FXUS61 KRNK 051526
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1026 AM EST SAT DEC 5 2009
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP AND MOVE RAPIDLY ALONG THE SOUTHEAST
COAST TODAY...REACHING THE OUTER BANKS OF NORTH CAROLINA
BY LATE THIS AFTERNOON...AND EXITING THE MID ATLANTIC COAST AREA
BY THIS EVENING. COLD HIGH PRESSURE WILL BUILD IN BEHIND THE
SYSTEM FOR OVERNIGHT.
&&
.NEAR TERM /THROUGH TONIGHT/...
WATER VAPOR SHOWS THE UPPER LOW LIFTING NEWD INTO THE SRN APPLNS
AT THIS TIME. RADAR SHOWS A BACK EDGE TO THE HEAVIER PRECIP
NORTHEAST OF THE UPPER LOW THAT IS MOVING ACROSS THE CWA AT THIS
TIME...BUT I EXPECT MOST OF THE CWA TO COME UNDER THE DEFORMATION
ZONE AS THE UPPER LOW MOVES ACROSS THIS AFTERNOON. SO I HAVE KEPT
CATEGORICAL TO LIKELY POPS GOING. MAIN QUESTION IS HOW HEAVY THE
PRECIP WILL BE THIS AFTERNOON. MODELS DO NOT SHOW MUCH WITH
IT...BUT I AM LEERY OF LOWERING QPF TOO MUCH. IN
ADDITION...COLDER AIR IS FILTERING INTO THE CWA FROM THE WEST AND
NW....WITH UPPER 20S ON THE EXTREME WESTERN EDGE OF THE CWA...SO
THINK THAT TEMPS MAY DROP A DEGREE OR TWO THIS AFTERNOON IN THE
MTNS AND ALL SNOW WILL ACCUMULATE. SO BOTTOM LINE IS THAT I AM
KEEPING SNOW TOTALS ABOUT THE SAME- MAIN CHANGE WAS TO RAISE THEM
AN INCH OR SO ACROSS THE SW VA MTNS AND SE WV WHERE THE TEMPS ARE
COLDER. WILL UPDATE ADVISORY WARNING PRODUCTS SOON.
PREVIOUS DISCUSSION...
MOST SURFACE OBSERVATION ABOVE FREEZING EARLY THIS MORNING WITH
ONLY PATCH DRIZZLE BEING REPORTED ALONG THE BLUE RIDGE. AS
MOISTURE CONTINUES TO ADVANCE INTO THE AREA WITH A DISTURBANCE
TRACKING ALONG THE COAST...WILL SEE TEMPERATURES DROP AS AIR
COLUMN COOLS TO THE WET BULB. LIGHT RAIN WILL QUICKLY TURN OVER TO
SNOW ACROSS THE WEST EARLY THIS MORNING. ALONG THE
FOOTHILLS...HIGHER ELEVATIONS WILL SEE THE CHANGE TO SNOW EARLY
THIS MORNING...THEN IN THE LOWER ELEVATIONS BY LATE IN THE
MORNING. ALONG THE VA/NC BORDER...MILD TEMPERATURES SHOULD HOLD
OFF SNOW CHANCES UNTIL LATE IN THE AFTERNOON. THE PIEDMONT OF
CENTRAL VIRGINIA...NORTH OF HIGHWAY 460...SHOULD SEE A CHANGE OVER
BY THE AFTERNOON. THIS STORM IS PICKING UP SPEED AND SHOULD EXIT
WITH PRECIPITATION ENDING THIS EVENING.
ACCUMULATIONS TRICKY FOR THE FIRST WIDESPREAD SNOW EVENT OF THE
SEASON. FIRST...MOISTURE ADVANCING INTO THE AREA WAS A FEW HOURS
LATE AND THIS HAS HELD TEMPERATURES UP THROUGH THE EARLY MORNING
HOURS. SECOND...GROUND TEMPERATURES IN THE UPPER 30S TO MID 40S
ACROSS THE AREA WILL MELT SNOW IN THE ONSET. INTO THE
AFTERNOON...GROUND TEMPERATURES WILL HAVE COOLED AND SNOWFALL RATES
WILL PICK UP FOR SNOW TO ACCUMULATE. ROAD SURFACES THROUGH THE DAY
SHOULD WITH STAND ANY ACCUMULATIONS WITH POSSIBLE SLUSH BY DAYS END.
