FXUS61 KRNK 260247
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
947 PM EST WED NOV 25 2009

.SYNOPSIS...
A WEAK COLD FRONT WILL SLIDE EAST THROUGH THE AREA TONIGHT BEFORE
DISSIPATING. ANOTHER STRONGER COLD FRONT WILL PASS ACROSS THE
APPALACHIANS THURSDAY AFTERNOON 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.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
CIRRUS SHIELD OVER THE AREA AT 03Z IS FORECAST TO MOVE EAST BY
MORNING. LOWER CLOUDS AHEAD OF THE APPROACHING COLD FRONT WILL
ONLY MOVE INTO THE WESTERN COUNTIES AFTER 06Z. SO ENOUGH CLEARING
FOR FOG FORMATION IN THE WESTERN VALLEYS AND EAST OF THE BLUE
RIDGE. HAVE ALSO ADDED PATCHY DENSE FOG IN THE PIEDMONT WHERE
TEMPERATURE DEW POINT SPREAD IS ALREADY AT OR NEAR ZERO. IN THE
WEST ON THE RIDGES THERE SHOULD BE ENOUGH OF A SOUTHWEST WIND TO
KEEP THE HIGHER ELEVATIONS MIXED AND SLIGHTLY WARMER THAN THE
VALLEYS. 

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY NIGHT/...
STRONG 500MB LOW OVER THE GREAT LAKES WILL SWING SURFACE COLD
FRONT ACROSS THE APPALACHIANS THURSDAY WITH STRONGEST COLD
ADVECTION FILTERING SLOWLY BEHIND IT. USED A BLEND OF SREF AND GFS
FOR POPS THURSDAY. WENT WITH HIGHS FROM THE MID 40S IN THE
NORTHWEST TO THE LOWER 60S IN THE SOUTHEAST.

COLD FRONT SHOULD BE EAST OF THE MOUNTAINS THURSDAY EVENING AS THE 
STRONG UPPER TROF ACROSS THE OHIO VALLEY PIVOTS EASTWARD. MODELS NOW 
DEPICT A BAND OF DEEPER RH GETTING PULLED UP ALONG THE FRONT ACROSS 
PARTS OF THE EAST IN RESPONSE TO STRONG SW FLOW ALOFT AND 
APPROACHING S/W ENERGY. HOWEVER GIVEN MOST LIFT TO THE NORTH THIS 
LOOKS A BIT SPURIOUS/OVERDONE UNTIL THE BOUNDARY MOVES JUST TO THE 
EAST SO ONLY ADDING IN A 30ISH POP PIEDMONT THURSDAY EVENING. MORE 
IMPORTANTLY THE LAGGING 85H FRONT WITH THE TRUE COLD AIR SHOULD 
PUNCH ACROSS THE WEST AFTER SUNSET...WITH THE STRONGEST COLD 
ADVECTION ENSUING ESPCLY AFTER MIDNIGHT INTO FRIDAY MIDDAY BEHIND 
THE 5H TROF/VORT AXIS. CRASHING THICKNESS VALUES SUPPORT A QUICK 
CHANGE TO SNOW WESTERN MOUNTAINS DURING THE EVENING WITH SNOW SHOWER 
COVERAGE EXTENDING OUT TOWARD THE BLUE RIDGE AFTER MIDNIGHT. LATEST 
TRAJECTORIES THO ARE A BIT MORE WESTERLY THAN EARLIER WITH ONLY A 
BRIEF PERIOD OF LAKE SUPERIOR CONNECTION POSSIBLE LATE THU NIGHT 
INTO EARLY FRIDAY. THIS COINCIDES WITH SOMEWHAT DEEPER 
RH/TRANSPORT...STRONGER 85H NW FLOW AND COLDER TEMPS ALOFT LATE THU 
NIGHT THRU MIDDAY FRIDAY MAINLY SE WVA COUNTIES. THUS APPEARS BEST 
ACCUMULATING SNOW AFTER MIDNIGHT INTO FRIDAY MORNING WITH A FEW 
INCHES POSSIBLE ALONG THE WESTERN SLOPES FROM JUST NORTH OF BLF INTO 
FAR WESTERN GREENBRIER CTY. ELSW THINKING AN INCH OR PERHAPS TWO 
NC/TN BORDER ACROSS FAR SW VA GIVEN RATHER WARM GROUND TEMPS AND 
QUICK NATURE OF THE SYSTEM. SINCE HIGHER AMOUNTS IFFY AND BELOW ANY 
WARNING CRITERIA...WILL ADDRESS AGAIN IN THE HWO AND NOT ISSUE ANY 
ADVISORIES GIVEN LATE 3RD/EARLY 4TH PERIOD TIMING. OTRW KEPT POPS 
SIMILAR WITH CAT/LIKELYS FAR NW INTO FRIDAY WHILE TRIMMING THE SW 
ZONES A BIT WHERE UPSLOPE MOISTURE LOOKS RATHER SKIMPY ATTM. 

