLOPE FROM THE EAST OR SOUTHEAST. AS A RESULT...
COLDEST TEMPERATURES OF UPPER TEENS TO LOWER 20S TONIGHT WILL LIKELY
BE NORTH AND EAST OF LYNCHBURG...WITH TEMPERATURES HOLDING TO MID OR
UPPER 20S FURTHER SOUTHWEST AND WEST UNDER CLOUD CANOPY.
&&
.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
WEDNESDAY WE WILL CONTINUE WITH A DRY FORECAST AS HIGH PRESSURE
BUILDS INTO THE REGION. WILL FAVOR TEMPERATURES BELOW GUIDANCE AS
EXPECT THERE TO STILL BE A GOOD COVERAGE OF SNOW ACROSS THE
AREA...ESPECIALLY OVER THE MOUNTAINS.
FORECAST CHALLENGE CONTINUES TO BE TIMING OF THE CHRISTMAS EVE AND
CHRISTMAS DAY FORECAST. GUIDANCE CONTINUES TO TREND SLOWER WITH THE
ONSET OF PRECIPITATION. THIS WILL ALSO MEAN A BETTER OPPORTUNITY FOR
TEMPERATURES TO BE MILDER A THE ONSET. FOR THE LATEST FORECAST
HAVE REMOVED PRECIPITATION ALMOST COMPLETELY DURING THE DAY ON
THURSDAY...SAVE A SLIGHT CHANCE IN THE FAR SOUTHWEST. HAVE ALSO
GONE A LITTLE MILDER WITH THE DAYTIME HIGH.
THURSDAY NIGHT...STILL EXPECTING A DECENT WARM NOSE TO YIELD
PRECIPITATION OF EITHER RAIN OR FREEZING RAIN...AND PERHAPS A
LITTLE SLEET. HAVE CONTINUED WITH LIKELY TO CATEGORICAL POPS IN
THE WEST...BUT NOW WITH TIMING AFTER MIDNIGHT AND CONTINUING INTO
CHRISTMAS DAY. AS CHRISTMAS DAY PROGRESSES...MILDER AIR ENTERING
THE REGION WILL MEAN A TRANSITION TO ALL RAIN BY THE AFTERNOON.
MAY HAVE TO WATCH FOR THE POTENTIAL OF SOME LOCALIZED FLOODING AS
WELL DURING PERIOD AS THE RAINS MELT THE REMAINING SNOW COVER IN
THE MOUNTAINS. PLUS...THE GROUND ITSELF IS GOING TO BE SOGGY FROM
WHAT SNOW HAS MELTED PRIOR TO THE RAIN.
HEADING INTO FRIDAY NIGHT...AS WE GET ON THE BACKSIDE OF THE
SYSTEM...WE WILL NEED TO WATCH FOR SOME UPSLOPE SNOW SHOWERS IN THE
MOUNTAINS. NOT MUCH WILL REMAIN OF A SATURATED PREFERRED CRYSTAL
GROW LAYER IN THE LOWER LEVELS...BUT FORECAST SOUNDINGS SHOW A
DECENT HIGH LEVEL CANOPY WHICH MAY LEAD TOWARD SOME SEEDER FEEDER
SNOWS.
&&
.LONG TERM /SATURDAY THROUGH MONDAY/...
5H TROF PIVOTING BY TO THE NORTH SHOULD ENHANCE UPSLOPE -SHSN A
BIT SAT INTO SAT NIGHT BUT GIVEN MORE OF A WESTERLY TRAJECTORY
ONLY CHANCE POPS WESTERN THIRD FOR NOW. MORE OF AN OVERALL ZONAL
FLOW WILL TAKE SHAPE LATER IN THE WEEKEND INTO EARLY NEXT WEEK
ALLOWING HIGH PRES TO BUILD IN FROM THE SW BY MONDAY. THUS OTHER
THAN SOME RESIDUAL UPSLOPE FLURRIES EXPECTING A DRY SCENARIO UNDER
MORE SUN FOR DAYS 6/7. TEMPS WILL REMAIN A BIT BELOW NORMAL SAT-
MON SPCLY AT NIGHT BUT NOT TERRIBLY COLD AS THE ARCTIC AIR
BASICALLY REMAINS LOCKED UP TO THE NORTH AT THIS POINT.
