Winter Storm and Winter Weather in Maryland, December 16 to 17, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
925 PM EST MON DEC 15 2008

.SYNOPSIS...
A STRONG COLD FRONT WILL MOVE THROUGH THE REGION...AND BECOME
STATIONARY TO OUR SOUTH TOMORROW AS COLD HIGH PRESSURE BUILDS
ACROSS NEW ENGLAND. WEAK WAVES OF LOW PRESSURE WILL TRACK ALONG
THE FRONT FOR THE MIDDLE OF THE WEEK...PROVIDING PARTS OF THE
REGION WITH A WINTRY MIX. ANOTHER COLD FRONT TRACKS ACROSS THE
REGION LATE FRIDAY INTO EARLY SATURDAY...BEFORE HIGH PRESSURE
BUILDS BACK IN LATER IN THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
CDFNT ALB-JYO-TRI ATTM. PCPN CVRG ALNG THE FNT RATHER SPARCE...W/
ADDTL ECHOES STRETCHING BACK TO THE OHVLY. THERE/S A SHARP TEMP
DROP AND EVEN SHARPER DEWPT DROP DISPLACED BHD THE FNT. 2G4 DWN TO
37F AT 01Z. XTRPLTN TAKES FNT THRU ENTIRE CWFA BY 06Z.

WHILE QPF AMTS NOT ALL THAT IMPRESSIVE...CVRG SHUD BE SUFFICIENT
TO JUSTIFY CAT POPS...SPCLY AFTR MIDNGT. FOR THE MOST PART THIS
SHUD BE RA. HWVR...IT DOESNT TAKE MUCH ICING TO JUSTIFY WINT WX
ADVY FOR FZRA /JUST A TRACE/...AND CONSIDERING WHERE 2G4 IS...
CAN/T RULE OUT THAT PSBLTY. MDL SNDGS DO DEPICT SFC COOLING WHILE
A WARM NOSE REMAINS ALOFT BTWN H8-7. THE TRICK IS...THAT LYR WL
EVENTUALLY WL BE COOLING TOO AS LRG/COLD HIPRES BUILDS FM THE
CNTRL CONUS... WHICH WL MAKE DURATION OF FZRA LMTD.

HV MADE A FEW ADJUSTMENTS TO POP/TEMP/WND GRIDS. SHUDNT BE MUCH
CHG TO TXT PRODUCTS. WL LEAVE ADVY INTACT. DO NOT HV CONFIDENCE TO
MAKE ANY ADDITIONS. HAMPSHIRE/HARDY/MORGAN WUD BE MOST LIKELY
SUSPECTS.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
COLD AIR XPCD TO MAKE MORE BLATANT INTRUSION TMW AS SFC HIPRES
BUILDS ACRS NEW ENGLAND. INVERTED SFC TROF WILL BE FOUND ACRS NWRN
FCST AREA. SUBTLE SHRTWV TROF TO PASS THRU STG SWLY FLOW
ALOFT...AS GOOD ISENTROPIC UPGLIDE OCCURS. THESE FEATURES SHUD
COMBINE TO YIELD WIDESPREAD PCPN...WITH ACCUMULATION ENHANCEMENTS
ACRS NWRN ZONES.

WHILE PRVS GDNC SUGGESTING ICE STORM...18Z GDNC LEANING MORE HVILY ON
EXTENT OF COLD AIR ALOFT...MAKING PL/SN A GREATER PSBLTY ALNG M-D
LN. 21Z SREFS JUST CAME IN SUGGESTING A MIX...BUT PL GETTING THE
GREATER PTYPE PROBABILITY. QUICK PEEK AT 00Z NAM SUGGEST HIGH
QPF...WHICH DOESNT SEEM TO FIT. RESPONSE WL BE TO LEAVE WATCH IN
PLACE...BUT BE LESS DETERMINISTIC IN PTYPE FCST. THINK CHO-IAD-DMH
SHUD STAY ABV FRZG...SO AREAL EXTENT OF WATCH LOOKS OK. /WRN
LOUDOUN AND UPR MONTGOMERY WL BE AFFECTED BY COLD WEDGE./ NOT SO
SURE ABT NRN BALTCO...BUT WONT BE MAKING A CHG FOR JUST 1 CNTY.

