Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 030850
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
450 AM EDT FRI JUL 3 2015

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE OUT OF THE OHIO VALLEY AND INTO THE
MIDDLE ATLANTIC REGION. THIS WILL BRING SHOWERS AND THUNDERSTORMS TO
THE AREA...ALONG WITH CONTINUED COOL TEMPERATURES...AS WE CLOSE OUT THE
WORKWEEK. UNFORTUNATELY OUR WEATHER WILL REMAIN UNSETTLED...WITH A
SERIES OF UPPER LEVEL DISTURBANCES BRINGING A CHANCE FOR SHOWERS AND
THUNDERSTORMS THE REGION THROUGHOUT THE HOLIDAY WEEKEND.

&&

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

SHORT WAVE ENERGY ENTERING THE MEAN UPPER TROF OVER THE EASTERN US WILL
DRIVE A WAVE OF LOW PRESSURE AT THE SURFACE FROM THE OHIO VALLEY TO THE
MID ATLANTIC REGION. THIS WILL TAKE THE FRONTAL BOUNDARY THAT PUSHED
SOUTH OF OUR AREA YESTERDAY AND DRAG IT BACK NORTHWARD AS A WARM FRONT
WITH WEAK HIGH PRESSURE WEDGING DOWN THE EAST SIDE OF THE APPALACHIANS.
EARLY MORNING SATELLITE AND RADAR LOOPS SHOW THAT THINGS ARE BEGINNING
TO COME TOGETHER AS THE VIGOROUS CONVECTION OVER TENNESSEE IS BEGINNING
TO MOVE MORE TOWARD THE EAST/NORTHEAST...WHICH IS HEADING IN OUR
DIRECTION.

THIS SYSTEM HAS A LOT GOING FOR IT WITH GOOD DYNAMIC ENERGY AND A VERY
MOIST AIRMASS IN PLACE. HODOGRAPHS ARE SMALL BUT SHOW A SIGNIFICANT
AMOUNT OF SHEAR AS WOULD BE EXPECTED IN THE VICINITY OF A FRONTAL
BOUNDARY. THE MISSING INGREDIENT FOR SEVERE WEATHER TODAY IS
INSTABILITY. ABUNDANT CLOUD COVER COMBINED WITH THE SOMEWHAT EARLY
ONSET TIME WILL LIMIT DAYTIME HEATING AND MODEL SOUNDINGS IN BUFKIT ARE
SHOWING A LONG AND SKINNY CAPE PRESENTATION WHICH DOES NOT FAVOR
VIGOROUS UPDRAFTS. BASED ON THESE FACTORS...CURRENTLY ANTICIPATE A
SEASONABLE WITH UPPER 60S EAST TO LOWER 60S WEST.EALTHY AREA OF
SHOWERS WITH EMBEDDED THUNDER WILL MOVE ACROSS THE AREA FROM WEST TO
EAST TODAY WITH ACTIVITY MOVING OUT AND WINDING DOWN THIS EVENING/EARLY
TONIGHT. THIS SITUATION WILL BE MONITORED VERY CLOSELY SINCE IF THE
CLOUD COVER IS LESS THAN CURRENTLY ANTICIPATED AND WE CAN GENERATE
GREATER AMOUNTS OF INSTABILITY...ESPECIALLY ACROSS THE SOUTHERN AND
EASTERN PORTIONS OF THE AREA...THE SEVERE THREAT WILL INCREASE. WITH
PRECIPITABLE WATER VALUES RUNNING WELL ABOVE NORMAL HEAVY DOWNPOURS CAN
BE EXPECTED...BUT THE LACK OF WIDESPREAD SIGNIFICANT RAINFALL ON
THURSDAY HAS EASED CONCERN FOR FLOODING A BIT SO WILL NOT BE ISSUING A
FLOOD WATCH WITH THIS PACKAGE. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL
FOR HEAVY RAIN AND POSSIBLE HYDRO ISSUES IN THE HWO.

AS THE LOW MOVES OFF TO OUR NORTHEAST TONIGHT THE FRONTAL BOUNDARY WILL
SWING BACK THROUGH THE REGION AS A COLD FRONT. THIS WILL YIELD SOME
LINGERING SHOWERS WEST OF THE BLUE RIDGE WITH SOME IMPROVEMENT TO THE
EAST

HIGH TEMPERATURES TODAY WILL CONTINUE ON THE COOL SIDE WITH READINGS IN
THE LOWER 80S EAST OF THE RIDGE TO THE LOWER 70S WEST...AND LOWS
TONIGHT RANGE FROM THE UPPER 60S EAST TO LOWER 60S WEST.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
AS OF 415 AM EDT FRIDAY...

