Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 300830 CCA
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
428 AM EDT SUN AUG 30 2015

.SYNOPSIS...
A SERIES OF WEAK UPPER LEVEL DISTURBANCES WILL LIFT NORTH ALONG
THE APPALACHIAN CHAIN THIS AFTERNOON INTO EARLY MONDAY...BRINGING
A GREATER CHANCE FOR SHOWERS TO THE REGION. UPPER LEVEL HIGH
PRESSURE WILL THEN STRENGTHEN AND KEEP US IN A RATHER STAGNANT
PATTERN...MAINTAINING A CHANCE FOR AFTERNOON AND EVENING SHOWERS
AND THUNDERSTORMS THROUGH THE MIDDLE OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 345 AM EDT SUNDAY...

STARTING THE MORNING OFF WITH A BROAD BUT WEAK UPPER LEVEL TROUGH
SITUATED FROM THE GREAT LAKES SOUTHWARD ALONG THE MISSISSIPPI RIVER
VALLEY...WHILE SUBTROPICAL RIDGING REMAINS PARKED OFF THE ATLANTIC
COAST OF THE SOUTHEAST STATES. THIS PATTERN IS MAKING FOR
SOUTHWESTERLY WINDFLOW ALOFT FOR THE MID ATLANTIC...WHICH WILL CARRY
A SERIES OF WEAK DISTURBANCE NORTHWARD ALONG THE APPALACHIAN CHAIN.

FOR TODAY...EXPECT THE MID AND HIGH CLOUDS CURRENTLY IN PLACE TO
LINGER THROUGH THE DAY...ALTHOUGH BRIEF BREAKS WILL OCCUR AT TIMES.
SOUTH SOUTHEASTERLY WINDS NEAR THE SURFACE WILL CONTINUE TO DRAW
MOISTURE INTO THE MOUNTAINS...AND EXPECT WE WILL SEE SHOWERS DEVELOP
DURING EARLY AFTERNOON ALONG THE RIDGES. THE MID AND HIGH CLOUDS
WILL KEEP INSTABILITY QUITE LIMITED...SO DO NOT REALLY MORE THAN
VERY ISOLATED AND BRIEF THUNDERSTORMS TO DEVELOP. AFTERNOON
TEMPERATURES WILL RANGE FROM THE MID 70S TO AROUND 80 ACROSS THE
MOUNTAINS...AND REACH INTO THE LOW/MID 80S ACROSS THE PIEDMONT.

SLIGHTLY BETTER CHANCES FOR SHOWER ACTIVITY ARE EXPECTED HEADING
INTO LATE SUNDAY EVENING AS A STRONGER UPPER LEVEL DISTURBANCE
APPROACHES FROM THE SOUTH. EVEN THEN...WEATHER FORECAST MODELS ARE
CALLING FOR THE BRUNT OF RAINFALL TO MISS OUR AREA TO THE
SOUTHEAST...AND BELIEVE THE PASSAGE OF THIS SYSTEM WILL AMOUNT TO
SPOTTY SHOWERS FOR THE MOUNTAINS...AND PERHAPS THE PIEDMONT SOUTH OF
HIGHWAY 460. SUNDAY NIGHT LOWS WILL RANGE FROM THE UPPER 50S AND LOW
60S WEST...TO THE MID 60S EAST.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
AS OF 400 AM EDT SUNDAY...

A WEAK UPPER LOW AND ASSOCIATED TROPICAL MOISTURE ASSOCIATED WITH
FORMER TROPICAL SYSTEMS DANNY AND ERIKA...WILL BE LIFTING NORTHEAST
ACROSS THE REGION MONDAY ON THE WESTERN PERIPHERY OF A BUILDING
SUBTROPICAL RIDGE ACROSS THE WESTERN ATLANTIC. MODEST LOW-LEVEL
MOISTURE INCREASE IS INDICATED WITH PRECIPITABLE WATER VALUES
CREEPING INTO THE 1.5/1.6 RANGE ACROSS MUCH OF THE CWA. AT THE SAME
TIME...HOWEVER...THE UPPER TROUGH IS WEAKENING AND SHEARING OUT. ON
THE OTHER END OF THE CWA A DIFFUSE AND STALLING FRONT BOUNDARY WILL
BE LOCATED JUST TO OUR NORTH WITH THE ASSOCIATED UPPER AIR SUPPORT
HAVING LIFTED WELL NORTHEAST OF THIS REGION. DESPITE THESE WEAK
SYSTEMS...THE UNDERLYING THEME WILL BE A BROAD SUBTROPICAL RIDGE
BUILDING ACROSS MUCH OF THE EASTERN 2/3RDS OF THE U.S.

