Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201927
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
327 PM EDT WED AUG 20 2014

.SYNOPSIS...
A WEAK STATIONARY FRONT WILL REMAIN IN THE AREA THROUGH THE REST
OF THE WEEK. UPPER LEVEL DISTURBANCES TRACKING EAST AND SOUTHEAST
ACROSS THE BOUNDARY WILL BRING SCATTERED SHOWERS AND STORMS TO THE
REGION EACH DAY. THE FRONT SHOULD SHIFT BACK SOUTH OF THE REGION
SATURDAY BRINGING A RETURN TO COOLER WEATHER FOR THE WEEKEND.
&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 220 PM EDT WEDNESDAY...

EARLIER CONVECTIVE BANDS FROM THIS MORNING HAVE BASICALLY PUT A LID ON
MOST ADDED SHRA/TSRA THIS AFTERNOON GIVEN DEEP WESTERLY FLOW SEEN OFF
THE VWP...AND LACK OF CU OFF VISIBLE PICS PER BUBBLE OF WEAK
SUBSIDENCE. THIS IN COMBINATION WITH MUCH DRIER AIR ALOFT WORKING IN
FROM THE WEST...BEHIND THE MID LEVEL TROUGH AXIS MOVING EAST OF THE
RIDGES...MAKES COVERAGE INTO EARLY THIS EVENING IFFY. HOWEVER SINCE
STILL HAVE INCREASING INSTABILITY OVER THE NEXT COUPLE OF HOURS...AND
TENDENCY FOR BETTER CONVERGENCE AFTER MIXING DECREASES...WILL LEAVE IN
SLIGHT TO LOW CHANCE POPS IN ALL EXCEPT THE FAR NW PORTIONS EARLY ON.

APPEARS BEST CHANCE AT SEEING MORE COVERAGE WILL BE JUST EAST OF THE
BLUE RIDGE AND OVER THE NORTH WHERE WILL BE RIGHT ALONG THE PASSING
VORTICITY AXIS. MAY ALSO HAVE ISOLATED TSRA REDEVELOP WEST OF THE CWA
WHERE HAVE SEEN BETTER MOISTURE/THETA-E AND HEATING ON THE OTHER SIDE
OF THE BOUNDARY. THUS KEEPING IN A TSRA MENTION INTO THE EVENING OVER
THE SW. OTRW EXPECT ANY ADDED COVERAGE TO FADE WITH LOSS OF HEATING AND
IN THE WAKE OF THE SHORTWAVE TO THE NORTH. THIS SHOULD GIVE WAY TO MORE
CLEARING AND PATCHY FOG ESPCLY AFTER MIDNIGHT. LOW TEMPS AGAIN SIMILAR
TO THE LAST FEW NIGHTS WITH MUGGY LOW/MID 60S WEST AND 65-70 EAST.

WEAK RESIDUAL FRONT WILL LIFT BACK NE ON THURSDAY AS THE WAVE CHANNEL
ALOFT AROUND THE RIDGE TO THE SW AMPLIFIES A BIT AND STARTS TO SHIFT
NORTH AS WELL. MODELS BRING ANOTHER IMPULSE QUICKLY SE OUT OF THE
UPSTREAM CONVEYOR BELT AND DRIVE IT TOWARD THE NW COUNTIES THURSDAY
MORNING SIMILAR TO TODAY...PERHAPS JUST A BIT SLOWER. HOWEVER LIFT WILL
BE ENCOUNTERING DEEP NW FLOW SO UNCERTAIN AS TO HOW FAR THIS COMPLEX
MAY GET BEFORE FADING. THUS RUNNING WITH INCREASING CHANCE POPS
THURSDAY MORNING...MAINLY BLUE RIDGE WEST...WITH HIGHEST ACROSS SE WEST
VA. EXPECT EARLY CONVECTION TO AGAIN FADE CROSSING THE RIDGES AS WE
SLIP IN BETWEEN WAVES BEFORE BETTER INSTABILITY/OUTFLOW HELPS REDEVELOP
AT LEAST SCATTERED AFTERNOON COVERAGE MOUNTAINS...AND ISOLATED OUT EAST
WHERE DOWNSLOPE ALOFT WILL BE STRONGER. THEREFORE TRIMMED BACK POPS TO
MORE CHANCE NATURE GIVEN TRENDS OF LATE AND LACK OF MUCH LIFT THURSDAY
AFTERNOON WITH THE NEXT WAVE IN OHIO. WARMING ALOFT AND WESTERLY WINDS
SHOULD COMBINE WITH SUNSHINE TO PUSH TEMPS ABOVE 90 SE WITH 80S MOST
OTHER SPOTS PENDING EARLY CLOUDS.
&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 245 PM EDT WEDNESDAY...

FORECAST AREA STAYS IN BROAD NORTHWEST SYNOPTIC FLOW. PROBABILITY
OF PRECIPITATION WILL DEPEND ON WHEN SHORT WAVES COME THROUGH.
SHOWERS AND THUNDERSTORMS THAT CROSS THE COUNTY WARNING AREA
DURING THE LATE NIGHT OR EARLY MORNING...OR UPSTREAM CLUSTERS OF
STORMS THAT SPREAD CLOUDS DOWNSTREAM OVER US WILL DIMINISH THE
AVAILABLE INSTABILITY.

