Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 011148
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
748 AM EDT WED JUL 1 2015

.SYNOPSIS...
A FRONTAL ZONE WILL REMAIN DRAPED ACROSS THE AREA FOR THE NEXT SEVERAL
DAYS. WAVES MOVING ALONG THIS FRONTAL ZONE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS IN OUR FORECAST THROUGH THE WEEKEND. HIGH
PRESSURE MOVING IN FROM THE UPPER MIDWEST ON SUNDAY MAY FINALLY NUDGE
THE FRONT FAR ENOUGH TO OUR SOUTH AND EAST TO BRING SOME DRIER WEATHER
TO THE REGION FOR THE FIRST PART OF NEXT WEEK.

&&

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

AN UPPER LEVEL TROF WILL REMAIN OVER THE EASTERN US AS IMPULSES OF
SHORT WAVE ENERGY ROTATE THROUGH THE FLOW. THIS WILL DRIVE A LOW
PRESSURE SYSTEM FROM THE GREAT LAKES REGION IN TO CANADA AND KEEP A
FRONTAL ZONE MEANDERING ACROSS THE REGION. THIS WILL SERVE AS A TRIGGER
FOR CONVECTION TODAY...BUT INSTABILITY AND SHEAR ARE LIMITED SO IT
LOOKS LIKE GENERAL THUNDERSTORMS WILL BE THE RULE WITH STRONGER
ACTIVITY CONFINED TO LOCATIONS FURTHER TO THE SOUTHWEST AS PER THE
LATEST SPC DAY 1 OUTLOOK. PRECIPITABLE WATER VALUES ARE NOT EXTREME
TODAY SO DO NOT ANTICIPATE ANY HYDRO ISSUES TO DEVELOP.

BELIEVE ACTIVITY WILL INITIALLY EXHIBIT A DIURNAL TREND AND START TO
TAPER OFF AFTER SUNSET...BUT MODEL GUIDANCE IS KEEN ON THE IDEA OF
SLIDING ANOTHER IMPULSE ALONG THE FRONTAL ZONE AND INTO THE AREA LATE
TONIGHT. WHILE WATER VAPOR IMAGERY DOES INDEED SUPPORT THE NOTION OF A
SERIES OF SHORT WAVES...CONFIDENCE IS LOW AS TO WHETHER OR NOT ONE OF
THESE WILL KICK OFF AN MCS THAT WILL BRING WIDESPREAD SHOWERS/THUNDER
TO THE REGION TONIGHT. FOR NOW WILL GO WITH A WETTER SOLUTIONS AND
RAISE POPS BACK UP TO HIGH CHC/LOW LIKELY WEST OF THE BLUE RIDGE IN
ANTICIPATION OF AN MCS REMNANT MOVING IN. WILL HAVE TO TAKE A LOOK AT
THE MESO MODELS LATER TODAY TO SEE IF THESE POPS CONTINUE TO LOOK VALID.

EXPECTING TEMPS TO BE RIGHT AROUND NORMAL WITH READINGS NEAR 90
PIEDMONT/SOUTHSIDE TO LOWER 80S IN THE MOUNTAINS FOR HIGHS...COOLING TO
UPPER 60S EAST/LOWER 60S WEST FOR LOWS TONIGHT.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 415 AM EDT WEDNESDAY...

