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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
436 AM EDT FRI JUL 25 2014

.SYNOPSIS...
WEAK HIGH PRESSURE BUILDS SOUTH ACROSS THE AREA TODAY INTO
TONIGHT...THEN OFF THE SOUTHEAST COAST SATURDAY. A STRONG COLD
FRONT AND UPPER LEVEL TROUGH IMPACTS US BY MONDAY. 

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM EDT FRIDAY...

DRY AIR HAS MOVED IN ALOFT...BUT IS FIGHTING THE MOISTURE IN THE LOW 
LVLS ACROSS OUR CWA. MESO TRENDS SHOWING LOWER DEWPOINTS SLOWLY 
TRACKING SOUTH FROM THE MID ATLANTIC. WE HAVE BEEN STUCK WITH QUITE 
A BIT OF STRATOCU OVERNIGHT WITH EVEN SHOWERS POPPING UP AROUND 
ROANOKE. THESE SHOWERS HAVE WEAKENED BUT GIVEN SOME THETA-E RIDGE
IN PLACE OVER THE SRN CWA...AND FLOW TURNING MORE EAST...THINK
DRIZZLE/PATCHY SHOWERS WILL BE POSSIBLE NEAR THE BLUE RIDGE INTO
DAWN. FOG WAS DENSE JUST WEST OF OUR CWA...AS LOW CLOUDS CLEARED
OUT EARLY. THE FOG THREAT OVERALL IS GOING TO BE MAINLY CONFINED
TO THE WRN MTNS AND SOME OF THE HIGHER ELEVATIONS ALONG THE BLUE
RIDGE.

THE FORECAST DILEMMA TODAY WILL BE THE STRATOCU CURRENTLY OUT THERE 
AND HOW MUCH LINGERS INTO THIS AFTERNOON AS SFC HIGH BUILDING SOUTH 
MAY LOCK IT IN ALONG THE BLUE RIDGE WITH SFC FLOW WORKING AROUND TO 
THE SOUTHEAST AND MODELS FAVORING THETA-E RIDGE IN THE LOW LVLS 
ACROSS THE SRN BLUE RIDGE. WITH HEATING FROM THE LATE JULY SUN THINK 
SKIES WILL BECOME MOSTLY SUNNY THIS AFTERNOON...EXCEPT ALONG THE 
BLUE RIDGE WHERE WILL BE VARYING FROM PARTLY SUNNY TO MOSTLY CLOUDY. 
THE 00Z NAM IS ACTUALLY SHOWING SOME LIGHT SHRA/TSRA FORMATION IN 
THE NC MTNS. WILL TAKE THIS SOLUTION BUT NOT AS AGGRESSIVE WITH
POPS AND HAVE A TOKEN ISOLATED SHRA/TSRA NEAR BOONE/WEST JEFFERSON
THIS AFTERNOON.

TONIGHT...CONVECTION IF ANY DISSIPATED WITH WEAK SFC HIGH OVERHEAD. 
THE ISSUE AGAIN TONIGHT WILL BE IF ANY CLOUDS STAY IN THE MTNS UNDER 
INVERSION. TAKING THE NAM SOLUTION WILL BE KEEPING THE BLUE RIDGE IN 
MORE CLOUDS WHILE THE REST OF THE CWA STAYS CLEAR TO PARTLY CLOUDY. 
SOME HIGH CLOUD WILL BE INCREASING FROM THE NW LATE. DO NOT FORESEE 
ANY DRIZZLE LATE TONIGHT AS SOUNDING FORECASTS ONLY SHOWING LAYER OF 
OF MOISTURE 2KFT AROUND BOONE-ROANOKE. ADDED PATCHY FOG IN THE 
FORECAST GIVEN FLOW TURNING MORE SOUTH...BUT REMAIN LIGHT.

AS FOR HIGHS WENT CLOSER TO THE MAV THINKING MORE SUN...AND DRIER 
AIR ALOFT MAY ALLOW TEMPS TO HEAT UP MORE...BUT STILL A LESS HUMID 
DAY. HIGHS WILL BE RANGING FROM THE MID TO UPPER 70S MTNS...TO MID 
80S PIEDMONT.

TONIGHT...TIGHTER GRADIENT BETWEEN HIGHER DEWPOINTS SOUTH AND DRIER 
AIR NORTH. THINK THE VALLEYS SHOULD DROP TO THE MID TO UPPER 50S 
WHILE THE SOUTHSIDE VA INTO NC PIEDMONT ONLY FALLS TO THE UPPER 60S.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
AS OF 345 AM EDT FRIDAY...

