Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 311427
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1027 AM EDT THU JUL 31 2014

.SYNOPSIS...
AN UPPER TROUGH OF LOW PRESSURE WILL RETROGRADE WEST TO THE
MISSISSIPPI RIVER VALLEY...AND THE CENTER OF SURFACE HIGH PRESSURE
WILL SHIFT TO OUR EAST INTO FRIDAY. THIS WILL RESULT IN A RETURN
OF MOISTURE TO THE REGION ALONG WITH INCREASING CHANCES OF SHOWERS
AND THUNDERSTORMS LATER TODAY INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1000 AM EDT THURSDAY...

ONLY MINOR ADJUSTMENTS MADE TO THE EARLY MORNING FORECAST PACKAGE.
INCREASED CLOUD COVER ACROSS THE NORTH CAROLINA MOUNTAINS AS HIGH
CLOUDS GRADUALLY SHIFT NORTHEAST FROM THE LOWER MISSISSIPPI VALLEY
IN RESPONSE TO THE UPPER LEVEL TROUGH STARTING TO RETROGRADE TO
THE WEST. WITH THE INCREASING CLOUDS ACROSS NORTH CAROLINA...ALSO
NUDGED AFTERNOON HIGHS DOWN A DEGREE OR TWO...MAINLY IN THE
MOUNTAINS.

STILL LOOKING FOR SPOTTY SHOWERS TO DEVELOP ACROSS THE SOUTH
DURING EARLY AFTERNOON...WITH RAINFALL COVERAGE FILLING IN SOUTH
OF HIGHWAY 460 DURING THE EVENING.

AS OF 235 AM EDT THURSDAY...

TRANSITION FROM THE DRY/COOL CONDITIONS OF LATE TO A WETTER SCENARIO
TO BEGIN TODAY AS THE LINGERING 5H TROUGH STARTS TO SHIFT WEST
WHILE THE PARENT SURFACE HIGH PRESSURE HEADS SLOWLY OFFSHORE. THIS
WILL ALLOW FOR DEEPER MOISTURE TO RETURN WITH INCREASING SOUTH/SW
FLOW ALOFT WITH THE UPPER TROUGH...AND LOW LEVEL SOUTH/SE FLOW
ALONG THE BACKSIDE OF THE EXITING SURFACE RIDGE. HOWEVER FORCING
TODAY REMAINS RATHER FAINT GIVEN A WEAK BUBBLE HIGH LINGERING
ALONG THE MOUNTAINS AND MOST MID LEVEL ENERGY STILL BACK TO THE SW
UNDER THE BASE OF THE COOL POOL. MODELS DO GRADUALLY BRING HIGHER
DEWPOINTS UP FROM THE SOUTH WITH SE FLOW PROVIDING CONVERGENCE
ALONG THE SOUTHERN BLUE RIDGE...AND PERHAPS FARTHER EAST IN THE
PIEDMONT WHERE SOME GUIDANCE FEEDS AN AXIS OF LOW LEVEL MOISTURE
IN FROM THE SE PER FORECAST RIBBON OF HIGHER THETA-E. THIS IN
CONJUNCTION WITH HEATING AT LEAST THROUGH HIGH CLOUDS SHOULD ALLOW
FOR INCREASING COVERAGE OF SHOWERS MAINLY SW EARLY ON...THEN
EXPANDING NORTH AND EAST BY THIS EVENING. APPEARS THUNDER LIMITED
TO THE FAR SOUTH AND SE GIVEN WEAK INSTABILITY BUT SUGGESTED BY A
FEW SOLUTIONS INCLUDING THE SPC WRF AND NCEP WRF/NAM. THUS
INCLUDED MENTION LATER WITH BUMP IN CHANCE POPS A BIT MAINLY SOUTH
OF HIGHWAY 460...WITH ONLY SLIGHT POPS FARTHER NORTH WHERE MORE
SUN LIKELY TODAY. HIGHS PERHAPS A LITTLE BELOW MOS SOUTH AND BLUE
RIDGE GIVEN CLOUDS AND SE FLOW BUT OVERALL SIMILAR TO
PREVIOUS...UPPER 70S/LOW 80S.

