FXUS61 KRNK 091533
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1033 AM EST WED DEC 9 2009
.SYNOPSIS...
A STRONG COLD FRONT WILL PASS THROUGH THE AREA TODAY. COLD HIGH
PRESSURE FOLLOWS THE FRONT WITH DRIER BUT MUCH COLDER AIR ON
STRONG WESTERLY WINDS TONIGHT INTO THURSDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
POST-RAIN SMALL STREAM FLOODING WILL CONTINUE INTO EARLY AFTERNOON
OVER PORTIONS OF THE WESTERN FORECAST AREA...WITH SOME RIVER
FLOODING ALSO POSSIBLE ALONG THE DAN RIVER NEAR SOUTH BOSTON.
OTHERWISE...WEATHER CONCERNS IN THE NEAR TERM PERIOD WILL SHIFT TO
INCREASING WINDS AND TEMPERATURES.
INCREASING PRESSURE GRADIENT AND MOMENTUM TRANSFER WITH ONSET OF
INSOLATION IS ALLOWING COOL WEDGE TO BE DISLODGED...WITH A TEMPERATURE
SPIKE INTO THE 50S NOW OCCURRING ACROSS THE SOUTHWESTERN PORTIONS
OF THE BLACKSBURG FORECAST AREA. COOL WEDGE AND LOW CLOUDS WILL
ALSO ERODE ACROSS THE REMAINDER OF THE FORECAST AREA BY EARLY
AFTERNOON...ALLOWING TEMPERATURES TO RAPIDLY RISE BEFORE LEVELING
OFF BY MID AFTERNOON AS ACROSS THE PIEDMONT...AND TRENDING
DOWNWARDS ALONG AND WEST OF THE BLUE RIDGE AS STRONG COLD AIR
ADVECTION AND AND UPSLOPE CLOUDS ADVECT INTO/FORM OVER THE AREA.
SOUTHWESTERLY WINDS OF 50-60 KNOTS AT 850 MILLIBARS...WITH 100
KNOT WINDS AS LOW AS 680 MILLIBARS...SHOULD BE MORE THAN SUFFICIENT
TO JUSTIFY EXISTING HIGH WIND WARNINGS AND ADVISORIES...WHICH MAY
HAVE TO BE EXTENDED BEYOND CURRENT EXPIRATION TIME OF 700 PM THIS
EVENING.
FOR NOW...HAVE TWEAKED GRIDS TO ACCOUNT FOR CURRENT CONDITIONS AND
ABOVE FORECAST REASONING...BUT NO SIGNIFICANT CHANGES MADE TO
FORECAST THROUGH TONIGHT. WINDS SHOULD GRADUALLY SUBSIDE AS THE
NIGHT PROGRESSES AS PRESSURE GRADIENT RELAXES...BUT STRONG COLD
ADVECTION SHOULD RESULT IN UPSLOPE SNOW SHOWERS ACROSS THE
WEST...WITH TEMPERATURES FALLING INTO THE LOWER 20S. EAST OF THE
BLUE RIDGE...INFLUENCE OF DOWNSLOPING WINDS SHOULD MAINTAIN MOSTLY
CLEAR SKIES...BUT ARRIVAL OF DEEPER COLD AIR BEHIND COLD FRONT
WILL BE DELAYED UNTIL LATER TONIGHT...SO TEMPERATURES PROBABLY
WILL NOT FALL MUCH BELOW FREEZING ACROSS THE EXTREME SOUTHEASTERN
POTIONS OF THE BLACKSBURG FORECAST AREA.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
NORTHWEST FLOW WITH RESIDUAL UPSLOPE MOISTURE SUPPORTS SCATTERED
SNOW SHOWERS AND SNOW FLURRIES IN THE SE WV MOUNTAINS...SOUTH INTO
THE NORTHERN MOUNTAINS OF NORTH CAROLINA. A REINFORCING TROUGH
BEHIND THE INITIAL COLD FRONT WILL ADD SOME INSTABILITY THURSDAY
MORNING. LIMITED THE SLIGHT CHC OF SNOW SHOWERS TO NORTHWEST
THURSDAY AFTERNOON. HIGH PRESSURE SETTLES OVER THE AREA ON
THURSDAY NIGHT AND FRIDAY WITH NOTABLE COLDER TEMPERATURES. USED A
BLEND OF MOSGUIDE AND CONTINUITY FOR TEMPERATURES DURING THE PERIOD.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
THERE ARE TWO SYSTEMS THAT CAN POTENTIALLY IMPACT THE LONG TERM
FORECAST. AN AREA OF LOW PRESSURE WILL MOVE ACROSS THE SOUTHEAST AND
TO THE ATLANTIC COAST SATURDAY. IN COMPARISON TO YESTERDAYS LONG
RANGE SUITE...MODELS ARE FURTHER SOUTH WITH THE TRACK...ESPECIALLY
THE 12Z ECMWF. THIS TREND HOWEVER WAS HINTED AT IN THE 12Z GEFS
RUNS. WITH NOT MUCH AMPLITUDE IN THE UPPER FLOW...AND THE ABSENCE
OF ANY HIGH LATITUDE BLOCKING ACROSS THE NORTH ATLANTIC...DIFFICULT
TO SEE THIS SYSTEM TAKE THE MORE NORTHERLY TRACK ALONG THE COAST
THAT THE 12Z GFS SUGGESTS. HIGH PRESSURE WHICH ARRIVES BEFORE THE
STORM FRIDAY AND FRIDAY NIGHT MAY BE STRONG ENOUGH TO KEEP THE
SYSTEM SOUTH. WITH THIS IN MIND...LOWERED POPS SOMEWHAT NORTH OF THE
VA/NC BORDER AND LOWERED SOUTH OF THE NC/VA BORDER. WILL KEEP
PTYPE JUST RAIN/SNOW FOR NOW...BUT SLEET MAY ALSO MIX IN AT TIMES.