BROAD TROUGHING CONTINUES THROUGH THE PERIOD WITH NUMEROUS
EMBEDDED DISTURBANCES TRACKING THROUGH THE BASE OF THE TROUGH
ROUGHLY ON A PERISTENT TRAJECTORY FROM THE NORTHERN PLAINS
SOUTHEASTWARD THROUGH THE MO/TN VALLEY INTO THE SOUTHERN
APPALACHIANS AND SOUTHEAST STATES. THIS PATTERN WILL CERTAINLY
SUPPORT CONTINUED MESOSCALE CONVECTIVE COMPLEXES AS IT HAS THE
PAST COUPLE OF DAYS. HOWEVER...THERE ARE SUBTLE DIFFERENCES AMONG
THE MODELS AS TO THE EXACT TRACK AND TIMING OF THE PROJECTED
MESOSCALE CONVECTIVE...WHICH LEADS TO LOW CONFIDENCE IN THE POP
FORECAST AND TO A LESSER EXTENT THE TEMPERATURE FORECAST. IN
ADDITION...MODELS PROJECT ASSOCIATED RAINFALL/QPF AT ALL HOURS OF
THE DAY AND NIGHT...WHICH IS MOST LIKELY NOT THE SCENARIO THAT
WILL PLAY OUT. GIVEN THE TIME OF YEAR...DIURNAL HEATING AND THE
NORMAL DIURNAL CYCLE OF PRECIPITATION CAN BE EXPECTED DESPITE THE
MODEL PROJECTIONS. IT DOES APPEAR MORE LIKELY THAT THE SOUTHWEST
PART OF THE CWA HAS A BETTER CHANCE OF SEEING REPEATED MCS
ACTIVITY THROUGH THE PERIOD THAN DOES THE NORTHEAST...BUT A SLIGHT
CHANGE IN THE PATH/TIMING WOULD RENDER THIS THEORY LESS ACCURATE.
OVERALL...THERE IS A TENDENCY FOR THE BAROCLINIC ZONE TO SHIFT
SOUTH MORE INTO AL/GA/SC BY THE WEEKEND.

AT THIS POINT...THE BEST DYNAMICS AND INSTABILITY APPEAR TO TRACK
ACROSS THE REGION FRIDAY...WHICH CORRESPONDS WITH THE ONLY PERIOD
IN WHICH SPC CURRENTLY HAS MORE THAN JUST A TINY CORNER OF THE CWA
IN A MARGINAL RISK. BOTH THURSDAY AND FRIDAY THERE APPEARS TO BE
SOME CHANCE FOR A REMNANT MCS TO BE DRIFTING INTO THE REGION AT
DAYBREAK...WHICH LEAVES CONSIDERABLE QUESTION AS TO HOW MUCH
INSTABILITY AND REDEVELOPMENT OF CONVECTION WILL TAKE PLACE LATER
IN THE DAY IF CLOUD COVER...PRECIPITATION...AND COOLER
TEMPERATURES LINGER. INSTABILITY PROGS ARE MEAGER AT BEST THROUGH
MUCH OF THE PERIOD AND THE BEST SHEAR AXIS REMAINS TO OUR
SOUTHWEST.

SO OVERALL...CONFIDENCE IS QUITE LOW IN THE POP FORECAST OTHER
THAN TO SAY THAT PRECIPITATION AND CONVECTION IS LIKELY WITHIN AT
LEAST 12 HOUR BLOCKS EACH DAY. TRACK AND TIMING WILL ONLY BE
POSSIBLE AS THESE EVENTS MOVE INTO THE NEAR TERM. FOR THIS
REASON...HAVE GENERALLY CAPPED POPS IN THE 50-60 PERCENT RANGE
DAYTIME AND 30-40 PERCENT RANGE NIGHTTIME...WITH THE HIGHEST POPS
THROUGH MUCH OF THE TIME FRAME FOCUSED ACROSS THE SOUTHWEST...MORE
LIKELY TO BE WITHIN THE PATH OF PROJECTED CONVECTIVE COMPLEXES.

850MB TEMPS HOVER IN THE +12C TO +16C RANGE NORTH TO SOUTH THROUGH
MOST OF THE PERIOD. THIS...COMBINED WITH THE EXPECTED CLOUD COVER
AND PRECIPITATION WILL HOLD MAX TEMPS SLIGHTLY BELOW NORMAL...BUT
MIN TEMPS ABOVE NORMAL.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 430 AM EDT WEDNESDAY...

