FXUS61 KRLX 160051
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
716 PM EST TUE DEC 15 2009
.SYNOPSIS...
MUCH COLDER TONIGHT WITH UPSLOPE SNOW SHOWERS IN NORTHERN MOUNTAINS.
HIGH PRESSURE WEDNESDAY THROUGH THURSDAY. UPPER LEVEL DISTURBANCE
CROSSES THIS WEEKEND.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
OVERNIGHT UPDATE...UPDATED TO SLOW CLEARING FROM WEST TO EAST
OVERNIGHT PER SATELLITE AND OBS. THIS IS SUPPORTED BY NEW HI RES
MODEL DATA WHICH SLOWS EXIT OF LOW LEVEL THERMAL TROUGH. ALSO ADDED
SPRINKLES AND FLURRIES MAINLY EAST PER RADAR FOR EARLY TONIGHT.
PREVIOUS DISCUSSION...
THERMAL TROUGH IS LAGGING BEHIND THE COLD FRONT THAT PASSED THROUGH
THIS MORNING...AND COMBINED WITH NORTHWEST SURFACE FLOW AND LOW
LEVEL MOISTURE...LIGHT UPSLOPE WILL AFFECT THE MOUNTAINS INTO
TONIGHT. TEMPERATURES ARE NEAR FREEZING AT THE HIGHEST
ELEVATIONS...SO LIGHT SNOW CAN BE EXPECTED...BUT ACCUMULATIONS
SHOULD BE LESS THAN AN INCH.
OTHERWISE...STRONG HIGH PRESSURE OVER THE CENTRAL PLAINS WILL SLIDE
EAST OVER THE NEXT 24 HOURS...EVENTUALLY ERODING THE LOW LEVEL
MOISTURE. THE MID AND UPPER LEVELS OF THE COLUMN SHOULD BE DRY...AND
WILL EXPECT SUN FOR WEDNESDAY. COLD AIRMASS IN PLACE WILL MAKE THE
SUN DECEPTIVE...AND IT WILL BE A CHILLY DAY.
WITH A PRESSURE GRADIENT IN PLACE...WIND WILL NOT GO CALM OVERNIGHT.
THIS WILL KEEP TEMPERATURES TONIGHT FROM BOTTOMING OUT COMPLETELY.
NAM MOS LOOKS TO BE TOO COLD...AND GENERALLY KEPT THE OVERNIGHT LOWS
ON THE HIGHER SIDE OF GUIDANCE NUMBERS...IF NOT SLIGHTLY ABOVE.
&&
.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 GUIDANCE.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
HI/LO CONFIDENCE FCST. RELATIVELY HIGH CONFIDENCE IN PNA PATTERN
WITH HIGH LATITUDE BLOCK TO BRING ABOUT BELOW NORMAL TEMPERATURES
FOR THE WEEKEND INTO THE HOLIDAY WEEK. LOW CONFIDENCE IN THE
DETAILS WITH VARIOUS SHORT WAVES MOVING THROUGH THE FLOW.
PERIOD BEGINS WITH UPPER LEVEL S/W OVER THE MIDWEST WITH POSITION /
TIMING DIFFERENCES ALREADY EVIDENT AMONG THE MODELS. DIFFERENCES
CONTINUE W/R WHERE THIS S/W GOES OVER THE WEEKEND INCLUDING WHERE IT
EXITS THE E COAST. THESE DIFFERENCES STEM...IN PART...FROM WHETHER
OR NOT UPPER LEVEL VORTEX LOBE OFF NOVA SCOTIA AT THE START OF THE
PERIOD RETROGRADES BACK OVER THE GREAT LAKES OR NOT. THERE IS LESS
MODEL AGREEMENT ON THIS SCENARIO THAN THERE WAS 24 HOURS AGO.
RETROGRESSION OF THE UPPER VORTEX WOULD ALLOW MORE SOUTHERLY FLOW
AHEAD OF MIDWEST S/W AND BRING ITS PRECIPITATION FARTHER N THAN
OTHERWISE. ACCEPTED HPC SOLUTION HERE WITH CHANCE POPS HIGHEST
ACROSS S HALF OF FCST AREA SAT NT.
ONCE THIS SYSTEM IS EXODUS SUNDAY...TRIED TO SHOW A BREAK BEFORE
ADDITIONAL SHORT WAVES IN THE FLOW ALOFT MOVE THROUGH. THERE IS
WIDE RANGE OF POSSIBILITIES W/R UPPER LEVEL PATTERN EARLY NEXT WEEK
ALTHOUGH BELOW NORMAL TEMPERATURES ARE IMPLIED...BUT HOW MUCH
BELOW? ECMWF AND GFS40 DO AGREE ON POLAR VORTEX OVER OR NEAR FCST
AREA SOMETIME EARLY NEXT WEEK.
USED BIAS CORRECTED MOSGUIDE FOR HIGHS SAT...THEN A MIX OF HPC AND
PREVIOUS FCST FOR HIGHS SUN-TUE. ROLLED WITH A BLEND OF THE BIAS
CORRECTED ADJMEX FOR LOWS SAT AND SUN MORNINGS...AND THEN PREVIOUS
FCST WITH SOME HPC BLENDING MON AND TUE MORNINGS...AND FINALLY CLOSE
TO A GFS40/ECMWF BLEND FOR WED MORNING...DAY 7 NIGHT.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
00Z WEDNESDAY THRU 00Z THURSDAY...
MVFR CEILINGS GIVE WAY TO VFR MOST PLACES OVERNIGHT. VFR REACHES
OHIO RIVER AROUND 04Z...CKB-CRW LINE AROUND 07Z...AND IN THE
MOUNTAINS BY 14Z. ALSO ADDED SOME SPRINKLE TO SNOW FLURRY ACTIVITY
THRU 06Z...MAINLY MOUNTAINS WHERE LOCAL IFR IS POSSIBLE IN THE
HIGHER ELEVATIONS.
AFTER 14Z...CEILINGS AND VISIBILITIES UNLIMITED FOR WEDNESDAY.
AFTER 00Z THURSDAY...
NO IFR WEATHER EXPECTED AT THIS TIME.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...NONE.
OH...NONE.
KY...NONE.
VA...NONE.
&&
$$
SYNOPSIS...26/TRM/MDP
NEAR TERM...JMV
SHORT TERM...MDP
LONG TERM...TRM
AVIATION...JMV
