633
FXUS61 KRNK 131100
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
700 AM EDT TUE AUG 13 2013
.SYNOPSIS...
A COLD FRONT WILL PASS ACROSS THE REGION ON TODAY. THEN A LARGE
HIGH PRESSURE SYSTEM WILL BUILD IN OVER THE OHIO VALLEY AND THE
MID ATLANTIC TONIGHT AND WEDNESDAY...BRINGING SOMEWHAT COOLER AND
DRIER WEATHER. THIS WILL LAST LATE INTO THE WEEK BEFORE MOISTURE
STARTS TO SLOWLY RETURN BY THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 658 AM EDT TUESDAY...
UPDATED POPS/WEATHER AND RAINFALL FOR NEXT FEW HOURS PER
CONCENTRATED AREA OF HEAVY RAIN SHOWERS AND ISOLATED THUNDER
ACROSS MT ROGERS REC AREA AND FAR NW NC. LATEST HRRR HAS
REASONABLE HANDLE ON THIS AND TAKES IT ALL THE WAY INTO PIEDMONT
THROUGH 13Z. THINK THIS MAY BE A LITTLE FAST AND MAY NOT SURVIVE
FULLY INTACT THAT FAR EAST...BUT DID INCREASE POPS OUT OF AHEAD OF
IT AND BROUGHT LIKELY INTO FOOTHILLS AND TOWARD LYH A LITTLE
EARLIER. WILL NEED CONSTANT TWEAKING. RAINFALL RATES ARE FROM 2-3
INCHES PER HOUR IN STRONGER RETURNS...BUT IT IS MOVING AT ABOUT 40
MPH. ANOTHER WAVE OF ACTIVITY WILL ENTER FROM EASTERN KY THOUGH BY
800 AM...SO MANY AREAS WILL NEED TO BE WATCHED CAREFULLY FOR FLASH
FLOOD POTENTIAL THROUGH AT LEAST THE MORNING HOURS.
PREV DISCUSSION AS OF 440 AM EDT TUESDAY...
SURFACE COOL FRONT CONTINUES TO SLOWLY MAKE ITS WAY SOUTHEASTWARD
THROUGH THE OHIO VALLEY EARLY THIS MORNING WITH WAVES RIPPLING
ALONG IT IN THE UPPER LEVELS. THIS IS RESULTING IN CONTINUED AREAS
OF ORGANIZED BUT FAIRLY SHALLOW CONVECTION FROM UPSTATE NY AND
PA...SOUTHWESTWARD ALONG THE WEST SIDE OF THE APPALACHIANS AND
INTO CENTRAL KY. AREAS OF SHOWERS AND ISOLATED THUNDERSTORMS HAVE
GENERALLY BEEN WEAKENING AS THEY MOVE INTO THE WESTERN PORTIONS OF
OUR FCST AREA WITH WEST FLOW AND LITTLE TO NO INSTABILITY
REMAINING. ONE WAVE MAY BRING A MORE ORGANIZED AREA INTO THE WEST
DURING THE FRIST PART OF THE DAYLIGHT HOURS JUST AHEAD OF FRONTAL
BOUNDARY. FRONT WILL THEN PUSH ACROSS DURING THE DAY...BUT AS
USUAL NOT CLEANLY...WITH SOME LEE SIDE TROUGHING ALREADY EVIDENT
THIS MORNING...IT MAY SHIFT INTO THE PIEDMONT THIS
AFTERNOON...WITH DEEPER CONVECTION FIRING ACROSS THE EASTERN
PORTIONS OF OUR AREA OR MAYBE EVEN OFF TO THE EAST BY MID TO LATE
AFTERNOON. WITH TIMING OF POPS...GENERALLY FOLLOWED A BLEND OF THE
06Z RAP13 AND HIGH RES WRF-ARW FROM 00Z.
DO NOT THINK THERE WILL BE MANY BREAKS IN CLOUD COVER SO
INSTABILITY REMAINS WEAK TO MODEST...MAYBE 1000-1500 SFC BASED
MOST AREAS...WITH UP TO 2000 J/KG IN THE EAST IF WE CAN GET A FEW
BREAKS IN CLOUDS. DO NOT SEE MUCH IN THE WAY OF SEVERE WEATHER
POTENTIAL GIVEN VERY MOIST AIRMASS AND NOT ESPECIALLY STEEP LAPSE
RATES. LOCALLY HEAVY RAIN WILL BE MAIN CONCERN AGAIN...AND GIVEN
RAINFALL LAST EVENING AND SOME CONTINUED LIGHT TO MODERATE
OVERNIGHT IN FAR WEST...BIGGEST THREAT FOR ANY FLASH FLOODING
REMAINS IN THE WEST...EVEN THOUGH THERE IS SOME QUESTION AS TO
WHETHER ANY DEEPER CONVECTION CAN SUSTAIN ITSELF OR GET GOING
DURING THE MORNING HOURS BEFORE THE FRONT PUSHES THROUGH THE
MOUNTAINS. WILL KEEP THE FLASH FLOOD WATCH GOING THROUGH THE
DAY...ALTHOUGH AREAS IN THE FOOTHILLS VERY MARGINAL...AND WE WILL
LIKELY BE ABLE TO CANCEL EARLY AS BELIEVE ANY ORGANIZED CONVECTION
AND HEAVIER RAINFALL RATES WILL SHIFT EAST BY EARLY TO MID
AFTERNOON.