MAY SEE A DECREASE IN CONVECTIVE COVERAGE THIS EVENING BEFORE THE
SHORTWAVE CURRENTLY PRODUCING THE SHRA OVER OKLAHOMA ROUNDS THE
TROUGH AND APPROACHES FROM THE SW LATE TONIGHT. SEVERAL MODELS
SHOWING QUITE AN ENHANCEMENT TO THE PRECIP AFTER MIDNIGHT WITH
GOOD OVERRUNNING RESULTING IN WIDESPREAD SHOWERS INTO A DEVELOPING
LOW LEVEL WEDGE. APPEARS SOME HEAVY RAIN POSSIBLE NW NC MOUNTAINS
TOWARD DAYBREAK WITH THE AIDED UPSLOPE FLOW AND STRONG MOISTURE
TRANSPORT OF 1.5 INCH PWATS INTO THE EASTERN SLOPES OF THE BLUE
RIDGE. SHOULD BE ENOUGH LIFT FOR SHOWERS TO SPREAD NE ACROSS THE
ENTIRE CWA BY DAYBREAK WITH THE HEAVIEST BLUE RIDGE AND SW...BUT
WITH ANY THUNDER BEING ELEVATED/ISOLATED AND MAINLY SW OF THE
AREA GIVEN THE BETTER LIFT SOUTH OF THE LOW LEVEL COOL POOL. THUS
RUNNING WITH HIGH LIKELY/LOW CAT POPS FROM THE NEW RIVER VALLEY
AND POINTS SW ALONG WITH HIGH CHANCES ELSW FOR NOW. LOW TEMPS A
BIT MORE WARM/HUMID AS MOISTURE SURGES BACK WITH MOST ONLY
DROPPING INTO THE LOW/MID 60S OVERNIGHT.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
AS OF 314 AM EDT THURSDAY...

VERY LITTLE CHANGE IN THE WEATHER PATTERN THROUGH THE WEEKEND...AS
A BERMUDA HIGH SETS UP SHOP IN THE WESTERN ATLANTIC. BY FRIDAY
MORNING A HYBRID WEDGE WILL LAY ACROSS THE MID ATLANTIC REGION.
MEANWHILE...AN UPPER LEVEL TROUGH WILL REMAIN OVER THE GREAT LAKES
AND UPPER MISSISSIPPI VALLEY. SHORT WAVES ROUNDING THIS TROUGH
WILL RIDE OVER THE WEDGE...BRINGING A LONG PERIOD OF GRAY DREARY
WEATHER TO THE REGION INTO THE WEEKEND. IT WILL NOT RAIN ALL THE
TIME...BUT IT WILL RAIN/DRIZZLE MOST OF THE TIME. THE BEST CHANCE
FOR AREA-WIDE RAIN WILL BE FRIDAY MORNING AND SATURDAY AFTERNOON.
WITH AN EASTERLY FLOW...HIGHEST RAINFALL AMOUNTS WILL BE ALONG THE
BLUE RIDGE WITH AMOUNTS NEAR 2 INCHES FOR THE 3 DAYS. THE WEDGE
SHOULD KEEP THE AREA STABLE ON FRIDAY...HOWEVER THERE EXIST SOME
INSTABILITIES ALOFT FOR AN ISOLATED RUMBLE OF THUNDER. BETTER
INSTABILITIES ARE POSSIBLE SATURDAY AFTERNOON...ESPECIALLY IF THE
WEDGE IS ALLOWED TO ERODE.

WITH A WEDGE AND EASTERLY FLOW IN PLAY THROUGH THE PERIOD...
TEMPERATURES WILL RUN WELL BELOW NORMAL. WITH THE ADDITION OF RAIN
AND/OR DRIZZLE...I UNDERCUT GUIDANCE BY 3F- 5F...PRODUCING
AFTERNOON HIGHS AROUND 15F COLDER THAN NORMAL EACH DAY. OVERNIGHT
TEMPERATURES WILL NOT DROP MUCH WITH READINGS IN THE 60S.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 330 PM EDT THURSDAY...

FRONT AT THE SURFACE REMAINS ALONG THE COAST SATURDAY NIGHT THROUGH
MONDAY. ON TUESDAY AND WEDNESDAY...A COLD FRONT WILL PUSH INTO THE
REGION FROM THE NORTHWEST.

UNTIL THIS FRONT GOES THROUGH...THERE WILL BE A DAILY THREAT OF
SHOWERS AND THUNDERSTORMS EACH AFTERNOON AND EVENING. CHALLENGING TO
NARROW DOWN WHICH DAY OF TIME FRAME WILL BE MORE FAVORABLE FOR
PRECIPITATION...ALTHOUGH MODELS SUGGEST A SHORT WAVE COMING THROUGH
THE OHIO VALLEY ON SUNDAY MAY BRING A MORE ORGANIZED AREA OF SHOWERS
AND THUNDERSTORMS TO THE COUNTY WARNING AREA.

POCKET OF WARMER 850 MB AIR WITH +20 TEMPERATURES COMES OUT OF THE
MISSISSIPPI VALLEY...REACHING THE FORECAST AREA ON WEDNESDAY BASED
ON THE ECMWF.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
AS OF 702 AM EDT THURSDAY...

OVERALL VFR CONTINUES EARLY THIS MORNING WITH THE EXCEPTION OF THE
MOUNTAIN VALLEYS AND SPOTS OVER THE PIEDMONT WHERE A BRIEF PERIOD
OF MVFR TO LIFR IN FOG/LOW CLOUDS LIKELY UNTIL AROUND 13Z/9AM.

