501
FXUS61 KRNK 040139
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
939 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 /UNTIL 6 AM SATURDAY MORNING/
STILL EXPECT STRATOCUMULUS IN SOUTHEAST WEST VIRGINIA TO SLOWLY
ERODE OVERNIGHT WITH ENOUGH CLEARING FOR FOG IN THE GREENBRIER
VALLEY DURING THE EARLY MORNING. HAVE MADE A SLIGHT UPWARD
ADJUSTMENT TO THE MINIMUM TEMPERATURES BASED ON THE LATEST
OBSERVATIONS AND THE MOST RECENT LAV GUIDANCE. NO OTHER CHANGES
NEEDED AT THIS TIME.
SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY NIGHT/
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 POTENTIAL UNTIL THE
SECOND HALF OF THE HOLIDAY WEEKEND.
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
BELIEVE 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. DEBRIS 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 FRIDAY/
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 /02Z SATURDAY THROUGH WEDNESDAY/
SOME MVFR CEILINGS IN AND AROUND BLF THIS EVENING BUT OVERALL
STRATOCUMULUS WILL BE DISSIPATING SLOWLY OVERNIGHT. EXPECT ENOUGH
CLEARING FOR MVFR FOG AT LYH...BLF AND LWB. DEW POINT DEPRESSION
WILL BE NEAR ZERO DURING THE EARLY MORNING AT LWB SO LEFT THE
TYPICAL LIFR FOG CONDITIONS IN. HIGH CLOUDS ARE EXPECTED TO
SPREAD ACROSS THE MOUNTAINS FROM THUNDERSTORMS OVER THE TENNESSEE
VALLEY ON SATURDAY...BUT IT SHOULD BE CLEAR ENOUGH AROUND 12Z FOR
THE FOG TO DISSIPATE AT LWB.
TSTM COMPLEXES DEVELOPING TO THE WEST MAY BRING A RETURN TO AT
LEAST SCTD STORMS AND POSSIBLE BRIEF MVFR CONDITIONS ON SATURDAY
NIGHT THROUGH MONDAY. AFTER MONDAY DEEP MOISTURE AND LIFT REMAINS
WELL TO THE SOUTH OF THE FORECAST AREA SO VFR CONDITIONS ARE
EXPECTED.
RNK WATCHES/WARNINGS/ADVISORIES
VA...NONE.
NC...NONE.
WV...NONE.
SYNOPSIS...JJ
NEAR TERM...AMS
SHORT TERM...KM/PM
LONG TERM...PM
AVIATION...AMS/KM
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page