Flash Flood Warning 104, NWS Blacksburg, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
657 PM EST TUE NOV 30 2010

.SYNOPSIS...
A STRONG STORM SYSTEM OVER THE GREAT LAKES WILL MOVE INTO NEW
ENGLAND TONIGHT...A STRONG COLD FRONT WILL SWEEP EAST ACROSS THE
MID ATLANTIC REGION DURING THE OVERNIGHT. COLD HIGH PRESSURE WILL
BUILD ACROSS THE AREA FOR THE END OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
SOUTHEAST WIND AHEAD OF THE FRONT ARE STILL STRONG ENOUGH TO
CONTINUE WITH WIND ADVISORY IN WESTERN COUNTIES THROUGH THIS
EVENING. KFCX VAD WINDS 40KTS AT 4KFT AND 50 KTS AT 5 KFT. AT 300
PM...BLUEFIELD AIRPORT HAD 15 MPH WINDS WITH GUSTS TO 30 MPH. BLF
HIGHEST GUST CAME AROUND 1130A AT 46 MPH.

EXPECT LIGHT RAIN/DRIZZLE AND FOG TO PERSIST THROUGH RUSH HOUR FOR
MOST OF THE AREA. PREFRONTAL SHOWERS WILL ENTER TAZEWELL AND MERCER
COUNTY DURING RUSH HOUR THEN SPREAD EASTWARD OVERNIGHT. PWAT
CLIMATOLOGY HAS A MAXIMUM FOR LATE NOVEMBER OF 1.3 INCHES AND MODELS
ARE FORECASTING 1.3-1.6 INCHES OVERNIGHT. WITH STRONG FORCING COMING
ACROSS THE AREA TONIGHT...2-3 INCHES OF RAIN IS LIKELY. MOST RAIN
THAT FELL TODAY WOULD PUT THE FLASH FLOOD THREAT FROM THE FOOTHILLS
AND MOUNTAIN COUNTIES TONIGHT. WE ALREADY HAVE A FLASH FLOOD WATCH
FOR THESE COUNTIES. ACROSS THE PIEDMONT...1-2 INCHES OF RAIN IS
POSSIBLE AS THE FRONT CROSSES THE REGION. WITH LITTLE RAIN TODAY IN
THE PIEDMONT...FLASH FLOOD THREAT IS LOW...BUT STILL POSSIBLE.
PONDING OF WATER ON ROADWAYS WILL BE THE COMMON THREAT FOR THE ENTIRE
AREA AS FALLEN LEAVES WILL CLOG DRAINS.

THERE IS A CHANCE FOR STRONG STORMS TO PRODUCE DAMAGING WINDS AND
MAY BE AN ISOLATED TORNADO TONIGHT FOR PIEDMONT COUNTIES ALONG THE
VA/NC BORDER. HIGH SHEAR AND HELICITY ENVIRONMENT FROM A
RETREATING WEDGE...A COLD FRONTAL BOUNDARY AND TRIPLE POINT LOW WILL
BRING THE THREAT OF SEVERE WEATHER TO THIS AREA THROUGH THE OVERNIGHT
HOURS. 85H JET IS AROUND 70KTS AND THE HODOGRAPHS ARE IMPRESSIVE.
WOULD NOT BE SURPRISED TO HAVE A RARE LATE NOVEMBER WATCH BOX ISSUED
FOR SE PART OF RNK CWA. DESPITE SEVERE THREAT BEING ENHANCED
TONIGHT...SHOWERS MAY NOT BE ACCOMPANIED BUT LIGHTNING OR THUNDER.