ALSO...THINK THAT THE MOST PRECIP WILL FALL LATE SATURDAY AND
SATURDAY NIGHT. BASICALLY TRIED TO FOLLOW THE 12Z ECMWF AND THE
12Z GEFS. FOR NOW...WILL LEAVE ANY MENTION OUT OF THE HWO
CONSIDERING THE SOUTHWARD TREND. AT THE END OF THE LONG
TERM...BOTH THE ECMWF AND GFS HAVE A SYSTEM AFFECTING THE CWA WITH
WINTRY PRECIPITATION POSSIBLE AGAIN. THE ECMWF MOVES THE POLAR
VORTEX TO JAMES BAY BY NEXT TUESDAY. THIS CAUSES ONE OF THE
DISTURBANCES MOVING OUT OF THE SOUTHERN STREAM TO PHASE. IT IS NOT
UNCOMMON FOR STRONG SYSTEMS TO FORM WITH SUCH A DRASTIC MOVEMENT
OF THE POLAR VORTEX INTO SE CANADA. ALSO...HIGH LATITUDE BLOCKING
MAY BE IN PLACE WITH THIS SYSTEM...WITH AN UPPER RIDGE CENTERED
JUST EAST OF GREENLAND. PLENTY OF TIME TO WATCH THIS SYSTEM WHICH
HAS PROMISE.
&&
.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
WINDS WILL HINDER AVIATION OPERATIONS TODAY AS A STRONG COLD FRONT
PUSHES EAST ACROSS THE REGION. MVFR CONDITIONS EXPECTED WITH
AREAS OF IFR/LIFR IN LOW CLOUDS/FOG AND RAIN THIS MORNING. PILOTS
SHOULD CHECK AIRMETS AND SIGMETS FOR ICING AND MOUNTAIN
OBSCURATIONS. A STRONG LOW LVL JET ABOVE THE COOL WEDGE WILL
CREATE LOW LVL WIND SHEAR CONDITIONS THIS MORNING AT ALL TAF
SITES.
AS WINDS VEER TO THE SOUTHWEST THIS MORNING WILL EXPECT TO SEE SOME
GUSTS AS THE WEDGE ERODES...WITH STRONG WINDS DURING THE AFTERNOON
ACROSS ALL SITES INCLUDING THE EAST WHERE WEST WINDS MAY GUST
ABOVE 30-35 KTS AT TIMES.
WINDS WILL STAY STRONG AND GUSTY THROUGH WEDNESDAY NIGHT...BUT
WILL BE OUT OF THE WEST TO NORTHWEST BEHIND THE COLD FRONT.
WINDY AND GUSTY CONDITIONS POSSIBLE INTO THURSDAY NIGHT. HIGH
PRESSURE BUILDS IN ON FRIDAY BRINGING A RETURN TO VFR ACROSS THE
REGION ALONG WITH LIGHTER WINDS INTO SAT. ANOTHER WEAK STORM SYSTEM
LOOKS TO BRING A POSSIBLE MIXED BAG OF PRECIP BACK TO THE AREA
WITH MVFR/IFR CONDITIONS BY SUNDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR VAZ007-
009>020.
WIND ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ022>024-
032>035-043>047-058-059.
NC...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR NCZ001-002-
018.
WIND ADVISORY UNTIL 7 PM EST THIS EVENING FOR NCZ003>006-019-
020.
WV...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR WVZ042>045.
&&
$$
SYNOPSIS...JH
NEAR TERM...WERT
SHORT TERM...DS/KK/WP
LONG TERM...KM
AVIATION...JH/KK/KM
