Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1148 PM EDT FRI SEP 4 2015

.SYNOPSIS...
A BACKDOOR COLD FRONT WILL STALL OVER THE SOUTHERN PORTION OF THE
REGION ON SATURDAY. COOLER AND SOMEWHAT DRIER WEATHER IS EXPECTED
TOWARDS THE END OF THE WEEKEND INTO EARLY NEXT WEEK. A RESURGENCE
OF ATLANTIC MOISTURE RETURNS TO THE AREA BY THE MIDDLE PART OF
NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 1140 PM EDT FRIDAY...

A LONE THUNDERSTORM NORTH OF LYH...WITH ISOLATED SHOWERS ACROSS
THE ALLEGHANY HIGHLANDS INTO THE SOUTHERN SHENANDOAH VLY. NOT
SEEING A LOT OF SIGNALS FOR GOOD COVERAGE OVERNIGHT SO KEPT POPS
IN THE ISOLATED REALM MOSTLY ALONG AND EITHER SIDE OF THE BLUE
RIDGE. THE 00Z NAM IS COMING IN TOO HOT...SHOWING EXCESSIVE
COVERAGE IN THE QPF FIELDS IN THE PIEDMONT 03-06Z. SO LEANED MORE
TOWARD LATEST HRRR/RAP...THEN BLENDED TOWARD OFFICIAL FORECAST BY
DAWN...INCREASING POPS TO CHANCE IN THE SOUTHERN AND SOUTHWEST CWA
BY MID MORNING...CLOSER TO THE UPPER IMPULSE.

SHOULD SEE SOME VARIABLY CLOUDY SKIES AFTER MIDNIGHT...MIX OF LOW
AND HIGH CLOUDS...THEN EASTERLY FLOW WILL SET UP MORE LOWER CLOUDS
FOR MUCH OF THE AREA BY DAWN. FOG IS EXPECTED AS WELL...ESPECIALLY
IN THE MOUNTAINS...ALONG THE BLUE RIDGE PEAKS...LIKE FANCY GAP.

PREVIOUS VALID DISCUSSION...

FOR SATURDAY...HIGH PRESSURE WILL SLOWLY START TO NOSE ITS WAY
SOUTH ALONG THE LEE OF THE APPALACHIANS. NOTABLY DRIER AIR WILL
STILL BE A COUPLE DAYS AWAY...BUT THE INSTABILITY WILL BE LESS
SATURDAY AS COMPARED TO TODAY. HOWEVER...IT WILL NOT BE TOO WEAK
AS TO PREVENT THE DEVELOP OF ISOLATED TO SCATTERED SHOWERS...THE
THE GREATEST CONCENTRATION OVER THE SOUTHWEST PARTS OF THE REGION.
AN ISOLATED THUNDERSTORM CANNOT BE RULED OUT...BUT ANY THAT FORM
WILL NOT BE AS POTENT AS THOSE OF TODAY. HIGH TEMPERATURES WILL BE
ABOUT TEN DEGREES COOLER THAN THOSE OF TODAY. EXPECT MID TO UPPER
70S ACROSS THE MOUNTAINS AND UPPER 70S TO AROUND 80 ACROSS THE
PIEDMONT.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 300 PM EDT FRIDAY...

WILL START SATURDAY EVENING OFF WITH WEAK HIGH PRESSURE WEDGING 
SOUTHWARD AGAINST THE EASTERN FACE OF THE APPALACHIANS...RESULTING 
IN LIGHT NORTHEASTERLY WINDFLOW. THE UPSLOPE WINDS ALONG THE RIDGES 
MAY SUPPORT A FEW SHOWERS INTO EARLY SUNDAY...BUT EXPECT ANY 
THUNDERSTORMS LEFT FROM EARLIER IN THE DAY TO WEAKEN BY SUNSET WITH 
THE LOSS OF DAYTIME HEATING. 

FOR SUNDAY...WEAK HIGH PRESSURE WILL REMAIN IN PLACE ACROSS THE MID 
ATLANTIC...WITH WINDS SHIFTING MORE EASTERLY. THE FLOW OFF THE 
ATLANTIC WILL MAKE FOR CONTINUED COOLER TEMPERATURES...WITH 
AFTERNOON HIGHS RANGING FROM THE MID 70S MOUNTAINS TO LOW 80S EAST 
OF THE BLUE RIDGE. THE HIGH PRESSURE WEDGE WILL BE SHALLOW ENOUGH 
ACROSS THE PIEDMONT OF NORTH CAROLINA THAT A FEW SHOWERS AND 
ISOLATED STORMS WILL DEVELOP WITH AFTERNOON HEATING. MAY ALSO SEE A 
FEW SHOWERS DEVELOP ALONG THE MOUNTAIN RIDGES DUE TO THE UPSLOPE 
WINDS...BUT EXPECT COVERAGE WILL BE SPOTTY AT BEST. RAINFALL WILL 
AGAIN FIZZLE AROUND SUNSET WITH THE LOSS OF DAYTIME HEATING.

