Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 231552
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
ISSUED BY NATIONAL WEATHER SERVICE RALEIGH NC
1152 AM EDT WED JUL 23 2014

.SYNOPSIS...
CYCLONIC FLOW ALOFT WILL PREVAIL ACROSS THE EASTERN UNITED STATES
THROUGH THURSDAY...DOWNSTREAM OF AN UPPER LEVEL RIDGE ANCHORED
OVER THE ROCKIES. WEAK UNIDIRECTIONAL FLOW ALOFT WILL PREVAIL ON
FRIDAY AND SATURDAY AS THE UPSTREAM RIDGE FLATTENS AND EXTENDS
EASTWARD INTO THE CENTRAL MISSISSIPPI RIVER VALLEY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1145 AM EDT WEDNESDAY...

AFTERNOON: LOW-TOPPED SHOWERS PROGRESSING TOWARD THE WV/VA BORDER
THIS MORNING ARE A RESULT OF ORORGRAPHIC ASCENT VIA WEST/NW LOW-
LEVEL FLOW AND A SMALL AMPLITUDE TROUGH AT 700 MB...IN THE
PRESENCE OF 500-100 J/KG MLCAPE ASSOCIATED WITH A VERY MOIST
BOUNDARY LAYER. EXPECT THIS ACTIVITY TO PERSIST ON THE HIGHER
RIDGES ALONG THE WV/VA BORDER THROUGH EARLY AFTERNOON...WITH
LITTLE OR NO ACTIVITY ELSEWHERE THROUGH MID AFTERNOON. EXPECT
HIGHS IN THE UPPER 80S TO LOWER 90S IN THE NC/VA PIEDMONT.

EVENING: STRENGTHENING CYCLONIC FLOW ALOFT OVER THE OH VALLEY AND
WESTERN MID-ATLANTIC LATE THIS AFT/EVE WILL RESULT IN A GRADUAL
INCREASE IN SYNOPTIC ASCENT FROM THE WEST VIA DPVA ASSOC/W SMALL
AMPLITUDE SHORTWAVES AND STRENGTHENING CYCLONIC SHEAR VORTICITY. A
COLD FRONT ATTENDANT THE AMPLIFYING UPPER LEVEL TROUGH EXTENDED
SOUTHWEST FROM THE LOWER GREAT LAKES THROUGH CENTRAL IN AND
SOUTHERN IL AT 15Z WILL PROGRESS SOUTHEAST INTO KY/WV AND SOUTHERN
OH/PA BY 00Z THIS EVENING...WITH A PRONOUNCED PRE-FRONTAL TROUGH
DEVELOPING EAST OF THE BLUE RIDGE IN VA/NC. WITH THE ABOVE IN
MIND...EXPECT THE BEST CHANCE FOR CONVECTION IN THE RNK CWA TO BE
LATE THIS AFT/EVE IN VICINITY OF THE WV/VA BORDER WHERE MODERATE
DIURNAL DESTABILIZATION (1000-1500 J/KG) IS EXPECTED AS STEEP MID-
LEVEL LAPSE RATES ADVECT EAST ATOP A SEASONABLY MOIST BOUNDARY
LAYER IN THE PRESENCE OF STRENGTHENING SYNOPTIC ASCENT. EXPECT A
MUCH LOWER POTENTIAL FOR CONVECTION EAST OF THE APPALACHIANS WHERE
FORCING FOR ASCENT WILL BE CONFINED TO SHALLOW CONVERGENCE ASSOC/W
THE PRE-FRONTAL TROUGH AND WHERE WEAK MID-LEVEL LAPSE RATES WILL
TEMPER DESTABILIZATION.

SEVERE POTENTIAL: RELATIVELY STEEP MID-LEVEL LAPSE RATES OF
6.0-6.5 C/KM...MODERATE INSTABILITY...AND 0-6 KM SHEAR OF 20-30
KT WOULD SUPPORT A POTENTIAL FOR MARGINALLY SEVERE HAIL AND/OR
ISOLD DOWNBURSTS IN ASSOCIATION WITH ANY VIGOROUS UPDRAFTS /DEEP
CONVECTION/ THAT DEVELOPS ALONG AND AHEAD OF THE FRONT LATE THIS
AFTERNOON AND EVENING FROM THE OH VALLEY EAST INTO THE
APPALACHIANS. -VINCENT

