Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 020721
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
321 AM EDT WED SEP 2 2015

.SYNOPSIS...
A RIDGE OF HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH THE
END OF THE WEEK. UPPER LEVEL DISTURBANCES TRACKING THROUGH THE
RIDGING WILL RESULT IN WIDELY SCATTERED MAINLY DIURNAL SHOWERS
AND STORMS INTO FRIDAY. A WEAK BACKDOOR COLD FRONT WILL DROP
SOUTH THROUGH THE AREA BY THE END OF WEEK BRINGING SOMEWHAT DRIER
AND COOLER AIR FOR THE WEEKEND.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 240 AM EDT WEDNESDAY...

OVERALL HOT AND HUMID WEATHER FOR EARLY SEPTEMBER TO PERSIST TODAY AS
SURFACE HIGH PRESSURE REMAINS IN PLACE ACROSS THE MOUNTAINS. HOWEVER
SHORTWAVE ENERGY IN THE FORM OF AN OPENING UPPER LOW ACROSS THE OHIO
VALLEY WILL RIDE SOUTHEAST THROUGH THE 5H RIDGE AND OVER THE NORTHERN
HALF OF THE AREA THIS AFTERNOON. THIS SHOULD RESULT IN BETTER LIFT
ESPCLY ALONG AND JUST SOUTH OF THE INTERSTATE 64 CORRIDOR EARLY ON AND
ACROSS THE EASTERN HALF THROUGH LATE IN THE DAY. LATEST GUIDANCE ALSO
SHOWING BETTER INSTABILITY WITH A LITTLE MORE COOLING ALOFT...BUT STILL
UNCERTAINTY WITH COVERAGE GIVEN OVERALL BROAD SUBSIDENCE IN PLACE UNDER
RATHER WARM 5H TEMPS. CURRENT SPC/RNK WRF SOLUTIONS ALONG WITH THE
LATEST HRRR REMAIN THE MOST WIDESPREAD WITH SHRA/TSRA NORTH HALF AND
ALONG THE BLUE RIDGE. THIS WHILE MOST OTHER SOLUTIONS INCLUDING
ENSEMBLES PRODUCING LESS INCLUDING ONLY WIDELY SCATTERED SHALLOW
CONVECTION MAINLY CONFINED FROM THE VIRGINIA HIGHLANDS EAST TO AROUND
KLYH FOR THE MOST PART. THEREFORE ALIGNED HIGHEST CHANCE POPS ACROSS
THE FAR NORTH WITH A PERIOD OF LOWER CHANCES SOUTH/EAST DURING MID/LATE
AFTERNOON AND ONLY ISOLATED COVERAGE FAR SW. GIVEN WEAK FLOW ALOFT NOT
EXPECTING MUCH OF A SEVERE THREAT BUT COULD SEE A BIT MORE CLUSTERING
OF SLOW MOVING CONVECTION RIGHT NEAR THE CORE OF THE UPPER WAVE LATE.

OTHERWISE LOOKING AT MAINLY PC WITH MID DECK EARLY...THEN MORE CU THIS
AFTERNOON WITH HIGHS AGAIN REACHING THE LOW 90S EAST AND WELL INTO THE
80S ELSEWHERE PENDING TIMING OF CONVECTIVE INITIATION.

IMPULSE PASSES THIS EVENING LEAVING THE REGION IN BETWEEN WAVES AND
UNDER SURFACE HIGH PRESSURE. THIS SHOULD ALLOW MOST CONVECTION TO FADE
BY MIDNIGHT GIVEN LOSS OF HEATING AND SOME OVERNIGHT CLEARING PER WEAK
NW FLOW ALOFT IN THE WAKE OF THE MID LEVEL SYSTEM. THUS KEEPING SOME
LOW END CHANCE POPS GOING MAINLY EAST THIS EVENING BEFORE TRENDING DRY
WITH FOG AGAIN OVERNIGHT. LOWS PERHAPS SLIGHTLY COOLER GIVEN SOME DROP
IN DEWPOINTS AND ESPCLY WHERE ANY COOLING EVENING RAINFALL OCCURS BUT
STILL MOSTLY LOW/MID 60S MOUNTAINS TO UPPER 60S EAST.
&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
AS OF 345 PM EDT TUESDAY...

THE GFS MOVES THE OHIO SHORT WAVE SLOWER THAN THE NAM/SREF. GIVEN
THE LACK OF A KICKER FOR THIS VORT MAX...THE SLOWER GFS SEEMS MORE
REASONABLE...BUT EVEN ON THIS SLOWER TRACK THE SHORT WAVE WILL STILL
BE SOUTHEAST OF THE FORECAST AREA BY THURSDAY AFTERNOON. WILL EXTEND
THE PROBABILITY OF PRECIPITATION IN THE FORECAST FOR WEDNESDAY
NIGHT. STAYED CLOSER TO MAV GUIDANCE THROUGH THE PERIOD.