BASED ON CONTD CAA...DONT SEE MUCH ROOM FOR A DIURNAL TEMP RISE.
GRIDS SUGGESTED THAT...AND FINE TUNED BASED ON LTST GDNC.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MODELS INDICATE ANOTHER WAVE OF LOW PRESSURE RIDING ALONG A FRONT
STALLED OUT TO OUR SOUTH TUESDAY NIGHT INTO WEDNESDAY...LIKELY
EXITING BY LATE WEDNESDAY. HAVE HIGH CONFIDENCE IN MEASURABLE
PRECIPITATION DURING THAT TIME WITH ISENTROPIC LIFT OCCURRING...
WITH LIKELY TO CATEGORICAL POPS ACROSS THE CWA. NEAR SURFACE AIR
MASS WILL BE RATHER COLD...WITH A WEDGE TYPE ORIENTATION. WENT
BELOW MOS GUIDANCE AS BELIEVE TEMPERATURES WILL BE CLOSER TO
DEWPOINTS FROM MOS. INCORPORATING THE SREF YIELDS TEMPERATURES
CLOSER TO THE DEWPOINTS FROM MOS. 850 MB TEMPERATURES ARE
GENERALLY FORECAST ABOVE 0C EXCEPT PERHAPS BEING SLIGHTLY BELOW 0C
ACROSS THE NORTHWEST CWA FOR A TIME TUESDAY NIGHT. SO...IN AREAS
WITH FREEZING OR SUBFREEZING SURFACE TEMPERATURES...THIS WILL
PRESENT A POTENTIAL FREEZING RAIN EVENT. THIS LOOKS TO BE MAINLY
WEST OF THE MTNS...BUT A FREEZING RAIN THREAT WILL EXIST A TIER
OF COUNTIES EAST OF THE MTNS ESPECIALLY IN NORTHERN MARYLAND CLOSE
TO THE PENNSYLVANIA BORDER AND ACROSS THE EXTREME NORTHWESTERN
WASHINGTON SUBURBS. USING A BLEND OF QPF FROM HPC AND SREF...
COMBINED WITH FORECAST P-TYPE...THERE IS A RISK OF QUARTER INCH OR
MORE OF ICE AMOUNTS ACROSS AREAS WEST OF THE BLUE RIDGE AND PARTS
OF NORTHERN MARYLAND. A WINTER STORM WATCH WILL CONTINUE FOR THIS
ENTIRE AREA TUESDAY NIGHT. LESS FREEZING RAIN AMOUNTS MAY OCCUR
ACROSS NORTH AND WEST SUBURBS OF BALTIMORE AND WASHINGTON AND
ACROSS CENTRAL VIRGINIA NEAR CHARLOTTESVILLE THAT WILL NOT MEET
WATCH CRITERIA BUT MAY STILL LEAD TO LIGHT ICING TUESDAY INTO
EARLY WEDNESDAY. SOME SLEET MAY MIX WITH THE FREEZING RAIN ACROSS
PARTS OF WESTERN MARYLAND AND THE EASTERN WEST VIRGINIA
PANHANDLE...BUT WANT TO HIGHLIGHT THE FREEZING RAIN ASPECT OF THIS
STORM AS THIS WILL BE THE MOST SIGNIFICANT P-TYPE. AT THIS
TIME...THE IMMEDIATE INTERSTATE 95 CORRIDOR AND SOUTHEAST LOOKS TO
BE RAIN...BUT SOMETIMES COLD AIR IN THESE SITUATIONS IS
UNDERFORECAST AND WILL NEED TO BE WATCHED.

ON WEDNESDAY...TEMPERATURES AT THE SURFACE ARE EXPECTED TO RISE
ABOVE FREEZING FROM SOUTH TO NORTH...THEREFORE FREEZING RAIN WILL
CHANGEOVER TO RAIN IN APPROPRIATE PLACES AND RAIN WILL END LATER IN
THE DAY AS THE WAVE EXITS.

