000
FXUS61 KRNK 031949
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
349 PM EDT FRI JUL 3 2009

.SYNOPSIS...
HIGH PRESSURE OVER THE UPPER MIDWEST WILL MOVE TO OVER THE REGION
TONIGHT. ON SATURDAY...A WARM FRONT OVER THE MID MISSISSIPPI
VALLEY WILL BEGIN MOVING TOWARD THE AREA. THE WARM FRONT WILL
REACH THE SOUTHERN APPALACHIANS SATURDAY NIGHT...AND THEN A LOW
PRESSURE WILL MOVE EASTWARD ALONG THE FRONT ON SUNDAY BRINGING A
GOOD CHANCE OF SHOWERS AND THUNDERSTORMS.

&&

.NEAR TERM /THROUGH SATURDAY/...
WX PATTERN TYPICALLY RESERVED FOR FALL AND SPRING HAS PRODUCED AN
EXTENSIVE STRATOCU FIELD...THANKS TO STRONG JULY SUNSHINE. IN THIS
SCENARIO...USUALLY INVERSION LOWERS IN THE EARLY EVENING AND
ERADICATES LLVLS MOISTURE/CLDS. HOWEVER...THIS AFFECT WILL NOT BE AS
DRASTIC IN JULY. THIS POSES SOME FORECASTING CONUNDRUMS FOR
TONIGHT...BUT ONLY WITH REGARDS TO TEMPS AND FOG. ALTHOUGH SOME OF
THE CU WILL FALL APART WITH LOSS OF HEATING...PLENTIFUL RH REMAINS
FOR A STRATUS LAYER TO PERSIST TONIGHT THROUGH SE WEST VA AND
POSSIBLY EXTREME WESTERN VA. THUS...HAVE HELD ONTO CLDS LONGER IN
THOSE PARTS UNTIL HIGH PRESSURE CELL IS DIRECTLY OVERHEAD NEAR 6Z
AND ONWARDS. DID INSERT FOG INTO THE GREENBRIER VALLEY...BUT THAT`S
CONTINGENT UPON CLOUDS BEHAVING. ALSO...TEMPS MAY RUN WARMER
ESPECIALLY AT LWB IF CLDS PERSIST DESPITE TEMPS STRUGGLING TO 70F
ATTM. IF LLVL MOISTURE IS NOT SCOURED OUT SAT MORNING...THEN HIGH
CLDS RIDING OVER TOP WILL MEAN A CLOUDIER DAY THAN MOS
INDICATES...AND THUS COOLER MAX T. WITH THIS IN MIND...TRIED TO KEEP
TEMPS IN THE WEST CLOSER TO THE COOLER END OF GUIDANCE. MOS HAS BEEN
TOO WARM FOR A COUPLE OF DAYS NOW IN THIS ANOMALOUS
REGIME...ALTHOUGH SATURDAY WILL BE SLIGHTLY MORE REMINISCENT OF
JULY...AS TROUGHINESS IN THE MIDDLE ATL IS NUDGED NORTH BY THE
CENTRAL CONUS RIDGE LEAKING EAST.

INDEPENDENCE DAY AS A WHOLE LOOKS DRY...MODEL GUIDANCE WITHOLDING
PRECIP POTENTENTIAL UNTIL THE SECOND HALF OF THE HOLIDAY WEEKEND.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
12Z MODEL GUIDANCE REMAINS IN LINE WITH 00Z GUIDANCE...FORECASTING A
SHORT WAVE TROF TO PASS OVERTOP THE RESIDENT UPPER LEVEL SOUTHERN
PLAINS RIDGE. THE RESULTANT SURFACE EVOLUTION IS FOR A WARM FRONT
TO ADVANCE NORTHEAST ACROSS THE MID MS VALLEY AND INTO THE OHIO
VALLEY SATURDAY...AND DEVELOPMENT OF A SURFACE LOW ALONG THIS
BOUNDARY AS THE ENTIRE SYSTEM MIGRATES TOWARD OUR FCST AREA
SATURDAY NIGHT INTO SUNDAY. MODELS HAVE TRENDED STRONGER WITH THE
MID LEVEL FORCING AND FARTHER NORTH...WITH THE NAM BOLDLY PAINTING
AN INCH TO AN INCH AND A HALF SWATH OF QPF ACROSS WV AND VA. ATTM
BELEIVE THE MODELS...ESP THE NAM...ARE OVERDOING THE QPF ACROSS
WV/VA...A BIAS RESULTING FROM THE SYNOPTIC SCALE FORCING IN THE
MODELS. A CLOSE LOOK AT THE MESOSCALE ENVIRONMENT SUGGESTS THE
CONVECTIVE TRIP SHOULD TAKE PLACE FARTHER SOUTH AND WEST WITHIN
WARM SECTOR. MESOSCALE FACTORS SHOULD DOMINATE WITH STRONGER
ISENTROPIC UPGLIDE ALONG 305K SURFACE TAKING PLACE OVER SOUTHERN
IL/IN ON SATURDAY...THE RESULTANT MESOSCALE CONVECTIVE SYSTEM
(MCS) DROPPING SOUTHEAST THROUGH KY AND INTO TN SATURDAY
NIGHT...CORFIDI VECTORS SUGGESTING POTENTIAL FOR STRONGEST DEEP
CONVECTION TO MISS OUR CWA ALTOGETHER LEAVING US IN A CLOUD DEBRIS
FIELD WITH MORE STRATIFORM ELEMENTS.