&&
.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
MVFR TO LOCALIZED IFR CEILINGS DUE TO UPSLOPING WINDS OVER SOUTHEAST
WEST VIRGINIA TERMINAL FORECAST POINTS WILL GRADUALLY GIVE WAY TO
VFR CONDITIONS BY LATE MORNING AS LOW LEVEL FLOW BACKS AROUND TO
LESS OF AN UPSLOPE COMPONENT IN ADVANCE OF APPROACHING SHORT WAVE
TROF. EAST OF THE BLUE RIDGE...DOWNSLOPING WINDS SHOULD HELP KEEP
FLIGHT CATEGORIES IN VFR RANGE THROUGHOUT THE DAY.
HIGH PRESSURE WILL BUILD SOUTHEAST INTO THE REGION TONIGHT INTO
WEDNESDAY FOLLOWING PASSAGE OF SHORT WAVE TROF. THIS SYSTEM WILL
INITIALLY SUPPORT VFR CONDITIONS AT ALL TERMINAL FORECAST POINTS.
HOWEVER...EXPECT SOME RETURN TO MVFR OR EVEN IFR RESTRICTIONS
TOWARD DAYBREAK WEDNESDAY DUE TO DEVELOPMENT OF PATCHY FOG GIVEN
SNOW ON GROUND AND SOME INCREASE IN TEMPERATURES AND MOISTURE
ALOFT. BEST THREAT FOR PATCHY FOG WILL BE IN NORMALLY FAVORED
MOUNTAIN VALLEYS AND NEAR WATERWAYS (SUCH AS/NEAR KLWB).
AS SURFACE RIDGE BUILDS FURTHER SOUTHEAST INTO AREA ON WEDNESDAY...MAY
SEE EXPANSION OF MVFR CEILINGS INTO SOUTHWESTERN VIRGINIA AND NORTHWESTERN
NORTH CAROLINA AS SURFACE WINDS EAST OF THE BLUE RIDGE TURN INTO
EASTERLY-SOUTHEASTERLY UPSLOPE COMPONENT.
AN APPROACHING STORM SYSTEM WILL LIKELY BRING ANOTHER LENGTHY PERIOD
OF WIDESPREAD IFR TO LIFR WEATHER THURSDAY NIGHT INTO CHRISTMAS
DAY...WITH FREEZING RAIN AND/OR RAIN THE MOST PROBABLE PRECIPITATION
THREAT. ARRIVAL OF STRONG COLD WESTERLY WINDS ON THE BACKSIDE OF
THIS SYSTEM SHOULD ALLOW FOR RETURN TO VFR WEATHER EAST OF THE
BLUE RIDGE FRIDAY INTO SATURDAY...BUT WITH TYPICAL MVFR TO LOCALIZED
IFR RESTRICTIONS CONTINUING IN UPSLOPE AREAS WEST OF THE BLUE
RIDGE (KBLF/KLWB) DUE TO SCATTERED SNOW SHOWER/FLURRY ACTIVITY.
&&
.HYDROLOGY...
WILL BE MONITORING POTENTIAL OF LOCALIZED FLOODING FOR CHRISTMAS
DAY AS NEXT WEATHER SYSTEM AND ASSOCIATED RAINS COMBINE WITH
MELTING SNOW PACK TO PRODUCE NOTABLE RUNOFF.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.
&&
$$
SYNOPSIS...WERT
NEAR TERM...WERT
SHORT TERM...DS
LONG TERM...JH
AVIATION...WERT
HYDROLOGY...DS
