000
FXUS61 KRNK 100450
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1150 PM EST TUE MAR 9 2010
.SYNOPSIS...
A COMPLEX LOW PRESSURE SYSTEM WILL DEVELOP AND MOVE SLOWLY
EASTWARD FROM THE SOUTHERN PLAINS INTO THE EASTERN U.S. FROM MID-
WEEK INTO THE WEEKEND. THIS SYSTEM WILL KEEP OUR TEMPERATURES
MILD...AND LIKELY BRING SIGNIFICANT RAINFALL TO MUCH OF THE AREA.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
SOUTH WINDS HAVE WARMED TEMPERATURES TO LEVELS NOT SEEN SINCE
LATE NOVEMBER...AT LEAST IN BLACKSBURG. AS THE SURFACE RIDGE
SLIDES EAST TONIGHT THE REGION BEGINS TO COME UNDER THE INFLUENCE
OF THE MAJOR SURFACE AND UPPER LEVEL SYSTEM NOW CENTERED OVER THE
SOUTHERN PLAINS. THIS FEATURE AND ITS FUTURE DEVELOPMENT WILL
DOMINATE OUR WEATHER OVER THE NEXT 3 TO 5 DAYS AS IT MAKE ITS WAY
SLOWLY ACROSS THE EASTERN HALF OF THE CONUS. INITIAL EFFECTS
ALREADY UNDERWAY WITH THE SHIFT TO SOUTHERLY FLOW ACROSS THE AREA
AND A NOTICEABLE INCREASE IN MOISTURE AS WELL AS TEMPERATURES.
DEWPOINTS WHICH WERE IN THE MID 20S LAST NIGHT RISE INTO THE UPPER
30S OR LOW 40S TONIGHT. THIS...ALONG WITH INCREASING CLOUD COVER
SHOULD KEEP LOW TEMPERATURES ABOVE FREEZING IN ALL AREAS
OVERNIGHT. BOTH SREF AND GFS INDICATE AT LEAST A POSSIBILITY OF
SOME VERY LIGHT QPF IN THE 03-09Z TIME FRAME AS A WARM FRONT LIFTS
NORTH ACROSS THE AREA. WITH CLOUDS AND HIGHER TDS...LOWS TONIGHT
WILL BE AS MUCH AS 10-15F WARMER THAN LAST NIGHT...REMAINING IN
THE 40S ACROSS NEARLY THE ENTIRE AREA. MAIN WORRY WOULD BE A QUICK
DROP DURING THE EVENING BEFORE CLOUDS MOVE IN ESPECIALLY IN THE
FAR EASTERN SECTIONS WHERE SLIGHTLY LOWER DEWPOINTS ARE HANGING
ON.
WEDNESDAY WILL BE QUITE MILD AS THE AREA WILL RESIDE IN THE WARM
SECTOR OF THE MIDWEST CYCLONE WHICH WILL BE SLOW TO MOVE FROM THE
CENTRAL PLAINS. HIGH TEMPERATURES WILL BE TRICKY AS FULL SUN AND H85
TEMPS OF +5 TO +8 ACRS THE AREA WOULD GIVE SOMEWHAT HIGHER TEMPS
THAN GRIDS CURRENTLY HAVE...BUT WITH EXTENSIVE CLOUDS SHOULD ACT TO
HOLD MAX TEMPS DOWN SOMEWHAT. POPS INCRS TO HIGHER CHANCE LATE IN
THE DAY..ESP IN THE NW NC MOUNTAINS BUT EXPECT THE BULK OF THE
PRECIP TO HOLD OFF FOR THE DAYTIME PERIOD TOMORROW.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS WE HEAD INTO WEDNESDAY NIGHT...THE LEAD UPPER LOW MOVES INTO
THE MID MISS VALLEY. SOUTHERLY WINDS AHEAD OF THE SYSTEM INCREASE
INTO THE TENN AND OHIO VALLEYS...WITH GOOD MOISTURE TRANSPORT INTO
THE SRN APPLNS. VERY LOW LEVEL WINDS ARE MORE SOUTHEAST ON THE
EAST SIDE OF THE APPLNS...AND SHOWERS SHOULD DEVELOP OVERNIGHT
WITH THE MOIST UPSLOPE FLOW. I HAVE INCREASED POPS TO CATEG ALONG