THE PERSISTENT UPPER TROUGH DURING THE SHORT TERM PERIOD BEGINS TO
SHEAR OUT AND LIFT NORTHEAST DURING THE LONG TERM AS UPPER
HEIGHTS BEGIN TO RISE IN RESPONSE TO BROAD UPPER RIDGING EXTENDING
FROM THE SOUTHWEST/SOUTH CENTRAL U.S. INTO THE NORTHEAST U.S. THE
TAIL END OF THE PRIOR UPPER TROUGH APPEARS DESTINED TO BECOME
CUTOFF ACROSS THE SOUTHEAST STATES. THIS PERIOD SHOULD BE
CHARACTERIZED BY A GENERAL DECREASE IN CONVECTION...CERTAINLY LESS
MCS ACTIVITY AS THE PATTERN BECOMES CONSIDERABLY LESS FAVORABLE
FOR SUCH THROUGH THE PERIOD...AND A SLIGHT INCREASE IN
TEMPERATURES. THE INCREASE IN MAX TEMPS...ESPECIALLY...WILL BE A
RESULT OF THE ENHANCED UPPER RIDGING...500MB HEIGHTS RISING INTO
THE 588-590DM RANGE AND INEVITABLY POCKETS OF 850MB TEMPS +20C TO
+21C APPEARING...ESPECIALLY ACROSS THE PIEDMONT. THIS WILL ALLOW
SOME MAX TEMPS IN THE LOW 90S TO REAPPEAR ACROSS THE SOUTHEAST...E.G.
KDAN.

ALTHOUGH HEIGHTS ARE RISING AND THERE IS LESS POTENTIAL FOR
MESOSCALE COMPLEXES...WEAK NORTHWEST FLOW ALOFT PERSISTS AND WILL
STILL SUPPORT A THREAT FOR CONVECTION. HOWEVER...POPS MORE IN THE
20-40 PERCENT RANGE APPEAR MORE REASONABLE DURING THIS PERIOD THAN
THE 50-60 POPS ADVERTISED THROUGH MUCH OF THE SHORT TERM.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 745 AM EDT WEDNESDAY...

ALL TAF SITES HAVE RE-ENTERED INTO VFR CONDITIONS THIS
MORNING...AS CONVECTIVE ACTIVITY AND LEFTOVER BR/FG HAVE BEGUN
LIFTING. A LOW TO MID-LEVEL CLOUD DECK IS CURRENTLY IN PLACE
ACROSS THE BLUE RIDGE... BUT EXPECTING GENERAL CIG HEIGHT RISES AS
THE DAY PROGRESSES.

A FRONTAL BOUNDARY WILL REMAIN DRAPED OVER THE AREA AND HELP
GENERATE SOME VFR CIGS AND POSSIBLY ANOTHER ROUND OF SHRA/TSRA
WEDNESDAY AFTERNOON. PUT A FEW VCSH INTO A FEW SPOTS...ESPECIALLY
ALONG AND EAST OF THE BLUE RIDGE...BUT NOT EXPECTING COVERAGE
TO BE AS GREAT AS SEEN ON MONDAY. DO NOT HAVE A LOT OF CONFIDENCE
IN TIMING OR LOCATION OF ANY CONVECTIVE DEVELOPMENT...SO WILL KEEP
TAFS MOSTLY DRY AND SEE IF LATER MESO MODEL RUNS CAN COME TO A CONSENSUS.

BR FORMATION IS EXPECTED OVERNIGHT INTO WEDNESDAY AT THE USUAL SITES...
ESP LWB/RNK WHO MAY APPROACH LIFR CONDITIONS FOR A PERIOD OF TIME EARLY
ON WEDNESDAY. OTHER SITES...WHO SEE A ROUND OF PRECIPITATION ON TUESDAY...
MAY DEVELOP BR CONDITIONS FOR A TIME...BUT KEPT THOSE OUT UNTIL SHRA/TS
LOCATIONS ARE DETERMINED.

WINDS WILL BE ON THE LIGHT SIDE WITH SOME LOW END GUSTS WEDNESDAY
AFTERNOON.

EXTENDED AVIATION DISCUSSION...

THE REGION WILL BE IN A GENERAL NORTHWEST FLOW PATTERN THROUGH
SATURDAY. WHILE ISOLATED TO SCATTERED SHOWERS AND STORMS CANNOT BE
RULE OUT ANY OF THESE DAYS...THE BEST POTENTIAL WILL BE ON
THURSDAY...THEN AGAIN LATER FRIDAY...FOLLOWED BY A THIRD
POTENTIAL INCREASE IN COVERAGE ON SATURDAY AS SEPARATE SHORTWAVE
TROUGHS PROGRESS TROUGH 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.

&&

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

&&

$$
SYNOPSIS...MBS
NEAR TERM...MBS
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...JM/MBS


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