Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 020850
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
450 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 SATURDAY NIGHT/...
AS OF 415 AM EDT WEDNESDAY...

WEAK UPPER-LEVEL SHORT WAVE WILL BE DISSIPATING ACROSS NORTH
CAROLINA DRIFTING SLOWLY INTO THE SOUTHEAST STATES WHERE IT
APPEARS IT IS DESTINED TO BECOME A WEAK CUTOFF THAT WILL
RETROGRADE/LINGER ACROSS THE SOUTHEAST/MID-SOUTH INTO NEXT WEEK AS
A LARGE HIGH AMPLITUDE UPPER RIDGE CONTINUES TO BUILD FROM THE
SOUTH CENTRAL/CENTRAL U.S. INTO SOUTHEAST CANADA AND THE NORTHEAST
U.S. OVER THE TOP OF THE WEAK CUTOFF LOW. UPPER SUPPORT WILL BE
MINIMAL AT BEST WITH BEST DYNAMICS...WHAT THEY ARE...HAVING
DRIFTED SOUTH OF THE AREA. ANY CONVECTION WILL LARGELY BE THE
RESULT OF DIFFERENTIAL HEATING AND FOCUSED PRIMARILY ACROSS THE
WESTERN MOUNTAINS. REALLY CANNOT SUPPORT MUCH MORE THAN 30 POPS AT
BEST.

BY FRIDAY...A LARGE SURFACE HIGH DEVELOPING ACROSS THE NORTHEAST
U.S. UNDERNEATH THE MAMMOTH UPPER RIDGE WILL BEGIN TO PUSH A
BACKDOOR FRONT FROM THE MID-ATLANTIC SOUTHWESTWARD. UPPER DYNAMICS
ARE VERY WEAK...BUT A MARKED DEWPOINT GRADIENT WILL EXIST ALONG
THE SOUTHWESTWARD ADVANCING BOUNDARY AS VERY DRY AIR ADVECTS
SOUTHWEST INTO NORTHERN VA. THIS SHOULD BE SUFFICIENT TO SUPPORT
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS...WITH THE BEST
COVERAGE SHIFTING SOUTHWEST TOWARD EVENING. INSTABILITY IS QUITE
NOTABLE ACROSS THE REGION IN ADVANCE OF THIS BACKDOOR FRONT...SO
EVEN WITH WEAK DYNAMICS...WITH THE NOTED INSTABILITY AND PWATS IN
THE 1.5 TO 1.7 INCH RANGE...30-40 PERCENT POPS SEEMS REASONABLE.

FOR SATURDAY...THE BACKDOOR FRONT CONTINUES TO DRIFT SOUTHWEST AND
SHOULD BE LOCATED FROM CENTRAL WV THROUGH SOUTHWEST VA...NEAR THE
I-77 CORRIDOR...INTO CENTRAL NC. VERY DRY AIR IS NOTED ADVECTING
INTO THE REGION FROM THE NORTHEAST WITH DEWPOINTS DROPPING INTO
THE 50S AND PWATS FALLING TO NEAR 0.50 INCH ACROSS THE NORTHEAST
PART OF THE CWA. ANY CONVECTION SATURDAY SHOULD BE LIMITED TO THE
I-77 CORRIDOR AND POINTS WESTWARD...PRIMARILY DURING THE
AFTERNOON/EVENING.

TEMPERATURES WILL REMAIN WELL ABOVE NORMAL THURSDAY AND FRIDAY
AHEAD OF THE BACKDOOR FRONT...WITH MAX TEMPS WELL INTO THE
80S...NEAR 90 ACROSS THE PIEDMONT. MIN TEMPS WILL HOLD MOSTLY IN
THE 60S TO EVEN NEAR 70 ACROSS THE PIEDMONT. THESE READINGS ARE
AROUND 5 AND 10 DEGREES ABOVE NORMAL...RESPECTIVELY. MOS GUIDANCE
HAS BEEN TRENDING TOO MUCH TOWARD CLIMATOLOGY...SO NEEDED TO NUDGE
UP MOST AREAS FROM 2-3 DEGREES TO BETTER MATCH WHAT HAS BEEN
OCCURRING RECENTLY.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 445 AM EDT WEDNESDAY...

THE FOCUS THROUGH THE PERIOD WILL BE ON THE AFOREMENTIONED WEAK
AND INCREASING BROAD UPPER LOW ANCHORED ACROSS THE SOUTHEAST/MID-
SOUTH PART OF THE U.S. OUR CWA WILL BE STUCK IN THE TRANSITION
ZONE BETWEEN THIS INCREASINGLY MOIST/UNSTABLE AIR MASS TO THE
SOUTH AND THE PERSISTING UPPER RIDGE AND ASSOCIATED
SUBSIDENCE/VERY DRY AND WARM AIR MASS ACROSS THE MID-ATLANTIC
REGION. SHOWER/THUNDERSTORM CHANCES WILL GRADUALLY CREEP NORTHWARD
THROUGH THE PERIOD...BUT LIKELY REMAIN CONFINED TO AREAS WEST OF
I-77 SUNDAY...THEN CREEP FURTHER NORTH TOWARD THE U.S. 460
CORRIDOR BY MONDAY AND MUCH OF THE CWA BY TUESDAY. THE BEST
CHANCES THROUGHOUT THE PERIOD WILL REMAIN ACROSS THE WESTERN NC
MOUNTAINS. THE MODELS HAVE CONTINUALLY DELAYED THE ARRIVAL OF A
FRONT TOWARD THE MID PART OF NEXT WEEK...AND WITH THE UPPER RIDGE
SANDWICHED IN BETWEEN THE LOW PRESSURE AREA TO THE SOUTH AND THE
STRONGER WESTERLIES ALONG THE CANADIAN BORDER...IT MAY BE SOME
TIME BEFORE IT ACTUALLY REACHES OUR AREA. HENCE...SUMMER APPEARS
DESTINED TO HANG ON MUCH OF NEXT WEEK.

MAX TEMPS SHOULD BE NEAR NORMAL AT THE BEGINNING OF THE
PERIOD...BUT PERHAPS STILL SLIGHTLY ABOVE NORMAL WEST OF I-77. MIN
TEMPS WILL REMAIN NEAR NORMAL TO SLIGHTLY ABOVE NORMAL FAR
SOUTHWEST. MAX AND MIN TEMPS WILL CREEP TO SLIGHTLY ABOVE NORMAL
LEVELS AGAIN AS WE MOVE INTO EARLY NEXT WEEK.

&&

.AVIATION /08Z 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...RAB
LONG TERM...AMS/RAB
AVIATION...JH/NF/WP
EQUIPMENT...


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