Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 190219
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1019 PM EDT MON AUG 18 2014

.SYNOPSIS...
A LOW PRESSURE AREA WILL MOVE EAST OF THE APPALACHIANS EARLY
TONIGHT...LEAVING ONLY SCATTERED SHOWERS AND A FEW THUNDERSTORMS
LINGERING BEHIND IT. A SERIES OF UPPER LEVEL DISTURBANCES WILL PASS
ACROSS THE AREA DURING THE WEEK...BRINGING A CHANCE FOR SHOWERS
AND THUNDERSTORMS JUST ABOUT EVERY DAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 1000 PM EDT MONDAY...

STRONG UPPER SHORT WAVE HAS MOVED ESE OF THE CWA...BUT UNSTABLE NW
FLOW LINGERS AND WILL DO SO FOR THE NEXT SEVERAL DAYS.
HOWEVER...THERE DO NOT APPEAR TO BE ANY MORE SUCH SIGNIFICANT
UNTIL THU NIGHT/FRI. NONETHELESS...WEAK SHORT WAVES WILL IMPINGE
ON AN INCREASINGLY UNSTABLE AIR MASS AS HEIGHTS AND 850MB TEMPS
SLOWLY RISE OVER THE NEXT FEW DAYS. THUS...EXPECT SCATTERED POP UP
SHRA/TSRA NEXT SEVERAL DAYS...MAINLY AFTERNOON/EVENING. FOR
TONIGHT...MODIFIED POPS EARLIER TO TREND DOWNWARD...BUT SCT -SHRA
WILL CONTINUE TO TRAVERSE THE REGION FROM NW-SE THROUGH THE NIGHT.
FOR THIS REASON HAVE MAINTAINED SLIGHT CHC TO LOW CHC POPS MOST
AREAS OVERNIGHT. REMOVED ALL MENTION OF THUNDER UNTIL EARLY
AFTERNOON TUE. WILL UPDATE HWO TO REMOVE ANY MENTION OF HAZARDS.

AS OF 315 PM EDT MONDAY...

STRONG MID LEVEL WAVE AND ASSOCIATED SURFACE LOW ACROSS WEST VA LATE
THIS AFTERNOON WILL WORK EAST JUST NORTH OF THE STALLED FRONT ACROSS
THE CENTRAL CWA THIS EVENING BEFORE REACHING THE COAST AFTER MIDNIGHT.
THIS WILL KEEP PERIODIC ROUNDS OF LIGHT TO MODERATE RAIN GOING ESPCLY
ALONG AND NORTH OF HIGHWAY 460 INTO THIS EVENING WITH MORE
SCATTERED/BANDED CONVECTIVE NATURE COVERAGE OVER NORTHERN N CAROLINA
INTO SOUTHSIDE VA WHERE WEAK INSTABILITY RESIDES JUST SOUTH OF THE
WIDESPREAD CLOUD CANOPY. STILL SOME POTENTIAL TO SEE SOME ISOLATED
MINOR FLOODING OR A PULSE SEVERE CELL GIVEN DIFFERENTIAL HEATING
SOUTH...OTRW GOING WITH A GRADUAL DECREASE IN HIGH POPS FROM WEST TO
EAST THIS EVENING.

WAVE SLIDES OFFSHORE LATER TONIGHT TAKING BEST LIFT TO THE EAST WHILE
THE LINGERING BOUNDARY REMAINS STUCK ACROSS THE SOUTHERN CWA INTO EARLY
TUESDAY. LITTLE IN THE WAY OFF ADDED SUPPORT ALOFT BUT MODELS INDICATE
A TRAILING AXIS OF DEEPER MOISTURE JUST NORTH OF THE FRONT WHICH MAY
KEEP A FEW SHRA GOING THROUGH MORNING SO HOLDING ONTO SOME LOW POPS
AFTER MIDNIGHT. OTRW HIGH PWATS AND LOW LEVEL MOISTURE LIKELY TO LEAD
TO FOG AS WELL AS PATCHY DRIZZLE OVER MUCH OF THE REGION. TEMPS NOT TO
FALL MUCH GIVEN SATURATED CONDITIONS WITH MOSTLY 60S FOR LOWS.

WILL BASICALLY BE IN BETWEEN THE DEPARTING LOW TO THE EAST TUESDAY AND
THE NEXT UPSTREAM IMPULSE TO THE NW. GUIDANCE SHOWS SOME WEAK
SUBSIDENCE SPILLING IN ON WEAK NW FLOW BEHIND THE EXITING SHORTWAVE BUT
WITH ONLY SLIGHT DRYING ALOFT SEEN ON FORECAST SOUNDINGS MAINLY OVER
THE WEST. ABUNDANT RESIDUAL LOW LEVEL MOISTURE WILL PERSIST ESPCLY EAST
AND WITH THE LEFTOVER FRONT AROUND EXPECT TO GET ISOLATED TO WIDELY
SCATTERED COVERAGE AIDED BY OROGRAPHICS NORTH AND WEAK LOW LEVEL
CONVERGENCE EAST WHERE WINDS WILL BE QUITE LIGHT. THIS ALSO DEPENDENT
UPON GETTING ENOUGH INSTABILITY AFTER EARLY LOW CLOUDS/FOG AS GUIDANCE
SHOWING 1-2K J/KG CAPES WHICH WOULD BE ENOUGH TO POP AT LEAST SOME
SHALLOW CONVECTION SO RUNNING WITH CHANCE TO SLIGHT POPS OVERALL.
LOWERED HIGHS SLIGHTLY BASED ON EARLY CLOUDS AND COOLER EC 2M TEMPS BUT
SHOULD BE ENOUGH WARMING ALOFT AND INSOLATION TO PUSH 80 WEST AND
MID/UPPER 80S EAST.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 355 PM EDT MONDAY...

