Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 231948
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
348 PM EDT SAT APR 23 2016

.SYNOPSIS...
HIGH PRESSURE BUILDS IN OVER THE REGION TONIGHT BEFORE SLIDING EAST
TO THE COAST SUNDAY...THEN OFF THE COAST MONDAY. THE NEXT COLD FRONT
WILL SLIDE SOUTH INTO THE AREA ON TUESDAY.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 305 PM EDT SATURDAY...

UPPER LOW HAS OPEN INTO A TROUGH AND IS SLIDING ACROSS THE EAST
COAST THIS AFTERNOON. THE DEW POINT FRONT IS STILL JUST WEST OF THE
AREA...THEREFORE THE UPPER LEVEL TROUGH HAS MOISTURE TO GENERATE A
FEW SHOWERS ACROSS THE PIEDMONT THIS AFTERNOON. STEEP LAPSE RATES
OVER THE PIEDMONT AND INCREASING INSTABILITIES UNDER COLD POOL WILL
GENERATE SCATTERED THUNDERSTORMS EAST OF HWY 29 THROUGH LATE THIS
AFTERNOON. SHOWER ACTIVITY WILL DECLINE THIS EVENING AS THE DEW POINT
FRONT MOVES SOUTH OF THE VA/NC BORDER AND ENERGY FROM THE TROUGH
MOVES OFFSHORE.

SURFACE HIGH PRESSURE BRIDGES IN FROM THE NORTH OVERNIGHT AS HEIGHTS
START TO RISE AND LEFTOVER MOISTURE FADES WITH LOSS OF HEATING.
HOWEVER DEW POINTS WILL REMAIN UP A BIT AND GIVEN THE WET GROUND
UNDER LIGHT WINDS/CLEAR SKIES...WOULD EXPECT SOME VALLEY FOG LATE.
OTHERWISE MOSTLY CLEAR BUT COOL WITH LOWS MAINLY IN THE
40S...INCLUDING POTENTIAL TO EVEN SEE SOME 30S DEEPER VALLEYS...IF
FOG IS NOT TOO WIDESPREAD BY DAYBREAK.

DRY SURFACE HIGH AND RIDGING ALOFT WILL BRING SLIGHTLY WARMER THAN
NORMAL TEMPERATURES SUNDAY WITH WIDESPREAD LOW TO MID 70S FOR
MOST AND MID TO UPPER 60S ALONG HIGHER RIDGES.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 PM EDT SATURDAY...

THE UNDERLYING ATMOSPHERIC PATTERN DURING THE TIME FRAME WILL
CONTINUE TO FAVOR AN EASTERN U.S. RIDGE AND A CENTRAL/WESTERN U.S.
TROUGH. THUS...AS UPPER LOWS/TROUGHS MOVE EASTWARD OUT OF THE
PLAINS...THEY WILL DAMPEN AND SHEAR OUT TO THE NORTHEAST OVER THE
UPPER RIDGE ANCHORED ACROSS THE SOUTHEAST STATES.

FOR MONDAY...WEAK HIGH PRESSURE WILL BE LOCATED EAST OF THE REGION
WITH A FAIRLY FLAT WSW FLOW ALOFT. THE FRONT OF THE WEEKEND WILL
HAVE RETURNED NORTH TOWARD NEW YORK/NEW ENGLAND BY THIS POINT AND
BECOME STATIONARY NEAR THE PA/NY BORDER. LITTLE MOVEMENT WILL BE
EXPECTED UNTIL TUESDAY WHEN A NORTHERN STREAM SHORT WAVE MOVES
SOUTHEAST THROUGH NEW ENGLAND...FORCING THE FRONT SOUTH...SOMEWHAT
IN THE MANNER OF A BACKDOOR FRONT. THE MAIN DYNAMICS WITH THE
ASSOCIATED UPPER TROUGH WILL TRACK TO THE NORTHEAST OF THE RNK CWA
THROUGH NEW ENGLAND.

MONDAY SHOULD BE DRY...WITH ONLY SMALL HINTS OF ANY
PRECIPITATION/QPF ACROSS THE WESTERN MOUNTAINS. WITH LITTLE IN THE
WAY OF FORCING...HAVE KEPT POPS BELOW MENTIONABLE VALUES.

FOR TUESDAY...THE FRONTAL ZONE/BAROCLINIC ZONE WILL SHIFT
SOUTHWARD INTO THE REGION...REACHING THE CWA DURING THE
AFTERNOON/EVENING. THERE ARE CONSIDERABLE DIFFERENCES BETWEEN THE
VARIOUS MODELS AS TO THE TIME OF ARRIVAL OF THE FRONT AND THE
DEGREE OF ASSOCIATED INSTABILITY/CONVECTION. THE GFS FAST AND VERY
UNSTABLE...THUS VERY ROBUST WITH CONVECTION AND GENERAL QPF. ALL
OTHER MODELS ARE A GOOD 6-12 HOURS SLOWER THAN THE GFS...AND ALSO
INDICATE NOTABLY LESS INSTABILITY AND MOISTURE. THE ECMWF SOLUTION
IS THE BEST COMPROMISE...SHOWING THE FRONT REACHING THE AREA TUE
EVENING AND THEN STALLING. BEST FORCING REMAINS NORTHEAST OF THE
REGION...BUT EVEN THE MEAGER INSTABILITY ADVERTISED BY THE
ECMWF....SUGGESTS IT IS PRUDENT TO INCLUDE MENTION OF THUNDER.
SHEAR/INSTABILITY ARE NOT IN PHASE...SO CURRENT THINKING IS THREAT
OF SEVERE WILL BE LIMITED IF AT ALL.