THE BLUE RIDGE IN FAR SW VA AND NW NC...WITH LIKELY SPREADING
FURTHER NE ALONG THE BLUE RIDGE. TEMPS SHOULD BE QUITE MILD. A
WAVE OF ISENTROPIC LIFT ASSOCIATED WITH A STRONGER SHORT WAVE
ROTATING AROUND THE UPPER LOW IN THE MIDDLE MISS VALLEY THU WILL
COMBINE WITH THE SOUTHEAST FLOW WHICH CONTINUES INTO THE DAY
THURSDAY FOR WHAT LOOKS LIKE WIDESPREAD PRECIP. I HAVE MAINTAINED
THE CATEGORICAL POPS FOR MOST OF THE CWA- JUST LIKELY IN THE FAR
WEST WITH THE DOWNSLOPE SE FLOW. THIS WAVE OF UPPER FORCING PASSES
NORTH OF THE CWA DURING THE NIGHT THURSDAY NIGHT...SO I HAVE POPS
GRADUALLY DECREASING THU NIGHT FROM SW TO NORTHEAST. OVERALL QPF
FROM THE PRECIP WED NIGHT INTO THU NIGHT LOOKS TO BE LESS THAN AN
INCH EVEN IN UPSLOPE AREAS...SO I DO NOT EXPECT ANY WATER PROBLEMS
UP TO THEN. THE NEXT STRONG WAVE ROTATING AROUND THE UPPER LOW
LOOKS TO AFFECT THE FORECAST AREA FRIDAY AFTERNOON INTO FRIDAY
NIGHT. THOUGH THERE ARE TIMING AND LOCATION DIFFERENCES IN THE
MODELS FOR THE UPPER LOW...THE MAIN THING IS THAT IT WILL BE
CLOSER TO THE AREA BY FRIDAY...THUS A MUCH BETTER MOISTURE
TRANSPORT INTO THE REGION...AND POTENTIALLY BETTER FORCING ALOFT.
THIS IS THE PERIOD WHERE WE MAY BE UNSTABLE ENOUGH FOR TSTMS...AND
THE MODELS ARE INDICATING A CONVECTIVE BAND MOVING THROUGH THE
FORECAST AREA- THE GFS FRIDAY NIGHT...AND THE ECMWF HAS SLOWED
DOWN TO DURING THE DAY SATURDAY. IF WE SEE THIS OCCUR...FLASH
FLOODING WILL BE A GOOD POSSIBILITY. PLEASE SEE HYDRO SECTION OF
THIS AFD FOR DETAILS ON OUR THINKING CONCERNING POSSIBLE FLOODING.
HAVE KEPT POPS HIGH...AND DIURNAL TEMP RANGE LOW...THOUGH TEMPS
WILL REMAIN MILD THROUGH FRIDAY NIGHT.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
CLOUDY...COOL AND RAINY WEATHER EXPECTED THIS WEEKEND. THE
COMBINATION OF SNOW MELT AND RAIN COULD RESULT IN POTENTIAL
FLOODING. A SFC LOW WHICH FORMS ACROSS THE TN VALLEY WITH A STACKED
UPPER LOW WILL MOVE EAST INTO OUR REGION ON SATURDAY. BY SATURDAY
NIGHT...LOOKING AT NW FLOW DEVELOPING AND THE AIR COOLING FROM WEST
TO EAST.
THREAT OF UPSLOPE RAIN/SNOW SHOWERS WILL PERSIST INTO MONDAY AS THE
LOW OFF THE MID ATLANTIC COAST DEEPENS AND SHIFTS NORTHEAST TOWARD
THE CANADIAN MARITIMES MONDAY WITH MAIN 5H AXIS OF TROUGH OVER EAST
COAST. KEPT LIGHT POPS IN THE WEST ON TUESDAY SIMILAR TO GFS.
AS THE UPPER LOW MOVES OVERHEAD SATURDAY INTO SUNDAY...TEMPERATURES
WILL DROP BACK TO NORMAL FOR THIS TIME OF YEAR. TEMPERATURES WILL
SLOWLY WARM EARLY NEXT WEEK.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
WARM FRONT WILL LIFT ACROSS THE AREA LATE TONIGHT AND WEDNESDAY.
