FXUS61 KRNK 012338
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
638 PM EST TUE DEC 1 2009
.SYNOPSIS...
HIGH PRESSURE GIVES WAY TO A STRONG AREA OF LOW PRESSURE JUST WEST
OF THE APPALACHIAN MOUNTAINS INTO WEDNESDAY. WEAK HIGH PRESSURE
SLOWLY BUILDS EAST INTO THE END OF THE WORK WEEK. ANOTHER SYSTEM
MAY DEVELOP ALONG THE SOUTHEAST COAST AND MOVE OFFSHORE THIS
WEEKEND.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
UPPER LOW IN NORTHERN MEXICO COMES OUT OF THE SOUTHERN STREAM TROF
AND LIFTS INTO THE OHIO VALLEY BY LATE WEDNESDAY. STILL SEEING
DIFFERENCES IN THE MODELS WITH THE TRACK OF THE LOW AND MORE
SIGNIFICANTLY HOW FAST THE AIRMASS SATURATES AND THE PRECIPITATION
BEGINS. GFS IS STILL SLIGHTLY FASTER BUT BOTH MODELS HAVE SOME
PRECIPITATION IN THE FAR SOUTHWEST BY 12Z WEDNESDAY.
EXPECT THE CIRRUS TO SPREAD ACROSS THE FORECAST AREA AFTER 00Z
TONIGHT WITH THE CLOUDS LOWERING AFTER 06Z. WITH VERY STRONG
SYNOPTIC LIFT AND IMPRESSIVE UPSLOPE DUE TO THE 55-65 KNOT 850 MB
JET...QPF AMOUNTS ALONG THE BLUE RIDGE AND IN THE FOOTHILLS WILL BE
AT LEAST 1.00 TO 2.00 INCHES PER 6 HOURS. HOWEVER...THIS LOOKS TO BE
A LONGER DURATION EVENT WITH NO EXCESSIVELY HIGH RATES IN THE 1 TO 3
HOUR TIME RANGE. 6 HOUR FFG IS CLOSE TO 3 INCHES SO WILL HOLD OFF ON
ANY FLOOD WATCH FOR NOW.
THE STRONG WINDS AND UPSLOPE WILL CONTINUE UNTIL THE WARM FRONT
CROSSES THROUGH THE FORECAST AREA WEDNESDAY AFTERNOON. WILL UPGRADE
THE HIGH WIND WATCH TO A HIGH WIND WARNING AND ADDED A WIND ADVISORY
FROM THE BLUE RIDGE TO THE WEST. NOT COMPLETELY CONVINCED THAT THE
STRONGER WINDS WILL GET INTO ALL THE VALLEYS BUT AT THE HIGHER
ELEVATIONS AND ON THE NORTHWEST/DOWNSLOPE SIDE OF THOSE RIDGES GUSTS
MAY BE UP TO 60 MPH.
EXPECT TEMPERATURES TO FOLLOW TYPICAL DIURNAL DROP THIS
EVENING...THEN BECOME NEARLY STEADY ONCE THE CLOUDS MOVE IN.
TEMPERATURES COULD DROP A DEGREE OR TWO MORE ONCE THE PRECIPITATION
STARTS DUE TO EVAPORATIVE COOLING. THIS PUTS EARLY MORNING
TEMPERATURES IN THE MID 30S IN THE MOUNTAINS. WILL KEEP SNOW MIXED
WITH THE RAINFALL AT THE ONSET...BUT ONCE THE STEADY LIGHT TO
MODERATE RAIN BEGINS THERE WILL BE ENOUGH WARM RAIN BEING BROUGHT
DOWN TO THE SURFACE THAT ALL PRECIPITATION WILL REMAIN LIQUID.
