Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 020847
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
447 AM EDT THU JUL 2 2015

.SYNOPSIS...
A FRONTAL BOUNDARY WILL REMAIN DRAPED ACROSS THE AREA FOR THE
NEXT SEVERAL DAYS. THERE WILL BE SEVERAL WAVES OF LOW PRESSURE
PASSING ACROSS THE BOUNDARY KEEPING THE THREAT OF SHOWERS AND
THUNDERSTORMS IN OUR FORECAST THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 400 AM EDT THURSDAY...

WE CONTINUE TO BE LOCKED IN TO THE SAME PATTERN WITH A LONG SERIES OF
SHORT WAVES MOVING THROUGH AN UPPER TROF OVER THE EASTERN US...AS AN
EAST TO WEST FRONTAL BOUNDARY STRETCHES ACROSS THE AREA. THIS WILL KEEP
OUR WEATHER QUITE UNSETTLED AND SHOWERS/STORMS CAN NOT BE RULED OUT AT
ANY TIME...THOUGH DIURNAL HEATING WILL KEEP THE BULK OF ACTIVITY BIASED
TO THE AFTERNOON/EVENING HOURS. INSTABILITY AND SHEAR ARE MODEST AT
BEST AND THIS WILL HELP LIMIT ANY SEVERE THREAT...BUT IF WE MANAGE TO
GET MORE SUN THROUGH THE EARLY CLOUDS TODAY WE MAY DESTABILIZE MORE
THAN ANTICIPATED. THE MAIN THREAT WILL BE INCREASING PRECIPITABLE WATER
VALUES LEADING TO A HYDRO THREAT FROM TRAINING HEAVY DOWNPOURS. ALL
MODELS DEVELOP VARYING DEGREES OF AN MCS AND MOVE IT EASTWARD ALONG THE
FRONTAL BOUNDARY...BUT THEY ALL HAVE ENOUGH DIFFERENCES IN LOCATION AND
TIMING TO LOWER CONFIDENCE IN WHERE HEAVY PRECIPITATION IS MOST LIKELY
BELOW THE THRESHOLD NECESSARY FOR ISSUING ANY SORT OF FLOOD WATCH. WILL
CONTINUE TO HIGHLIGHT THE POTENTIAL FOR HEAVY PRECIPITATION AND
POSSIBLE FLOODING ISSUES IN THE HWO AND WAIT TO SEE IF A THREAT AREA
REVEALS ITSELF WITH TIME. AFTER A DOWNTURN IN ACTIVITY EARLY TONIGHT
INDICATIONS ARE THAT ANOTHER WAVE WILL BE SET TO MOVE THROUGH THE
REGION LATE TONIGHT/TOWARD DAYBREAK FRIDAY.

EXTENSIVE CLOUD COVER WILL HELP KEEP TEMPERATURES A FEW DEGREES COOLER
TODAY THAN YESTERDAY WITH LOW TO MID 80S FOR THE PIEDMONT/SOUTHSIDE AND
LOW TO MID 70S WEST OF THE BLUE RIDGE. LOWS TONIGHT REMAIN MILD WITH
UPPER 60S EAST TO LOWER 60S WEST.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
AS OF 420 AM EDT THURSDAY...

BROAD TROUGHING AND NORTHWEST FLOW ALOFT REMAINS IN PLACE AT THE
BEGINNING OF THE PERIOD. A REMNANT MCS...MOST LIKELY IN THE FORM
OF WIDESPREAD LIGHT TO MODERATE RAIN AND EMBEDDED THUNDER APPEARS
LIKELY AT THE START OF THE DAY FRI...ONE OF TWO POTENTIAL
CONVECTIVE COMPLEXES OR THE REMNANTS OF SUCH TO DRIFT INTO THE
AREA FROM THE TN VALLEY. GIVEN TIME OF DAY...THREAT OF SEVERE
SHOULD BE LITTLE TO NONE. MAIN CONCERN WOULD BE HEAVY RAINFALL ON
TOP OF RAINFALL EXPECTED THU. MODEL AND WPC QPC AMOUNTS OVER THE
24-48 HOUR PERIOD ARE MOSTLY IN THE 1.5 TO 2.0 INCH RANGE...WHICH
SHOULD BE HANDLED WITHOUT ANY SIGNIFICANT PROBLEMS. LOCALIZED
PROBLEMS ARE ENTIRELY POSSIBLE...BUT THIS SHOULD LARGELY BE THE
RESULT OF COMBINED RAINFALL FROM THU INTO FRI MORNING RATHER THAN
NEW EVENTS FRI MORNING...GIVEN THE EXPECTED LACK OF HEAVIER
CONVECTION DURING THE MORNING.

