FXUS61 KRNK 232334
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
634 PM EST WED DEC 23 2009
.SYNOPSIS...
HIGH PRESSURE ACROSS THE GREAT LAKES WILL DRIFT SLOWLY EAST AND
GRADUALLY WEDGE SOUTH ALONG THE BLUE RIDGE TONIGHT INTO THURSDAY.
STRONG LOW PRESSURE WILL PASS WELL TO THE WEST THURSDAY NIGHT AND
FRIDAY...PUSHING A COLD FRONT EAST ACROSS THE REGION FRIDAY NIGHT
INTO EARLY SATURDAY.
&&
.NEAR TERM /THROUGH THURSDAY/...
AXIS OF SURFACE HIGH PRESSURE REMAINS JUST EAST OF THE FORECAST
AREA. HEIGHTS AT 500 MB RISE TONIGHT IN THE EAST AS PATTERN BECOMES
MORE AMPLIFIED. BY THE END OF THE NIGHT SURFACE WINDS IN THE
MOUNTAINS WILL COME AROUND TO THE SOUTHEAST. THIS MAY KEEP THE
RIDGES SLIGHTLY MIXED LATE TONIGHT BUT THERE WILL STILL BE PLENTY OF
TIME FOR RADIATIONAL COOLING OVERNIGHT. EXPECT ONLY SCATTERED TO
BROKEN HIGH CLOUDS THROUGH THURSDAY MORNING. CLOUDS WILL FILL IN
DURING THE AFTERNOON. WILL TAKE A BLEND OF MET/MAV GUIDANCE FOR LOWS
TONIGHT WITH COOLER TEMPERATURES IN THE VALLEYS. FOR HIGH
TEMPERATURES ON THURSDAY WILL STAY CLOSER TO THE WARMER MAV NUMBERS.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
STRONG HIGH PRESSURE WILL BE WEDGED DOWN THE EAST COAST BEGINNING
THU NIGHT. MEANWHILE...THE UPPER LOW OVER NM WILL BE LIFTING NEWD
THRU THE LOWER MISS VALLEY IN RESPONSE TO THE KICKER UPPER
DROPPING SOUTHEASTWARD INTO MT. A STRENGTHENING SOUTHEAST LOW
LEVEL JET DEVELOPS OVER THE REGION AHEAD OF THE UPPER LOW LIFTING
THRU THE MISS VALLEY. LOOKS LIKE THIS WILL TRANSPORT VERY MOIST AIR
INTO THE AREA LATE THU NIGHT AND FRIDAY. BOTH THE GFS AND NAM SHOW
PWATS OF >1.00 MOVING INTO THE SERN CWA. THIS STRONG MOISTURE
TRANSPORT SHOULD PRODUCE A WIDESPREAD AREA OF RAIN OVER THE CAD
WEDGE IN PLACE. ALTHOUGH THE TEMPS ALOFT WARM RAPIDLY AND SUPPORT
JUST LIQUID PRECIP...WITH THE EXCEPTION OF THE POSSIBILITY OF SOME
SLEET AT THE ONSET...THE BOUNDARY LAYER WILL REMAIN COLD ENOUGH
FOR FREEZING RAIN ALONG AND EITHER SIDE OF THE BLUE RIDGE. WITH
THE STRONG HIGH PRESSURE KEEPING EAST TO NORTHEAST LOW LEVEL
WINDS...THIS UPSLOPE FLOW WILL REINFORCE THE SUB-FREEZING TEMPS
ALONG THE BLUE RIDGE. THINK MODELS ARE BRINGING TEMPS ABOVE
FREEZING TOO QUICKLY. FOR THIS REASON...I HAVE KEPT FREEZING RAIN
IN THRU NOON IN NW NC...AND THRU MUCH OF THE DAY IN SW VA NEAR THE
BLUE RIDGE...AND EASTERN SLOPES AREAS OF SE WV. THIS EXTENDED
PERIOD OF FREEZING RAIN SUPPORTS A WINTER STORM WATCH FOR THE
THREAT OF A QUARTER OF AN INCH OR MORE OF ICING. HEAVIEST ICING OF
NEAR HALF AN INCH WOULD OCCUR ALONG THE EAST SIDE OF THE CREST OF
THE BLUE RIDGE.