WEAK HIGH PRESSURE WILL PUSH OFF TO THE EAST EARLY SATURDAY...MAKING 
FOR SUSTAINED SOUTHWESTERLY WIND FLOW IN THE LOW LEVELS THAT WILL 
CARRY TROPICAL AIR NORTHWARD ALONG THE APPALACHIAN CHAIN. WINDS 
HIGHER ALOFT WILL BE OUT OF THE WEST NORTHWEST HOWEVER...WHICH WILL 
RESULT IN A DECENT CAPPING INVERSION ACROSS MOST OF THE AREA. THE 
INVERSION APPEARS WEAKEST ACROSS THE PIEDMONT...WHERE ISOLATED 
SHOWERS AND THUNDERSTORMS MAY DEVELOP DURING LATE AFTERNOON/EARLY 
EVENING AS MAXIMUM DAYTIME HEATING COMBINES WITH A DEVELOPING LEE 
SIDE TROUGH TO HELP DESTABILIZE THE ATMOSPHERE IN THAT AREA. OUTSIDE 
OF THAT HOWEVER...EXPECT ABUNDANT SUNSHINE WHICH WILL HELP AFTERNOON 
TEMPERATURES WARM INTO THE MID TO UPPER 80S ACROSS THE MOUNTAINS... 
AND INTO THE LOW 90S EAST OF THE BLUE RIDGE. 
 
LOOKING INTO EARLY SUNDAY...MODELS ARE PICKING UP ON THE REMNANTS OF 
A THUNDERSTORM COMPLEX ASSOCIATED WITH AN UPPER LEVEL DISTURBANCE 
AFFECTING THE INTERSTATE 64 CORRIDOR...WITH SOME RAIN REACHING 
POSSIBLY AS FAR SOUTH AS HIGHWAY 460. TIMING WILL BE CRITICAL...AS 
THE LATER IN THE NIGHT THE SYSTEM ARRIVES...THE GREATER THE LOSS OF 
INSTABILITY AND THEREFORE THE WEAKER THE STORMS. GIVEN THAT THIS 
ACTIVITY IS EXPECTED TO ARRIVE SHORTLY BEFORE DAWN...BELIEVE THAT 
THE SEVERE THREAT WILL BE REDUCED...BUT CANNOT RULE OUT SOME GUSTY 
WINDS. 

ON SUNDAY EVENING HOWEVER...ANOTHER STRONGER UPPER LEVEL DISTURBANCE 
IS EXPECTED TO FOLLOW A MORE SOUTHERLY TRACK...APPROACHING FROM THE 
WESTERN GREAT LAKES THROUGH THE DAY...AND TRIGGER ANOTHER LINE OF 
THUNDERSTORMS THAT WILL AFFECT OUR AREA DURING THE EVENING. MODELS 
ARE IN DECENT AGREEMENT THAT WE WILL HAVE 45KTS TO 50KTS OF LOW 
LEVEL WINDS ENTERING THE CENTRAL APPALACHIANS WITH THE 
DISTURBANCE...MAKING FOR A DECENT THREAT OF STRONG WINDS AS THE LINE 
OF THUNDERSTORMS ENTERS THE WESTERN HALF OF OUR AREA. CONFIDENCE IS 
INCREASING ON THIS SCENARIO. STORMS WILL MOVE ACROSS OUR AREA DURING 
LATE EVENING...GRADUALLY WEAKENING AS THEY PROCEED EAST IN THE 
DOWNSLOPE FLOW. 

A STRONG COLD FRONT WILL ENTER OUR AREA MONDAY MORNING...SHIFTING 
WINDS NORTHWESTERLY WHICH WILL USHER IN DRIER MORE STABLE AIR. WILL 
BE CONCERNED MAINLY WITH A FEW UPSLOPE SHOWERS ACROSS THE MOUNTAINS 
DURING THE DAY...BUT IT IS POSSIBLE A FEW STORMS MAY DEVELOP ACROSS 
THE PIEDMONT EARLY MONDAY AFTERNOON JUST AHEAD OF THE FRONT. THE 
COLD FRONT WILL THEN PUSH ANY CONVECTION EAST OF OUR AREA BY LATE 
AFTERNOON...WITH UNSEASONABLY COOLER AIR BUILDING IN FROM THE 
NORTHWEST. 

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
AS OF 330 PM EDT THURSDAY...

LONG TERM PERIOD WILL BE CHARACTERIZED BY UNUSUALLY DEEP LONG WAVE 
TROF THAT WILL REMAIN CENTERED OVER THE UPPER GREAT LAKES THROUGHOUT 
MUCH OF NEXT WEEK AS SERIES OF SHORT WAVE TROFS HELP TO AMPLIFY THIS 
FEATURE. 

MOSTLY DRY AND COOL CONDITIONS AS SURFACE RIDGE OF HIGH PRESSURE
NOSES INTO AND THEN OVER BLACKSBURG FORECAST AREA. MOST AREAS WILL
REMAIN 5-10F BELOW NORMAL THROUGH THE PERIOD. MANY MOUNTAIN
VALLEYS...ALONG WITH THE HIGHEST RIDGES WILL LIKELY EXPERIENCE AT
LEAST A COUPLE OF NIGHTS WHERE TEMPERATURES FALL INTO THE 40S.