BY AFTERNOON...WEAK SFC LOW PRESSURE DRIFTS TOWARD THE VA/MD COAST
AND THE BETTER THREAT FOR DIURNAL CONVECTION SHIFTS EAST WITH THE
MORNING MCS. HOWEVER...AMPLE MOISTURE REMAINS IN PLACE AND BROAD
TROUGHING ALSO REMAINS IN PLACE...WITH THE AXIS STILL TO THE WEST
ACROSS THE TN/OH VALLEY. WILL NEED TO KEEP AT LEAST CHANCE POPS
ALL AREAS...KEEPING THE HIGHER POPS EAST AND SOUTH. ANOTHER MCS
APPEARS LIKELY TO DEVELOP UPSTREAM LATE SATURDAY AND TRANSLATE
ACROSS MUCH OF THE SOUTHERN PART OF THE CWA SATURDAY NIGHT/SUNDAY
MORNING BEFORE THE UPPER TROUGH FINALLY WEAKENS AND BEGINS TO
DRIFT ESE INTO THE CAROLINAS...WHILE A SHORT WAVE RIDGE RIDES OVER
THE TOP OF THE TROUGH INTO THE OH VALLEY/PA REGION. THE FOCUS FOR
CONVECTION SUNDAY SHOULD BE MAINLY EAST-SOUTH OF THE BLUE RIDGE
AS DEEPER MOISTURE IS SHOVED SLIGHTLY SOUTHWARD.

OVERALL...AS NOTED YESTERDAY...POPS CANNOT BE REDUCED BEYOND
MENTIONABLE 15 PERCENT VALUES ANYTIME DURING THIS PERIOD.
HOWEVER...THE EXACT TRACK AND TIMING OF CONVECTIVE COMPLEXES OR
THE REMNANTS OF SUCH WILL REMAIN DIFFICULT TO DETERMINE AND WILL
ONLY BE RESOLVED NEAR THE EVENT AND ON THE MESOSCALE...NOT THE
SYNOPTIC SCALE LEVEL.

ABUNDANT CLOUD COVER AND LIMITED DAYTIME HEATING WILL HOLD MAX
TEMPS BELOW NORMAL. HOWEVER...HIGH HUMIDITY LEVELS/DEWPOINTS WILL
RESULT IN WELL ABOVE NORMAL MAX TEMPS.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 430 AM EDT THURSDAY...

A SURFACE BOUNDARY WILL STALL ACROSS THE CAROLINAS OVER THE
WEEKEND. MEANWHILE...THE TAIL END OF THE LONGSTANDING EASTERN
UPPER TROUGH WILL BECOME CUTOFF ACROSS SOUTHEAST VA/NORTH NC AND
SLOWLY DRIFT SOUTH INTO SOUTH CAROLINA. THE GFS ADVERTISES THIS TO
A MUCH GREATER EXTENT THAN THE OTHER MODELS. MEANWHILE...A SHORT
WAVE RIDGE DRIFTS OVER THE TOP OF THIS WEAK CUTOFF UPPER
LOW/TROUGH. CONVECTION SHOULD BECOME MUCH MORE DIURNAL IN NATURE
AS THE FAVORABLE MCS PATTERN OF THE CURRENT WEEK FADES GIVEN THE
CHANGE IN THE SYNOPTIC PATTERN AND AN END TO THE STRONG WNW-NW
FLOW ALOFT. AREAS SOUTH AND EAST OF THE BLUE RIDGE SHOULD SEE THE
BEST CHANCE OF CONVECTION THROUGH THIS PERIOD CLOSER TO THE
SURFACE BOUNDARY...UPPER LOW...AND DEEPER MOISTURE. BEYOND
MON...THE MODELS TO VARYING DEGREES DEPICT A COLD FRONT
APPROACHING THE REGION FROM THE NORTHWEST...THEN LIKELY STALLING
IN/NEAR THE REGION BY WED AS BROAD UPPER RIDGING DEVELOPS ACROSS
THE SOUTHERN STATES. THUS...WE ARE LEFT IN A CONTINUAL UNSETTLED
PATTERN. ANY DECREASE IN CONVECTION ACROSS THE CWA IN THE MON/TUE
TIME FRAME WILL BE FOLLOWED BY AN UPTICK IN SUCH BY WED.