IN ADDITION TO THE THREAT OF HEAVY ICING...THE STRONG SOUTHEAST
JET WILL LIKELY BRING SOME VERY STRONG WIND GUSTS THU NIGHT INTO
FRI MORNING FROM MTN WAVE ACTION TO AREAS ON THE NW SIDE OF THE
HIGHER RIDGES IN SW VA/SE WV. THIS TYPICALLY AFFECTS
SMYTH...TAZEWELL AND BLAND COS IN VA...AND MERCER IN WV. WILL
ISSUE A HIGH WIND WATCH FOR THOSE LOCATIONS.
WITH A SECONDARY SFC LOW FORMING ALONG THE OCCLUDED FRONT IN NC
TOWARD FRI EVENING...THIS WILL LIKELY HOLD SOME RAIN INTO THE NERN
CWA INTO THE EVENING FRIDAY...BUT SFC TEMPS BY THAT TIME WILL
LIKELY BE ABOVE FREEZING. RAIN SHOULD TAPER OFF TOWARD
MIDNIGHT...WITH SOME RAIN/SNOW SHOWERS POSSIBLE WITH THE FRONTAL
PASSAGE LATE FRIDAY NIGHT IN THE MTNS.
ONE FINAL WEATHER CONCERN IS CENTERED AROUND THE POTENTIAL FOR
FLOODING ON CHRISTMAS DAY IF RAINFALL AND SNOW MELT ARE MAXIMIZED.
THE HEAVIEST PRECIPITATION WILL OCCUR ALONG AND EAST OF THE BLUE
RIDGE...WITH AROUND AN INCH POSSIBLE. HOWEVER...IT WILL BE COLD
ENOUGH THAT THERE WILL BE LITTLE MELTING OF THE SNOW COVER IN THE
CAD AREA. THE MAIN THREAT FOR A COMBO OF MELTING SNOW AND THE 1
INCH OF RAIN IS ACROSS THE NW PIEDMONT OF NC AND SOUTHSIDE
VA...WHERE MINOR FLOODING COULD OCCUR. WILL HOLD OFF ON A FLOOD
WATCH FOR NOW SINCE THIS IS THIRD PERIOD- SEE IF THE STORM EVOLVES
AS EXPECTED AND THAT NO COASTAL CONVECTION CUTS OFF THE GOOD
INFLOW OF MOISTURE TO LESSEN RAINFALL AMOUNTS.
THE OLD UPPER LOW REMAIN OVER THE WESTERN GREAT LAKES SATURDAY.
SO...DESPITE THE FRONTAL PASSAGE...TEMPS MAY BE FAIRLY
WARM...ESPECIALLY IN THE EAST. SATURDAY NIGHT...THE UPPER LOW
PROGRESSES EASTWARD...WITH COLD AIR ADVECTION/POSSIBLE SNOW
SHOWERS IN THE MTNS.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
WEAKENING VORTEX OVER UPPER MS VALLEY SUNDAY LIFTS NORTHEAST INTO
NEW ENGLAND MONDAY...WHICH WILL KEEP UPSLOPE SNOW GOING INTO MONDAY
AND MONDAY NIGHT. REINFORCING SURGE OF COLD AIR ARRIVES MONDAY WHICH
WILL ENHANCE UPSLOPE SNOW. AS A RESULT...EXPANDED CHANCE POPS EVEN
INTO THE NW NORTH CAROLINA MTNS. A QUICK LOOK AT THE 12Z ECMWF
BRINGS 40+ KT 850MB WINDS INTO THE REGION MONDAY AND MONDAY
NIGHT...SO INCREASED WIND SPEEDS DURING THIS TIME.