OTRW ANY LOW CONDITIONS SHOULD FADE INTO ANOTHER ROUND OF
DEVELOPING 4-6K FT CU FIELDS UNDERNEATH A SCTD/BKN CI SHIELD INTO
THIS AFTERNOON. APPEARS MORE IN THE WAY OF BKN CLOUDS ACROSS THE
SW BY EARLY AFTERNOON WITH THIS SPREADING NE TO KBLF/KBCB AND KROA
LATER THIS AFTERNOON. A FEW SHRA AND ISOLATED TSRA MAY ALSO
DEVELOP ALONG THE BLUE RIDGE BUT COVERAGE LACKING AND LIKELY NOT
FAR ENOUGH NORTH TO AFFECT MOST TAF SITES LATER TODAY. THUS ONLY
INCLUDING A VCSH AT KBCB FOR NOW AND LEAVING ELSW DRY. OTRW VFR
WITH WINDS TURNING MORE SOUTH TO SW AT 5-10 KTS THIS AFTERNOON.

IMPULSE ROUNDING IN FROM THE SW SUPPORTS INCREASING MID CLOUDS
THIS EVENING WITH BASES LOWERING OVERNIGHT AS DEEP MOISTURE
RETURNS. THIS MAY BRING WIDESPREAD MVFR CIGS TO MUCH OF THE REGION
AFTER MIDNIGHT TONIGHT WITH IFR IN SHOWERS POSSIBLE ESPCLY ALONG
THE BLUE RIDGE BY FRIDAY MORNING. HOWEVER TIMING AND COVERAGE OF
PRECIP LOW CONFIDENCE OVERNIGHT BUT APPEARS INCREASING MVFR
LIKELY IN MOST SPOTS FROM SW TO NE BY DAYBREAK. THEREFORE ADDED
MVFR VSBYS IN SHOWERS AS WELL AT MOST LOCATIONS NEAR THE END OF
THE VALID LATE NIGHT TAF PERIOD.

EXTENDED AVIATION DISCUSSION...
A BROAD TROUGH OF LOW PRESSURE WILL BE ACROSS THE EASTERN UNITED
STATES THROUGH SUNDAY. IT WILL SLOWLY RETROGRADE FROM THE
EASTERN/CENTRAL GREAT LAKES TO THE WESTERN GREAT LAKES BY THE
WEEKEND. THIS WILL BEGIN TO TURN THE UPPER FLOW TO THE SOUTHWEST
WITH TIME. THE AFOREMENTIONED DISTURBANCE COMING FROM THE SE
STATES THU...WILL MOVE NORTHEASTWARD ACROSS THE REGION FRI.
EXTENSIVE OVERRUNNING LIKELY WITH EMBEDDED ISOLD TSRA. SFC AIR
MASS REMAINS QUITE STABLE...ESPECIALLY EAST OF THE ALLEGHANY
FRONT...SO THUNDER APPEARS ISOLATED AT THIS POINT.
HOWEVER...WIDESPREAD MVFR CIGS/VSBYS WILL BE POSSIBLE FRI WITH
THIS SCENARIO IN -RA -DZ BR. FOR SAT-SUN...AIR MASS WILL SLOWLY
BECOME WARMER AND MORE UNSTABLE. SCT SHRA/TSRA AGAIN SAT WITH ONLY
LIMITED INSTABILITY EVIDENT. FOR SUN...BETTER CHANCE OF TSRA WITH
BETTER INSTABILITY ACROSS MUCH OF THE CWA...SW FLOW ALOFT...AND
INCREASING MOISTURE LEVELS. THUS...BRIEF PERIODS OF MVFR-IFR
CIGS/VSBYS EXPECTED IN SHRA/TSRA SAT AND MORE LIKELY SUN
AFTERNOON. SOME DRYING WITH A RETURN TO OVERALL VFR POSSIBLE
MONDAY AS ANOTHER WEAK COOL FRONT SWEEPS IN FROM THE NW AND TAKES
MOST MOISTURE TO THE SE OF THE REGION. OTHERWISE...POTENTIAL FOR
LATE NIGHT/EARLY MORNING IFR- LIFR BR/FG INCREASES THROUGH THE
PERIOD...BUT MAINLY AT THE USUAL SITES...LWB/BCB/LYH.

&&

.EQUIPMENT...
THE NOAA WEATHER RADIO AT WYTHEVILLE VA...WZ2500...BROADCASTING
ON A FREQUENCY OF 162.450 MHZ...IS OFF THE AIR. TECHNICIANS ARE
WAITING ON DELIVERY OF PARTS TO MAKE REPAIRS. THE EARLIEST THE
RADIO WILL BE WORKING AGAIN IS FRIDAY.

&&

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

&&

$$
SYNOPSIS...DS/JH
NEAR TERM...JH/NF
SHORT TERM...RCS
LONG TERM...AMS
AVIATION...JH/RAB
EQUIPMENT...DS


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