TONIGHT...STILL WILL SEE SOME CONVECTION AROUND BUT DISSIPATING OUT
EAST AFTER MIDNIGHT. FRONTAL BOUNDARY WILL MAKE ITS WAY TOWARD THE
WV/KY LINE BY THU MORNING...AND MODELS AGREE THAT PRECIP WILL BE IN
THE SE WV/FAR SW VA CORRIDOR BY LATE TONIGHT SO HAVE KEPT LIKELY
POPS HERE FADING TO SLIGHT CHANCE EAST OF THE BLUE RIDGE. MORE CLOUD
COVER AND HIGH DEWPOINTS WILL KEEP LOWS ELEVATED IN THE MID 60S TO
LOWER 70S. -WP

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 345 AM EDT WEDNESDAY...

WILL START THURSDAY OFF WITH THE COLD FRONT MAKING ITS WAY ACROSS
WEST VIRGINIA TOWARD OUR AREA. WITH THE FRONT IN SUCH CLOSE
PROXIMITY...WILL ALREADY HAVE SPOTTY SHOWERS AND A FEW THUNDERSTORMS
PASSING MAINLY ACROSS THE MOUNTAINS BY SUNRISE...WITH COVERAGE
INCREASING THROUGH LATE MORNING AS THE FRONT ENTERS OUR AREA AND
DAYTIME HEATING INCREASES. WHILE MUCH OF OUR AREA WILL EXPERIENCE
RAINFALL DURING THE MORNING AND AFTERNOON...BELIEVE INSTABILITY WILL
BE MORE MUTED COMPARED TO WEDNESDAY DUE IN PART TO THE INCREASED
CLOUD COVER. AS SUCH...MOST OF THE THUNDERSTORM ACTIVITY THAT
DEVELOPS ACROSS THE MOUNTAINS WILL BE WEAK...ALTHOUGH CANNOT RULE
OUT A FEW STRONG STORMS ACROSS THE SOUTHSIDE DURING THE AFTERNOON/
EVENING WHERE HEATING AND INSTABILITY WILL BE STRONGEST. AFTERNOON
HIGHS WILL RANGE FROM THE MID 70S ACROSS THE MOUNTAINS TO THE MID
80S ACROSS THE SOUTHSIDE.

THE COLD FRONT IS EXPECTED TO SHIFT SOUTH OF OUR AREA THURSDAY NIGHT
BEFORE STALLING ACROSS THE CAROLINAS FRIDAY MORNING. REGARDLESS...
HIGH PRESSURE BUILDING IN BEHIND THE FRONT IS NOT VERY STRONG...AND
WITH MID TO UPPER 60 DEGREE DEWPOINTS LINGERING ACROSS THE
SOUTHSIDE...MAY STILL SEE A FEW SHOWERS AND ISOLATED THUNDERSTORMS
DEVELOP WITH AFTERNOON HEATING. OTHERWISE...INCREASED SUNSHINE WILL
HELP AFTERNOON HIGHS REACH NEAR NORMAL FOR LATE JULY...WITH
TEMPERATURES RANGING FROM THE UPPER 70S WEST TO THE UPPER 80S EAST.

WIND FLOW ALOFT WILL SHIFT NORTHWESTERLY FRIDAY AS AN UPPER LEVEL
TROUGH PASSES EAST ACROSS THE GREAT LAKES...WHILE A LARGE DOME OF
HIGH PRESSURE REMAINS SITUATED OVER THE SOUTHWEST U.S. THIS WILL
OPEN THE DOOR FOR UPPER LEVEL DISTURBANCES TO ENTER THE AREA FROM
THE MIDWEST FOR THE WEEKEND. THE NAM/ECMWF/CANADIAN MODELS ALL ARE
PICKING UP ON ONE DISTURBANCE APPROACHING BY SUNRISE SATURDAY...MOST
LIKELY TRIGGERING A BAND OF STORMS THAT WILL BE SIGNIFICANTLY
WEAKENED AS IT ENTERS OUR SOUTHEAST WEST VIRGINIA/MOUNTAIN EMPIRE
COUNTIES. STILL NOT ENTIRELY CONFIDENT IN THIS SCENARIO PLAYING OUT
AT THIS POINT...SO WILL STICK WITH A SLIGHT CHANCE OF SHOWERS AND
STORMS FOR SATURDAY MORNING.

