FXUS61 KRLX 151822
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
120 PM EST TUE DEC 15 2009
.SYNOPSIS...
BLUSTERY WILL FALLING TEMPERATURES TODAY. MUCH COLDER TONIGHT.
UPSLOPE SNOW SHOWERS IN NORTHERN MOUNTAINS TONIGHT. HIGH PRESSURE
WITH COLD TEMPERATURES WEDNESDAY INTO THURSDAY.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
FRONT SLIPPING FAIRLY QUICKLY THROUGH CWA...NOW LYING ALONG A ROUGH
EKN/BKW/LNP LINE. TRUE COLDER AIR LAGS A FEW HOURS BEHIND
FRONT...AND WE HAVE YET TO SEE THE REAL TEMPERATURE DROP. THE MAX
TEMPERATURE FOR TODAY WILL BE THE TEMPERATURE AT 12Z...SOMETIMES
SURPRISINGLY TRICKY TO NAIL. ELECTED TO FOLLOW CLOSE TO LAV NUMBERS
FOR HOURLY TEMPS. ENDED UP WITH MAX VALUES AT/ABOVE THE WARMER
MAV...WHICH SEEMS TO MAKE SENSE GIVEN CURRENT TRENDS. TEMPERATURES
WILL BE FALLING INTO THE 30S DURING THE DAY. STRONG COLD ADVECTION
WILL ALLOW 20-25 KNOT WINDS TO MIX DOWN TO THE SURFACE THIS
AFTERNOON.
MOISTURE DEPTH BEHIND FRONT IS NOT THE BEST...MOSTLY FROM H850
BELOW. STILL...IT REMAINS TRAPPED BELOW INVERSION ALOFT...SO CLOUDS
WILL REMAIN ENTRENCHED TODAY. COLD ADVECTION-INDUCED SHOWERS SHOULD
BE LIMITED MAINLY TO THE MOUNTAINS...WHICH WILL SEE THE TYPICAL
POSTFRONTAL UPSLOPE KICK BY MIDDAY. EXPECT MOSTLY LIQUID UNTIL
ABOUT 18Z...UNTIL SUBZERO H850 TEMPERATURES ARRIVE AND CAUSE THE
CHANGEOVER TO SNOW. THESE WILL CONTINUE THROUGH THE NIGHT...SLOWLY
DECREASING IN COVERAGE...WITH ONLY FLURRIES REMAINING BY 12Z AS
MOISTURE NEARLY DISAPPEARS AND THERMAL TROUGH PASSES. EXPECTING
SNOW AMOUNTS TO BE LIGHT WITHOUT IDEAL CRYSTAL GROWTH...GENERALLY
AROUND AN INCH OR SO ON THE HIGHER PEAKS. MILDLY CONCERNED THAT WE
MAY SEE FREEZING DRIZZLE IN SOME NORTHERN MOUNTAIN LOCATIONS...AS
PRESENCE OF ICE CRYSTALS IN CLOUD LAYER IS QUESTIONABLE AT TIMES.
LEAVING THIS OUT FOR NOW BUT WILL ALERT DAY SHIFT TO POSSIBILITY.
WEST OF THE MOUNTAINS...SIMPLY HAVE A DECREASING CLOUD TREND WITH
INVERSION BREAKING OVERNIGHT AND ALLOW MOISTURE TO BE SCOURED OUT.
USED BIAS-CORRECTED SREF FOR LOW TEMP BASIS...WHICH IS CLOSE TO A
MET/MAV BLEND.
WITH ONLY VERY SHALLOW MOISTURE LEFT ON FORECAST SOUNDINGS FOR
WEDNESDAY MORNING...ONLY MENTIONED SOME SCATTERED MOUNTAIN FLURRIES
IN SCT TO BKN CLOUDS. THE 850 MB THERMAL TROF STILL APPEARS TO BE
BY 12Z WEDNESDAY...WITH ABOUT MINUS 10C ACROSS OUR N.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
THERE WILL BE A LARGE 1000-500MB THICKNESS GRADIENT ACROSS THE
NORTHEAST QUARTER OF THE LOWER 48...WITH A VERY COLD ARCTIC AIR
MASS ACROSS ONTARIO/QUEBEC AND INTO NEW ENGLAND...AND THE MILDER
YET STILL SLIGHTLY COOLER THAN NORMAL AIR IN THE OHIO VALLEY.
