FXUS61 KLWX 090641
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
141 AM EST WED DEC 9 2009
.SYNOPSIS...
LOW PRESSURE WILL MOVE INTO THE GREAT LAKES LATE TONIGHT AND
WEDNESDAY...DRAGGING A COLD FRONT AND WIDESPREAD PRECIPITATION
THROUGH THE MID ATLANTIC. A WINTRY MIX IS LIKELY FOR MOST LOCALES
WEST OF THE BLUE RIDGE...WHILE ALL RAIN IS LIKELY FOR AREAS EAST OF
THE BLUE RIDGE AND THE NORTHERN SHENANDOAH VALLEY. HIGH PRESSURE
WILL BUILD ACROSS THE AREA FOR THURSDAY AND FRIDAY. A COASTAL LOW
PRESSURE SYSTEM IS EXPECTED FOR THE LATE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
SURFACE LOW PRESSURE ACROSS WESTERN IL WILL MOVE TO LAKE MI
REST OF THE NIGHT...WHILE A WARM FRONT HAS STALLED ALONG THE
EASTERN SEABOARD /WITH NELY FLOW EAST OF THE BLUE RIDGE MTNS/.
REGIONAL RADAR SHOWS WIDESPREAD PRECIPITATION FROM THE MID
ATLANTIC TO THE CENTRAL TN VALLEY /WHERE THE COLD FRONT IS BLOWING THROUGH/.
SURFACE TEMPS AT OR BELOW 32 DEGREES CONTAINED AT HIGHER
ELEVATIONS ALONG AND WEST OF THE BLUE RIDGE/CATOCTIN MTN.
ACCUMULATING ICE IS OCCURRING IN THIS AREA...WITH UP TO A QUARTER OF
A INCH STILL POSSIBLE. DESPITE OBS INDICATING A COLD RAIN
ATTM...UP TO A TENTH OF AN INCH OF ICE ACROSS THE SHENANDOAH
VALLEY IS STILL POSSIBLE.
PREVIOUS DISCUSSION...
MOISTURE LEVELS REMAIN ARE VERY HIGH
THROUGHOUT MUCH OF THE VERTICAL PROFILE THROUGH TNGT...WITH PWATS
EXCEEDING ONE INCH BY 4Z. WITH PLENTY OF LIFT...LOOK FOR
WIDESPREAD ONE TO TWO INCHES OF RAIN ACRS THE CWA. ISOLATED HIGHER
TOTALS XPCD ALONG AND EAST OF INTERSTATE 95...PARTICULARLY IF ANY
CNVCTN IMPACTS THE REGION. WITH MELTING SNOW ADDING TO THE RUNOFF
IN MANY LOCATIONS...AND FFG INDICATING 1 TO 2 INCHES OF RAIN
WITHIN 6 HOURS WILL CAUSE FLOODING...HAVE HOISTED FLOOD WATCH FOR
ALL AREAS E OF THE BLUE RIDGE AS WELL AS THE SHENANDOAH VALLEY.
WITH 50-60KT SLY 925-850MB JET DVLPG OVR THE APPALACHIANS
TNGT...GUSTY WINDS WILL BE PSBL. LOW LEVELS SHUD RMN
STABLE...HINDERING THE MIXING DOWN OF THESE STRONGEST WINDS.
STILL...GUSTS TO 45 MPH ARE PSBL OVR HIEST ELEVATIONS ALONG
ALLEGHENY FRONT.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
A COLD FRONT WILL MOVE THROUGH TOMORROW...WITH ENDING RAIN CHANCES
DURING THE LATE MORNING/EARLY AFTERNOON FOR MOST LOCALES. BY
12Z...MOST OF THE WINTRY MIX SHOULD HAVE CHANGED OVER TO ALL RAIN.
THE ONLY EXCEPTIONS MAY BE IN THE SHELTERED VALLEYS IN THE FAR
WESTERN CWFA. LOCALLY HEAVY RAINFALL MAY CONTINUE EAST OF THE BLUE
RIDGE MOUNTAINS THROUGH MID MORNING.
