FXUS61 KLWX 221744
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1244 PM EST TUE DEC 22 2009

.SYNOPSIS...
HIGH PRESSURE WILL BUILD ACROSS THE REGION THROUGH WEDNESDAY
NIGHT. A STRONG STORM SYSTEM OVER THE MIDWEST WILL BRING WINTRY
PRECIPITATION AND RAIN TO THE AREA THURSDAY NIGHT THROUGH
SATURDAY. HIGH PRESSURE AND MORE COLD CONDITIONS ARE EXPECTED TO
RETURN SUNDAY INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
ZONAL FLOW ALOFT WILL REMAIN IN PLACE ACROSS THE MID ATLANTIC 
TODAY...AS SURFACE HIGH PRESSURE STARTS TO BUILD IN FROM THE 
NORTHWEST.

SURFACE HIGH PRESSURE WILL BE SOMEWHAT DIRTY TODAY...AS MUCH OF THE 
CWA WAS ALREADY STARTING OFF WITH AMPLE COLD STRATOCU COVER EARLY 
THIS MORNING...AND CONTINUED BKN-OVC CLOUD COVER IS EXPECTED INTO 
THE AFTERNOON HOURS TODAY AS A MID LEVEL SHORTWAVE OVER THE MID 
MISSISSIPPI VALLEY TRANSLATES EAST. 

MID LEVEL SHORTWAVE WILL BE HARD PRESSED TO PRODUCE PRECIP...BUT MAY 
ENHANCE/EXTEND THE CHANCES FOR LIGHT SNOW SHOWERS ACROSS FAVORED 
WEST FACING SLOPE LOCATIONS OF THE HIGHLANDS. SNOW ACCUMULATIONS 
ARE EXPECTED TO BE LESS THAN AN INCH. 

BASED ON CRRNT TEMPS AND PRVS MAXT PAST CPL DAYS...HV ADJUSTED
MAXT UPWD A CPL DEG. CRRNT TEMPS DEPICTING QUITE A RNG. MANY SITES
ABV FRZG...AND A FEW HV ALREADY EXCEEDED FCST. COOLEST READINGS
BTWN OMH-CJR-HEF AND ACRS SRN MD. HV ALSO BUMPED UP CLDCVR BASED
ON SATPIX.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
MID LEVEL SHORTWAVE EXITS THE CWA BY EVENING AS HIGH PRESSURE AT THE 
SURFACE CONTINUES TO BUILD ACROSS THE AREA. 00Z GFS INDICATES A BAND 
OF 850-500 MB MOISTURE /DENOTING MOSTLY CLOUDY SKIES/ BECOMING  
SUPPRESSED TO THE SOUTH OVERNIGHT. SO CLOUDS IN THE EVENING MAY 
START TO BREAK/SCATTER NEAR THE PENNSYLVANIA BORDER OVERNIGHT. 

CLOUD COVER MAY PREVENT TEMPERATURES FROM FALLING LIKE A ROCK 
OVERNIGHT...BUT WITH THE SNOW PACK EXPECT A COLD NIGHT WITH LOW 
TEMPERATURES BELOW CLIMO. GRIDDED DATABASE REFLECTS AROUND 20 IN 
THE CITY CENTERS NEAR THE BAY AND ALSO HIGHER ELEVATIONS 
/INVERSION/...AND TEENS ELSEWHERE.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
A POWERFUL SURFACE RIDGE WILL REMAIN CENTERED OVER QUEBEC THRU 
FRI...ALLOWING COLD DRY AIR TO FUNNEL DOWN THE E SIDE OF THE APLCNS 
AT THE LOW LEVELS. KEPT TEMPS...SPCLY MAXIMA...AT THE LOW END OF 
GUIDANCE...WITH TEMPS STRUGGLING TO RISE ABOVE FREEZING DRNG THE DAY 
DESPITE AMPLE SUNSHINE. MINIMA IN U10S MOST AREAS WED/THU NGTS.

POTENT CLOSED LOW DRIFTS NEWARD OUT OF MO VLY THRU GREAT LAKES THU 
THRU SAT...ESTABLISHING WARM/MOIST FLOW ABOVE 850MB OVR THE 
MID-ATLC. SYNOPTIC LIFT ABOVE VERY COLD BOUNDARY LAYER WILL SUPPORT 
IP/ZR BREAKING OUT ACRS POTOMAC HIGHLANDS/SHENANDOAH VLY ERY THU 
NGT...XPNDG TO URBAN CORRIDOR AND ENTIRE CWA BY SUNRISE XMAS. MODELS 
DEPICT SFC TEMPS RISING ABOVE FREEZING BY LT FRI MRNG MOST 
AREAS...THOUGH HIPRES AT SFC LOOKS STRONG ENUF TO HINDER EROSION OF 
CAD. POTENTIAL FOR SIGNIFICANT RAIN ON FRI...WITH UP TO 1 INCH QPF. 
STILL HAVE MAXIMA IN U30S FRI...BUT DEPENDING ON STRENGTH OF 
CAD...ICING COULD BE AN ISSUE THRU MOST OF DAY XMAS...SPCLY W OF 
BLUE RIDGE. IF TEMPS WARM ENUF...THEN MELTING SNOW COMBINED WITH 
RAIN POSE FLOOD RISK AS WELL.

SFC CDFNT PASSES THRU DRNG DAY SAT...WITH COLD AIR FILTERING IN 
BEHIND AND TRANSITIONING PRECIP TO SNOW. NW FLOW FAVORS UPSLOPE SNOW 
SAT NGT THRU RMNDR OF XTND. TEMPS BELOW AVERAGE.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
DESPITE SURFACE HIGH PRESSURE BUILDING INTO THE AREA...EXPECT A DECK
OF CLOUDS TO PREVAIL TODAY INTO THIS EVENING WITH BASES AVERAGING
4-6K FT. MRB HAS JUST RISEN ABV 3K FT. SO...VFR CONDS WL PREVAIL
AREAWIDE. CLDS WL DSPT OVNGT.

VFR CONDS XPCD THRU THU. THU NGT WINTRY PRECIP AND ASSOCIATED 
SUB-VFR CONDS XPND NEWD INTO THE AREA...WITH PRECIP LIKELY CONTG 
THRU XMAS DAY.

&&

.MARINE...
GRADIENT IS WEAKER TODAY THAN IN RECENT DAYS. BUT...OBS IN MD
INVOF BAY GUSTING HV BEEN GUSTING NEAR SCA FOR A CPL HRS. XPCT
SIMLR CONDS THRU AT LEAST SUNSET. SO...HV RAISED HEADLINE THRU 00Z.

NLY WINDS 10 TO 15 KT XPCD WED THRU FRI. LT FRI INTO SAT WINDS BCM 
ELY AND HAVE POTENTIAL TO REACH SPEEDS WARRANTING SMALL CRAFT ADZY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR 
     ANZ530>534-539>541-543.

&&

$$
SYNOPSIS...PELOQUIN/SBK
NEAR TERM...PELOQUIN/HTS
SHORT TERM...PELOQUIN
LONG TERM...SBK
AVIATION...HTS/SBK
MARINE...HTS/SBK