FRONT PUSHES WELL EAST BY EARLY EVENING IF NOT SOONER..QUICKLY
LOWERING THREAT OF SHWRS/STORMS ACROSS THE ENTIRE AREA BEFORE
MIDNIGHT. KEPT CHC POP GOING IN EAST UNTIL MIDNIGHT...BUT MY
FEELING IS THIS MAY MOVE OUT EVEN QUICKER. ALSO THERE IS LINGERING
LOW LEVEL MOISTURE ON WEST SLOPES BEHIND FRONT AND MAYBE SOME
SPRINKLES OR DRIZZLE IS POSSIBLE FOR A WHILE THIS EVENING BACK
THERE AS WELL...SO KEPT LOW CHC POPS INTO EARLY EVENING AS WELL.
TEMPERATURE WISE...AM LEANING TO COOLER MET GUIDANCE FOR HIGHS GIVEN
EXPECTED CLOUD COVER...AND EVEN NUDGED DOWN A DEG OR TWO FROM
THERE. ONE AREA THAT MAY END SEEING A LITTLE MORE SUN IS FAR
SOUTHEAST AND IF THERE ARE MORE THAN JUST A COUPLE HOURS OF IT
DURING TEH AFTERNOON THE LOW 90S TEMPS THE MAV IS ADVERTISING
COULD BE REALIZED...SO WILL HAVE TO WATCH THIS. TONIGHT WE MAY SEE
THE FIRST 50S IN THE WEST IN QUITE SOME TIME WITH LOWER DEW PTS
MOVING IN AND SOME CLEARING.
&&
.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
AS OF 400 AM EDT TUESDAY...
LOOKING AT MAINLY DRY CONDITIONS FOR WEDNESDAY...POSSIBLY WITH A FEW
LINGERING SHOWERS ACROSS OUR NORTHWEST WIND UPSLOPE AREAS DURING THE
MORNING...AS CANADIAN HIGH PRESSURE CONTINUES TO BUILD IN FROM THE
UPPER MIDWEST. THIS AIRMASS WILL BRING A SIGNIFICANT COOL DOWN TO OUR
AREA...WITH AFTERNOON HIGHS RANGING FROM 7 TO 9 DEGREES BELOW NORMAL
FOR MID AUGUST. HIGH PRESSURE WILL SHIFT EAST DURING THE DAY...AND
THEN BUILD SOUTHWARD ALONG THE EASTERN FACE OF THE APPALACHIANS
WEDNESDAY NIGHT...WHICH WILL SHIFT OUR WINDS TO A NORTHEASTERLY
DIRECTION.
THURSDAY WILL REMAIN RELATIVELY DRY AS WELL...ALTHOUGH MAY SEE A
LITTLE LIGHT RAIN ENTER THE NORTH CAROLINA MOUNTAINS AND THE
MOUNTAIN EMPIRE ON THURSDAY AS WINDS AROUND THE HIGH PRESSURE WEDGE
PICK UP MOISTURE FROM UPPER LEVEL DISTURBANCES RIDING ALONG THE COLD
FRONT STALLED WELL TO OUR SOUTH. RAINFALL WILL REMAIN ISOLATED
HOWEVER...AND WOULD NOT MAKE ANY CHANGES TO OUTDOOR PLANS AT THIS
POINT. THE COOL EASTERLY FLOW WILL AGAIN KEEP TEMPERATURES SEVERAL
DEGREES BELOW NORMAL...WITH MOST AREAS HOLDING IN THE 70S FOR
AFTERNOON HIGHS.
WILL SEE A BETTER RETURN OF MOISTURE FOR FRIDAY AS A DEEP UPPER
LEVEL TROUGH MOVES INTO THE CENTRAL MISSISSIPPI RIVER VALLEY. WHILE
HIGH PRESSURE WILL REMAIN IN PLACE IN THE LOW LEVELS...WINDS ALOFT
ALONG THE EASTERN SEABOARD WILL BECOME INCREASINGLY SOUTHWESTERLY AS
THE TROUGH AMPLIFIES. THIS UPPER FLOW WOULD BE FAVORABLE FOR
CARRYING DISTURBANCES ACROSS THE CAROLINAS...WHICH WOULD POTENTIALLY
TRIGGER SPOTTY SHOWERS AND THUNDERSTORMS FOR OUR AREA SOUTH OF
INTERSTATE 81.
&&
.LONG TERM /SATURDAY THROUGH MONDAY/...
AS OF 400 AM EDT TUESDAY...