WINDS WILL ALSO BE AN ISSUE LATE THU NIGHT PER STRONG JET/COLD 
ADVECTION AND THEN ON FRIDAY WITH MIXING ESPCLY EARLY ON. LATEST 
RAOBS SHOW THE INVERSION LOWERING BUT STILL ONLY WEAK PRESSURE RISES 
DESPITE A 45-50 KT 85H JET. HOWEVER WITH SUCH AN ABRUPT TEMP CHANGE 
ALOFT AND SURFACE LOW PRESSURE DEEPENING OFF THE NE COAST APPEARS 
COULD SEE ADVISORY SPEEDS A BIT FARTHER NE ALONG THE BLUE RIDGE TO 
PERHAPS FLOYD OR ROANOKE CTYS. THEREFORE WILL INCLUDE IN THE HWO AS 
WELL AS THE POTENTIAL FOR BLOWING SNOW AT TIMES MAINLY SE WVA WHERE 
SOME ACCUMULATIONS LOOK MORE LIKELY. 

FLOW STARTS TO TURN MORE ANTICYCLONIC LATER FRIDAY INTO FRIDAY NIGHT 
AS HIGH PRES STARTS TO NOSE IN FROM THE SW. THIS SHOULD ACT TO 
SLOWLY CUT OFF UPSLOPE MOISTURE BUT STRONG NW FLOW SUGGESTS ANY RH 
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. 

WENT A BIT WARMER EAST WITH LOW TEMPS THU NIGHT PER LAGGING COLD 
ADVECTION BUT THEN COLDER ACROSS THE REGION FRIDAY UNDER THE COLD 
POOL...LOW THICKNESS AND CLOUDS WEST. EVEN APPEARS THAT SOME SPOTS 
ACROSS THE HIGHER ELEVATIONS WHERE MORE PERSISTENT SNOW SHOWERS ARE 
ONGOING MAY NOT BREAK FREEZING FRIDAY AFTERNOON...OTRW 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.

&&

.LONG TERM /SUNDAY 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.

WHAT IS CONSISTENT AMONG THE GUIDANCE IS SATURDAYS HIGH PRESSURE 
SYSTEM CONTINUING THROUGH SUNDAY...WITH A DRY FORECAST AND 
TEMPERATURES TRENDING MILDER. 

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 /03Z THURSDAY THROUGH MONDAY/...
AS OF 23Z...SKIES HAVE CLEARED ACROSS THE AREA...ALL BUT SOME
DEPARTING CIRRUS IN THE EAST. EXPECT VFR CIGS TO CONTINUE THROUGH
THE EVENING IN ALL LOCATIONS. WILL NEED TO WATCH FOR THE RETURN OF
SOME MVFR CIGS ALONG A KBLF-KLWB LINE AFTER 05Z. VSBYS IN THE EAST
SHOULD DECREASE TO AT LEAST MVFR LEVELS AS LIGHT FOG FORMS. MAY
SEE SOME LOCATIONS DROP TO IFR LEVELS FOR A WHILE RIGHT BEFORE
DAYBREAK. ANY SUB-VFR VSBYS SHOULD RAPIDLY IMPROVE TO VFR AFTER
SUNRISE THURSDAY. CLOUD COVER SHOULD INCREASE THE ENTIRE AREA ON
THURSDAY AT THE LOW END VFR LEVEL. AN APPROACHING SURFACE COLD
FRONT WILL MAKE IT ABOUT HALF WAY ACROSS THE FORECAST AREA BETWEEN
22-24Z TOMORROW. HAVE INDICATED THIS WITH A WIND SHIFT AND GUSTIER
WINDS IN THE KBLF...KLWB...AND KROA TAF SITES. 

FOR THURSDAY NIGHT...ARRIVAL OF THIS COLD FRONT WILL LIKELY BRING
A RETURN TO MVFR TO IFR CONDITIONS IN UPSLOPE AREAS WEST OF THE
BLUE RIDGE ALONG WITH COLDER AIR AND MOUNTAIN RAIN TO SNOW
SHOWERS. DOWNSLOPE WINDS EAST OF THE BLUE RIDGE WILL KEEP THOSE
AREAS MAINLY VFR RANGE INTO SUNDAY.

&&

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

&&

$$
SYNOPSIS...JH/SK
NEAR TERM...AMS/KK
SHORT TERM...JH
LONG TERM...DS
AVIATION...DS/KK