FXUS61 KLWX 151617 AAA
AFDLWX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1117 AM EST TUE DEC 15 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE ACROSS THE MID ATLANTIC TODAY. A COLDER
AIR MASS WILL MOVE IN BEHIND THE FRONT TONIGHT AND WEDNESDAY AS
HIGH PRESSURE GRADUALLY BUILDS INTO THE REGION. HIGH PRESSURE
PERSISTS OVER THE MID ATLANTIC THROUGH THE END OF THE WEEK AND INTO
THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
CDFNT MAKING SLOW EWD PROGRESS AT LOW ELEVATIONS AS EROSION OF THE
COOL STABLE LYR HAS BEEN DELAYED. GUSTY NWLY WINDS BCMG MORE
COMMON JUST W OF BLUE RDG MTNS. HAVE SLOWED ONSET OF NWLY WINDS
WITH THIS FCST UPDATE...AND RETAINED PATCHY FOG THRU MID-DAY.
DIURNAL INCR IN TEMPS XPCD E OF BLUE RDG MTNS...WHILE MAXIMA HAVE
LKLY BEEN REACHED AT HIGH ELEVATIONS. TEMPS IN THESE AREAS WILL
TREND SLOWLY DOWNWARD THRU RMNDR OF TDA.
STRONG COLD AIR ADVCTN ABV SFC ALONG WRN SLOPES OF POTOMAC
HIGHLANDS WILL PROMOTE INCRG LLVL INSTBY. SHRA XPCD TO DVLP AFTER
18Z...WITH CONVERSION TO SNOW SHOWERS BY LATE THIS AFTN. PREV
DISCUSSION FOLLOWS...
LOW PRESSURE OVER THE EASTERN GREAT LAKES WILL MOVE TO THE EAST
THROUGH THE NEW ENGLAND STATES TODAY. A COLD FRONT ATTACHED TO LOW
PRESSURE WILL SWIFTLY MOVE EASTWARD ACROSS THE APPALACHIANS AND
THROUGH THE MID ATLANTIC THIS MORNING.
FOGGY AREAS MAINLY EAST OF THE MTNS TO START THIS MORNING WILL
DISSIPATE WITH THE PASSAGE OF THE COLD FRONT. LOW CEILINGS IN STRATUS
WILL ALSO RISE...ALTHOUGH MODELS INDICATE THAT EVEN BEHIND THE FRONT
IN A NORTHWEST FLOW LOW LEVEL MOISTURE WILL REMAIN FOR AWHILE FOR
MOSTLY CLOUDY SKIES UNDER PLENTY OF STRATOCU.
FRONT IS FORECAST TO HAVE A DRY PASSAGE. PRECIP CHANCES WILL BE
RELEGATED TO THE HIGHLANDS AND GENERALLY THE UPSLOPE SIDE AS
WEST/NORTHWEST WINDS BEHIND THE FRONT PRODUCE OROGRAPHICALLY INDUCED
SHOWERS. SOME COLD ADVECTION WILL MEAN THAT RAIN SHOWERS MIX
WITH/CHANGE TO SNOW SHOWERS LATER IN THE AFTERNOON ALTHOUGH NO
ACCUMULATION IS EXPECTED.
HIGH TEMPERATURES WILL BE ABOVE NORMAL TODAY AS COLD ADVECTION WILL
LAG A BIT BEHIND THE FRONT...ALLOWING TEMPERATURES EAST OF THE MTNS
TO RISE INTO THE 50S.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
500 MB SHORTWAVE TROUGH SWINGS ACROSS THIS EVENING. EXPECT UPSLOPE
SNOW SHOWERS TO PERSIST...PERHAPS ACCUMULATING A HALF INCH TO INCH
IN THE MOST FAVORABLE LOCATIONS.
DOWNSLOPING WILL START TO FOSTER CLEARING EAST OF THE MTNS
OVERNIGHT. GRADIENT REMAINS TIGHT WITH LOW PRESSURE NEAR THE
CANADIAN MARITIMES AND HIGH PRESSURE GRADUALLY BUILDING IN FROM THE
OHIO VALLEY. WITH COLD ADVECTION CONTINUING OVERNIGHT...ATMOSPHERE
WILL REMAIN MIXED WITH OCCASIONAL 20 KT GUSTS.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
A RESIDENT CUT-OFF UPPER LOW MEANDERING OVER NOVA SCOTIA FOR THE
LATTER HALF OF THE WEEK MEANS A SET-UP FOR WAVES OF UPPER TROFS TO
SLIDE DOWN ACROSS THE GREAT LAKES AND DOWN INTO THE MID ATLC. THE
FURTHER OUT IN TIME...THE MORE UNCERTAIN HOW STRONG EACH UPPER WAVE
WILL BE. REGARDLESS OF THE EXACT TRACK OR STRENGTH...THE TREND WILL
BE THAT THESE FEATURES WILL AT LEAST REINFORCE A STEADY COLD
CANADIAN AIRMASS DOWN THE EASTERN HALF OF THE CONUS AND ESPECIALLY
THE UPPER MIDWEST/NE.