UNSETTLED WX PATTERN WILL CONTINUE THROUGH MUCH OF THE EXTENDED
PERIODS. ZONAL FLOW AT UPPER LEVELS SETS UP ACROSS THE EASTERN
TWO-THIRDS OF THE U.S. WED NIGHT. DURING THIS TIME...A STRONG UPPER
JET MAX OVER THE MIDWEST/GREAT LAKES REGION WILL BE LOCATED BETWEEN
A H5 RIDGE CENTERED OVER THE GULF AND A POLAR VORTEX OVER HUDSON BAY.
AT LOWER LEVELS...A STALLED OUT FRONTAL BOUNDARY WILL REMAIN
SITUATED ACROSS THE MID ATLANTIC REGION. LATEST 12Z OPERATIONAL
GUIDANCE BRIEFLY TRIES TO DRY US OUT WEDNESDAY NIGHT INTO
THURSDAY AS SFC HIGH PRESSURE QUICKLY TRACKS NORTH OF THE REGION.
STILL MENTIONED CHANCE POPS ACROSS WESTERN AREAS DURING THIS TIME
AS MOISTURE WILL LINGER ALONG THE STALLED BOUNDARY. ANY PRECIP
COULD MIX WITH SLEET ACROSS FAR WESTERN ZONES WEDNESDAY
NIGHT...WHERE LOW LEVEL COLD AIR WILL BE HARDEST TO ERODE.

THE NEXT STORM SYSTEM AND ASSOCIATED COLD FRONT WILL APPROACH THE
REGION FROM THE WEST FRIDAY. STRONG SOUTHERLY FLOW AHEAD OF THE
FRONT SHOULD LEAD TO MORE RAIN ALONG WITH MAX TEMPS IN THE 60S ON
FRIDAY. MUCH COOLER CONDITIONS ARE EXPECTED FOR THE WEEKEND AS THE
COLD FRONT PUSHES THROUGH LATE FRIDAY INTO EARLY SATURDAY. KEPT
CHANCE POPS FOR THE WEEKEND. NIGHTTIME TEMPS WILL BE COLD ENOUGH TO
SUPPORT A LIGHT RAIN/SNOW MIX FOR MUCH OF THE AREA FRI AND SAT
NIGHT. LAST FEW ECMWF RUNS SHOW ANOTHER COLD FRONT MOVING THROUGH
THE REGION EARLY NEXT WEEK.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
CDFNT THRU MRB...AND WL BE THRU REST OF TERMINALS BY 05Z. ONCE
AGN...OBSVD FLGT CONDS MORE OPTIMISTIC THAN GDNC. WL REDUCE TO
MVFR OVNGT IN MAINLY RA.

PCPN WONT BE ALL THAT HVY...AND WL BRK SLGTLY TMRW MRNG BEFORE
ANTHR RND SWEEPS NMOST TERMINALS WL REMAIN WARM ENUF /JST BARELY/
FOR RA. HWVR...MRB LIKELY TO RECEIVE MIXED PCPN. PTYPE WL BE A
TUFF CALL. ATTM...CANNOT RULE OUT SN/PL IN ADDITION TO PRVSLY FCST
FZRA. IF ANYTHING...LTST GDNC LEANING MORE ON THE COLD SIDE
/PLSN/-- EVEN MORE SO THAN 00Z TAFS. IN TERMS OF FLGT
CATEGORIES...CONDS SHUD DETERIORATE TO IFR BY/THRU AFTN.

POOR CONDITIONS CONT THRU WED. S FLOW AND RAIN WILL DEVELOP OUT
AHEAD OF AN APPROACHING COLD FRONT FRIDAY WITH SUB VFR CONDITIONS
POSSIBLE. WINDS WILL SHIFT TO THE N SATURDAY AS THE COLD FRONT
PUSHES THROUGH THE REGION.

&&

.MARINE...
TPLM2 REALIZING SCA CONDS ATTM...WHILE REST OF MAROBS ARENT. THIS
IS THE LULL THAT WAS PRVSLY FCST. CDFNT WL CROSS WATERS 04-07Z.
N/NWLY SURGE BHD FNT WL RTN SCA WNDS/GUSTS. UNSETTLED WX CONTS
THRU MID WK.

A COLD FRONT WILL TRACK ACROSS THE REGION LATE THIS WEEK WITH
SMALL CRAFT CONDITIONS POSSIBLE LATE FRIDAY INTO EARLY SATURDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...WINTER WEATHER ADVISORY UNTIL 6 AM EST TUESDAY FOR MDZ501-502.
     WINTER STORM WATCH FROM 6 AM EST TUESDAY THROUGH WEDNESDAY
     MORNING FOR MDZ003-501-502.
     WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
     MORNING FOR MDZ004-005-009.
VA...WINTER STORM WATCH FROM 6 AM EST TUESDAY THROUGH WEDNESDAY
     MORNING FOR VAZ028.
     WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
     MORNING FOR VAZ021-025>027-029>031-042.
WV...WINTER WEATHER ADVISORY UNTIL 6 AM EST TUESDAY FOR WVZ054-
     501>504.
     WINTER STORM WATCH FROM 6 AM EST TUESDAY THROUGH WEDNESDAY
     MORNING FOR WVZ050>052-054-055-501>504.
     WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
     MORNING FOR WVZ053.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST TUESDAY FOR ANZ532>534-537.
     SMALL CRAFT ADVISORY UNTIL 1 PM EST TUESDAY FOR ANZ530-531-535-
     536.

