Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 011747
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
147 PM 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 NOON EDT WEDNESDAY...

MODIFIED MORNING SOUNDING SUGGESTS SBCAPE OF 1200 J/KG THIS
AFTERNOON OVER THE REGION. FORECAST AREA REMAINS IN A LULL BETWEEN
UPPER WAVES. HAD A FEW SHOWERS MOVE NORTH OF GREENBRIER COUNTY
THIS MORNING...AND RADAR IS NOW CLEAR OF PRECIP. HIGH-RES AND 12Z
NAM SUGGEST THE DEVELOPMENT OF SHOWERS AND STORMS EAST OF THE BLUE
RIDGE BY EARLY AFTERNOON...WITH LITTLE OR NONE BETWEEN THE BLUE
RIDGE AND THE WV/VA/ BORDER...WITH MORE ACTIVITY
ARRIVING/DEVELOPING OVER THE MTN EMPIRE INTO THE NC MTNS MID
AFTERNOON...AS UPSTREAM WAVE AND MCS OVER WRN TN MOVES SE TOWARD
THE SOUTHERN APPALACHIANS. ADJUSTED POPS TO LOWER IN THE NORTH AND
CENTRAL PART OF THE FORECAST AREA INTO THE PIEDMONT WITH
LOW/SLIGHT CHANCE AT BEST. KEPT HIGHER POPS OVER THE MTN EMPIRE
INTO THE NC MTNS THOUGH. HIGH TEMPS WILL BE STILL BE WARM/NEAR
NORMAL FROM NEAR 90 SOUTHEAST TO UPPER 70S/LOWER 80S WEST.


PREVIOUS VALID DISCUSSION...

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.

BELIEVE ACTIVITY WILL 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 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 PERSISTENT 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 /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 135 PM EDT WEDNESDAY...

HAVE VFR THROUGH THE AFTERNOON WITH LIMITED CONVECTION. HIGH-RES
MODELS ARE FAVORING SHOWERS AND STORMS TO FORM BETWEEN LYH/DAN BUT
THE CONFIDENCE IS LOW TO EVEN ADD VCTS AT THOSE TERMINALS. TOWARD
EVENING THERE IS A POTENTIAL CONVECTION NOW OVER TN/KY TO MOVE
INTO BLF/TRI AREA...AND THIS WILL BE MAINLY AFTER 21Z...SO HAVE
VCTS AT BLF. MODELS SHOW THIS ACTIVITY INCREASING TONIGHT WITH
MORE OF A SRN CWA TRACK...WHERE LYH/ROA MAY NOT SEE ANYTHING...BUT
ENOUGH CONFIDENCE TO HAVE PREDOMINANT SHRA AT BLF/LWB/BCB LATE.
GIVEN MORE CLOUDS THINK THE FOG THREAT WILL BE LIMITED...SO KEPT
IT MORE IFR/MVFR.

WINDS WILL BE ON THE LIGHT SIDE WITH SOME LOW END GUSTS EARLY THIS
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.

SUNDAY INTO MONDAY HEIGHTS RISE BUT 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/WP
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...JM/WP


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