917
FXUS61 KRNK 150552
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
152 AM EDT SUN SEP 15 2019
SYNOPSIS
A COLD FRONT TO OUR WEST WILL MOVE EAST TONIGHT INTO SUNDAY.
HIGH PRESSURE WILL BUILD SOUTH INTO OUR REGION EARLY NEXT WEEK.
NEAR TERM /THROUGH TODAY/
AS OF 830 PM EDT SATURDAY...
CONVECTION IN ADVANCE OF A COLD FRONT CONTINUED TO LINGER
ACROSS THE ROANOKE VALLEY. THIS ACTIVITY WAS SLOWLY MOVING TO
THE EAST, BUT STRUGGLING TO MAKE IT MUCH FARTHER THAN THE CREST
OF THE BLUE RIDGE. EXPECTATION IS FOR THIS ACTIVITY TO DISSIPATE
AS WE HEAD THROUGH THE EVENING HOURS...FALLING APART AS IT MOVES
INTO BEDFORD AND NORTHERN FRANKLIN. MESOANALYSIS FROM SPC SHOWS
LITTLE OR NO CAPE EAST OF THE BLUE RIDGE, ALTHOUGH THERE IS
STILL A FINGER OF MODEST SBCAPE (1500 J/KG) WHICH LINGERS
FROM ROANOKE SOUTHWEST INTO THE NORTHWEST PIEDMONT OF NC, RIGHT
ALONG THE BLUE RIDGE ESCARPMENT. CURRENT THINKING, IS IF THERE
IS ANY LINGERING SHOWERS IT WILL BE WITHIN THIS CORRIDOR, AND IT
TOO SHOULD DISSIPATE AS WE HEAD INTO THE OVERNIGHT.
A COLD FRONT EXTENDS FROM CENTRAL PENNSYLVANIA EXTENDING
SOUTHWARD ALONG THE SPINE OF THE APPALACHIANS TO NORTHERN
ALABAMA. THIS FRONT IS FORECAST TO SLOWLY MOVE EAST AND INTO THE
PIEDMONT BY SUNDAY.
THE COMBINATION OF LIGHT WINDS AND LOW LEVEL MOISTURE WILL
RESULT IN AREAS OF FOG OVERNIGHT INTO SUNDAY MORNING. LOW
TEMPERATURES TONIGHT WILL RANGE FROM THE MID 50S IN THE
MOUNTAINS TO THE MID 60S IN THE PIEDMONT. HIGH PRESSURE WILL
BUILD IN FROM THE NORTH ON SUNDAY AND PUSH DOWN THE SPINE OF THE
APPALACHIANS AS TROPICAL CYCLONE HUMBERTO SPINS OFF THE COAST
OF THE CAROLINAS. ISOLATED SHOWERS AND THUNDERSTORMS MAY BE
POSSIBLE ON SUNDAY MAINLY IN THE SOUTHEAST. WITH THE TREND OF
THE MODELS LIGHTER WITH POTENTIAL FOR CONVECTION ON SUNDAY,
DECIDED TO DECREASE POPS ON SUNDAY. HIGH TEMPERATURES ON SUNDAY
WILL VARY FROM THE UPPER 70S IN THE MOUNTAINS TO THE MID 80S IN
THE PIEDMONT.
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
AS OF 215 PM EDT SATURDAY...
GENERALLY QUIET AND MOSTLY DRY WEATHER CONDITIONS EXPECTED
THROUGH THIS PERIOD AS THE REGION INCREASINGLY COMES UNDER THE
INFLUENCE OF A HIGH AMPLITUDE SUBTROPICAL RIDGE DRIFTING SLOWLY
EASTWARD FROM THE CENTRAL U.S. THE WEAK FRONT THAT IS MOVING
THROUGH THE FORECAST AREA TODAY WILL STALL AND EVENTUALLY WASH
OUT JUST TO OUR SOUTH ACROSS NORTH CAROLINA. MEANWHILE, TROPICAL
STORM HUMBERTO WILL BE MOVING NORTHEASTWARD OFF THE GA/SC COAST,
WHICH WILL LIKELY HELP INDUCE SUBSIDENCE TO SOME EXTENT ACROSS
OUR AREA.
THE ONLY REAL POTENTIAL FOR PRECIPITATION DURING THIS TIME FRAME
WILL BE ACROSS THE NORTHWEST NC MOUNTAINS AND THE FAR SOUTHWEST
CORNER OF VA WHERE TERRAIN INFLUENCE AND DIFFERENTIAL HEATING
ALONG WITH THE LINGERING FRONT, NORTHEAST SURFACE FLOW BEHIND
THE DISSIPATING FRONT, AND IMPROVED MOISTURE CONVERGENCE, COULD
LEAD TO A FEW AFTERNOON SHOWERS OR THUNDERSTORMS. A WEAK UPPER
TROUGH WILL BE MOVING THROUGH THE MEAN FLOW ACROSS OH/PA/MD
AREA, WHICH MAY RESULT IN AN ISOLATED THREAT FOR
SHOWERS/THUNDERSTORMS NORTH OF I-64, AGAIN MAINLY
AFTERNOON/EVENING. THUS, AT THIS POINT, POPS THROUGH THE PERIOD
ARE 30% AT BEST, CONFINED TO THE FAR SOUTHWEST. MUCH OF THE
PERIOD WILL BE DRY WITH POPS BELOW 15%.