HEIGHTS RISE ON TUESDAY IN ADVANCE OF THE NEXT SOUTHERN PLAINS STORM
SYSTEM...KEEPING DRY CONDITIONS DRY. HOWEVER...WEAK SHORTWAVES IN
SOUTHWEST FLOW IN ADVANCE OF THE SYSTEM ALONG WITH WAA...MAY BRING
PRECIP BACK INTO THE REGION LATE WEDNESDAY OR WEDNESDAY
NIGHT...WITH A BETTER CHANCE BEYOND THE LONG TERM. GFS AND ECMWF
DISAGREE ON THE AMPLITUDE OF THE UPPER AIR PATTERN...WITH THE GFS
KEEPING THE FLOW MORE ZONAL ALLOWING COLDER AIR TO REMAIN IN
PLACE...WHILE THE 12Z ECMWF BUILDS A RIDGE IN ADVANCE OF THE LATE
WEEK SYSTEM RESULTING IN WARMER TEMPERATURES. THEREFORE...KEPT
PRECIP GRIDS AS RAIN AND/OR SNOW. ENSEMBLES SUGGEST A SOLUTION
BETWEEN GFS/ECMWF.
TEMPERATURES WILL BE BELOW AVERAGE THROUGH MONDAY UNDER THE
INFLUENCE OF THE NEW ENGLAND UPPER VORTEX...BUT MODERATING TUESDAY
AND WEDNESDAY. DOWNSLOPING WINDS WILL HELP MITIGATE THE COLD AIR
ADVECTION EAST OF THE BLUE RIDGE.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
FOG WILL FORM AGAIN IN THE WESTERN VALLEYS OVERNIGHT DUE TO OLD
SNOW COVER...AND EXPECTIN DENSE FOG ONCE AGAIN TO IMPACT LWB BY
10Z. OTHERWISE EXPECT VFR CONDITIONS THROUGH THE FORECAST PERIOD
WITH OCCASIONAL SCATTERED TO BROKEN MID/HIGH CLOUDS.
WINDS ARE GOING TO PICK UP OVER SE WV LATE THIS PERIOD OUT OF THE
EAST TO SOUTHEAST WITH GUSTS TO 20 KNOTS EXPECTED BY 00Z FRI IN
BLF.
BEYOND THIS PERIOD...THE APPROACHING STORM SYSTEM WILL
LIKELY BRING ANOTHER LENGTHY PERIOD OF WIDESPREAD IFR TO LIFR
WEATHER THURSDAY NIGHT THROUGH CHRISTMAS DAY...WITH
SLEET...FREEZING RAIN AND/OR RAIN THE MOST PROBABLE PRECIPITATION
THREAT. VERY STRONG SOUTHEAST WINDS ARE POSSIBLE THURSDAY NIGHT
INTO FRIDAY/CHRISTMAS DAY AT BLUEFIELD. GUSTS MAY REACH 50 KNOTS
AROUND 12Z ON FRIDAY. LOW LVL WIND SHEAR MAY ALSO BECOME PROMINENT
EVERYWHERE THU NIGHT INTO CHRISTMAS.
THE ARRIVAL OF STRONG COLD WESTERLY WINDS ON THE BACKSIDE OF THIS
SYSTEM SHOULD ALLOW FOR RETURN TO VFR WEATHER EAST OF THE BLUE
RIDGE SATURDAY INTO SUNDAY...BUT WITH TYPICAL MVFR TO LOCALIZED
IFR RESTRICTIONS CONTINUING IN THE UPSLOPE AREAS WEST OF THE BLUE
RIDGE (KBLF/KLWB) DUE TO STRATOCUMULUS AND SCATTERED SNOW SHOWERS.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH FRIDAY
AFTERNOON FOR VAZ011-013-014-017>020-022>024-032>035.
HIGH WIND WATCH FROM THURSDAY EVENING THROUGH FRIDAY MORNING
FOR VAZ007-009-010.
WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
MORNING FOR VAZ012-015-016.
NC...WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
MORNING FOR NCZ001>003-018-019.
WV...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH FRIDAY
AFTERNOON FOR WVZ044-045.
HIGH WIND WATCH FROM THURSDAY EVENING THROUGH FRIDAY MORNING
FOR WVZ042.
&&
$$
SYNOPSIS...JJ
NEAR TERM...AMS
SHORT TERM...JJ
LONG TERM...PH
AVIATION...AMS/WP