FOR LABOR DAY...HIGH PRESSURE WILL GRADUALLY SLIDE EAST...DECREASING 
ITS INFLUENCE ACROSS THE MID ATLANTIC. THIS WILL ALLOW WINDS TO 
SHIFT INCREASINGLY SOUTHERLY TO DRAW MORE UNSTABLE AIR FROM THE 
CAROLINAS INTO OUR AREA. AS SUCH...EXPECT SLIGHTLY BETTER COVERAGE 
OF SHOWERS DEVELOPING WITH AFTERNOON HEATING. WILL ALSO SEE 
INCREASED INSTABILITY AS SUBTLE UPPER LEVEL DISTURBANCES PASS ACROSS 
THE AREA...AND THEREFORE EXPECT SLIGHTLY BETTER COVERAGE OF 
THUNDERSTORMS. UPPER LEVEL WINDS WILL BE LIGHT...RESULTING IN SLOW 
CELL MOVEMENT...WHICH WOULD MAKE FOR LOCALLY HEAVY RAIN AS STORMS 
REMAIN PARKED OVER LOCATIONS FOR EXTENDED PERIODS OF TIME. 
TEMPERATURES WILL TAKE ON A WARMING TREND...WITH AFTERNOON HIGHS 
RANGING FROM THE LOW 80S WEST TO THE UPPER 80S EAST. 

OVERNIGHT TEMPERATURES THROUGH THE PERIOD WILL REMAIN SEASONABLE... 
GENERALLY RANGING FROM THE LOW TO MID 60S MOST LOCATIONS...WITH A 
FEW MID/UPPER 50S IN THE DEEPER MOUNTAIN VALLEYS. PATCHY MOUNTAIN 
VALLEY FOG WILL ALSO BE A COMMON OCCURRENCE EACH NIGHT.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 330 PM EDT FRIDAY...

A GENERAL SUMMERTIME WEATHER PATTERN WILL RETURN FOR THE MIDDLE OF 
NEXT WEEK...WITH SPOTTY SHOWERS AND THUNDERSTORMS DEVELOPING EARLY 
EACH AFTERNOON WITH DAYTIME HEATING...AND DIMINISHING TOWARD SUNSET 
AS HEATING ENDS. EXPECT ONLY SPOTTY COVERAGE OF RAINFALL ON TUESDAY 
DUE TO WEAK SUPPORTING DYNAMICS...HOWEVER COVERAGE WILL INCREASE 
EACH DAY FOR WEDNESDAY AND THURSDAY AS A COLD FRONT APPROACHES FROM 
THE NORTHWEST. 

BY NEXT THURSDAY...LONG RANGE WEATHER FORECAST MODELS DIFFER AS TO 
WHERE THE COLD FRONT WILL BE LOCATED...WITH THE ECMWF MODEL BRINGING 
THE FRONT ACROSS OUR AREA...WHILE THE GFS MODEL KEEPS THE FRONT WELL 
TO OUR NORTH. GIVEN WHAT APPEARS TO BE WEAK UPPER LEVEL SUPPORT TO 
GIVE THE FRONT A SOUTHWARD PUSH...HAVE TRENDED TOWARD THE GFS MODEL 
AND TRIMMED BACK RAIN CHANCES FOR THAT DAY.

EXPECT WARM AND MUGGY CONDITIONS FOR THE PERIOD...WITH HIGHS RANGING 
FROM THE UPPER 70S/LOW 80S ACROSS THE MOUNTAINS...TO THE UPPER 80S 
FOR THE PIEDMONT. LOWS WILL HOLD GENERALLY IN THE LOW TO MID 
60S...PERHAPS WITH A FEW UPPER 50S ACROSS THE MOUNTAINS.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
AS OF 735 PM EDT FRIDAY...