MODELS HAVE AXIS OF BEST LIFT SHIFTING JUST NORTH OF THE FORECAST
AREA ON FRIDAY. THIS MAY LIMIT THE COVERAGE OF PRECIPITATION FOR
FRIDAY THROUGH SATURDAY. BUT SURFACE BOUNDARY POSSIBLY MOVING SOUTH
THROUGH THE EASTERN PART OF THE FORECAST AREA ON FRIDAY MAY TRIGGER
SHOWERS AND THUNDERSTORMS. PRECIPITABLE WATER VALUES REMAIN HIGH
THROUGH THE PERIOD. LARGE RAINFALL RATES WILL BE POSSIBLE IN ANY OF
THE STORMS.

EXPECTING MUGGY CONDITIONS OVERNIGHT WITH DEW POINTS REMAINING WELL
INTO THE 60S. 850 TEMPERATURES ON THE EASTERN SIDE OF THE FORECAST
AREA WILL BE COOLER THAN IN THE WEST. OVERALL PRECIPITATION AND
CLOUD COVER WILL HOLD TEMPERATURES AT OR JUST BELOW NORMAL FOR
MAXIMUM TEMPERATURES.
&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 300 PM EDT WEDNESDAY...

LARGE UPPER RIDGE BUILDS FROM THE LOWER MISSISSIPPI VALLEY. 500 MB
HEIGHTS OVER THE FORECAST AREA BEGIN TO RISE ON TUESDAY WITH THE
RIDGE CENTERED OVER THE TENNESSEE VALLEY.

SURFACE HIGH PRESSURE WILL BE OVER NEW ENGLAND AND WEDGED DOWN THE
APPALACHIANS THROUGH TUESDAY. BY THURSDAY A STRONG BERMUDA HIGH WILL
BE IN PLACE.

CHALLENGING TO TIME SHORT WAVES COMING OVER THE TOP OF THE RIDGE.
WPC WAS FAVORING A BLEND OF ENSEMBLE GFS AND ECMWF THROUGH THE
PERIOD. THIS KEEPS FORECAST AREA IN A PERSISTENT CHANCE OF
PRECIPITATION THROUGH MONDAY NIGHT. AT THIS TIME WILL BE
EMPHASIZING SUNDAY NIGHT AS THE BEST CHANCE IN THIS TIME FRAME.

WILL BE WARMING UP CLOSER TO ABOVE NORMAL TEMPERATURES ASSOCIATED
WITH THE UPPER RIDGE ON WEDNESDAY.
&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
AS OF 100 PM EDT WEDNESDAY...

ACTIVE AND VARIABLE WEATHER PATTERN CONTINUES THIS TAF PERIOD.
EARLY CONVECTION WITHERED ON THE VINE AS IT MOVED OFF THE BLUE
RIDGE AND HELPED STABILIZE THE ATMOSPHERE FOR A BIT. HOWEVER...
LATEST ANALYSES INDICATE INSTABILITY IS RECOVERING AND MESO MODELS
DO SHOW SOME CONVECTIVE DEVELOPMENT DURING THE AFTERNOON. EASTERN
AREAS ARE ON THE FRINGE OF HIGH PRESSURE WEDGING DOWN THE COAST
WHERE THERE WAS EXTENSIVE LOW CLOUD COVER THIS MORNING. BELIEVE
CONDITIONS WILL GENERALLY BE VFR BY ISSUANCE TIME AND WILL USE
VICINITY TO COVER EXPECTED SHOWER/STORM DEVELOPMENT. CONDITIONS
WILL DIP DOWN WITH ANY PRECIPITATION BUT FEEL A TEMPO GROUP WILL
BE TOO HEAVY HANDED SO WILL LEAVE OUT MENTION OF LOWER CONDITIONS.

TONIGHT WILL BE ANOTHER TOUGH CALL FOR FOG/LOW STRATUS DEVELOPMENT.
INDICATIONS IN MESO RH FIELDS ARE THAT IFR/LIFR WILL BE LESS
WIDESPREAD SO WILL TRY TO CONFINE LOW CONDITIONS TO A SMALLER PERIOD
TOWARD DAYBREAK...JUST IN TIME TO MENTION SOME ADDITIONAL SHOWER
ACTIVITY WITH THE NEXT WAVE OF ENERGY ENTERING FROM THE WEST. WINDS
WILL NOT BE PROBLEMATIC FOR AVIATION PURPOSES THROUGH THIS TAF PERIOD.

EXTENDED AVIATION...

UPPER LEVEL DISTURBANCES WILL BE MOVING THROUGH PERIODICALLY AND
INTERACTING WITH A STATIONARY FRONT OVER THE AREA FOR THE NEXT
FEW DAYS...RESULTING IN PERIODS OF SHOWERS AND THUNDERSTORMS. DUE
TO THE HIGH MOISTURE CONTENT OF THE AIR...EXPECT STRATUS AND FOG
DURING THE OVERNIGHT PERIODS WITH AREAS OF MVFR/IFR MOST PRONOUNCED
BETWEEN MIDNIGHT AND 9AM EACH DAY. MODELS ARE INDICATED THAT A DEEPER
EASTERLY SORT OF WIND FLOW WILL SETUP FOR THIS UPCOMING WEEKEND.
THIS SUGGEST THAT LOW CIGS MAY PERSIST EVEN DURING THE DAYTIME
PERIODS...SATURDAY AND SUNDAY...WITH WIDESPREAD MVFR CONDITIONS
ACROSS THE AREA THIS WEEKEND DUE TO MOISTURE BANKING UP AGAINST THE
EAST SIDE OF THE APPALACHIANS.

&&

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

&&

$$
SYNOPSIS...JH
NEAR TERM...JH
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...MBS



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