Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 081925
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
325 PM EDT TUE JUL 8 2014

.SYNOPSIS...
A SLOW MOVING COLD FRONT WILL APPROACH FROM THE NORTHWEST TONIGHT
AND WEDNESDAY...BEFORE CROSSING THROUGH THE AREA WEDNESDAY NIGHT.
HIGH PRESSURE WILL FOLLOW THE FRONT FOR THURSDAY INTO SATURDAY. A
MUCH STRONGER COLD FRONT WILL BE PASSING THROUGH THE REGION NEXT
MONDAY AND TUESDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 315 PM EDT TUESDAY...

WATER VAPOR LOOP SHOWED THE FIRST OF TWO SHORT WAVES THAT WILL
DEEPEN THE NORTHEAST TROF. THE SECOND WAVE CROSSES THE GREAT LAKES
THEN INTO THE NORTHEAST WEDNESDAY NIGHT.

LAST FEW RUNS OF THE LOCAL WRF AND HRRR WERE VERY CONSISTENT WITH
THE TIMING OF A BAND OF THUNDERSTORMS MOVING IN FROM THE WEST...WHAT
WAS CURRENTLY DEVELOPING FROM AROUND PITTSBURGH TO NORTHWEST OF
CHARLESTON WV. STILL EXPECTING THIS TO REACH SOUTHEAST WEST VIRGINIA
BETWEEN 20-22Z/4-6PM.

GUSTY SOUTHWEST SURFACE WINDS AND LOW LEVEL MIXING HAS BROUGHT
SURFACE DEW POINTS DOWN INTO THE UPPER 50S TO LOWER 60S...SO CAPES
HAVE PEAKED AROUND 2000 J/KG. HOWEVER...AS INDICATED WITH A CLASSIC
INVERTED V SOUNDING...DCAPE WAS A HIGH AS 1300 J/KG IN THE FAR
SOUTHEAST COUNTY WARNING AREA. IF STORMS MANAGE TO GET INTO THIS
ENVIRONMENT AND OVERCOME THE DOWNSLOPING EAST OF THE BLUE RIDGE
THERE IS A POTENTIAL FOR STRONG TO DAMAGING WINDS.

WITH THE REMOVAL OF HEATING...INTENSITY AND COVERAGE OF
PRECIPITATION WILL DIMINISH...MAINLY AFTER 02Z/10PM. THE SOUTHERN
END OF THE LINE OF STORMS...EXTENDING ACROSS THE TENNESSEE VALLEY
MAY CONTINUE OVERNIGHT. HAVE KEPT A HIGHER PROBABILITY OF
PRECIPITATION IN THE SOUTHWEST COUNTY WARNING AREA THROUGH WEDNESDAY
MORNING.

EXPECTING LITTLE PROGRESS IN THE EASTWARD MOVEMENT OF THE SURFACE
COLD FRONT TONIGHT AND WEDNESDAY WITH BROAD SOUTHWEST FLOW PARALLEL
TO THE BOUNDARY AND LIMITED MOVEMENT OF THE UPPER TROF. BEST
PROBABILITY OF PRECIPITATION WEDNESDAY WILL BE IN THE AFTERNOON WITH
AREAS OF SURFACE BASED IN STABILITY AND CONVERGENCE...PLUS ALONG ANY
OUTFLOW PRODUCED BY THE THUNDERSTORMS THAT DEVELOP THIS AFTERNOON.
NARROWING DOWN WHERE THIS WILL BE IS THE BIGGEST CHALLENGE.

LOOKING FOR MUGGY CONDITIONS WILL DEW POINTS RISING BACK UP THROUGH
THE 60S TONIGHT...ESPECIALLY WHERE IT RAINS. AMOUNT OF CLOUDS WILL
DETERMINE HOW HOT TEMPERATURES WILL GET ON WEDNESDAY. WILL BE
DEPENDENT ON WHERE IT IS RAINING IN THE MORNING. FOR NOW STAYED
CLOSED TO THE MET GUIDANCE FOR MAXIMUM TEMPERATURES.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 310 PM EDT TUESDAY...