AS WE PROGRESS INTO THE WEEKEND...CURRENT MODEL TRENDS OFFER A
STALLED DEEPENING LOW OVER THE CENTRAL U.S. WITH THE LOW ALONG THE
GULF BEING TRANSPORTED NORTHWARD ON THE EAST SIDE OF THE CENTRAL
CONUS TROUGH. THIS WOULD ALLOW FOR BETTER DYNAMICS AND MOISTURE FLOW
ACROSS THE REGION. THIS WILL LEAD TO BETTER CHANCE OF LIGHT TO
MODERATE RAIN OVER THE AREA THROUGH SATURDAY...AND THEN BETTER
CHANCES OF SHOWERS AND SOME THUNDERSTORMS BY SUNDAY. WHILE ACTIVITY
MAY TAPER OFF A BIT ON MONDAY...THE CENTRAL CONUS TROUGH WOULD STILL
BE TO OUR WEST...AND BE A FEATURE TO POTENTIALLY INFLUENCE OUR
WEATHER PAST DAY 7.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 200 AM EDT TUESDAY...
BETWEEN 06Z AND 12Z THERE WILL BE ANOTHER WAVE OF SHOWERS WITH
MODERATE RAINFALL AND ISOLATED THUNDER MOVING FROM KY INTO
SOUTHEAST WV AND LIKELY TO IMPACT BLF/LWB AGAIN WITH PERIODS OF
IFR CONDITIONS. LEFT MENTION OF THUNDER OUT OF LWB HOWEVER AS
LINGER WEAK INSTABILITY CONFINED A LITTLE FARTHER SOUTH. MORE
SHALLOW CONVECTION ORGANIZATION CONTINUES TO DEVELOP UPSTREAM SO
THERE MAY NOT BE TOO MANY BREAKS IN PRECIP ACTIVITY...AND FOG MAY
NOT BE AS DENSE AS ONCE EXPECTED AT LWB UNLESS SOME REAL BREAKS IN
PRECIP CAN OCCUR LATE. THUS MAKING FOR TROUBLESOME TAF
FORECAST ESPECIALLY AT THESE SITES. FARTHER EAST EXPECT A FEW
SHOWERS MAY REACH BCB/ROA/LYH BY 08Z TO 09Z BUT CIGS SHOULD REMAIN
VFR OR MVFR...WITH EXCEPTION OF BCB...BUT LIKELY TO GET SOME IFR
FOG FARTHER EAST LATE TONIGHT. OVERALL...EXPECT THE USUAL HARD TO
PIN DOWN FLUCTUATION BETWEEN IFR/LIFR TO VFR AT TIMES THROUGH
EARLY MORNING GIVEN THE TROPICAL AIRMASS AND THREAT OF SHOWERS.
FOR TUESDAY THE FRONT SHIFTS SLOWLY SOUTHEAST AND TURNS THE WINDS
TO THE WNW BY AFTERNOON. EXPECT MOST OF THE CONVECTION IN THE
MORNING IN THE WEST TO TRANSFER EAST OF THE MOUNTAINS IN THE
AFTERNOON. COVERAGE FOR SHOWERS SHOULD BE 50/50 AT LEAST IF NOT
MORE BUT KEPT THUNDER OUT OF THE PREDOMINANT GROUP FOR NOW...BUT
LEFT IN VICINITY. MAINLY VFR CONDITIONS FOR THE DAY...EXCEPT IN
THE CASE THAT ANY HEAVIER RAIN OR STORMS MOVE RIGHT OVER AN
AIRPORT.
THE COLD FRONT...AND ASSOCIATED HIGH PRESSURE...WILL LIKELY BE
STRONG ENOUGH TO PUSH THE TROPICAL AIRMASS OUT OF THE AREA FOR A
COUPLE OF DAYS...BRINGING A GOOD OPPORTUNITY FOR WIDESPREAD VFR
WEATHER THAT MAY LAST OVER MUCH OF THE AREA LATER TUESDAY NIGHT INTO
THURSDAY BEFORE MOISTURE BEGINS TO RETURN NORTHWARD ON THE BACK SIDE
OF THE HIGH LATE IN THE WEEK. ONE EXCEPTION WILL BE AT THE
SOUTHEASTERN WV TERMINAL FORECAST SITES WHERE RETURN TO VFR
WEATHER WITH NO FLIGHT RESTRICTIONS MAY BE DELAYED UNTIL MID TO
LATE WEDNESDAY DUE TO COOL UPSLOPING WINDS AND LINGERNIG LOW
CLOUDS AND PERHAPS EVEN SOME DRIZZLE TUES NIGHT.
&&
.HYDROLOGY...
AS OF 355 PM EDT MONDAY...
NO CHANGES TO FLASH FLOOD WATCH. SOME AREAS RECEIVED 3"+ OVER THE
MOUNTAIN EMPIRE OF SW VA...INCLUDING THE RICHLANDS AREA.
MORE HEAVIER DOWNPOURS ARE POSSIBLE AGAIN OVERNIGHT AND TUESDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR VAZ007-009>017-032.
NC...FLASH FLOOD WATCH THROUGH THIS EVENING FOR NCZ001>003-018-019.
WV...FLASH FLOOD WATCH THROUGH THIS EVENING FOR WVZ042>045.
&&
$$
SYNOPSIS...SK
NEAR TERM...SK
SHORT TERM...NF
LONG TERM...DS/NF
AVIATION...CF/SK/WP
HYDROLOGY...AMS/SK