TEMPERATURES SHOULD BE AT THEIR COLDEST THIS EVENING ALONG AND EAST
OF THE BLUE RIDGE. SOME AREAS MAY SEE A RISE IN TEMPERATURES DURING
THE EVENING...ESPECIALLY THOSE THAT REMAINED IN THE WEDGE ALL DAY.
AT 300 PM...ROANOKE WAS AT 48F AND DAN AT 68F. DEFINITE SIGNS OF
THE WEDGE ERODING. COLD AIR WILL FILTER IN BEHIND THE FRONT AND
WESTERN SLOPES AND HIGH ELEVATIONS COULD SEE SNOW FALLING BY SUNRISE.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
COLD FRONT WILL JUST BE EXITING THE FAR EASTERN PORTION OF OUR CWA
AT 7 AM WEDNESDAY. BEHIND THIS FRONT WE WILL SEE FALLING
TEMPERATURES AND DEW POINTS. MOST OF THE PRECIPITATION WILL COME
TO AN END WITH THE FRONTAL PASSAGE...BUT LOOK FOR LINGERING
SHOWERS IN THE MOUNTAINS...ESPECIALLY ALONG THE WINDWARD SLOPES.
STRONG COLD AIR ADVECTION WILL RESULT IN STEADY OR FALLING
TEMPERATURES DURING THE DAY WEDNESDAY...THE WARMEST TEMPS
OCCURRING DURING THE MORNING. TEMPERATURES FALLING INTO THE 30S
WILL SUPPORT A P-TYPE CHANGE TO SNOW IN THE MOUNTAINS WITH SOME
LIGHT ACCUMULATION POSSIBLE IN THE HIGHEST ELEVATIONS.  HOWEVER
MODELS CURRENTLY SHOWING ENOUGH DRYING ALOFT TO KEEP UPSLOPE
PRECIPITATION AMOUNTS LOW. COMBINE THAT WITH AN UNFAVORABLE
TRAJECTORY WITH THE WINDS...AND CURRENT THINKING IS THAT ANY
UPSLOPE SNOWS WILL BE MINIMAL.

GUSTY WINDS CAN BE EXPECTED WEDNESDAY. INCREASING AMOUNTS OF SUN
ALONG AND EAST OF THE BLUE RIDGE WILL AID IN GOOD MIXING WHICH
WILL RESULT IN MIX DOWN OF RATHER STRONG 850MB WINDS OF NEAR 40 KTS.
THUS EXPECTING WIND GUSTS OF 30 TO 40 MPH FROM BOONE...TO
ROANOKE...AND IN THE VA HIGHLANDS ALONG WARM SPRINGS MOUNTAIN.
ANY UPSLOPE SNOW SHOWERS SHOULD TAPER TO FLURRIES WEDNESDAY
EVENING AS DRIER AIR MOVES IN ALOFT...AND LAPSE RATES CONTINUE TO
WEAKEN.

THURSDAY MORNING WILL BE A COLD ONE WITH LOWS DIPPING INTO THE MID
20S AREA WIDE. 850MB TEMPERATURES IN THE -4 TO -8C RANGE WILL
LEAD TO A COLD DAY THURSDAY...WITH HIGHS TEN DEGREES BELOW
NORMAL. SHOULD SEE INCREASING MID AND HIGH CLOUDS THURSDAY
AFTERNOON AND INTO EARLY FRIDAY AS WARM AIR ADVECTION BEGINS ALOFT.
MODELS SPIT OUT SOME TRACE PRECIP...FLURRIES...BUT REFRAINED FROM
PUTTING IT IN THE FORECAST ATTM SINCE THE BOUNDARY LAYER REMAINS
RELATIVELY DRY. CLOUDS THURSDAY INTO FRIDAY WILL KEEP
TEMPERATURES RATHER COOL...BUT THEN AGAIN ITS SUPPOSE TO BE COOL
FOR DECEMBER.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
THE FORECAST WILL BE INFLUENCED GREATLY DURING THIS TIME PERIOD BY A
CLOSED UPPER LOW THAT WILL RETROGRADE THROUGH SOUTHEAST CANADA. THIS
WILL KEEP OUR REGION IN PREVAILING NORTHWEST FLOW. THE FORECAST
ISSUE THAT HAS THE MOST UNCERTAINTY IS THE TIMING AND TRAJECTORY OF
A NUMBER OF SHORTWAVE TROUGHS THAT WILL SPIRAL THROUGH THE REGION IN
RELATION TO THE PARENT LOW. MODELS ARE ALL ACROSS THE BOARD
REGARDING THESE. WILL BE FOLLOWING CLOSELY THE GRIDDED FORECAST
PROVIDED BY HPC DURING THIS PERIOD. NOTABLE DIFFERENCES WILL BE
HIGHER THAN SLIGHT CHANCE POPS DURING MUCH OF THE PERIOD ACROSS THE
WESTERN SLOPES OF SE WV DUE THE PREVAILING STRONG
NORTHWEST...UPSLOPE...FLOW DURING THIS PERIOD. ALSO...CONFIDENCE IS
VERY LOW AT THIS POINT IN A CWA-WIDE CHANCE POP COVERAGE SUNDAY
NIGHT. HAVE KEPT PRECIPITATION CHANCES IN THE MOUNTAINS ONLY WITH A
MIX OF SLIGHT CHANCE AND CHANCE. TEMPERATURES WILL TREND COLDER
DURING THE PERIOD AND HAVE FOLLOWED VERY CLOSELY WITH HPC NUMBERS
FOR THESE. BY MONDAY NIGHT...LOWS WILL BE IN THE LOWER 20S IN THE
MOUNTAINS AND MID 20S EAST OF THE BLUE RIDGE. ON TUESDAY...HIGHS
WILL BE IN THE LOWER 30S IN THE MOUNTAINS AND MID 30S TO NEAR 40
EAST OF THE BLUE RIDGE.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
SOUTH WINDS ABOVE THE SFC INVERSION ARE STILL 40-50 KNOTS AS SHOWN
ON THE KFCX VAD WIND PROFILER...AND LLWS WILL BE AN ISSUE AHEAD OF
THE APPROACHING COLD FRONT.