WEAK COOL FRONT EXPECTED TO DRIFT SOUTHEAST THROUGH THE BLACKSBURG
FORECAST AREA WEDNESDAY NIGHT. ACTUAL SURFACE REFLECTION WILL LIKELY
BE DIFFICULT TO DEFINE CONSIDERING DIFFUSE NATURE OF FRONT...AND
CONTAMINATION FROM COOL OUTFLOW BOUNDARIES GENERATED BY CONVECTIVE
ACTIVITY PRECEDING IT.  HOWEVER...UPPER TROF WILL REMAIN TO THE
WEST...AND WITH SUBTLE BACKING OF LOW LEVEL FLOW EXPECTED AHEAD OF
UPPER TROF...ALONG WITH GRADUAL COOLING ALOFT...SUPPORT FOR PRE- AND
POST-FRONTAL PRECIPITATION MAY PERSIST WELL INTO THE EVENING...AND
PERHAPS THOUGH MUCH OF THE NIGHT ACROSS SOUTHERN/SOUTHEASTERN AREAS.
NORTHWESTERN AREAS SHOULD REMAIN DRY...OTHER THAN PERHAPS A
LINGERING EARLY EVENING SHOWER.

ALTHOUGH NORTHWESTERN AREAS EXPECTED TO REMAIN DRY ON
THURSDAY...PROXIMITY OF OLD FRONTAL BOUNDARY LYING JUST TO THE SOUTH
AND EAST...AND LIMITED ADDITIONAL MOVEMENT EAST OF UPPER TROF
WARRANTS CONTINUED AT LEAST LOW THREAT FOR DIURNALLY DRIVEN SHOWERS
OR THUNDERSTORMS ACROSS THE SOUTH AND SOUTHEAST PORTION OF
THE FORECAST AREA DURING THE AFTERNOON INTO THE EVENING.

UPPER TROF FINALLY EXPECTED TO MOVE OVER AND THEN JUST TO THE EAST
OF THE FORECAST AREA ON FRIDAY...BUT PLACEMENT SUPPORTS
AMPLIFICATION OF SURFACE RIDGE JUST TO OUR NORTHEAST WHICH ALLOWS
LOW LEVEL FLOW TO VEER AROUND BY DAYS END INTO THE EAST. COMBINATION
OF COOLER AIR ALOFT...PLENTY OF INSOLATION...AND LIGHT UPSLOPING
AGAINST THE EASTERN FLANKS OF THE BLUE RIDGE MAY BE SUFFICIENT TO
OVERCOME DEVELOPING CAP TO SUPPORT ISOLATED TO WIDELY SCATTERED
CONVECTION ALONG AND EAST OF THE BLUE RIDGE BEFORE DIMINISHING WITH
LOSS OF DAYTIME HEATING FRIDAY EVENING.

POST FRONTAL TEMPERATURES WILL BE SLIGHTLY COOLER THAN THE PAST
SEVERAL DAYS...MAINLY 70S TO AROUND 80 ACROSS THE HIGHER ELEVATIONS
TO MAINLY 80S PIEDMONT...WITH 50S IN THE MOUNTAIN VALLEYS TO MAINLY
60S ACROSS THE PIEDMONT AT NIGHT.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 310 PM EDT TUESDAY...

DAILY THREAT OF WIDELY SCATTERED TO SCATTERED DIURNALLY DRIVEN
SHOWERS/THUNDERSTORMS APPEARS TO BE IN THE OFFING DURING THE LONG
TERM PERIOD AS A SERIES OF WEAK SHORT WAVES IN RELATIVELY ZONAL FLOW
FORECAST TO MOVE EAST THROUGH THE BLACKSBURG FORECAST AREA.

FIRST WAVE EXPECTED ON SATURDAY...WITH SECOND WAVE ON SUNDAY...TO BE
FOLLOWED BY MUCH MORE SUBSTANTIAL WAVE IN MONDAY/TUESDAY TIMEFRAME
AS EASTERN CANADIAN UPPER LOW AMPLIFIES AND RETROGRESSES
SOUTHWESTWARD INTO THE UPPER GREAT LAKES AREA.

DEEPENING VERY BROAD UPPER TROF/CLOSED SYSTEM WILL SUPPORT A GOOD
PUSH OF UNUSUALLY COOL AIR INTO THE MID APPALACHIAN AND MID ATLANTIC
REGION BY THE END OF THE LONG TERM PERIOD...BUT WITH THE COOLEST
PORTION OF THE AIRMASS TO ARRIVE JUST OUTSIDE OF THIS FORECAST
PERIOD...ON WEDNESDAY.

AT LEAST THROUGH MONDAY...EXPECT RELATIVELY SEASONAL TEMPERATURES
WITH NO SIGNIFICANT DAY TO DAY CHANGES IN AIRMASS. HIGHS SHOULD
RANGE FROM THE MID 70S TO LOWER 80S ACROSS THE HIGHER ELEVATIONS TO
UPPER 80S TO LOWER 90S ACROSS THE PIEDMONT. OVERNIGHT LOWS SHOULD BE
GENERALLY IN THE 60S...BUT WITH SOME UPPER 50S POSSIBLE ACROSS THE
HIGHEST ELEVATIONS AND IN THE DEEPER MOUNTAIN VALLEYS. TEMPERATURES
SHOULD BEGIN TRENDING DOWNWARD ABOUT 5F DAILY BEGINNING TUESDAY AS
LEADING EDGE OF SUCCESSIVE WAVES OF COOLER AIR BEGIN TO IMPINGE UPON
THE AREA.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
AS OF 145 PM EDT TUESDAY...