BACKDOOR FRONT MOVES SOUTH THROUGH THE NEW ENGLAND AND MID ATLANTIC
COAST. MODELS WERE SHOWING SOME CONVERGENCE IN EASTERN VIRGINIA BUT
STILL QUESTIONABLE HOW MUCH LIFT THIS FEATURE MAY PROVIDE FOR THE
COUNTY WARNING AREA. BEST PROBABILITY OF PRECIPITATION WILL BE IN
THE NORTHEAST COUNTIES OF THE FORECAST AREA...EAST OF THE BLUE
RIDGE. AS THIS FRONT MOVES DOWN THE COAST AND HIGH PRESSURE BUILDS
SOUTH OVER THE APPALACHIANS...WINDS WILL TURN FROM NORTH TO EAST.
THIS EASTERLY COMPONENT OF THE WIND AT THE SURFACE THROUGH LOW
LEVELS MAY ALSO EXPAND THE CLOUD COVER AND PROBABILITY OF
PRECIPITATION ALONG THE BLUE RIDGE.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 100 PM EDT TUESDAY...

LOWER 500 MB HEIGHTS REMAINED TRAPPED UNDER THE RIDGE OVER THE
SOUTHEAST UNITED STATES FRIDAY NIGHT THROUGH SUNDAY. SUNDAY NIGHT
INTO TUESDAY...THE CENTER OF THE UPPER RIDGE...DRIFTS SOUTH INTO THE
MID ATLANTIC REGION. HEIGHTS WILL BE CLOSE TO 594DM ACCORDING TO THE
00Z GFS. AT THE SURFACE FRIDAY NIGHT ANY REMNANTS OF THE BACKDOOR
FRONT WASH OUT AND BY SATURDAY THE WEDGE WILL BE FULLY ESTABLISHED
AND THIS FEATURE WILL REMAIN IN PLACE THROUGH SUNDAY. HIGH PRESSURE
WILL COVER THE MID ATLANTIC STATES THROUGH TUESDAY. UNSEASONABLY
WARM TEMPERATURES...WITH 850 MB TEMPERATURES APPROACHING +20...MOVE
INTO THE REGION WITH THE HIGHER HEIGHTS.

A DRIER AIR MASS BEGINS TO APPROACH THE REGION AS THE WEDGE BUILDS
IN ON SATURDAY. SUNDAY AND MONDAY...ECMWF WAS SHOWING MUCH DRIER AIR
ABOVE 850MB. BELOW 850 MB THE DRIER AIR REMAINS EAST AND SOUTH OF
THE FORECAST AREA THROUGH MONDAY.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
AS OF 100 AM EDT WEDNESDAY...

OTHER THAN FOR DEBRIS MID/HIGH CLOUDS...FOG THE MAIN CONCERN
OVERNIGHT WITH POTENTIAL AGAIN GIVEN LESS CLOUDS OF SEEING THE
VALLEYS SUCH AS KLWB/KBCB DROP INTO LIFR/IFR FOR A PERIOD PRIOR TO
DAYBREAK. ALSO SOME FOG POSSIBLE AROUND KLYH-KDAN WHERE BRIEF MVFR
TO IFR POSSIBLE WHILE COVERAGE LOOKS QUITE SPOTTY AT KBLF WHERE
LIMITED TO JUST A VERY BRIEF INCLUSION OF MVFR CONDITIONS AROUND
DAWN.

FOR WEDNESDAY...SHOULD SEE ANY LOW CLOUDS/FOG FADE WITH THE ONSET
OF HEATING ALLOWING FOR VFR CONDITIONS TO QUICKLY RETURN BY MID
MORNING IF NOT SOONER. THEN EXPECT THE UPPER WAVE OVER THE OHIO
VALLEY TO SLOWLY SHIFT SOUTHEAST INTO VIRGINIA. THIS WILL ALLOW
MORE INSTABILITY WITH STEEPER LAPSE RATES AND LIFT. SHOWERS AND
STORMS WILL BE MORE SCATTERED WEDNESDAY AFTERNOON WITH BEST
FORCING ACROSS THE FOOTHILLS/PIEDMONT TO THE NEW RIVER VALLEY. AS
OF NOW WILL KEEP THE GOING VCTS AT KROA/KLYH AND KBCB AFTER
19Z/3PM...BUT THINK COVERAGE WILL BE LESS FURTHER WEST AND
SOUTHEAST...SO ONLY GOING WITH A VCSH AT KLWB-KBLF WHILE KEEPING
MENTION OUT OF KDAN.

OVERALL EXPECT VFR CONDITIONS WEDNESDAY WITH CIGS OF 4-6KFT WITH
TCU AND CB IN THE AFTERNOON.


EXTENDED AVIATION DISCUSSION...

THE FORECAST AREA WILL REMAIN IN A WEAKLY FORCED SYNOPTIC
ENVIRONMENT THROUGH THURSDAY...WITH CHANCES FOR DIURNAL
CONVECTION MAINLY FROM THE BLUE RIDGE WEST...AND SOME MVFR/IFR
FOG/STRATUS DEVELOPMENT AT NIGHT...ESPECIALLY AT KBCB AND KLWB.

FOR FRIDAY INTO SUNDAY WILL SEE HIGH PRESSURE IN CONTROL THOUGH
THE POSITION OF THE HIGH OVER THE MID ATLANTIC MAY SLIDE MORE MVFR
CIGS OFF THE ATLANTIC INTO OUR EASTERN TAF LOCATIONS.

&&

.EQUIPMENT...
AS OF 400 PM EDT TUESDAY...

THE DEW POINT READING AT KJFZ...RICHLANDS VA AWOS...IS INCORRECT.
AT THIS TIME WE DO NOT KNOW WHEN THIS SENSOR WILL BE REPAIRED.

&&

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

&&

$$
SYNOPSIS...JH/NF
NEAR TERM...JH
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...JH/NF/WP
EQUIPMENT...



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