THE BAND OF MODERATE TO HEAVIER SHOWERS WILL ARRIVE JUST AFTER
00Z TONIGHT AT KBLF AND KLWB AND WILL MOVE EAST OVERNIGHT...ENDING
AT KLYH AND KDAN BY 10Z AS A COLD FRONT MOVES SLOWLY EAST.

SURFACE WINDS AT KDAN AND KLYH MAY BE GUSTY OUT OF THE SOUTHEAST
AHEAD OF THE FRONT AS THE SHALLOW WEDGE OF COLD AIR RETREATS
NORTH. LOW CONFIDENCE THAT CEILINGS WILL IMPROVE TO EVEN IFR AT
KROA UNTIL JUST BEFORE THE COLD FRONT COMES THROUGH...BETWEEN
04-08 UTC.

COLDER AIR SWINGS IN BEHIND THE FRONT LATE TONIGHT IN THE WEST
WITH A SHARP DROP IN TEMPERATURES...SO A MIX OF SNOW WITH RAIN IS
EXPECTED AT KBLF AND KLWB...BUT BY THEN THE MOISTURE WILL BE
SHALLOW. HOWEVER...CIGS WILL STAY DOWN IN THE MVFR TO IFR RANGE
FOR MUCH OF THE DAY. FROM KROA EAST...LOOK FOR CIGS TO IMPROVE TO
VFR AFTER 12Z WED WITH CLOUDS BECOMING SCATTERED BY AFTERNOON.

PERSISTENT UPSLOPING WINDS WEST OF THE BLUE RIDGE MAY HELP
MAINTAIN AT LEAST MVFR CONDITIONS AT KBLF AND KLWB INTO/THROUGH
THURSDAY.

HIGH PRESSURE WILL MOVE INTO THE AREA LATE THIS WEEK...ALTHOUGH
SOME UPPER DISTURBANCES MAY KEEP THE WV TAF SITES WITH MVFR CIGS
INTO SAT.