TEMPERATURES SHOULD BE SLIGHTLY WARMER MON/TUE WITH DECREASED
CLOUD COVER AND HENCE GREATER INSOLATION. OVERALL...TEMPERATURES
SHOULD AVERAGE NEAR NORMAL FOR HIGHS...BUT CONTINUE TO BE QUITE A
BIT ABOVE NORMAL FOR MIN TEMPS GIVEN CONTINUED HIGH MOISTURE
CONTENT.

&&

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

CURRENTLY VFR CONDITIONS AT TAF SITES BUT RADAR SHOWS SHOWERS
SCATTERED ACROSS THE MAJORITY OF THE AREA...WITH MORE UPSTREAM
FLOWING IN OUR DIRECTION ALONG A FRONTAL BOUNDARY DRAPED ACROSS
THE REGION. BELIEVE THE BEST WAY TO PRESENT THIS IN THE TAFS IS TO
GO WITH VCSH AND AMEND AS NEEDED...EXCEPT AT KLWB WHERE A TEMPO
GROUP SEEMS BETTER SUITED BASED ON CURRENT COVERAGE AND TRENDS
FROM RADAR. ALSO EXPECT MVFR OR LOWER CIGS TO BE SPREADING IN FORM
THE WEST TO AFFECT KLWB/KBLF/KBCB BEFORE DAYBREAK.

WITH A STEADY SUPPLY OF SHORT WAVE ENERGY MOVING THROUGH THE
UPPER TROF OVER THE EASTERN US WE CAN EXPECT SHOWERS/THUNDERSTORMS
TO CONTINUE TO DEVELOP AND STREAM ALONG THE FRONTAL BOUNDARY.
THIS WILL LEAD TO PERIODS OF MVFR OR LOWER CONDITIONS. QUITE
DIFFICULT TO PINPOINT TIMES/LOCATION OF PRECIPITATION SO WILL GO
WITH ANTICIPATED TRENDS OF DIURNAL INSTABILITY AND ATTEMPT TO
CONFINE MOST PESSIMISTIC CONDITIONS TO THE AFTERNOON HOURS...BUT
THERE WILL LIKELY BE A SIGNIFICANT AMOUNT OF ACTIVITY PERSISTING
INTO EARLY THURSDAY NIGHT. PRECIPITABLE WATER VALUES WILL ALSO BE
ON THE INCREASE SO HEAVY DOWNPOURS WILL BE INCREASINGLY LIKELY.
THE MORE CERTAIN PART OF THE TAF PERIOD IS THAT WINDS WILL BE
ON THE LIGHT SIDE WITH HIGHER GUSTS NEAR THUNDERSTORMS.

EXTENDED AVIATION DISCUSSION...

THE REGION WILL BE IN A GENERAL NORTHWEST FLOW PATTERN THROUGH
SATURDAY. WILL AGAIN SEE SHOWERS AND THUNDERSTORMS DEVELOP ON
FRIDAY AND SATURDAY AS SEPARATE SHORTWAVE TROUGHS PROGRESS ACROSS
THE FORECAST AREA WITHIN THE NORTHWEST FLOW.

VFR CONDITIONS ARE EXPECTED FOR MOST OF THE AREA MUCH OF THE
TIME. THE EXCEPTIONS WILL COME AS TEMPORARY DECREASES WITHIN ANY
HEAVIER RAIN SHOWERS OR THUNDERSTORMS...AND THEN LATE AT NIGHT AND
EARLY MORNING DUE TO RIVER OR MOUNTAIN VALLEY FOG...ESPECIALLY IN
AREAS THAT RECEIVED PRECIPITATION THE DAY BEFORE.

SUNDAY INTO MONDAY...WHILE UPPER LEVEL HEIGHTS RISE DURING THE
PERIOD...THERE REMAINS AN UPPER TROUGH MOVING OVER THE MID
ATLANTIC DURING THIS TIME...SO STORMS ARE NEVER OUT OF THE
FORECAST.

&&

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

&&

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


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