THAT SAID...STILL THINK IT WARRANTS HIGH POPS FOR OUR CWA...THE
STRONG MID LEVEL FORCING AND PROXIMITY OF MID LEVEL BAROCLINIC
ZONE ALLOWING FOR SATURATION OF MID AND UPPER LEVEL CLOUD
LAYERS...BUT QPF REMAINING BLO A HALF INCH. I THINK THE ONE INCH
QPF THE NAM IS PAINTING IS OVERDONE (ACTUALLY ITS IN THE WRONG
PLACE) AND INSTEAD SHOULD BE PAINTED FARTHER SOUTHWEST ALONG THE
TRACK OF THE ORGANIZED CONVECTIVE FEATURE. TAKING A LOOK AT THE
FORECAST THETA E...925-850 MB LAYER...AND IT SCREAMS FOR THE MCS
TO TAKE A NOSE DIVE INTO KY/TN...THE 340K+ AIR REMAINING OVER THE
TN VALLEY.

FOR THE SENSIBLE FORECAST HAVE RAISED POPS SATURDAY NIGHT INTO
EARLY SUNDAY. STILL THINK PRECIP WILL HOLD OFF FOR OUR CWA UNTIL
AFTER FIRE WORKS DISPLAYS ARE DONE. IF ANYTHING WILL SEE OVERCAST
CONDITIONS EARLY SATURDAY NIGHT...BLOW OFF FROM THE EVOLVING MCS
OVER THE OHIO VALLEY. IF THINKING IS CORRECT...STRONGER DEEP
CONVECTION FROM MCS WILL PASS JUST SOUTHWEST OF OUR CWA...ALONG A
SDF-LEX-TYS LINE. DEBIS CLOUDS AND MOISTURE WILL STILL PASS OVER
OUR CWA WITH THE POTENTIAL OF A PERIOD OF SHOWERS AND EMBEDDED
THUNDERSTORMS...THE GREATEST THREAT FROM ABOUT 11 PM SATURDAY
NIGHT THROUGH NOON SUNDAY. ONCE WE GET ON THE BACK SIDE OF THE
UPPER LEVEL SUPPORT ON SUNDAY WINDS SHOULD SWING AROUND TO THE
NORTH OR NORTHWEST AND BEGIN THE DRYING PROCESS.

TEMPS SUNDAY WILL BE COOL DUE TO THE EXTENSIVE CLOUD COVER...60S
AND 70S MOST AREAS. WILL NEED SUN TO CRACK 80...AND NOT THAT
CONFIDENT FOR MUCH SOLAR INSOLATION.

MONDAY SHOULD BE A TRANSITION DAY. INCREASED SUN WILL PROVIDE A
TEMPERATURES BOOST. LINGERING MOISTURE MAY BUBBLE UP IN TO SOME
SCATTERED SHOWERS DURING THE AFTERNOON...BUT POPS MAINLY LIMITED
TO THE DIURNAL HEATING CYCLE.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
LONGWAVE PATTERN IS FORECAST TO GRADUALLY REAMPLIFY WITH THE MID
CONUS RIDGE NOSING TOWARD CANADA AND TROUGHS ON BOTH COASTS. THIS WILL
RESULT IN A NET SLOWING OF FRONTAL SYSTEMS ACROSS THE COUNTRY AND
FOR US SHOULD SUPPRESS WARM FRONT BACK TO THE SOUTH LEAVING OUR
FORECAST AREA DOMINATED BY NORTHWEST FLOW ALOFT AND MAINLY DRY
SENSIBLE WEATHER. THE NET EFFECT FOR OUR CWA SHOULD BE A DRY WEEK
WITH TEMPS NEAR NORMAL. CAN`T RULE OUT SOME ISOLATED DIURNAL
SHOWERS...BUT THE PROBABILITY IS JUST TO LOW TO INCLUDE ATTM.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
STRATOCU WILL DISSIPATE THIS EVENING...BUT LAST A FEW HRS INTO
TONIGHT THROUGH PARTS OF SE WEST VA. OVC TO BKN CLDS ALL DAY AND
PART OF TONIGHT WILL KEEP SMALL DEWPOINT DEPRESSIONS...MAKING
LIFR/VLIFR FOG ALL THE MORE LIKELY AT LWB AND POSSIBLY EVEN
BLF...WITH HIGH PRESSURE CELL DIRECTLY OVER THE LATTER. ALTHOUGH
KBLF IS A DIFFICULT PLACE TO FOG IN...DID INCLUDE SOME TEMP IFR
VIS FOR NOW. MITIGATING FACTOR IS THE ARRIVAL OF HIGH CLDS OFF OF
CONVECTION FROM THE MIDWEST. FARTHER EAST...ALTHOUGH HIGH PRESSURE
MAY ARRIVE TOO LATE...LAV GUIDANCE IS LETTING WINDS DIE FOR A FEW
HRS BEFORE SUNRISE. THIS MAY LEAD TO SOME MVFR/IFR FOG THERE LATE.
HIGH CLDS OVERSPREAD THE REGION NEAR THE END OF THE TAF PERIOD.

TSTM COMPLEXES DEVELOPING TO THE WEST MAY BRING A RETURN TO AT
LEAST SCTD STORMS AND POSSIBLE BRIEF MVFR CONDITIONS ON SUNDAY AND
MONDAY.

&&

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

&&

$$
SYNOPSIS...JJ
NEAR TERM...KM
SHORT TERM...PM
LONG TERM...PM
AVIATION...JJ/KM

NWS RNK Office Area Forecast Discussion