THE BROAD UPPER TROUGH PLAUGING THE EASTERN U.S. WILL UNDERGO
SOME SUBTLE MODIFICATIONS DURING THIS PERIOD. SAT-SUN...THE UPPER
TROUGH WILL TAKE ON A POSITIVE TILT AS A SHORT WAVE RIDGE BUILDS
INTO THE GREAT LAKES/PA REGION. MEANWHILE...THE SOUTHERN END
BECOMES CUTOFF ACROSS THE CAROLINAS AND LINGERS ACROSS THAT REGION
SUN...THEN GRADUALLY DRIFTS BACK NORTHWARD INTO EASTERN VA MON AND
NORTHERN VA TUE. THUS...THE AREA REMAINS UNSETTLED AND WET...BUT
WITH A GRADUAL SHIFT OF THE BETTER COVERAGE OF SHOWERS AND
THUNDERSTORMS TOWARD THE EASTERN PART OF THE CWA WITH TIME.

FOR SATURDAY...YET AGAIN...POTENTIAL FOR WIDESPREAD SHOWERS AND
EMBEDDED THUNDERSTORMS TO START OFF THE DAY...JUST AS HAS BEEN THE
CASE THE PAST TWO DAYS. HOWEVER...CONFIDENCE IN THIS IS LOW AT
THIS POINT AS IT WILL LARGELY BE BASED ON UPSTREAM CONVECTIVE
COMPLEXES...TRACK...AND INTENSITY. HOWEVER...FEEL THAT CONFIDENCE
IN ONGOING PRECIPITATION AT 12Z IS SLIGHTLY GREATER THAN THE PAST
TWO DAYS AS THE UPPER TROUGH SHIFTS EAST MOVING THE CURRENT
CORRIDOR OF PRECIPITATION ACROSS THE TN VALLEY EASTWARD INTO OUR
REGION. THE EXTENT OF CLOUDS AND PRECIPITATION IN THE MORNING WILL
DETERMINE THE DEGREE OF INSTABILITY AND HENCE CONVECTIVE COVERAGE
LATER IN THE DAY. UPPER FLOW TENDS TO BECOME MORE SOUTHWEST
INSTEAD OF NORTHWEST DURING THIS PERIOD GIVEN THE TRANSITION OF
THE WEAK UPPER LOW TO THE SOUTH OF THE REGION. THIS SHOULD BE
ENOUGH TO SUPPORT HIGH CHANCE TO LIKELY POPS INTO THE
AFTERNOON/EVENING. SPC CURRENTLY ONLY HAS GENERAL THUNDER ACROSS
THE REGION GIVEN THE LACK OF INSTABILITY. WITH FAIRLY WET
ANTECEDENT CONDITIONS...THE MAIN CONCERN WILL BE HEAVY RAINFALL
AND LOCALIZED FLOODING. HOWEVER...IT APPEARS UNLIKELY THAT FFG
WILL BE EXCEEDED AS RAINFALL AMOUNTS WOULD NEED TO EXCEED 2-2.5
INCHES IN 1-3 HRS MOST LOCATIONS FOR THIS TO OCCUR. PROJECTED
RAINFALL FOR THE THREE DAY PERIOD TODAY THROUGH SUNDAY IS MOSTLY
1.5 TO 2.5 INCHES.

FOR SUNDAY...THE WEAK UPPER LOW DRIFTS BACK NORTH INTO THE CWA.
WIDESPREAD SHOWERS AND THUNDERSTORMS APPEAR LIKELY...BUT THE
EXTENSIVE CLOUD COVER WILL AGAIN LIMIT INSTABILITY. ONCE
AGAIN...LOCALIZED HEAVY RAINFALL WILL BE THE MAIN CONCERN...BUT
GIVEN THAT THE HEAVIEST RAINFALL SHOULD REMAIN MOSTLY EAST OF THE
MOUNTAINS...THIS FURTHER REDUCES CONCERNS OF FLOODING.
HOWEVER...THE PATTERN DOES ONCE AGAIN SUPPORT LIKELY POPS ACROSS
MUCH OF THE CWA...ESPECIALLY EASTERN SECTIONS.

MONDAY PROMISES TO BE YET ANOTHER WET DAY AS THE REMNANT UPPER LOW
DRIFTS INTO NORTHERN VA. ONCE AGAIN...THE BEST COVERAGE OF
PRECIPITATION SHOULD BE ACROSS THE EASTERN SECTIONS...BUT
DIFFERENTIAL HEATING ACROSS THE MOUNTAINS SHOULD RESULT IN AN
UPTICK OF AFTERNOON CONVECTION THERE AND FURTHER NORTH COMPARED
TO SUN. AGAIN...HIGH CHANCE TO LIKELY POPS APPEAR IN ORDER.
INSTABILITY ONCE AGAIN APPEARS MARGINAL AND THE MAIN CONCERN WILL
REMAIN THAT OF LOCALIZED HEAVY RAINFALL.

MAX TEMPS SHOULD REMAIN WELL BELOW NORMAL THROUGH THE PERIOD
THANKS TO CLOUD COVER AND PRECIPITATION...WITH HIGHS MOSTLY IN THE
70S...TO LOWER 80S EAST IF A FEW BREAKS IN THE OVC CAN OCCUR. ON
THE OTHER HAND...LOW TEMPERATURES WILL REMAIN ABOVE NORMAL THANKS
TO HIGH PWATS/DEWPOINTS AND CONSIDERABLE CLOUD COVER.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
AS OF 430 AM EDT FRIDAY...