ON WEDNESDAY TEMPERATURES WILL BE NEARLY STEADY UNTIL THE WARM FRONT
COMES THROUGH. LOCATIONS...INCLUDING ROANOKE AND LYNCHBURG ALONG AND
NORTH OF 460 WILL STAY IN THE LOWER TO MID 40S SINCE THE WARM FRONT
DOES NOT COME THROUGH UNTIL LATER IN THE DAY.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
RAIN SHOULD BE ENDING ACROSS THE CWA WED NIGHT...WITH HIGHER POPS
REMAINING IN THE UPSLOPE REGIONS OF SE WEST VA AND NW
NC...ALTHOUGH THIS IS USUALLY OVERDONE BY THE MODELS. ALTHOUGH
CAPE ONLY REACHES 500 J/KG ALONG THE FAR SE...INSTABILITY MAY BE
ENOUGH WHEN COMBINED WITH IMPRESSIVE SHEAR TO PRODUCE TSTORMS AS
OCCLUDED BOUNDARY AND PERHAPS TRIPLE POINT CROSSES THE PIEDMONT.
ALTHOUGH SLT RISK IS JUST TO THE EAST...ANY STORMS COULD PRODUCE
STRONG WIND GUSTS AT LEAST. TEMPS OVERNIGHT WILL BE RATHER
STEADY...PERHAPS EVEN RISING AHEAD OF THE BOUNDARY WITH AOA +10C
AT H85 ARRIVING ALONG THE SOUTH. WINDS COULD GUST TO ADVISORY
LEVELS ALONG AND JUST BEHIND THE BOUNDARY WED EVENING. IF
CONVECTION DOES DEVELOP...THIS MAY PRODUCE LOCALIZED HVY RAIN
WHICH MAY CAUSE WATER PROBLEMS...HOWEVER...NO FLOOD HEADLINES
ATTM. UPSLOPE LOOKS MEAGER ON THURSDAY...SO CUT BACK THE DURATION
AND MAGNITUDE OF POPS DURING THURSDAY...WITH LACK OF MOISTURE
DEPTH AND UNFAVORABLE TRAJECTORIES. CLDS MAY PERSIST LONGER THAN
GUIDANCE INDICATES ALONG SE WEST VA...WITH MOISTURE STAYING TRAPPED
UNDER INVERSION AND CONTINUED WEAK CAA. WEAK HIGH PRESSURE TRIES
TO BRIDGE INTO THE MIDDLE ATLANTIC ON FRIDAY...BEFORE A
DEVELOPMENT MOVES ALONG THE COAST INTO SATURDAY. GEFS KEEPS SYSTEM
AND POPS WELL OFF THE COAST...ALTHOUGH OP GFS/ECMWF INDICATE
DEFORMATION ZONE OVER THE CWA. WILL FOR NOW ONLY GO WITH SLT CHC
POPS INTO SATURDAY MORNING...WHICH WOULD BE MOSTLY SNOW.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
AN UPPER LEVEL TROUGH WILL MOVE QUICKLY FROM THE MID WEST SATURDAY
MORNING TO THE EAST COAST SATURDAY NIGHT. A STRONG SHORT WAVE AT THE
BASE OF THIS TROUGH WILL TRACK FROM TEXAS SATURDAY MORNING TO OFF
THE VA/NC COAST SATURDAY EVENING. THIS DISTURBANCE WILL PICK UP SOME
MOISTURE DURING ITS TRAVEL AND BRING A CHANCE FOR PRECIPITATION TO
THE AREA ON SATURDAY. YESTERDAY...THE 12Z GFS WAS THE ONLY MODEL
SHOWING THIS DISTURBANCE WITH PRECIPITATION OVER THE AREA.
TODAY...THE 12Z GFS IS STILL SHOWING IT AND NOW THE ECMWF HAS IT AS
WELL. THE 12Z GEM MAINTAINING ITS CONTINUITY AND LOOKS SIMILAR TO
YESTERDAY ECMWF...KEEPING ANY PRECIPITATION OVER FLORIDA. MODELS
CONTINUE TO SHOW WEST TO NORTHWEST LOW LEVEL FLOW OVER THE REGION
AND AHEAD OF THE FRONT FRIDAY NIGHT/SATURDAY MORNING. WITH THE SPEED
OF THIS SYSTEM COMING IN TO A RELATIVELY DRY AIR MASS...STILL THINK MODELS
ARE OVER DOING LIQUID PRECIPITATION OVER THE AREA. IN LIGHT OF
ANOTHER MODEL MOVING THIS DISTURBANCE OVER THE REGION...WILL ADD LOW
CHANCE POPS ON SATURDAY...BUT CONFIDENCE IS VERY LOW.
