FXUS61 KRNK 261412
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
912 AM EST THU NOV 26 2009
.SYNOPSIS...
A STRONG COLD FRONT WILL PASS THROUGH THE APPALACHIANS THIS
EVENING...BRINGING MUCH COLDER AIR ALONG WITH GUSTY WINDS AND
MOUNTAIN SNOW SHOWERS INTO FRIDAY NIGHT. HIGH PRESSURE WILL BUILD
EAST ACROSS THE SOUTHEAST STATES DURING THE WEEKEND ALLOWING FOR A
MODERATION IN TEMPERATURES THROUGH SUNDAY. THE NEXT FRONTAL SYSTEM
BRINGING THE NEXT CHANCE FOR RAIN WILL APPROACH FROM THE WEST
EARLY MONDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
ISSUED A QUICK UPDATE TO ALLOW FOG ADVISORY TO EXPIRE AT 9 AM.
DENSE FOG IS DISSIPATING AS WIND SPEED AND MIX INCREASES THIS
MORNING. VISIBILITY HAS BEEN INCREASING IN MOST LOCATIONS...AS SEEN
IN SFC OBS. THE ONLY EXCEPT IS IN THE SOUTHEAST CORNER OF CWA
WHERE THICKER FOG MAY LINGER A LITTLE LONGER. ADJUSTED CLOUD COVER
AND POPS FOR CURRENT TRENDS IN OBS AND MODELS.
.PREVIOUS DISCUSSION...
AREAS OF DENSE FOG CONTINUE TO COVER MUCH OF THE FCST AREA EAST OF
THE BLUE RIDGE AS UPPER CLOUDS HAVE MOVED EAST ALLOWING FOR RAPID
COOLING DOWN TO DEW PTS. SO FAR ONLY PATCHY FOG IN MTN VALLEYS AND
FAIRLY LIGHT. MAINTAINING DENSE FOG ADV THROUGH 9AM EAST OF BLUE RIDGE.
OTHERWISE STRONG LOW PRESSURE SYSTEM SPINNING ACROSS SOUTHERN GREAT
LAKES AND WITH STRONG JET ON BACK SIDE GETTING READY TO DIG TOWARD
APPALACHIANS DURING THE DAY TODAY. LATEST GUIDANCE JUST A BIT SLOWER
WITH TIMING OF WHEN SURGE OF COLDER AIR AND STRONGER WINDS
ARRIVE...AS WELL AS DEEPER MSTR AND BEGINNING OF SNOW SHWR ACTIVITY.
00Z AND NOW 06Z NAM DONT START UPSLOPE PRECIP UNTIL AFTER 06Z LATE
TONIGHT NOW...WITH GFS STILL SOMETIME AFTER 00Z. LOCAL WRF JUST
AFTER 03Z. SLOWED DOWN TIMING SEVERAL HOURS...BUT NOT AS SLOW AS
NAM...YET. ACCUMULATING SNOW AFTER MIDNIGHT...AND BEST WINDOW
PROBABLY 09Z THROUGH 15Z FRIDAY. NO CHANGES IN THINKING AS FAR AS
OVERALL AMOUNTS...WITH VERY SHALLOW MSTR AND NO TRAJECTORIES OVER
GREAT LAKES FOR NW NC MTNS...SO ONLY AN INCH OR SO IN HIGHEST
ELEVATIONS THERE...WITH BETTER TRAJECTORIES AND DEEPER MSTR FROM
FLAT TOP NORTHWARD INTO NW GREENBRIER CO WV. LOOKING AT 4-5 INCHES
HIGHEST ELEVATIONS AND WEST FACING SLOPES. THUS...HAVE GONE WITH
WINTER WX ADV FOR SNOW ABOVE 3000 FT...AND WILL MENTION SOME BLOWING
SNOW AS WELL AS WINDS PICK UP OVERNIGHT.
MODELS CONTINUE TO SHOW SOME LEE SIDE DEVELOPMENT BY THIS EVENING
ACROSS THE PIEDMONT WITH LIGHT QPF. HAVE MY DOUBTS THAT THIS WILL
BE FAR ENOUGH WEST TO IMPACT THE RNK FCST AREA AS MODELS
SUGGEST...BUT FOR NOW WILL MAINT A LOW CHC POP FOR A WHILE THIS
EVENING BEFORE MOVING IT EAST.