TIMING INDIVIDUAL UPPER LEVEL WAVES REMAINS TRICKY DURING THE
PERIOD...ALTHOUGH CONSENSUS AGREEMENT IS THAT THE NEXT BEST WAVE
ROUNDING THE BOTTOM OF GREAT LAKES AREA UPPER TROUGH WILL BE
APPROACHING WESTERN SLOPES LATE TUES NIGHT INTO WED MORNING...AND
MAY BE BRINGING WITH IT WEAKENING CONVECTION INTO WESTERN SLOPES.
WHAT HAPPENS DURING THE DAY MAY DEPEND ON AMOUNT OF HEATING...AND
IF THERE IS ANY KIND OF OUTFLOW FROM WHATEVER MOVES IN THE FROM
THE WEST EARLY. ONE POSSIBLE SCENARIO IS AN AREA OF SHOWERS MAKES
IT ALL THE WAY ACROSS BLUE RIDGE INTO PIEDMONT DURING THE MORNING
BUT STABILIZES THE ATMOS FOR THE AFTERNOON. IF IT DOESNT MAKE IT
ACROSS...THE CHANCES FOR AFTERNOON SCATTERED CONVECTION ARE A
LITTLE HIGHER...AND MODEL FCST INSTABILITY RANGES FROM 1000-1500
J/KG...WITH NAM AND ECMWF SHOWING A LITTLE BETTER SW LOW LEVEL
FLOW IN PIEDMONT COMPARED TO GFS...BUT STILL WESTERLY DOWNSLOPE AT
RIDGE TOP LEVEL. WILL KEEP CHANCE POPS ALL DAY IN WEST BUT A
LITTLE HIGHER IN MORNING...AND SLIGHT CHANCE FAR EAST.

NEXT DISTURBANCE LOOKS LIKE IT WILL ARRIVE DURING THE DAY
THURSDAY...WHICH TIMED WITH DAYTIME HEATING WOULD GIVE BETTER
CHANCES FOR DEEPER CONVECTION AND MAYBE MORE WIDESPREAD
COVERAGE. IF THIS COMES IN A LITTLE SOONER IT COULD BE A REPEAT OF
WEDNESDAY WITH SHOWERS AND A FEW STORMS CROSSING IN THE MORNING
AND THEN NOT MUCH ELSE DEVELOPING LATER IN THE DAY. LEANING POPS
TOWARD THE SLOWER IDEA.

BOTH WED AND THUR TEMPS WILL BE WARMER WITH MORE CHANCES FOR AT
LEAST A COUPLE HOURS OF SUN...ESPECIALLY PIEDMONT. THE RIDGE MAY
ALSO TRY TO BUILD A LITTLE INTO THE FAR SOUTHWEST AS WELL. WENT
PRETTY CLOSE TO GUIDANCE NUMBERS FOR HIGHS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 100 PM EDT MONDAY...

TREND OF BUILDING UPPER RIDGE INTO GREAT LAKES REGION SPREADING INTO
OHIO VALLEY WITH DEEPENING AMPLITUDE TROUGH OVER NEW ENGLAND AND
ALONG MID ATLANTIC COAST IS STILL ADVERTISED BY EXTENDED
MODELS...AND TREND LAST 24 HRS HAS BEEN A BIT DEEPER AMPLITUDE AND
POSSIBLY A BIT OF RETROGRESSION OF THE TROUGH BY LATE IN WEEKEND. AT
LEAST A GOOD BET THAT FLOW WILL BECOME BLOCKED AND CONFIDENCE A
LITTLE HIGHER THAT MUCH OF BLACKSBURG CWA WILL BE INFLUENCED BY BACK
DOOR PUSH OF FRONTAL BOUNDARY OFF TO THE SOUTH BY AS EARLY AS FRI OR
AT LEAST BY SAT AND THUS WEDGE OF COOLER AIR FOR MUCH OF WEEKEND AND
POSSIBLY INTO MONDAY. SO WHILE STRONG RIDGE AND MORE TYPICAL AUGUST
LIKE TEMPERATURES WILL BE ON OUR DOOR STEP AND AT TIMES THIS WARMER
AIRMASS MAY INFLUENCE PARTS OF THE SOUTHWEST FCST AREA...LOOKS LIKE
MOST LOCATIONS WILL BE BACK IN THE WELL BELOW NORMAL REGIME AGAIN.
NEVERTHELESS TEMP FCST STILL TRICKY SINCE BACK DOOR FRONT COULD TAKE
DEEPER MOISTURE SOUTH AND THUS DRY THINGS OUT ENOUGH TO GET MORE SUN
THAN OTHERWISE MIGHT.  FCST TEMPS IN GENERAL CLOSER TO ECMWF
GUIDANCE...BUT LATEST 12Z MEX/GFS GUIDANCE SHOWING THE LOWERING
TREND COMPARED TO PREVIOUS 00Z GUIDANCE.