FORECAST ACCUMULATIONS CAN BE SEE ON RNK WEBSITE...WITH THE HIGHEST
AMOUNTS OVER THE ALLEGHANY HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY.
AS THE STORM TRACKS ALONG THE VA/NC COAST...DYNAMICS AND ISENTROPIC
LIFT INCREASES OVER RNK NORTH. WITH 4 OR MORE INCHES EXPECTED...HAVE
UPGRADED ALLEGHANY HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY TO A
WINTER STORM WARNING INTO THIS EVENING.
TEMPERATURES ANOTHER TOUGH CALL AS AREAS ALONG AND WEST OF THE BLUE
RIDGE WILL SEE MAXIMUM TEMPERATURES THIS MORNING. IN THE
PIEDMONT...MAXIMUM TEMPERATURE MAY BE REACHED BY NOON. WITH
PRECIPITATION FALLING THROUGH THE AFTERNOON AND COLD AIR FILTERING
IN...TEMPERATURES WILL REMAIN STEADY AND/OR FALL. THE COLDEST AIR OF
THE SEASON WILL CONTINUE TO FILTER INTO THE REGION WITH SURFACE HIGH
PRESSURE OVER THE AREA SUNDAY MORNING. WITH COLD AIR AND SNOW ON THE
GROUND...TEMPERATURE WILL RADIATE DOWN INTO THE 20S...SOME TEENS
ACROSS THE MOUNTAINS. WITH TEMPERATURES DROPPING VERY QUICKLY
SATURDAY EVENING...WATER AND SLUSH ON THE ROADS WILL FREEZE
OVERNIGHT. BLACK ICE WILL BE A PROBLEM...ESPECIALLY ON SECONDARY
ROADWAYS.
&&
.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
500 MB HEIGHTS RISE AND SURFACE HIGH PRESSURE BUILDS INTO THE AREA
ON SUNDAY. THE CENTER OF THE HIGH CROSSES THE FORECAST AREA ON
SUNDAY NIGHT. WENT WITH COOLER MET GUIDANCE FOR MAXIMUM TEMPERATURES
ON SUNDAY EXPECTING THERE WILL STILL BE SOME SNOW ON THE GROUND FROM
THE FOOTHILLS WEST ACROSS THE MOUNTAINS.
MODELS ARE SHOWING A WEAK SHORT WAVE IN THE NORTHERN STREAM ON
MONDAY. THIS FEATURE PUSHES A WEAK FRONT INTO THE OHIO VALLEY ON
MONDAY. AS THE HIGH MOVES OFFSHORE...SOUTHWEST LOW LEVEL FLOW WILL
START INCREASING THE MOISTURE ACROSS THE AREA. LEFT A LOW CHANCE OF
UPSLOPE SHOWERS IN THE MOUNTAINS. TOOK A BLEND OF GUIDANCE FOR
SUNDAY NIGHT AND MONDAY.
A COLDER HIGH MOVES INTO THE AREA ON TUESDAY. SLIGHTLY INCREASES
PROBABILITY OF PRECIPITATION ON TUESDAY NIGHT BASED ON THE TIMING
AND LIFT OF THE 00Z GFS ENSEMBLE AND ECMWF WITH THE LARGE SOUTHERN
STREAM SYSTEM.
&&
.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
LEANED MEDIUM RANGE GRIDS TOWARDS A BLEND OF HPCGUIDE AND ECMWF 00Z.