WINDS ALSO LOOKING A BIT STRONGER IN LATEST NAM GUIDANCE...WITH
SURGE RIGHT WITH FRONT LATE THIS EVENING...AND PERHAPS ANOTHER SURGE
LATER FRIDAY. 800MB WINDS AROUND 50 KTS AFTER MIDNIGHT OVER NW NC
MTNS WITH GOOD MTN TOP INVERSION AND SUBSIDENCE. MAY EVEN NEED TO
WATCH WARNING CRITERIA CLOSELY. FOR NOW...AHVE GONE WITH WIND ADV
FROM MIDNIGHT THROUGH FRIDAY...AND MAY NEED TO EXTEND THIS OR
UPGRADE INTO FRI NIGHT AND FOR LARGER AREA AS DEEPENING COASTAL LOW
HELPS TO STRENGTHEN GRADIENT.
AS FAR AS TEMPS...BUMPED UP A LITTLE TODAY MAINLY FROM NEW RIVER
VALLEY EASTWARD WITH PLENTY OF SUNSHINE FOR AT LEAST FIRST HAVE OF
THE DAY. CLOSER TO WARMER MET GUIDANCE THERE. OTHERWISE CLOSE TO
COOLER MAV GUIDANCE ON FAR WEST WITH MORE CLOUD COVER. RAISED
TEMPS A FEW DEG FOR OVERNIGHT LOWS PER SLOWER TIMING TO SURGE OF
COLDEST AIR.
&&
.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
SURFACE HIGH PRESSURE ENTERS THE AREA FROM THE SOUTHWEST WITH WINDS
OUT OF THE WEST NORTHWEST THROUGH FRIDAY NIGHT. THIS FLOW REGIME
WILL SLOWLY CUT OFF UPSLOPE MOISTURE BUT STRONG NW FLOW SUGGESTS ANY
MOISTURE WILL LIKELY KEEP AT LEAST FLURRIES GOING NW UNTIL ABOUT DAYBREAK
SAT. WILL SEE MORE BACKING DEVELOP ALOFT SAT AS HIGH PRES RIDGES BY
TO THE SOUTH IN A MORE ZONAL FLOW REGIME WHICH SUPPORTS MAINLY SUNNY
SKIES AND MODERATING TEMPS.
A POTENT LOW LEVEL JET WILL REMAIN OVER THE NORTH CAROLINA HIGH
COUNTRY THROUGH LATE FRIDAY EVENING DUE TO THE TIGHT GRADIENT THAT
EXISTS BETWEEN THE LOW PRESSURE SYSTEM MOVING OFF TO THE NORTHEAST
AND THE HIGH PRESSURE BUILDING IN FROM THE SOUTHWEST. THESE WINDS
LOOK TO SUBSIDE TO BELOW WIND ADVISORY CRITERIA IN THE OVERNIGHT
HOURS.
TEMPERATURES WILL BE COLDER ACROSS THE REGION FRIDAY UNDER THE COLD
POOL...LOW THICKNESS AND CLOUDS WEST. BUFKIT SOUNDINGS SUPPORT
TEMPERATURES BELOW FREEZING FOR BLUEFIELD AND LEWISBURG DURING THE
DAY FRIDAY. EXPECT SOME AREAS IN THE HIGHER ELEVATIONS TO STRUGGLE
TO BREAK FREEZING WITH STRONG COLD AIR ADVECTION LASTING THROUGH
FRIDAY NIGHT. THESE WILL BE THE AREAS WHERE MORE PERSISTENT SNOW
SHOWERS WILL BE ONGOING. ACROSS THE REST OF THE COUNTY WARNING AREA
TEMPERATURES WILL RANGE FROM ARND 50 SE TO LOW 30S NW. MUCH COLDER
UNDER CLEARING SKIES FRIDAY NIGHT BUT WONT BOTTOM OUT AS STRONG
GRADIENT REMAINS IN PLACE. COLD AIR QUICKLY EXITS SAT WITH A 10-15C
TEMP JUMP AT 85H BETWEEN FRIDAY NIGHT AND SAT AFTERNOON. THIS IN
COMBO WITH WESTERLY FLOW...HEATING AND DRY AIR SUPPORTS HIGHS
JUMPING BACK WELL INTO THE 50S EAST AND 45-52 WEST.
HIGH PRESSURE WILL CONTINUE THROUGH SUNDAY. MAINTAINED A DRY
FORECAST WITH TEMPERATURES BECOMING MILDER.
&&
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
THE EXTENDED PORTION OF THE FORECAST CONTINUES TO BE ONE OF A
PROGRESSIVE PATTERN WITH SYSTEMS IN BOTH THE NORTHERN AND SOUTHERN
JET TRACKS IMPACTING THE AREA. THE CHALLENGE CONTINUES TO BE NOTABLE
DIFFERENCES WITHIN THE VARIOUS MODEL GUIDANCE AS TO PATH AND TIMING
OF EACH OF THESE SYSTEMS.