&&

SYNOPSIS...KRAMAR/HTS
NEAR TERM...HTS
SHORT TERM...KRAMAR/HTS
LONG TERM...PELOQUIN
AVIATION...HTS/PELOQUIN
MARINE...HTS/KRAMAR/PELOQUIN

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1025 PM EST MON DEC 15 2008

ANZ530>537-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
161000-
CHESAPEAKE BAY NORTH OF POOLES ISLAND MD-
CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT MD-
CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH MD-
CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT MD-
CHESAPEAKE BAY FROM DRUM POINT MD TO SMITH POINT VA-
TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD MD-
TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND MD-
TIDAL POTOMAC FROM COBB ISLAND MD TO SMITH POINT VA-
DISTRICT OF COLUMBIA-NORTHERN BALTIMORE-HARFORD-
SOUTHERN BALTIMORE-PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS-
CALVERT-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
KING GEORGE-
1025 PM EST MON DEC 15 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MARYLAND PORTION OF THE
CHESAPEAKE BAY...TIDAL POTOMAC RIVER...AND ADJACENT COUNTIES IN
CENTRAL MARYLAND AND NORTHERN VIRGINIA AS WELL AS THE DISTRICT OF
COLUMBIA.

.DAY ONE...TONIGHT

A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE TIDAL POTOMAC AND
MARYLAND CHESAPEAKE BAY THROUGH TONIGHT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

SMALL CRAFT CONDITIONS WILL PERSIST ACROSS THE WATERS THROUGH
TUESDAY AFTERNOON. SMALL CRAFT ADVISORY CONDITIONS ARE POSSIBLE
AGAIN FRIDAY AND FRIDAY NIGHT AS A COLD FRONT MOVES ACROSS THE
REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED THROUGH TONIGHT.

MDZ003>005-009-010-501-502-VAZ021-025>031-036>042-050-051-
WVZ050>055-501>504-161000-
WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD-
EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-HIGHLAND-
AUGUSTA-ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-
NELSON-ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-FAUQUIER-LOUDOUN-
ORANGE-CULPEPER-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-PENDLETON-
HARDY-WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL-
1025 PM EST MON DEC 15 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN WEST VIRGINIA...
NORTHERN AND CENTRAL VIRGINIA...AND CENTRAL AND WESTERN MARYLAND
WITH THE EXCEPTION OF GARRETT COUNTY.

.DAY ONE...TONIGHT

FREEZING RAIN...MIXED WITH SLEET...IS EXPECTED OVERNIGHT ALONG
THE ALLEGHENY FRONT AS A COLD AIRMASS INVADES THE REGION. ICE
ACCUMULATIONS UNDER ONE TENTH INCH WILL BE POSSIBLE. A WINTER
WEATHER ADVISORY IS IN EFFECT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

A MIX OF SNOW...SLEET...AND FREEZING RAIN WILL BE POSSIBLE WEST OF
THE BLUE RIDGE AS WELL AS THE IN THE CATOCTINS AND CENTRAL
MARYLAND TUESDAY THROUGH WEDNESDAY MORNING. A WINTER STORM WATCH
REMAINS IN EFFECT FOR THIS AREA. SIGNIFICANT SNOW AND SLEET OR ICE
ACCUMULATIONS WILL BE POSSIBLE. LATER FORECASTS WILL PIN DOWN THE
EXACT PRECIPITATION TYPE AND AMOUNT. PLEASE REFER TO THE WINTER
WEATHER MESSAGE PRODUCT FOR DETAILS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED THROUGH TONIGHT. PLEASE
RELAY REPORTS OF WINTRY CONDITIONS AND ICE ACCUMULATIONS TO THE
NATIONAL WEATHER SERVICE.

HTS