FXUS61 KRLX 241639
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
1139 AM EST THU DEC 24 2009
.SYNOPSIS...
WARMER TODAY. RAINY AND WINDY OCCLUDED FRONT PASSES LATE TONIGHT
THROUGH CHRISTMAS. SOME ICE EXPECTED IN EASTERN MOUNTAINS. STRONG
GUSTS ON RIDGES TONIGHT THROUGH CHRISTMAS. COLDER THIS WEEKEND.
&&
.NEAR TERM /THROUGH FRIDAY/...
LARGE LOW PRESSURE SYSTEM TO IMPACT MUCH OF THE EASTERN TWO-THIRDS
OF THE COUNTRY...WITH ITS OCCLUDED FRONT PASSING THROUGH OUR REGION.
MAIN CONCERNS ARE FREEZING RAIN POTENTIAL IN THE EASTERN SLOPES OF
THE MOUNTAINS LATE TONIGHT THROUGH CHRISTMAS MORNING...AND
POSSIBLE HIGH WINDS IN THE HIGHER ELEVATIONS BEGINNING THIS EVENING.
MOST NOTABLE TREND IN THE MODELS...IS THE CONTINUED SLOWING OF THE
TIMING OF THE OCCLUDED FRONT THAT SPREADS RAIN ACROSS THE AREA.
OTHERWISE...MODELS REMAIN SIMILAR COMPARED TO PRIOR RUNS. POPS WERE
ADJUSTED TO REFLECT THE SLOWER TIMING...YET ALSO RAISED TO 100 PCT
DURING THE SMALL WINDOW OF PASSAGE OF OCCLUDED FRONT LATE TONIGHT
THROUGH FRIDAY MORNING.
WHILE MODELS CONTINUE TO SHOW VERY STRONG WINDS AT THE 850MB LEVEL
/40-50 KTS THIS EVENING...TO 60-75 KTS 12Z THRU 18Z FRIDAY/...MODEL
SOUNDINGS ALSO SHOW THAT BOUNDARY LAYER WILL BE VERY STABLE BECAUSE
OF THE DEGREE OF WARMING ALOFT. THUS IT WILL BE DIFFICULT FOR THE
HIGHER WINDS TO MIX DOWN TO THE SURFACE. THAT BEING SAID...SURFACE
PRESSURE GRADIENT WILL BE TIGHT...AND RIDGETOPS WILL STILL BE
VULNERABLE TO THE HIGH WINDS. WITH THIS PACKAGE...I DROPPED HIGH
WIND WATCH IN THE SOUTHERN MOUNTAINS AND WENT AHEAD WITH A WIND
ADVISORY FOR ALL OF THE MOUNTAINOUS ZONES THIS EVENING THROUGH
CHRISTMAS AFTERNOON. WIND STRENGTH WILL BE VERY
ELEVATION-DEPENDENT...WITH THE RIDGES BEING VULNERABLE TO WIND GUSTS
TO MORE THAN 50 MPH. VALLEYS WILL BE IN THE STABLE BOUNDARY
LAYER...WITH CONSIDERABLY LOWER GUSTS.
AS FOR FREEZING RAIN...SIGNIFICANT COLD AIR DAMMING IS SET TO OCCUR
DOWN THE EAST SLOPES OF THE APPALACHIANS...WITH LARGE SURFACE HIGH
OVER QUEBEC AND RIDGE EXTENDING DOWN THE MIDATLANTIC COAST. PROFILES
CONTINUE TO SUPPORT FREEZING RAIN POTENTIAL...THROUGH FRIDAY MORNING
IN POCAHONTAS COUNTY AND EASTERN RANDOLPH COUNTY. HOWEVER...TWO
FACTORS MAY LIMIT ACTUAL AMOUNT OF ICE THAT OCCURS. ONE...IF FURTHER
DELAY IN RAINFALL ONSET OCCURS...AND TWO...CONVECTION WELL UPSTREAM
IN THE MID-SOUTH TO SOUTHEAST STATES MAY LIMIT FULL MOISTURE
ADVECTION...THUS LOWERING RESULTING PRECIPITATION AMOUNTS HERE.
BECAUSE OF TIMING UNCERTAINTY...AND WITH MOST OF ICE TO OCCUR IN
THIRD PERIOD...WILL CONTINUE TO HOLD THE WINTER STORM WATCH UNTIL
FURTHER REVIEW.
TEMPERATURES WILL BE NON-DIURNAL IN NATURE THROUGH CHRISTMAS.
DERIVED MAX AND MIN TEMPERATURES AFTER COMPLETING NON-DIURNAL
TEMPERATURE TRACE BASED ON BLENDED GUIDANCE...AND PLACING COOLER
BIAS ON THE EASTERN MOUNTAINS.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
THE WEEKEND WILL BE DOMINATED BY THE LARGE LOW PRESSURE SYSTEM THAT
WILL TRACK FROM THE UPPER MIDWEST...ACROSS THE GREAT LAKES...AND
INTO NEW ENGLAND BY MONDAY.