SUFFICIENT MOISTURE...INSTABILITY...AND DYNAMICS...GIVEN THE
FRONT TO THE NORTH AND UPPER TROUGH LIFTING ACROSS THE REGION...
SHOULD BE PRESENT MONDAY TO SUPPORT ISOLATED TO SCATTERED DIURNAL
CONVECTION...WITH A FEW SPRINKLES OR LIGHT SHOWERS EVEN POSSIBLE
DURING THE MORNING...TYPICAL FOR A POCKET OF REMNANT TROPICAL
MOISTURE DRIFTING ACROSS THE REGION. AM NOT CONCERNED ABOUT A HEAVY
RAIN THREAT GIVEN THE LACK OF ANY FOCUSING MECHANISM AND NOTING THAT
THE PLUME OF DEEP TROPICAL MOISTURE REMAINS GENERALLY OFF THE EAST
COAST. MODEL QPF IS VERY LACKLUSTER...GENERALLY 1/4 INCH AMOUNTS AT
BEST. THIS AGREES WELL WITH WPC.

FOR TUE-WED...THE MAIN STORY WILL BE THE BUILDING UPPER RIDGE. ANY
VESTIGE OF THE TROPICAL SYSTEMS...FRONTAL BOUNDARY...AND UPPER
TROUGH IS COMPLETELY GONE IN THIS TIME FRAME WITH 588DM OR GREATER
HEIGHTS ENCOMPASSING MOST OF THE U.S. SOUTH OF THE CANADIAN
BORDER...WEST TO THE ROCKIES. A VERY WEAK UPPER LOW TROUGH
WILL LINGER ACROSS THE WESTERN TN VALLEY INTO THE SOUTHERN
PLAINS. LINGERING TRAPPED TROPICAL MOISTURE AND DIFFERENTIAL HEATING
ACROSS THE MOUNTAINS WILL LIKELY BE SUFFICIENT EACH AFTERNOON TO
TRIGGER ISOLATED CONVECTION...BUT LITTLE TO SUPPORT MORE THAN 30
POPS AT THIS TIME. BY WED AFTERNOON...THE GFS AND ECMWF BOTH DEPICT
A POTENTIAL BACKDOOR FRONT SLIPPING INTO THE REGION FROM THE
NORTHEAST...WITH A SLIGHT INCREASE IN CONVECTION POSSIBLE ACROSS THE
NORTHERN AREAS AS A RESULT.

TEMPERATURES WILL BE ON THE INCREASE THROUGH THE PERIOD AS 850MB
TEMPS RISE FROM THE CURRENT LEVELS AROUND +14C TO +16C TOWARD +20C
DURING THE PERIOD. THIS WILL SUPPORT HIGHER MAX TEMPS...WITH SOME
AREAS ACROSS THE PIEDMONT APPROACHING 90 DEGREES...WITH 75 TO 80
MOUNTAINS AND 80S ELSEWHERE. MIN TEMPS WILL ALSO BE ON THE INCREASE
WITH HIGHER DEWPOINTS/RH/PWATS IN PLACE THROUGH THE PERIOD. OVERALL
MIN TEMPS WILL AVERAGE 10 DEGREES ABOVE NORMAL THROUGH THE PERIOD
WITH MAX TEMPS ABOUT 5 DEGREES ABOVE AVERAGE.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
AS OF 415 AM EDT SUNDAY...