THE PRECIP FCST ALSO REMAINS CHALLENGING THROUGH THIS PERIOD...ALL
DEPENDENT ON HOW FAR SOUTH BOUNDARY PUSHES AND TIMING OF UPSTREAM
SHORT WAVE ENERGY FROM NORTHWEST. CHANCES ARE HIGHER FRIDAY INTO
SATURDAY WITH BOUNDARY CLOSER TO SW PART OF FCST AREA AND WILL
CONTINUE CARRYING A MID CHANCE POP FOR MTNS...LINGERING INTO
OVERNIGHT GIVEN THIS BOUNDARY AND UNKNOWN TIMING OF DISTURBANCES
COMING FROM NW. BUT WILL THEN INDICATE SOMEWHAT LOWERING CHANCES
SUNDAY AND ESPECIALLY BY MONDAY AS BOUNDARY LIKELY TO PUSH WELL
SOUTH...BUT KEEPING A SLIGHT CHANCE SINCE BY THIS TIME RIDGING COULD
ACTUALLY BUILD BACK IN TO THE WEST...WHICH OF COURSE IS ANOTHER
CHALLENGE FOR TEMPERATURES AS WELL.

OVERALL...STILL A FAIR AMOUNT OF UNCERTAINTY WITH THIS PATTERN...AND
WOULD ALMOST LIKE TO SEE A RETURN TO RIDGE AND TYPICAL DIURNAL
PATTERN TO CONVECTION...AT LEAST FROM A FCST CHALLENGE
PERSPECTIVE...AND THERE ARE SOME GOOD SIGNS OF THAT HAPPENING AS WE
GET FARTHER INTO NEXT WEEK.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
AS OF 700 PM EDT MONDAY...

LOW CONFIDENCE CEILINGS EARLY...INCREASING CONFIDENCE LATE.
MEDIUM CONFIDENCE IN VISIBILITY. HIGH CONFIDENCE IN BENIGN WINDS.

WAVE OF ENERGY MOVING ALONG THE SURFACE FRONT MEANDERING AROUND
THE VA/NC PIEDMONT THIS EVENING CONTINUES TO DRIVE THE AREA OF
PRECIPITATION AFFECTING TAF SITES THIS EVENING. BULK OF THE
STRONGER STORMS WILL MOVE EAST OF THE FORECAST AREA AND INTO THE
COASTAL PIEDMONT THROUGH THE REST OF THE EVENING. AS THE WAVE
DRIFTS EAST...LOW LEVEL FLOW WILL TURN AROUND FROM THE WEST.
HOWEVER... AMPLE MOISTURE WILL REMAIN OVERNIGHT TO SUPPORT SOME
SHOWERS... SPRINKLES...OR DRIZZLE SO NOT EXPECTING COMPLETELY DRY
CONDITIONS ONCE THE MAIN RAIN IS DONE. FOG AND STRATUS WILL ALSO
BE A GOOD BET AND LIFR CONDITIONS CAN BE EXPECTED.

CONDITIONS WILL BEGIN TO IMPROVE AFTER DAYBREAK. HOWEVER...AS
DIURNAL INSTABILITY INCREASES WE WILL START TO SEE DEVELOPMENT OF
SCATTERED SHOWERS/STORMS BUT BELIEVE THIS WILL BE MAINLY BEYOND
THIS TAF PERIOD SO WILL NOT INCLUDE ANY MENTION WITH THIS PACKAGE.

EXTENDED AVIATION...A SURFACE FRONT IS EXPECTED TO REMAIN STALLED
NEAR OUR AREA THROUGH THE MIDDLE OF THE WEEK AS A SERIES OF UPPER-
LEVEL DISTURBANCES TRACK FROM WNW-ESE ACROSS THE REGION. MAIN
ACTIVITY EXITS THE EAST BY TUESDAY MORNING...WITH MAINLY DIURNALLY
DRIVEN SHOWERS AND THUNDERSTORMS ANTICIPATED FOR THE REMAINDER OF
THE WEEK. INCREASED MOISTURE AND RAIN CHANCES WILL RESULT IN A
DAILY THREAT FOR LATE NIGHT/EARLY IFR- LIFR CONDITIONS IN FOG AND
LOW CLOUDS AT THE USUAL SITES...LWB/BCB/LYH...WITH MVFR POSSIBLE
AT OTHER LOCATIONS.

&&

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

&&

$$
SYNOPSIS...SK
NEAR TERM...JH/RAB
SHORT TERM...SK
LONG TERM...SK
AVIATION...MBS/RCS



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