EXPECT A FEW SHRA/TSRA AROUND THROUGH ABOUT MIDNIGHT/04Z...WITH
ROA HAVING A LIGHT RAIN SHOWER TIL 02Z. LYH MAY SEE A SHOWER IN
THE VICINITY AS SMALL AREA MOVES SOUTHWEST FROM BUCKINGHAM COUNTY.
STRONGEST CONVECTION WILL STAY IN A CORRIDOR FROM TRI-HLX AT 00Z
THEN DISSIPATE...MOVING SOUTH INTO TNB-UKF BY 02-3Z.

ISSUE OVERNIGHT WILL BE BACKDOOR FRONT AND LOWER CIGS PLUS
PROSPECTS OF FOG. 

WILL LEAN TOWARD PREVIOUS FORECAST COMBINED WITH OUR LOCAL WRF
WHICH FAVORS SOME IFR/MVFR CIGS/VSBYS LATE TONIGHT AT ALL
SITES...WITH THE BLF/LWB/BCB AREA HAVING WORSE CONDITIONS.

CONFIDENCE IS HIGH THAT SUB VFR WILL OCCUR...BUT LOW ON HOW FAR
DOWN THE CIGS/VSBYS GO.

SATURDAY MORNING INTO THE EARLY AFTERNOON...EXPECT A GRADUAL
TREND OF CEILINGS AND VISIBILITIES IMPROVING TO VISUAL FLIGHT
RULES LEVELS. ISOLATED SHOWERS WILL BE ON THE INCREASE AROUND
NOONTIME...BUT CONFIDENCE IN THEIR LOCATION IS NOT GREAT ENOUGH TO
INCLUDE ANY IN THE PREVAILING WEATHER OF THE FORECASTS.

EXTENDED AVIATION DISCUSSION...

HIGH PRESSURE WILL GRADUALLY WORK INTO THE REGION BY THE END OF
THE WEEKEND...AND REMAIN OVER THE AREA INTO THE EARLY PART OF
NEXT WEEK. LINGERING MOISTURE AND AN EASTERLY FETCH WILL HELP
MAINTAIN SOME ISOLATED TO SCATTERED SHOWERS ACROSS MAINLY WESTERN
AND SOUTHERN PARTS OF THE AREA...ESPECIALLY ON SATURDAY AND SUNDAY
AFTERNOON.

MOISTURE STARTS TO INCREASE AGAIN MONDAY INTO TUESDAY WHILE THE
INFLUENCE OF THE RIDGE WEAKENS. COVERAGE OF SHOWERS...AND POSSIBLY
A FEW STORMS...WILL LIKEWISE START TO INCREASE. PAST
SATURDAY...CEILINGS AND VISIBILITIES WILL PRIMARILY BE VISUAL
FLIGHT RULES. THE EXCEPTION WILL BE LINGERING PATCHY MVFR RULES
ACROSS PARTS OF THE REGION SATURDAY AFTERNOON. ALSO...OVERNIGHT
AND EARLY MOUNTAIN AND RIVER VALLEY INSTRUMENT FLIGHT
RULES/MARGINAL VISUAL FLIGHT RULES FOG/MIST ARE EXPECTED.

&&

.HYDROLOGY...
AS OF 745 PM EDT THURSDAY...

THE WEEKLY UNITED STATES DROUGHT MONITOR ISSUED ON SEPTEMBER 3RD
SHOWS THE EFFECT OF A DRIER THAN NORMAL AUGUST ACROSS MUCH OF THE
AREA. ABNORMALLY DRY CONDITIONS...D0 ON THE DROUGHT SCALE HAVE
BEEN EXPANDED INTO A LARGE PORTION OF SOUTHSIDE VIRGINIA COVERING
MUCH OF THE DAN AND LOWER ROANOKE RIVER BASINS. PARTS OF THE UPPER
YADKIN RIVER BASIN IN NORTH CAROLINA ARE ALREADY IN D1 OR MODERATE
DROUGHT. AUGUST RAINFALL WAS AS LOW AS 50 PERCENT OF NORMAL OR
LESS IN PARTS OF THE AFOREMENTIONED AREAS. SEVERAL NWS COOPERATIVE
CLIMATE STATIONS IN SOUTHERN VIRGINIA RECORDED WELL UNDER 2 INCHES
OF RAIN THE ENTIRE MONTH OF AUGUST INCLUDING HUDDLESTON IN BEDFORD
COUNTY AT 1.17 INCHES AND ROCKY MOUNT IN FRANKLIN COUNTY AT 1.36
INCHES.

&&

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

&&

$$
SYNOPSIS...DS/WP
NEAR TERM...DS/WP
SHORT TERM...NF
LONG TERM...NF
AVIATION...DS/WP
HYDROLOGY...PC

National Weather Service Glossary of Abbreviations