MORE DISTURBANCES ARE SLATED TO ARRIVE ON SATURDAY AND SATURDAY
NIGHT...ALTHOUGH TIMING OF THESE DISTURBANCES THIS FAR IN ADVANCE IS
ALWAYS DIFFICULT.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 400 PM EDT TUESDAY...

INTO EARLY NEXT WEEK...THE AREA REMAINS VULNERABLE TO NW FLOW
DISTURBANCES TRACKING AROUND THE LARGE WESTERN/CENTRAL CONUS UPPER
RIDGE. A PARTICULARLY STRONG DISTURBANCE...NOTED BY ALL THE
MODELS...PROMISES TO AMPLIFY THE EASTERN LONG WAVE TROUGH...A
FEATURE THAT SHOULD KEEP CONDITIONS UNSETTLED WITH NEAR TO
SLIGHTLY BELOW NORMAL TEMPERATURES WHILE THE EXTREME HEAT REMAINS
WELL TO OUR WEST AND WELL AWAY FROM OUR PART OF THE COUNTRY.

THE BEST CHANCE FOR SHOWERS/STORMS LOOKS TO BE SUNDAY AS THE
SURFACE FRONT ASSOCIATED WITH THE STRONG DISTURBANCE CROSSES THE
FORECAST AREA FROM THE NORTHWEST. POTENTIAL EXISTS FOR STORMS TO
BE ORGANIZED WITH UPSTREAM MCS IMPACTING THE FORECAST AREA.

GENERALLY FOLLOWED HPC GUIDANCE THROUGH THE PERIOD. TRENDED POPS
UP FOR SUNDAYS FROPA...THEN DOWN FOR A DAY OR TWO AFTER SUNDAYS
FRONTAL PASSAGE. TENDENCY FOR FRONTAL PASSAGES IS TO BRING SOME
DOWNTIME AS WITH RESPECT TO POPS BEFORE MOISTURE AND INSTABILITY
CAN RETURN.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
AS OF 725 AM EDT WEDNESDAY...

FOG BECAME DENSE AT LWB/BCB WITH MVFR AT DAN/LYH. FOG WILL
DISSIPATE BY 13Z...WITH VFR EXPECTED MUCH OF THE DAY. HIGH-RES
MODELS ARE FAVORING CONVECTION OVER THE BLUE RIDGE AND ALLEGHANY
HIGHLANDS BY 18Z...SO HAVE VCTS AT ROA/BCB/BLF/LWB...PER HRRR. THE
CONVECTION WILL WANE LATE AFTERNOON/EARLY EVENING BEFORE FRONTAL
PRECIP ARRIVES AFTER MIDNIGHT IN THE BLF/LWB CORRIDOR. AMENDMENTS
MAY BE NEEDED FOR TSRA TODAY IF TERMINALS ARE THREATENED.
OTHERWISE...COVERAGE DOES NOT DICTATE HAVING PREDOMINANT TSRA IN
THE TAFS.

EXTENDED AVIATION DISCUSSION...

NEXT NORTHERN STREAM UPPER TROUGH AND ITS ASSOCIATED COLD FRONT
WILL APPROACH WORK THROUGH THE REGION ON THURSDAY. THIS WILL
BRING THE BEST CHANCES OF MORE WIDESPREAD SHOWERS TO THE MOUNTAINS
AND PERHAPS SOME DEEPER CONVECTION EAST OF THE BLUE RIDGE PENDING
TIMING OF THE BOUNDARY THURSDAY AFTERNOON. AIRMASS WILL DRY OUT
BEHIND THE FRONT GOING INTO FRIDAY- SATURDAY. OVERALL EXPECT SUB
VFR AT TIMES THURSDAY WITH SHRA/TSRA AND MAYBE SOME FOG THU
NIGHT...FOLLOWED BY VFR FRI- SAT OUTSIDE OF ANY VALLEY FOG AT
KLWB/KBCB EACH MORNING.

&&

.EQUIPMENT...
AS OF 405 AM EDT WEDNESDAY...

KFCX RADAR IS DOWN. TECHNICIANS WILL AGAIN BE WORKING ON THE
RADAR TODAY..

&&

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

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT/WP
SHORT TERM...NF
LONG TERM...PM
AVIATION...PH/WP
EQUIPMENT...PH/WP



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