QUASI ZONAL FLOW EXPECTED WITH SOME AMPLIFICATION OF THE PATTERN ON
TUESDAY INTO WEDNESDAY. HIGH PRESSURE WILL SLIDE EASTWARD ON
TUESDAY. DECIDED TO DECREASE POPS FOR TUESDAY AND PLAY BEST CHANCES
IN THE WEST. MOISTURE SLOWLY INCREASES AS A FRONTAL BOUNDARY
APPROACHES FROM THE WEST TUESDAY AFTERNOON. AS THE LOW PRESSURE
CENTER AND FRONT SPREAD EAST THE CHANCES OF PCPN INCREASE TUESDAY
NIGHT AND WEDNESDAY. ELECTED TO GO WITH LIKELY POPS FOR WEDNESDAY
WITH THE CONSISTENCY OF THE MODELS. AS LOW PRESSURE LIFTS NORTHEAST
AND COLD FRONT PUSHES INTO THE ATLANTIC OCEAN. KEEP SOME CHCY POPS
IN THE WESTERN MOUNTAINS WEDNESDAY NIGHT INTO THURSDAY. PLAYED
HIGHEST POPS IN THE NORTHWEST. HIGH PRESSURE WILL BUILD EAST INTO
THE AREA FROM THE TENNESSEE VALLEY ON THURSDAY INTO THURSDAY NIGHT.
KEPT SOME CHCY POPS IN THE WEST WITH THE PASSAGE OF A WARM FRONT
ON FRIDAY.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
IFR TO LIFR CEILINGS AND VISIBILITIES ARE EXPECTED TODAY WITH
WIDESPREAD RAIN AND SNOW. A LOW PRESSURE SYSTEM OFF THE
SOUTH CAROLINA COAST WILL MOVE NORTHEAST TODAY AND TONIGHT. THE
PRECIPITATION WILL BE MAINLY ALL SNOW AT BLF AND LWB. THE
PRECIPITATION WILL BE A RAIN AND SNOW MIX AT ROA AND LYH THEN
CHANGE TO ALL SNOW AROUND 17Z AS THE STORM SYSTEM MOVES NORTHEAST AND
COLD AIR GETS PULLED INTO THE WEST SIDE OF THE LOW. THE CHANGE TO
SNOW AT DAN WILL BE LATER...AROUND 21Z. THE SNOW BE HEAVY ENOUGH
TO ACCUMULATE...THOUGH SHOULD BE SLUSHY AND WET.
THE PRECIP WILL MOVE OUT OF THE AREA QUICKLY THIS EVENING FROM
SOUTHWEST TO NORTHEAST. CLOUDS WILL BECOME SCATTERED EAST OF THE
BLUE RIDGE AFTER 00Z WITH ROA...LYH AND DAN ALL VFR AFT 06Z. THE
CLEARING WILL BE SLOWER AT BLF AND LWB DUE TO AND WEST TO
NORTHWEST LOW LEVEL WIND AND RESIDUAL LOW LEVEL MOISTURE.
ALL SITES SHOULD BECOME VFR BY 12Z SUNDAY.
HIGH PRESSURE WILL CONTINUE THE VFR CONDITIONS INTO MONDAY.
A WEAK COLD FRONT MAY BRING BRIEF MVFR CONDITIONS IN CLOUDS AND
POSSIBLY LIGHT PRECIP BY MONDAY NIGHT INTO TUESDAY IN THE MOUNTAINS. IFR
CONDITIONS MAY BE POSSIBLE TUESDAY NIGHT AND WEDNESDAY WITH A
LARGER LOW PRESSURE SYSTEM DEVELOPING IN THE SOUTHERN PLAINS.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ007-
009>018.
WINTER STORM WARNING UNTIL 11 PM EST THIS EVENING FOR VAZ019-
020-023-024.
WINTER WEATHER ADVISORY UNTIL 11 PM EST THIS EVENING FOR
VAZ022-034-035-045>047.
NC...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR NCZ001-
002-018.
WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
WVZ042>045.
&&
$$
SYNOPSIS...RCS
NEAR TERM...JJ/RCS
SHORT TERM...AMS
LONG TERM...KK
AVIATION...AMS/PM