THE EXTENDED PERIODS CONTINUE TO BE LARGELY DOMINATED BY A BROAD
LATE SUMMER UPPER RIDGE ACROSS THE EASTERN HALF OF THE U.S.
INCREASING TROUGHING ALONG THE WEST COAST WILL ALLOW THE UPPER RIDGE
TO PUSH FURTHER EAST...QUICKLY ERASING ANY MIDWEEK EFFECTS OF A
BACKDOOR FRONT AND WEAK SHORTWAVE TRAVERSING THE NORTHEASTERN
PERIPHERY OF THE UPPER RIDGE. TROPICAL MOISTURE WILL LINGER ACROSS
THE REGION WITH NO CHANGE IN AIR MASS EXPECTED. ON THE OTHER
HAND...THERE IS SIMPLY NO SYNOPTIC/DYNAMIC TRIGGERING MECHANISM.
THIS LEAVES CONVECTION TO BE DRIVEN ENTIRELY BY DIFFERENTIAL DIURNAL
HEATING THROUGH THE END OF THE WORK WEEK.

TEMPERATURES ARE EXPECTED TO CONTINUE ABOVE NORMAL THROUGH THE
PERIOD WITH HIGHS 75 TO 80 MOUNTAINS AND 80S ELSEWHERE...NEAR 90
ACROSS THE PIEDMONT. MIN TEMPS WILL BE MORE SIGNIFICANTLY ABOVE
NORMAL WITH MAINLY 60S TO NEAR 70 PIEDMONT. THESE READINGS ARE 5 TO
10 DEGREES ABOVE NORMAL.

LOOKING AHEAD...SOME MODELS ARE ADVERTISING PERHAPS THE FIRST FALL
COLD FRONT INTO THE FOLLOWING WEEK...BUT ENTIRELY TOO FAR OUT TO
PUT ANY CREDIBILITY IN AT THIS POINT.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AS OF 200 AM EDT SUNDAY...

FOR THE OVERNIGHT...MAINLY MID/HIGH CLOUDS WILL CONTINUE MOVING
IN FROM THE SOUTH. LOW LEVELS REMAIN DRY ENOUGH HOWEVER FOR
SUFFICIENT RADIATIONAL COOLING TO ALLOW FOR SOME LIGHT FOG/MIST
ACROSS THE AREA...DROPPING VISIBILITIES TO 4SM IN SPOTS. MAY ALSO
SEE RIVER VALLEY FOG DEVELOP ACROSS THE MOUNTAINS...WHICH MAY
LOWER VISIBILITIES IN THE IMMEDIATE AREA TO LESS THAN 1SM.

ANY FOG DEVELOPING OVERNIGHT WILL DISSIPATE QUICKLY AFTER 30/14Z
SUNDAY WITH INCREASED DAYTIME HEATING...RESULTING IN VFR
CONDITIONS THROUGH THE DAY. WITH AN UPPER LEVEL DISTURBANCE
APPROACHING...SHOWER COVERAGE WILL BE INCREASED SUNDAY AFTERNOON...
BUT STILL EXPECT ONLY A SCATTERED THREAT. AS SUCH...BELIEVE ANY
REDUCTIONS IN VISIBILITIES WILL BE LIMITED TO THOSE IN RAINFALL...
WHICH SHOULD BE BRIEF. WITH SHORT WAVE ENERGY LIFTING NORTHWARD
FROM THE GULF COAST REGION...WILL SEE MORE WIDESPREAD CONVECTION
SUNDAY NIGHT INTO MONDAY MORNING.

EXTENDED AVIATION DISCUSSION...
GENERALLY EXPECT THE BEST CHANCES FOR MVFR/IFR TO BE LATE
NIGHT/EARLY MORNING DUE TO FOG AND STRATUS DEVELOPMENT FROM THE
BLUE RIDGE WEST ESPECIALLY AT KLWB/KBCB. WILL THEN REMAIN IN A
WEAKLY FORCED SYNOPTIC ENVIRONMENT THROUGH MIDWEEK 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.

&&

.EQUIPMENT...
AS OF 400 PM EDT SATURDAY...

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...NF
NEAR TERM...NF
SHORT TERM...RAB
LONG TERM...AMS/RAB
AVIATION...NF/WP
EQUIPMENT...



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