THE CURRENT MOISTURE STREAMING ACROSS THE SE GULF COAST WILL SET-UP
ANOTHER WAVE ACROSS THIS REGION FOR THU-FRI. THE GFS AND ECM BOTH
DROP A SHORT-WAVE TROF DOWN THE NRN PLAINS DURING THIS TIME...AND
THEN CREATE A SUBSEQUENT COASTAL LOW GOING INTO THE WEEKEND. THE
EUROPEAN IS A BIT STRONGER AND CLOSER TO THE CAROLINA COAST. BY THE
COMING WEEKEND...AT LEAST SOME OF THIS UPPER ENERGY SWINGING AROUND
THE BACKSIDE OF THE NOVA SCOTIA LOW WILL BEGIN TO AFFECT THE MID
ATLC. THESE CONTINENTAL FEATURES WILL BE CARRYING RELATIVELY LITTLE
MOISTURE...AND THE COASTAL SYSTEM WILL BE TAKING THE MORE RICH LOW
LEVEL MOISTURE WELL OFF THE ATLC COAST. A PASSAGE OF ANY STRONG
UPPER VORT LOBES COULD PUSH AREAS OF FROZEN PRECIP OVER THE MID
ATLC...THO AGAIN THE MOISTURE CONTENT LOOKS LIMITED FOR ANY ONE
FEATURE...ALONG W/ A RECOVERY PERIOD BEFORE THE NEXT UPPER WAVE
REACHES THE AREA. THIS SCENARIO MAY CARRY INTO THE EARLY PART OF
NEXT WEEK...W/ COLD OVERNIGHT LOWS AND HIGH TEMPS BARELY REACHING
THE U30S/L40S.
&&
.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
HIGH CONFIDENCE IN IFR/LIFR CIGS AT THE HUBS THIS MORNING THROUGH
14-15Z. LOWER CONFIDENCE AT KMRB/KCHO. VSBYS MAINLY
MVFR...ALTHOUGH NEAR SUNRISE MAY CONTEND WITH IFR VSBYS AT THE
HUBS. SOME GUIDANCE SUGGESTS A DROP TO LTE 1SM VSBYS AROUND THE
HUBS BTWN 09Z AND 12Z. ALL FLIGHT RESTRICTIONS IMPROVE TO VFR
LATER IN THE MORNING/MIDDAY AS A COLD FRONT MOVES ACROSS THE AREA.
FRONT WILL USHER IN A WIND SHIFT FROM SOUTH TO THE NORTHWEST.
EXPECT LATE AFTERNOON/OVERNIGHT GUSTS AOA 20 KT FROM 300-330
DEGREES.
WINDS WILL REMAIN BREEZY ON WED...TAPERING OFF LATE WED. HIGH
PRESSURE WILL KEEP CONDITIONS QUIET INTO NEXT WEEKEND. UPPER LEVEL
LOW PRESSURE TROFS THIS WEEKEND AND INTO EARLY NEXT WEEK...WILL
BRING THE POSSIBILITY FOR PERIODS OF GUSTY WINDS AND POSSIBLY SOME
LIGHT INTERMITTENT PRECIP.
&&
.MARINE...
HAVE DELAYED ONSET OF SMALL CRAFT ADZY CONDITIONS GIVEN SLOWER
THAN XPCD PASSAGE OF CDFNT. OTHERWISE...MARINE FCST APPEARED
REASONABLE. PREV DISCUSSION FOLLOWS...
WINDS WILL BE BREEZY ON WED INTO THU...SUBSIDING THRU THE REST OF
THE WEEK AS HIGH PRESSURE SETTLES INTO THE REGION. WINDS WILL PICK
UP THIS WEEKEND...WITH A SEVERAL- DAY ACTIVE PERIOD FROM A SERIES
OF UPPER LEVEL LOW PRESSURE AREAS OVER THE EASTERN US.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 6 PM EST
WEDNESDAY FOR ANZ530>534-537>543.
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM EST
WEDNESDAY FOR ANZ535-536.
&&
$$
UPDATE...KRAMAR
PREV DISCUSSION...PELOQUIN/GMS