FOR SAKE OF AGREEMENT...LETS SAY THIS SYSTEM DOES MOVE IN WITH
PRECIPITATION. GFS FORECAST SOUNDINGS SHOWING A SHALLOW WARM SURFACE
BOUNDARY LAYER...LESS THAN A 1000 FT ALONG THE FOOTHILLS AND FROZEN
SOUNDING ACROSS THE MOUNTAINS. IF PRECIPITATION DOES FALL SATURDAY
MORNING...IT WILL MOSTLY LIKELY BE SNOW. INTO THE
PIEDMONT...BOUNDARY LAYER A LITTLE THICKER AND AROUND 1400-1800 FEET
FOR P-TYPE TO BE RAIN...POSSIBLY MIXED WITH SNOW EARLY. OF COURSE
THIS DEPENDS ON THE GFS VERIFYING...WHICH HAS A HISTORY OF A COLD
BIAS DURING THE COOL SEASON...ESPECIALLY IN THE LONG RANGE.
ONCE THE UPPER LEVEL TROUGH TRACKS OFF THE EAST COAST...HIGH
PRESSURE WILL BUILD IN WITH ZONAL FLOW ALOFT. THE REGION SHOULD
REMAIN PRECIPITATION FREE THROUGH EARLY NEXT WEEK. TEMPERATURES
THROUGH THE PERIOD WILL STAY BELOW NORMAL BUT MODERATE EACH DAY.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
CIRROSTRATUS HAS MOVED IN ACROSS THE REGION BUT EXPECT THE LOWER
CIGS WITH RAIN TO NOT BEGIN IMPACTING OUR FORECAST AREA UNTIL
AFTER 12Z. ALSO...A STRONG SOUTHEAST LOW LEVEL JET WILL BRING LOW
LEVEL WIND SHEAR TO ALL TAF SITES WEDNESDAY. THE MAIN ISSUE WITH
THE TAFS WILL BE LOW CLOUD THREAT. IF THE RAIN COMES DOWN HARD
ENOUGH...WE USUALLY KEEP CIGS ABOVE IFR...BUT IF THE RAINS ARE
VERY LIGHT THEN EXPECT IFR OR LOWER TO IMPACT THE SITES. AT THIS
POINT LEANING TOWARD MVFR CIGS WITH A PERIOD OF IFR VSBYS IN RAIN
ESPECIALLY FROM ROANOKE EAST TO LYH/DAN.
THIS LOW PRESSURE STORM SYSTEM LIFTS NORTHEAST WEDNESDAY NIGHT
WITH IMPROVING CONDITIONS EAST OF THE MOUNTAINS ON THURSDAY.
EXPECT UPSLOPE SNOW SHOWERS TO LINGER MVFR CONDITIONS ACROSS SE
WVA INTO FRIDAY WITH VFR ELSEWHERE. ANOTHER STORM SYSTEM COULD
BRING LOWER CIGS AND POSSIBLY A LITTLE MORE WINTRY PRECIP FOR
SATURDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WIND ADVISORY FROM 6 AM WEDNESDAY TO MIDNIGHT EST WEDNESDAY
NIGHT FOR VAZ011-013-014-016>020-022>024-032>035.
HIGH WIND WARNING FROM 6 AM WEDNESDAY TO MIDNIGHT EST
WEDNESDAY NIGHT FOR VAZ007-009-010-012-015.
NC...WIND ADVISORY FROM 6 AM WEDNESDAY TO MIDNIGHT EST WEDNESDAY
NIGHT FOR NCZ001>003-018-019.
WV...WIND ADVISORY FROM 6 AM WEDNESDAY TO MIDNIGHT EST WEDNESDAY
NIGHT FOR WVZ043>045.
HIGH WIND WARNING FROM 6 AM WEDNESDAY TO MIDNIGHT EST
WEDNESDAY NIGHT FOR WVZ042.
&&
$$
SYNOPSIS...JH/KM
NEAR TERM...AMS
SHORT TERM...KM
LONG TERM...RCS
AVIATION...AMS/WP