COMMS ISSUES REMAIN AT KDAN DESPITE AN INTERMITTENT RETURN OF
OBSERVATION DATA. AMD NOT SKED CONTINUED IN THE TAF.

BAND OF SHOWERS AND THUNDERSTORMS WILL FORM FROM WESTERN
PENNSYLVANIA TO EASTERN KENTUCKY AND MOVE EAST DURING THE
EVENING. LAST FEW RUNS OF THE HRRR...AS WELL AS THE RUC AND LOCAL
WRF HAVE THE STORMS REACHING KBLF AND KBLF FROM 20-21Z/4-5PM.

LOWER CONFIDENCE AS TO HOW FAR EAST SHOWERS AND THUNDERSTORMS WILL
PROGRESS. HAVE LEFT VCNTY THUNDER IN THE KBCB...KROA AND KLYH
TAFS. THE LEAST LIKELY LOCATION TO GET STORMS WILL BE AT KDAN AS
LONG AS SCATTERED TO ISOLATED THUNDERSTORMS DO NOT DEVELOP IN THE
FOOTHILLS OF THE BLUE RIDE. AS LOWER DEW POINTS MIX DOWN TO THE
SURFACE THIS AFTERNOON...THE INSTABILITY WAS BECOMING LESS
FAVORABLE FOR THUNDERSTORMS IN THE LEE-TROF.

LOSS OF HEATING AND WESTERLY DOWNSLOPE WIND WILL WEAKEN SHOWERS
AND THUNDERSTORMS BY 02Z/10PM. MODELS SHOWED LINGERING SHOWERS
FROM SOUTHERN WEST VIRGINIA TO EASTERN TENNESSEE OVERNIGHT. DO
NOT HAVE ANY IMPACT FROM THIS POTENTIAL RAINFALL IN THE TAFS BUT
HAVE ADDED MVFR CEILINGS TO KBLF AFTER MIDNIGHT. ALSO ADDED LIFR
FOG AND CEILINGS IN FOR KLWB OVERNIGHT..EXPECTING THERE WILL BE
RAIN AT THAT AIRPORT LATE THIS AFTERNOON.

EXTENDED AVIATION...

BEST CHANCE FOR THUNDERSTORMS ON WEDNESDAY WILL BE IN THE
AFTERNOON IN CENTRAL AND EASTERN VIRGINIA AND NORTH CAROLINA
WHERE THE INSTABILITY WILL COMBINE WITH OUTFLOW FROM PREVIOUS
STORMS. THE COLD FRONT WILL FINALLY PUSH THROUGH THE REGION ON
WEDNESDAY NIGHT.

THE FRONT WILL LINGER ACROSS SOUTHERN/EASTERN AREAS THROUGH THE
END OF THE WEEK WITH IMPULSES RIDING ALONG IT. THIS WILL KEEP
UNSETTLED CONDITIONS AT TAF SITES THROUGH THE END OF THE WEEK.
EXPECT DIURNAL TRENDS FOR AFTERNOON CONVECTIVE PRECIPITATION WITH
ASSOCIATED MVFR OR LOWER CONDITIONS... ESPECIALLY FOR
KDAN/KLYH...AND POSSIBLE IFR FOG LATE NIGHTS...MAINLY KBCB AND
KLWB.

&&

.CLIMATE...
AS OF 315 PM EDT TUESDAY...

THIS WAS THE 3RD DRIEST JUNE ON RECORD AT DANVILLE WITH ONLY 1.23
INCHES OF PRECIPITATION. RECORDS GO BACK TO 1948. THE DRIEST JUNE ON
RECORD IS 1.06 INCHES IN 2008.


&&

.EQUIPMENT...
AS OF 315 PM EDT TUESDAY...

COMMUNICATIONS OUTAGE CONTINUES WITH KDAN ASOS NOT TRANSMITTING.
THE FAA IS AWARE OF THE OUTAGE AND WILL BE WORKING ON IT...BUT NO
ESTIMATED TIME OF WHEN IT WILL BE WORKING AGAIN.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...AMS
SHORT TERM...WERT
LONG TERM...AMS/WERT
AVIATION...AMS/JH
CLIMATE...AMS/PC
EQUIPMENT...WP


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