&&

.HYDROLOGY...
SHORT TERM FLOOD THREAT IS BEING COVERED BY CURRENT FLASH FLOOD
WATCH. THIS IS MAINLY FOR THE SMALLER STREAMS AND DOES NOT
ENCOMPASS THE RIVERS. AS FOR THE MAIN STEM RIVERS...CURRENT
FORECAST RAINFALL ACROSS THE DAN RIVER BASIN OF 1 TO 2.5 INCHES
OVER THE NEXT 24 HOURS WILL CAUSE SUBSTANTIAL RISES IN RIVER
LEVELS. IF THE PRECIPITATION DEVELOPS AS EXPECTED THE DAN RIVER
AT DANVILLE AND PACES WILL RISE TO JUST BELOW FLOOD STAGE BY LATE
TOMORROW EVENING. THE CURRENT FORECAST BRINGS THE RIVER AT SOUTH
BOSTON ABOVE FLOOD STAGE LATE TOMORROW EVENING AS WELL. THIS MAY
REQUIRE ISSUANCE OF A FLOOD WARNING LATE TODAY OR THIS EVENING AS
THE UNCERTAINTY IN THE FORECAST DIMINISHES. ASIDE FROM THE DAN
RIVER...OTHER RIVERS MAY SEE RISES BUT REMAIN BELOW BANK FULL AS
LONG AS QPF DOES NOT EXCEED 2.5 INCHES OVER THE BASIN.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...FLASH FLOOD WATCH UNTIL 6 AM EST WEDNESDAY FOR VAZ007-009>020-
     022>024-032>035.
     WIND ADVISORY UNTIL 9 PM EST THIS EVENING FOR VAZ007-009-010-
     015.
NC...FLASH FLOOD WATCH UNTIL 6 AM EST WEDNESDAY FOR NCZ001>003-018-
     019.
     WIND ADVISORY UNTIL 9 PM EST THIS EVENING FOR NCZ001-018.
WV...FLASH FLOOD WATCH UNTIL 6 AM EST WEDNESDAY FOR WVZ042>045.
     WIND ADVISORY UNTIL 9 PM EST THIS EVENING FOR WVZ042-043-045.

&&

SYNOPSIS...PM
NEAR TERM...RCS
SHORT TERM...PM
LONG TERM...DS
AVIATION...AMS/RCS
HYDROLOGY...

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
933 PM EST TUE NOV 30 2010

NCZ002>004-019-020-VAZ015>017-032-010330-
ALLEGHANY NC-CARROLL VA-FLOYD VA-GRAYSON VA-PATRICK VA-STOKES NC-
SURRY NC-WILKES NC-YADKIN NC-
933 PM EST TUE NOV 30 2010

...SHOWERS WITH HEAVY RAIN AND GUSTY WINDS WILL AFFECT
ALLEGHANY...CARROLL...FLOYD...GRAYSON...PATRICK...STOKES...SURRY...
WILKES AND YADKIN COUNTIES...

AT 931 PM EST...A LINE OF SHOWERS WITH HEAVY RAIN AND STRONG WIND
GUSTS WERE ALONG A LINE FROM 6 MILES SOUTHEAST OF MOUTH OF WILSON TO
BOOMER...MOVING EAST AT 25 MPH.

WIND GUSTS TO 45 MPH ARE POSSIBLE WITH THESE SHOWERS. COMBINED WITH
THE WET GROUND...THIS COULD BE ENOUGH TO UPROOT A FEW TREES WITH
SHALLOW ROOT SYSTEMS. VERY HEAVY RAIN WILL FALL FROM THESE
SHOWERS...AND WILL CAUSE WATER TO POND ON ROADS AND QUICKLY FILL
ROADSIDE DITCHES AND SMALL STREAMS.

THESE SHOWERS WILL BE NEAR DOUGHTON PARK...WHITEHEAD...TWIN OAKS...
AND WILKESBORO AROUND 940 PM...INDEPENDENCE...SPARTA...HAYS...AND
ABSHERS AROUND 945 PM...DOCKERY AND AND WILKES COUNTY AIRPORT AROUND
950 PM.

THE PUBLIC IS ENCOURAGED TO RELAY REPORTS OF STRONG WINDS...HAIL OR
FLOODING TO THE NATIONAL WEATHER SERVICE IN BLACKSBURG BY CALLING
1...8 6 6...2 1 5...4 3 2 4...WHEN YOU CAN DO SO SAFELY.

LAT...LON 3606 8124 3636 8126 3639 8125 3640 8126
      3662 8128 3694 8034 3629 8030

SK