APPROACH OF ANOTHER SHORT WAVE TROF RIDING AROUND THE BASE OF THE 
UPPER TROF MAY HELP BACK LOW LEVEL FLOW SUFFICIENTLY ON THURSDAY TO 
WARRANT A LOW CHANCE THREAT FOR SOME SHOWERS ACROSS THE SOUTHWESTERN 
MOUNTAIN ON THURSDAY...BUT PRECIPITATION AMOUNTS FROM THIS 
DISTURBANCE...IF ANY...APPEAR TO BE SCANT AT BEST.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
AS OF 140 AM EDT FRIDAY...

AVIATION FORECAST PROVING DIFFICULT THIS MORNING WITH SHRA POPPING
UP IN ROANOKE. CIGS AROUND THE AREA VARY FROM VFR AT
LWB/LYH/BLF...TO IFR AT ROA/DAN. THINK THE OVERALL REGIME THIS
MORNING WILL BE OF MVFR/IFR CIGS AND OCCASIONAL IFR/LIFR FOG.
DRIER AIR SIFTING SE TOWARD SE WV...AND IF THE LEVELS ABOVE THE
BOUNDARY LAYER DRY OUT...FOG AND LOW CLOUDS WILL BE REALIZED AT
BLF/LWB...AS WE ARE ALREADY SEEING THIS JUST WEST TOWARD FAR SW VA
INTO ERN KY. HIGHER DEWPOINTS OUT EAST PLUS HEAVIER RAIN FROM
THURSDAY WILL KEEP/BRING CIGS UNDER 1KFT THIS MORNING. SAME FOR
ROANOKE. BCB IS IFFY BUT WE HAD SHOWERS...SO VARIABLY IFR TO MVFR
HERE. CONFIDENCE HIGH ON SUB VFR CONDITIONS THIS MORNING BUT LOW
ON VSBYS/CIGS.

SFC HIGH OVER THE MID ATLANTIC/OHIO VALLEY SHIFTS SE OVERHEAD. MAY
BE A CASE WHERE CLOUDS STAY STUCK UNDER INVERSION LONGER WITH LACK
OF MIXING. DRIER AIR WILL TRY TO WORK IN LATE MORNING/AFTERNOON
WITH VFR EXPECTED THOUGH SOME LOW LVL MOISTURE REMAINS STUCK
ACROSS DAN-TNB CORRIDOR...SO COULD SEE SOME BKN HIGH END MVFR CIGS
HERE...LOWER IN THE MTNS...AND PERHAPS AS FAR NORTH AS BCB.
CONFIDENCE IS NOT HIGH THOUGH SO KEPT VFR FOR NOW. MODELS ALSO
SHOWING SOME SHRA DEVELOPMENT ACROSS THE SRN BLUE RIDGE AND
POTENTIALLY UP TO BCB/BLF. AGAIN THINK DRY AIR ALOFT WILL KEEP
THIS SITUATED SOUTH OF BLF/BCB/DAN.



EXTENDED AVIATION DISCUSSION...

EXPECT MAINLY VFR THROUGH SUNDAY EXCEPT FOR OVERNIGHT FOG IN THE
VLYS OF LWB/BCB. ANOTHER FRONT IS GOING TO ARRIVE BY MONDAY.
BEFORE THIS SEVERAL DISTURBANCES IN NW FLOW ALOFT MAY BRING
SHRA/TSRA TO THE BLF/LWB CORRIDOR. SATURDAY IS LESS LIKELY AS
MODELS FAVOR A NWD TREND IN CONVECTION TOWARD PA/NRN VA. SUNDAY
COULD BE MORE FAVORABLE...BUT STILL LOOKS LIKE A NWD TRACK. WILL
HAVE TO WATCH HOW THIS DEVELOPS...BUT POTENTIAL FOR SUB VFR
SHRA/TSRA IN THE MTNS IS POSSIBLE LATE THIS WEEKEND. BETTER THREAT
WILL BE WITH THE FRONT MONDAY WITH UPPER TROUGH MOVING ACROSS BY
TUESDAY DRYING THINGS OUT.

&&

.HYDROLOGY...
AS OF 330 PM EDT THURSDAY...

U.S. DROUGHT MONITOR ISSUED THIS MORNING AND VALID THROUGH 12Z
TUESDAY JULY 22 SHOWED EXPANSION OF THE EXISTING ABNORMALLY DRY
CONDITIONS INTO MOST OF OUR SE WV COUNTIES AND FAR WESTERN
VA...MAINLY THE UPPER JAMES RIVER BASIN. 30-DAY RAINFALL DEFICITS
IN MUCH OF THIS AREA ARE RUNNING 2 TO 3 INCHES OR ONLY 25 TO 50
PERCENT OF NORMAL AND 60-DAY RAINFALL NUMBERS NOT MUCH BETTER.
JULY IS CLIMATOLOGICALLY THE WETTEST MONTH IN OUR CWA WITH AN
AVERAGE RANGING FROM 4 TO 5 INCHES.

&&

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

&&

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

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