TEMPERATURES WILL BE ON THE WARM SIDE AND WELL ABOVE NORMAL, BUT
NOT TO THE DEGREE WE EXPERIENCED LAST WEEK. GFS/ECMWF ARE A BIT
AT ODDS WITH REGARD TO THE 500MB TEMPERATURES, BUT AN AVERAGE
AROUND +18C APPEARS TO BE A GOOD BET, AS COMPARED TO THE +20 TO
+22C WE SAW EARLIER THIS WEEK. AMPLIFYING NORTHERLY FLOW ALOFT
ON THE EAST SIDE OF THE UPPER RIDGE COULD SAVE US FROM THE
EXTREME HEAT WE SAW LAST WEEK. THUS, NOT EXPECTING THE
WIDESPREAD 90S LIKE LAST WEEK, MORE IN THE RANGE OF MID 80S WEST
TO LOWER 90S EAST/PIEDMONT.
/CONFIDENCE IN FORECAST PARAMETERS/
TEMPERATURES - MODERATE,
PRECIPITATION PROBABILITIES - LOW TO MODERATE,
THUNDERSTORM PROBABILITIES - LOW,
WINDS - MODERATE.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
AS OF 230 PM EDT SATURDAY...
MOSTLY DRY WITH NORMAL TO SLIGHTLY ABOVE NORMAL TEMPERATURES
THROUGH THE PERIOD. THE SYNOPTICS WILL CONTINUE TO BE A LARGE
SCALE, HIGHLY AMPLIFIED UPPER RIDGE DOMINATING THE EASTERN HALF
OF THE U.S., WITH THE AXIS REMAINING JUST TO OUR WEST. TROPICAL
CYCLONE HUMBERTO WILL TURN EAST AND MOVE FURTHER AWAY FROM THE
U.S. AND OUT TO SEA. SURFACE HIGH PRESSURE WILL LINGER OVER AND
TO THE NORTHEAST OF THE AREA. THIS WILL RESULT IN MOSTLY SUNNY
TO PARTLY SUNNY CONDITIONS, YET WITH A VERY WEAK WEDGE IN PLACE,
TEMPERATURES SHOULD STAY NEAR TO JUST ABOVE NORMAL AND NOT REACH
THE WIDESPREAD 90S OF THIS PAST WEEK. HOWEVER, THE ECMWF/GFS TO
DIFFER NOTABLY FROM +20C ECMWF TO CLOSER TO +16C-+18C GFS.
GENERALLY FOLLOWED THE NBM FOR POP GUIDANCE, WHICH PAINTS SOME
20-30% VALUES IN THE SOUTHWESTERN AND WESTERN MOUNTAINS, BUT
LITTLE TO NONE ELSEWHERE. CONFIDENCE IN RAINFALL IS LOW AND
MEANINGFUL RAINFALL APPEARS HIGHLY UNLIKELY AT THIS TIME,
LEAVING SOME AREAS IN A CONTINUING LOW-END DROUGHT.
/CONFIDENCE IN FORECAST PARAMETERS/
TEMPERATURES - MODERATE TO HIGH,
PRECIPITATION PROBABILITIES - LOW,
THUNDERSTORM THREAT - LOW,
AVIATION /06Z SUNDAY THROUGH THURSDAY/
AS OF 150 AM EDT SUNDAY...
A COLD FRONT STRETCHES FROM NORTH TO SOUTH ALONG THE SPINE OF
THE APPALACHIANS. SOME IFR TO LIFR CLOUDS COVERED THE SOUTHERN
BLUE RIDGE AND FOOTHILLS SOUTH AND EAST OF KPSK.
MVFR TO IFR CLOUDS WILL FILL IN EAST OF THE FRONT EARLY THIS
MORNING. FOG WILL DEVELOP IN THE MOUNTAINS, WITH MVFR TO IFR
VISIBILITY, ESPECIALLY WHERE IT RAINED SATURDAY AFTERNOON AND
EVENING. SOME MID AND HIGH CLOUDS MAY DELAY THE FORMATION OF FOG
UNTIL AFTER 4AM/08Z.
THE FRONT WILL SLOWLY MOVE EAST AND INTO THE PIEDMONT OF VA/NC
BY NOON TODAY. ISOLATED SHOWERS AND A FEW THUNDERSTORMS WILL BE
ENCOUNTERED ALONG THE FRONT. GRADUALLY IMPROVEMENT BACK TO VFR
IS EXPECTED TODAY WITH A RETURN TO WIDESPREAD VFR FOR THE
AFTERNOON.
MEDIUM CONFIDENCE IN CEILINGS,VISIBILITIES AND WINDS.
EXTENDED AVIATION DISCUSSION
VFR CONDITIONS WILL CONTINUE SUNDAY NIGHT. A TROPICAL CYCLONE
ALONG THE SOUTHEAST ATLANTIC COAST EARLY IN THE WEEK, WILL
INDUCE A DRY NORTH WIND. THIS SHOULD PROMOTE VFR FROM MONDAY
THROUGH WEDNESDAY. ISOLATED TO SCATTERED MVFR STORMS ARE
POSSIBLE IN THE MOUNTAINS OF THE CENTRAL APPALACHIANS ON
THURSDAY.
FORECAST CONFIDENCE THIS TIME PERIOD IS AVERAGE.
RNK WATCHES/WARNINGS/ADVISORIES
VA...NONE.
NC...NONE.
WV...NONE.
SYNOPSIS...KK
NEAR TERM...DS/KK
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...AMS/PM
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