FOR TUESDAY INTO THE WEDNESDAY...THE FORECAST BECOMES INCREASINGLY
PROBLEMATIC WITH THE GFS TAKING THE FRONTAL BOUNDARY SOUTH OF OUR
REGION AND STALLING IT ACROSS GA/SC BEFORE RETURNING NORTHWARD
LATER IN THE WEEK AS A WARM FRONT. THE ECMWF/NAM/CANADIAN STALL
THE FRONT IN/NEAR THE RNK CWA...LEAVING AN UNSETTLED WEATHER
PATTERN IN PLACE. ALOFT...A WEAK UPPER RIDGE EVOLVES OVER THE
REGION AGAIN AS ANOTHER DEEP TROUGH DEVELOPS IN THE CENTRAL U.S.
AM FORCED TO KEEP LOW CHANCE POPS THROUGHOUT THE PERIOD...MAINLY
DIURNAL...WITH MENTION OF THUNDER BECAUSE OF LINGERING
INSTABILITY.

TEMPERATURES ARE EXPECTED TO AVERAGE JUST ABOVE NORMAL THROUGH THE
PERIOD WITH NO APPRECIABLE CHANGE IN AIR MASS.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 345 PM EDT SATURDAY...

UNSETTLED WEATHER EXPECTED THROUGH THE PERIOD WITH ALMOST MULTIPLE
DAILY CHANCES FOR SHOWERS/THUNDERSTORMS AS A STALLED FRONTAL
BOUNDARY LINGERS ACROSS THE REGION. ALBEIT SCATTERED...THE
RAINFALL WILL BE WELCOME TO ALLEVIATE THE DRY/CRITICAL FIRE
WEATHER CONDITIONS. BUT...NO WIDESPREAD GENERAL SOAKING RAIN IS
FORESEEN THROUGH THE PERIOD...MAINLY SCATTERED CONVECTION.

AS NOTED ABOVE...THERE ARE DIFFERENCES AMONG THE MODELS AS TO
WHERE THE BOUNDARY WILL STALL...BUT IN ANY EVENT...IT WILL RETURN
OR BE LOCATED OVER THE REGION IN THE THU- SAT TIME FRAME. IN
ADDITION...THE NEXT IN THE SERIES OF STRONGER CENTRAL U.S. UPPER
TROUGHS/SHORT WAVES WILL BE SHEARING OUT AND HEADING EASTWARD BY
FRIDAY...WHICH WILL SERVE TO ENHANCE FOR CHANCES FOR SHOWERS AND
THUNDERSTORMS. THERE IS ENOUGH INSTABILITY PRESENT AND GIVEN THE
TIME OF YEAR TO SUPPORT MENTION OF THUNDER MOST AFTERNOON/EVENINGS
THROUGH THE PERIOD.

TEMPERATURES WILL CONTINUE TO BE ABOVE NORMAL THROUGH THE PERIOD
WITH SW-WSW FLOW ALOFT AND UPPER RIDGING JUST TO OUR
SOUTHEAST...AGAIN WITH NO APPRECIABLE CHANGE IN AIR MASS.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AS OF 115 PM EDT SATURDAY...

AN UPPER DISTURBANCE ROTATING BY TO THE EAST WILL CAUSE VFR CIGS
TO REDEVELOP THIS AFTERNOON FROM THE BLUE RIDGE EAST AND PERHAPS
ACROSS THE SE WEST VA SITES. A FEW AFTERNOON SHOWERS OR SPRINKLES
ALSO POSSIBLE MAINLY ALONG THE KLYH-KDAN CORRIDOR BUT TOO ISOLATED
AT THIS POINT TO INCLUDE MENTION. NW WINDS WILL ALSO INCREASE AS
HIGH PRESSURE BUILDS IN FROM THE NORTH WITH GUSTS TO 20- 25 KTS
POSSIBLE ACROSS THE RIDGES THIS AFTERNOON.

WINDS SHOULD QUICKLY DIMINISH TONIGHT WITH WIDESPREAD VFR
RETURNING DURING THE EVENING. HOWEVER LIGHTER WINDS AND MOIST
GROUND CONDITIONS TO LEAD TO FOG ACROSS THE VALLEYS WHERE PERIODS
OF SUB- VFR LIKELY AFTER MIDNIGHT ESPCLY KLWB/KBCB. SOME UPSLOPE
LOW CLOUDS FOG MAY ALSO REDEVELOP AROUND KBLF BUT QUITE IFFY
THERE. THEREFORE WILL INCLUDE LIFR IN FOG/STRATUS LATE TONIGHT AT
KLWB...AND IFR VSBYS AT BOTH KBCB/KBLF AS WELL BEFORE DAYBREAK ON
SUNDAY. SOME PATCHY FOG POSSIBLE ACROSS THE EAST BUT SHOULD BE TOO
ISOLATED/SHALLOW TO AFFECT VSBYS AT THIS POINT SO VFR ELSEWHERE
OVERNIGHT.


EXTENDED AVIATION DISCUSSION...

WEAK HIGH PRESSURE BUILDS ACROSS THE REGION SUNDAY...REACHING THE
COAST SUNDAY NIGHT...THEN OFFSHORE MONDAY. THIS SHOULD ALLOW FOR
OVERALL VFR CONDITIONS TO PREVAIL INTO EARLY NEXT WEEK. THE NEXT
WEAK BACKDOOR COLD FRONT MAY BRING A BAND OF SHOWERS ALONG WITH
MOUNTAIN MVFR ON TUESDAY...FOLLOWED BY POSSIBLE SUB-VFR MAINLY
MOUNTAINS IN LOW CLOUDS/SHOWERS UNDER WEAK WEDGING ON WEDNESDAY.

&&

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

&&

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



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