THE REMNANTS OF THE COLD FRONTAL PRECIP WILL EXIT THE NORTHERN
MOUNTAINS EARLY FRIDAY NIGHT...WITH RAIN SHOWERS TO CHANGING TO SNOW
SHOWERS BEFORE ENDING...AS COLD ADVECTION SETS IN. LITTLE SNOW
ACCUMULATION EXPECTED.
ALL MODELS AGREE OUR AREA WILL THEN BE IN A DRY SLOT SATURDAY...AS
THE LOW CENTER WILL STILL BE OVER THE WESTERN GREAT LAKES. DESPITE
CONTINUED LOW LEVEL COLD ADVECTION ACROSS THE AREA SATURDAY...WEST
TO SOUTHWEST WINDS...RELATIVELY DRY AIR...AND POOR UPSLOPE
FLOW...WILL KEEP IT DRY FOR SATURDAY. TEMPERATURES...WITH SOME
SUNSHINE...WILL MAKE IT TO 40 OR BETTER MANY AREAS SATURDAY.
WRAPAROUND MOISTURE AND REAL GOOD ADVECTION FINALLY WORKS BACK IN
SATURDAY NIGHT AND ESPECIALLY SUNDAY...AS THE LOW CENTER TRACKS EAST
AND FLOW BECOMES MORE WEST TO NORTHWEST. WHILE THE AREA WILL BE
UNDER DEEP MOIST CYCLONIC FLOW...THE UPSLOPE COMPONENT OF THE WIND
WILL STILL BE LESS THAN IDEAL. THUS...SNOW SHOWERS WILL BE
WIDESPREAD ACROSS THE AREA...BUT NO HEAVY SNOW EXPECTED FOR THE
MOUNTAINS.
EXPECT TEMPERATURES TO BE WELL BELOW NORMAL BY SUNDAY.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
UPPER LEVEL LOW AND ASSOCIATED FORCING FOR PRECIPITATION WILL
PUSH EAST OF REGION MONDAY. HOWEVER....NORTHWEST UPSLOPE SNOW WILL
CONTINUE INTO TUESDAY...BEFORE HIGH PRESSURE BUILDS IN.
ANOTHER SYSTEM WILL THEN BEGIN TO APPROACH THE REGION...WITH
PRECIPITATION CHANCES BEGINNING WEDNESDAY...AND THEN CONTINUING
THROUGH THURSDAY.
MODELS SUGGEST AN SURFACE AREA OF LOW PRESSURE WILL MOVE FROM THE
NORTHERN GULF OF MEXICO INTO THE ATLANTIC OCEAN THURSDAY...WITH
THE STORM EXPECTED TO INTENSIFY AS IT MOVES UP THE EAST COAST NEW
YEARS DAY.
HPC TEMPERATURE GUIDANCE WAS GENERALLY USED...WITH SOME TWEAKS TO
REFLECT THE LATEST ENSEMBLE GUIDANCE.
&&
.AVIATION /12Z THURSDAY THROUGH TUESDAY/...
GREENBRIER AND TYGART VALLEYS IN THE MOUNTAINS WILL HAVE IFR TO
LIFR CIG AND/OR VIS FROM VALLEY FOG THROUGH 14Z OR SO. VFR
ELSEWHERE...WITH HIGH CLOUDS AND DRIER AIR MASS PREVENTING FOG
THIS MORNING. GOING INTO TONIGHT...LLWS WILL BE A THREAT AS
PRESSURE GRADIENT GREATLY INCREASES...AND NEAR-SURFACE INVERSION
KEEPS HIGHEST WINDS NOT VERY FAR OFF OF THE GROUND. STILL A DECENT
SOUTHEAST WIND DEVELOPING EVEN AT THE SURFACE...ESPECIALLY IN THE
MOUNTAINS. CIGS LOWER AS OCCLUDED FRONT ENTERS THE AREA WITH RAIN
TOWARDS 12Z...AND FREEZING RAIN POSSIBLE IN THE MOUNTAINS.
AFTER 18Z FRIDAY...
SYSTEM IMPACTS AREA FRIDAY...WITH RAIN AND POSSIBLE IFR. FREEZING
RAIN ALSO A THREAT IN THE WV MOUNTAINS...AND LOW LEVEL WIND SHEAR
NOT OUT OF THE QUESTION AREAWIDE FRIDAY MORNING.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...WIND ADVISORY FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY FOR
WVZ033>038-046-047.
WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR WVZ046-047.
OH...NONE.
KY...NONE.
VA...WIND ADVISORY FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY FOR
VAZ003-004.
&&
$$
SYNOPSIS...MDP/JMV
NEAR TERM...MDP
SHORT TERM...JMV
LONG TERM...JSH
AVIATION...MDP