HOWEVER...UNLESS A SURPRISE YET-TO-BE-RESOLVED WEAK FAST-MOVING
CLIPPER WERE TO SOMEHOW MATERIALIZE ALONG THAT TEMPERATURE
GRADIENT...IT IS LOOKING QUITE METEOROLOGICALLY MUNDANE FOR THE
SHORT TERM PERIOD. MOST OF THE TIME WE WILL BE STUCK BETWEEN THE
NORTHERN AND SOUTHERN STREAMS. SURFACE HIGH WILL BE IN CHARGE
WEDNESDAY NIGHT THROUGH THURSDAY. THURSDAY NIGHT INTO FRIDAY...SOME
HIGH TO MID LEVEL CLOUDS MAY ADVECT OVER THE AREA...AS A NORTHERN
STREAM WAVE BEGINS TO APPROACH FROM THE WEST...AND A SOUTHERN STREAM
SURFACE LOW GETS ORGANIZED OVER THE GULF COAST. HIGH AND LOW
TEMPERATURE FORECASTS THROUGH THE PERIOD ARE A BLEND OF
MET/MAV/SREF/MOS GUIDANCES.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
MINOR CHANGES IN THE LONG RANGE TO INCLUDE AT LEAST CHANCE POPS IN
A MORE EXTENDED TIME FRAME OVER THE WEEKEND...SINCE 20 POPS DO NOT
GET MENTIONED IN OUR CRWZFPRLX. THIS COMPLEX PATTERN WILL BE
REEVALUATE...AS USUAL...DURING OUR DAY SHIFT.
HI/LO CONFIDENCE FCST. RELATIVELY HIGH CONFIDENCE IN PNA PATTERN
WITH HIGH LATITUDE BLOCK TO BRING ABOUT BELOW NORMAL TEMPERATURES
FOR THE WEEKEND INTO CHRISTMAS WEEK. LOW CONFIDENCE IN THE DETAILS
WITH VARIOUS SHORT WAVES MOVING THROUGH THE FLOW.
PERIOD BEGINS WITH WEAK HIGH PRESSURE IN PLACE UNDERNEATH WNW FLOW
ALOFT. UPPER LEVEL VORTEX CENTER PROGGED TO BE NEAR THE MOUTH OF
THE SAINT LAWRENCE RIVER VALLEY AT THE START OF THE PERIOD
RETROGRADES WWD INTO THE GREAT LAKES AREA UNDERNEATH THE HIGH
LATITUDE BLOCK OVER THE WEEKEND...AND THEN S AND THEN LATER IN THE
WEEKEND AND INTO EARLY NEXT WEEK. MODEL DIFFERENCES SHOW UP IN THE
EXACT TRACK OF THIS UPPER FEATURE WITH THE ECMWF AMONG THE MODELS
BRINGING IT FARTHEST S AT LEAST WITH ONE OF WHAT BECOMES A THREE
CENTER FEATURE.
BELOW TO MUCH BELOW NORMAL TEMPERATURES ARE STRONGLY SUGGESTED BY
ALL OF THESE SOLUTIONS WHILE TIMING AND INTENSITY OF PRECIPITATION
VARY. ECMWF IS ONLY MODEL AT THIS TIME SHOWING A SYNOPTIC SCALE
STRATIFORM PRECIPITATION EVENT PER PHASING WHILE OTHER GUIDANCE
SUGGESTS UPSLOPE EVENTS AMPLIFIED SOMEWHAT BY COLD ADVECTION AND
UPPER LEVEL SUPPORT. WENT WITH HPC/GFS SOLUTION WHICH DOES NOT
SINGLE OUT ANY ONE STRONGER SYSTEM FROM THE OTHERS.
USED THE FOLLOWING SCHEMES FOR TEMPERATURES WHICH ARE MOSTLY A BLEND
OF HPC...GFS...MEX...MOSGUIDE AND EVEN THE PREVIOUS FCST IN SOME
CASES...AS DETAILED BELOW...
MAX
FRI - PREV
SAT - GFS40/HPC
SUN - ADJMEX/HPC THEN AT LEAST 2 LOWER THAN SAT
MON - GFS40/ECMWF/HPC
(TUE - GFS40/ECMWF)
MIN
FRI - GFS40/ECMWF/HPC/PREV
SAT - GFS40/MOSG/HPC/PREV
SUN - GFS40/MOSG/HPC/PREV
MON - GFS40/MOSG/HPC/PREV
TUE - GFS40/ADJMEX/MOSG/ECMWF
&&
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
MVFR CEILINGS GIVE WAY TO VFR THIS EVENING...THEN LOW LEVEL
MOISTURE DISSOLVES GENERALLY AFTER 03Z. SURFACE WINDS GRADUALLY
DECREASE TO 10KTS TONIGHT...AND REMAIN NORTHWESTERLY. LIGHT UPSLOPE
PRECIPITATION IN THE MOUNTAINS WILL SLOWLY TAPER OFF INTO THE
OVERNIGHT WITH THE DISSOLVING MOISTURE. NOT EXPECTING IFR
VISIBILITIES...AND HAVE LEFT THAT OUT OF THE FORECAST.
CEILINGS AND VISIBILITIES UNLIMITED FOR WEDNESDAY.
AFTER 18Z WEDNESDAY...
NO IFR WEATHER EXPECTED AT THIS TIME.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...NONE.
OH...NONE.
KY...NONE.
VA...NONE.
&&
$$
SYNOPSIS...KTB/CL
NEAR TERM...CL
SHORT TERM...MDP
LONG TERM...KTB/TRM
AVIATION...26