AS SUCH...EXPECT CLOUDS TO THICKEN AND LOWER OVERNIGHT AS
MOISTURE INCREASES FROM THE SOUTHWEST. MODERATE CONFIDENCE THAT
CLOUD BASES TONIGHT AND WEDNESDAY WILL REMAIN AT LEVELS PERMISABLE
FOR VFR. SOME LIGHT SHOWER ACTIVITY WILL OCCUR WHICH MAY RESTRICT
VSBYS INTO MVFR CATEGORY FOR A BRIEF PERIOD OF TIME...BUT
CONFIDENCE LESS THAN 50 PERCENT SO WILL REFRAIN FROM MENTIONING IN
THE TAFS.
AFTER THE FRONT GOES THROUGH EXPECT WEAK SOUTHERLY FLOW ON
WEDNESDAY AFTERNOON. WILL MAINTAIN LAYER OF HIGH BASED CU...BUT
NO SIGNIFICANT WEATHER CONCERNS NOTED UNTIL WEDNESDAY NIGHT AND
BEYOND.
LARGE AND SLOW-MOVING UPPER LOW OVER THE MIDWEST WILL BRING
INCREASINGLY POOR FLYING CONDITIONS FOR THE LATER HALF OF THE WEEK.
CHANCES FOR RAINFALL INCREASE DRAMATICALLY ON THURSDAY WITH
OVERRUNNING RAINFALL AND THEN THE POSSIBILITY OF SCATTERED
CONVECTIVE STORMS ON FRIDAY. CEILINGS AND VISIBILITIES WILL FALL
BACK INTO THE MVFR TO IFR RANGE DURING MUCH OF THE EXTENDED
FORECAST PERIOD.
&&
.HYDROLOGY...
CONTINUING TO MONITOR THE POSSIBILITY OF FLOODING DUE TO COMBINED
SNOW MELT/HEAVY RAINFALL SCENARIO LATE THIS WEEK. PER COORDINATION
WITH WFO CHARLESTON AND OHIO RIVER FORECAST CENTER WILL BE ISSUING A
FLOOD WATCH FOR MAINLY THE GREENBRIER RIVER IN WEST VIRGINIA FOR
LATE IN THE WEEK. THE WATCH IS BEING ISSUED SOMEWHAT SOONER THAN IS
TYPICAL DUE TO THE HIGHER CONFIDENCE THAT THE SNOW MELT WILL OCCUR
AND WOULD BE ENOUGH TO BRING THE GREENBRIER RIVER CLOSE TO FLOOD
STAGE. NCEP AND MODEL QPF BY EARLY SUNDAY COULD RANGE FROM 1 TO 3
INCHES IN SOME RIVER BASINS. THE ESTIMATES OF SNOW WATER EQUIVALENT
(SWE) IN PORTIONS OF THE WESTERN MOUNTAINS..MAINLY THE GREENBRIER
BASIN ARE STILL OVER 2 INCHES WITH ISOLATED AMOUNTS OVER 5 INCHES.
CURRENT THINKING IS THAT MOST IF NOT ALL OF THIS SNOW WILL MELT
UNDER THE ONSLAUGHT OF RAINFALL AND HIGHER DEWPOINT AIR. DEWPOINTS
MAINLY REMAIN IN THE UPPER 40S IN THE WEST BUT COULD REACH LOW 50S
WHICH IS VERY EFFECTIVE IN MELTING SNOW ESPECIALLY IF COMBINED WITH
STRONG WINDS. THERE IS SUBSTANTIALLY LESS SWE IN THE UPPER JAMES AND
NEW RIVER BASINS...HENCE THE POTENTIAL FOR RIVER FLOODING IS
LESS...BUT 2 TO 3 INCHES OF RAINFALL ON TOP OF BASICALLY SATURATED
GROUND MIGHT STILL BE ENOUGH IN THOSE BASINS TO CAUSE AT LEAST MINOR
RIVER FLOODING BY LATE IN THE WEEK OR THE WEEKEND. THE POSSIBILITY
OF MORE RAPID RUNOFF AND FLASH FLOODING ALSO EXISTS ON FRIDAY AS
CONVECTIVE ELEMENTS WITH LOCALLY HEAVY RAINFALL MAY DEVELOP AND
TRACK ACROSS THE PARTS OF THE AREA.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...FLOOD WATCH FROM THURSDAY EVENING THROUGH SATURDAY AFTERNOON
FOR WVZ043>045.
&&
$$
SYNOPSIS...JJ
NEAR TERM...JJ
SHORT TERM...PC
LONG TERM...KK
AVIATION...PM
HYDROLOGY...
NWS Office Area Forecast Discussion
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