WHILE DIFFERENCES EXIST...THE GENERAL TREND FOR MONDAY THROUGH
WEDNESDAY IS FOR FIRST A NORTHERN STREAM TROUGH AND ASSOCIATED COLD
FRONT TO MOVE INTO AND THROUGH THE REGION MONDAY INTO MONDAY NIGHT.
LITTLE OR NO TIME EXISTS AFTER THE PASSAGE OF THIS SYSTEM BEFORE A
SOUTHERN STREAM SYSTEM TRACKS NORTHEAST EITHER THROUGH THE AREA OR
JUST TO OUR WEST OVER THE OHIO VALLEY TUESDAY NIGHT INTO WEDNESDAY.
THE FIRST SYSTEM WOULD PROVIDE MORE OF QUICK MOVING CLIPPER TYPE
SYSTEM...WITH THE SECOND HAVING A GREATER CHANCE OF PROVING A MORE
WIDESPREAD COVERAGE OF PRECIPITATION AHEAD OF THE MAIN SYSTEM.
HAVE FOLLOWED CLOSELY TO THE HPC GUIDANCE GRIDS WITH ADJUSTMENTS TO
BETTER COLLABORATE WITH NEIGHBORING OFFICES WHERE NOTABLE
DIFFERENCES EXISTED.
&&
.AVIATION /14Z THURSDAY THROUGH MONDAY/...
LIFR FOG TO HOLD ON IN THE PIEDMONT FOR AN HOUR OR TWO AFTER
SUNRISE...THEN LIFTING TO VFR BY 14-15Z. ALSO ISOLATED FOG NOW IN
GREENBRIER VALLEY AS MVFR STRATUS DECK TO THE WEST IS ERODING FROM
EASTERN EDGE. THIS SHOULD ALLOW IFR CONDITIONS AT LWB TO ALSO LIFT
TO VFR WITHIN A COUPLE HOURS AFTER SUNRISE. A STRONG COLD FRONT
WILL CROSS THROUGH THE FORECAST AREA BY THIS EVENING. WINDS ARE
ALREADY WEST TO SOUTHWEST SO ONYL SUBTLE SHIFT IN WIND DIRECTION
TO MORE WEST OR WEST NORTHWEST...BUT SPEEDS WILL BEGIN TO INCREASE
AFTER 00Z AND GUST TO 20-25 KTS FOR ROA AND BLF
ESPECIALLY...SOMEWHAT LESS FOR TEH OTHER TAFS SITES. MVFR CIGS
EVENTUALLY WILL MOVE IN TO THE WESTERN SITES...PROBABLY AFTER
MIDNIGTH NOW...ALONG WITH SOME SNOW SHWRS MAINLY AT BLF. PERHAPS A
FEW AT LWB AS WELL. AT TIMES...SNOW SHWRS AT BLF COULD REDUCE
VSBYS TO MVFR OR IFR...BUT DID NOT PUT IN TAF SINCE BELIEVE IT WILL BE
MORE LIKELY TO REMAIN VERY LIGHT. PERHAPS BEST CHANCE OF BRIEF IFR
CONDITIONS AND EVEN A LIGHT COATING OF SNOW AT THE BLF AIRPORT
WOULD BE AROUND OR JUST AFTER 12Z FRIDAY. MODELS ARE TRENDING LESS
AGRESSIVE WITH THIS AND A LITTLE SLOWER.
GUSTY WINDS MAY CONTINUE THROUGH FRIDAY NIGHT AS GRADIENT REMAINS
STRONG...BEFORE EVENTUALLY HIGH PRESSURE BUILDS BACK INTO THE
REGION BY SATURDAY AND SUNDAY. THIS WILL END THE UPSLOPE CLOUDS AND
PRECIPITATION AND RETURN BLF BACK TO VFR CONDITIONS. NEXT FRONTAL
SYSTEM WITH A CHANCE OF RAIN AND POSSIBLE IFR CONDITIONS
APPROACHES FROM THE WEST ON MONDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WIND ADVISORY FROM 11 PM THIS EVENING TO 6 PM EST FRIDAY FOR
VAZ015.
NC...WIND ADVISORY FROM 11 PM THIS EVENING TO 6 PM EST FRIDAY FOR
NCZ001-002-018.
WV...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 6 PM EST
FRIDAY FOR WVZ045.
&&
$$
SYNOPSIS...JH/SK
NEAR TERM...KK/SK
SHORT TERM...JH/REB
LONG TERM...DS
AVIATION...SK