BY TUESDAY...THERE IS FAIRLY GOOD AGREEMENT AMONG THE MODELS THAT
THE CUT OFF UPPER LOW LINGERING ACROSS THE REGION WILL SPLIT IN
TWO...WITH THE PART ACROSS NORTHERN VA LIFTING NORTHEAST TOWARD
NY/NEW ENGLAND...AS THE PARENT UPPER LOW SINKS SOUTHWARD TOWARD
THE FL PANHANDLE/SOUTH GA. MEANWHILE...A SHORT WAVE AND ASSOCIATED
FRONT WILL APPROACH FROM THE NORTHWEST BY TUESDAY...THEN DRIFT
INTO THE REGION AND STALL WED-THU. AT THIS POINT...TUE SHOULD BE
THE DAY WITH THE LOWEST POPS OVERALL...AND LIKELY LOWER THAN ANY
PRIOR DAYS OR SUCCEEDING DAYS. ONCE THE FRONT DRIFTS INTO THE
REGION WED AND STALLS...WAVES OF LOW PRESSURE WILL RIDE ALONG THE
FRONT AND KEEP GOOD CHANCES OF SHOWERS/THUNDERSTORMS ACROSS THE
REGION. HOWEVER...COMPARED TO THE CURRENT WEEK WITH NORTHWEST
FLOW...UPPER FLOW WILL BE MORE WEST-SOUTHWEST AS BROAD UPPER
RIDGING IS NOTED ACROSS THE SOUTHERN STATES. PRECIPITATION OVERALL
SHOULD BE SLIGHTLY MORE DIURNAL IN NATURE...I.E...LESS
NOCTURNAL...AS A RESULT AND TEMPERATURES WILL CERTAINLY BE
TRENDING WARMER...BUT REMAIN MOSTLY 70S MOUNTAINS AND 80S PIEDMONT
AS 850MB TEMPS TOP OUT IN THE +16C TO +18C RANGE.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
AS OF 155 AM EDT FRIDAY...

NOT A HIGH CONFIDENCE FORECAST AS THE SYNOPTIC REGIME IS MAKING IT
DIFFICULT TO PIN DOWN DETAILS AND TAF SITES WILL EXPERIENCE A GOOD
DEAL OF VARIABILITY IN CONDITIONS. CURRENT RADAR SHOWS LIMITED
SHOWER ACTIVITY THAT CAN BE HANDLED WITH VCSH AT ALL SITES EXCEPT
KLYH WHERE THEY SHOULD BE DRY THROUGH DAYBREAK. FOG HAS BEEN IN
AND OUT AT SEVERAL SITES AND BELIEVE THIS WILL CONTINUE TO BE THE
CASE AS CLOUD COVER WILL LIMIT RADIATIONAL COOLING AND PROHIBIT
THICK RADIATIONAL FOG FROM FORMING. AT THE SAME TIME LOW LEVEL
MOISTURE WILL BE STREAMING IN FROM THE SOUTHWEST SO CIGS WILL BE
COMING DOWN AND KBLF MAY WELL BE IN CLOUD FROM TIME TO TIME WITH
LIFR VSBY.

THE FRONTAL BOUNDARY THAT HAS BEEN WAVERING OVER THE AREA FOR THE
PAST FEW DAYS PUSHED TO THE SOUTH AND HAS LEFT THE REGION WITH A
DEVELOPING WEDGE. AS THE UPPER TROF SHARPENS TODAY AND SHORT WAVE
ENERGY COMES AT US FROM THE SOUTHWEST...A SURFACE LOW WILL MOVE
INTO THE OHIO VALLEY AND DRAG THE FRONT BACK TO THE NORTH. THIS
SCENARIO WILL KEEP A GOOD AMOUNT OF CLOUD COVER OVER THE AREA AND
HELP LIMIT INSTABILITY. BELIEVE THE NET RESULT WILL BE FOR A LARGE
AREA OF SHOWERS WITH EMBEDDED THUNDER MOVING ACROSS FROM WEST TO
EAST THIS AFTERNOON INTO THIS EVENING.

AS THE LOW CONTINUES TO MOVE INTO THE MID ATLANTIC REGION THE
BOUNDARY WILL COME BACK SOUTHWARD AS A COLD FRONT. THIS SHOULD
ALLOW FOR SOME IMPROVEMENT IN CONDITIONS TOWARD THE END OF THE TAF
PERIOD EAST OF THE BLUE RIDGE WITH A LIGHT DOWNSLOPE WIND...WHILE
KBCB/KBLF/KLWB SEE LIGHT UPSLOPE AND DETERIORATING CONDITIONS.

EXTENDED AVIATION DISCUSSION...

THE REGION WILL REMAIN IN A GENERAL NORTHWEST FLOW PATTERN ON
SATURDAY...AND AGAIN EXPECT ANOTHER ROUND OF SHOWERS AND STORMS AS
ANOTHER UPPER LEVEL DISTURBANCE PASSES ACROSS THE FORECAST AREA.
VFR CONDITIONS ARE EXPECTED FOR THE MOST PART. 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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