FXUS61 KRLX 142341
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
641 PM EST MON DEC 14 2009
.SYNOPSIS...
COLD FRONT WITH A FEW SCATTERED SHOWERS AND PATCHY DRIZZLE LATE
TONIGHT INTO TUESDAY MORNING. UPSLOPE SNOW SHOWERS IN NORTHERN
MOUNTAINS TUESDAY NIGHT. COLD TUESDAY NIGHT THRU THURSDAY MORNING.
&&
.NEAR TERM /THROUGH TUESDAY/...
UPDATED THIS EVENING TO REFINE SKY GRIDS AND SHOWER CHANCES WITH
FRONT...THEN QUICKLY CONFINED POPS TO MOUNTAINS AFTER THE FRONT.
HOWEVER...ALSO INCLUDED MENTION OF PATCHY DRIZZLE FOR A TIME WELL
BEHIND THE FRONT INTO TUESDAY MORNING.
PREVIOUS DISCUSSION...
A STRONG COLD FRONT COMING THRU TONIGHT WILL BE EAST OF THE
MOUNTAINS BY 12Z TUESDAY. MODELS STRONGLY AGREE ON A SOUTHERN
STREAM SYSTEM STAYING WELL SOUTH ACROSS THE SOUTHEASTERN STATES AS
THE FRONT COMES THRU TONIGHT. THUS...THERE WILL NOT BE MUCH MOISTURE
TO WORK WITH FOR THIS COLD FRONT. HOWEVER...DYNAMICS FROM THE
SUPPORTING NORTHERN STREAM SHORT WAVE WILL BE ENOUGH TO SQUEEZE OUT
SCATTERED LIGHT RAIN SHOWERS AS IT COMES ACROSS TONIGHT.
BEHIND THE FRONT...STRONG COLD ADVECTION WILL BE THE BIG STORY
TUESDAY. BELIEVE THE NAM TEMPERATURE GUIDANCE IS CORRECT ON A SLOWLY
FALLING TEMPERATURE REGIME TUESDAY...FROM THE 40S EARLY TO THE 30S
LATE MOST AREAS. ALSO...WITH THE STRENGTH OF THE COLD
ADVECTION...OVERTURNING OF THE ATMOSPHERE IS EXPECTED TO BRING GUSTY
WINDS TUESDAY...MORE SO THAN THE MODELS INDICATE...BUT CERTAINLY
BELOW WIND ADVISORY CRITERIA EVEN IN THE MOUNTAINS. FOR
PRECIP...MOISTURE BEHIND THE FRONT BECOMES SHALLOW...WHICH RAPIDLY
BECOMES MORE OF AN UPSLOPE EVENT BY EARLY AFTERNOON. EXPECT A
CHANGEOVER TO SNOW SHOWERS LATER IN THE AFTERNOON...MOSTLY IN THE
NORTHERN AND CENTRAL MOUNTAINS AS FLOW BECOMES NORTHWESTERLY.
STILL...AMOUNTS BY THE END OF THE DAY WILL BE QUITE LIGHT GIVEN THE
SHALLOW MOISTURE AND NOT IDEAL CRYSTAL GROWTH IN THE SHALLOW MOIST
LAYER.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
SHALLOW LAYER OF LOW LEVEL MOISTURE REMAINS IN PLACE AFTER FRONT
PASSAGE. 85H THERMAL TROUGH PERSISTS...WITH NW FLOW ALOFT IN
PLACE...FOR A SHORT LIVED UPSLOPE SNOW EVENT TUESDAY NIGHT. KEPT
SNOW AMOUNTS LIGHT...WITH ABOUT AN INCH OR TWO EXPECTED OVER THE
HIGHEST MOUNTAIN PEAKS.
MODELS GENERALLY AGREE THAT MOISTURE WILL SCOUR OUT BY WEDNESDAY
MORNING WITH END OF PRECIPITATION ACTIVITY. WITH INTRUSION OF SFC
HI FROM THE WEST...DID NOT HANG ON TO SHOWER ACTIVITY IN
WEDNESDAY. HOWEVER...DID LEAVE SOME MORNING CLOUDS OVER THE
MOUNTAINS.
WEAK NORTHWEST FLOW AT THE SFC AND NEARLY ZONAL FLOW ALOFT SETTLES
WEDNESDAY THROUGH THURSDAY. MODELS IN DECENT AGREEMENT IN KEEPING
THE ATMOSPHERIC COLUMN DRY.
FOR TEMPS...WITH STRONG CAA OCCURRING TUESDAY NIGHT...HAVE
UNDERCUT GUIDANCE VALUES. WARMER AIR RETURNS AT THE 85H LEVEL
WEDNESDAY AFTERNOON AND EVENING FOR A SLIGHT REBOUND IN TEMPS.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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 /00Z TUESDAY THROUGH SATURDAY/...
COLD FRONT SWINGS THROUGH 03Z-08Z...WITH A FEW SHOWERS AND ABRUPT
DROP INTO MVFR CIGS. BEHIND THE FRONT...PATCHY DRIZZLE AND MVFR
CIGS EXPECTED...THOUGH SOME IFR POSSIBLE FOR MOUNTAIN TERMINALS
DURING 08Z-13Z TIME PERIOD. MVFR CIGS PERSIST BEHIND THE FRONT
THROUGH MOST OF TUESDAY...ESPECIALLY SOUTH AND EAST OF THE OHIO
RIVER. ALSO ON TUESDAY...FAIRLY STIFF NORTHWEST WINDS
EXPECTED...WITH GUSTS EXCEEDING 30 MPH FOR THE HIGHER RIDGES.
UPSLOPE WIND WILL PRODUCE UPSLOPE RAIN SHOWERS IN THE WV
MOUNTAINS...CHANGING TO SNOW BEFORE 00Z WEDNESDAY...WHICH COULD
LEAD TO INTERMITTENT IFR VIS FOR THE AFFECTED SITES.
AFTER 00Z WEDNESDAY...
POSSIBLE IFR CONDITIONS IN SCATTERED SNOW SHOWERS IN THE NORTHERN
WEST VIRGINIA MOUNTAINS TUESDAY NIGHT.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...NONE.
OH...NONE.
KY...NONE.
VA...NONE.
&&
$$
SYNOPSIS...MDP
NEAR TERM...MDP/JMV
SHORT TERM...KMC
LONG TERM...TRM
AVIATION...MDP