WITH RISING TEMPS/DEWPOINTS DURING THE OVERNIGHT HOURS...SOME
INSTABILITY IS POSSIBLE ALONG AND AHEAD OF THE COLD FRONT. THUNDER
IS POSSIBLE MAINLY ACROSS LOWER SOUTHERN MARYLAND AND PORTIONS OF
THE VIRGINIA PIEDMONT DURING THE EARLY MORNING HOURS AND RIGHT
BEFORE THE FROPA. THUNDERSTORMS WILL BRING ADDITIONAL LOCALLY HEAVY
RAINFALL AMOUNTS.
STRONG SWLY WINDS AT 850MB MAY BE ABLE TO MIX DOWN VIA MOMENTUM
TRANSFER BY WED AFTN...PARTICULARLY HIGHER ELEVATIONS IF SFC TEMP
CAN RISE ENOUGH TO STEEPEN LAPSE RATES. A WIND ADVISORY MAY BE
NECESSARY FOR SOME AREAS ALONG AND WEST OF THE BLUE RIDGE ON WED.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
ARCTIC AIRMASS BEHIND CDFNT BEGINS TO ENTER WED NGT AND WILL
DOMINATE WEATHER THRU SAT. THIS WILL MEAN MAXIMA IN THE 30S/L40S
WITH MINIMA IN THE TEENS W OF BLUE RIDGE...20S TO THE EAST.
PRESSURE GRADIENT WILL REMAIN STRONG AND NW WINDS WILL CREATE
SINGLE DIGIT WIND CHILLS W OF BLUE RIDGE THU NGT.
LOPRES PASSES S OF AREA LT SAT INTO SUN...BRINGING RISK FOR
ACCUMULATING SNOW TO PORTIONS OF THE CWA. HIGH RMN WELL BELOW
NORMAL THRU MON.
&&
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
CIGS/VSBYS WILL CONTINUE TO BE REDUCED IN PRECIP WHICH WILL
PRIMARILY BE COLD RAIN...WITH FREEZING RAIN LIMITED TO HIGHER
ELEVATIONS. CIGS/VSBYS ARE NOT EXPECTED TO IMPROVE UNTIL WEDNESDAY
AFTERNOON WITH FROPA. PRECIP WILL END FROM WEST TO EAST DURING THE LATE
MORNING/EARLY AFTERNOON. A WINTRY MIX IS MOST LIKELY AT KMRB
OVERNIGHT. WINDS WILL REMAIN EAST/SE THROUGH THE OVERNIGHT HOURS.
WINDS WILL SHIFT AROUND TO THE SOUTH DURING THE EARLY
MORNING...AND FINALLY TO THE WEST AFTER THE FROPA. WIND SPEEDS
WILL QUICKLY PICK UP INTO THE 25 TO 30 KT RANGE DURING THE EARLY
AFTERNOON.
HIGH PRESSURE BUILDS IN FOR THURSDAY AND FRIDAY. NO CIG/VSBY
RESTRICTIONS ARE ANTICIPATED. A COASTAL LOW PRESSURE SYSTEM MAY
AFFECT THE AREA DURING THE WEEKEND.
&&
.MARINE...
SELY WINDS 20 TO 25 KT WITH POSSIBLE 30 KT REST OF TONIGHT. GALE
CONDITIONS NOT EXPECTED REST OF TONIGHT. WINDS TO SUBSIDE SOME AROUND
SUNRISE AS CDFNT PASSES THRU THE AREA. HOWEVER...WNW FLOW AND VERY
STRONG CAA DRNG THE DAY WILL ALLOW WINDS TO RAPIDLY REACH ADVISORY
SPEEDS...WITH 30 KT GUSTS XPCD DRNG THE AFTN. SMALL CRAFT ADVISORY
HAS BEEN EXTENDED FOR ALL THE WATERS OF THE TIDAL POTOMAC AND
MARYLAND CHESAPEAKE THROUGH WED NGT...AS TIGHT PRESSURE GRADIENT
WILL SUPPORT GUSTS TO 25KT THROUGH THE PERIOD. THESE WINDS MAY
CONTINUE INTO THURSDAY.
SMALL CRAFT WINDS MAY CONTINUE INTO THURSDAY.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLOOD WATCH UNTIL 10 AM EST THIS MORNING FOR DCZ001.
MD...FLOOD WATCH UNTIL 10 AM EST THIS MORNING FOR MDZ003>007-
009>011-013-014-016>018.
WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR
MDZ003>007-009-010.
WINTER STORM WARNING UNTIL 7 AM EST THIS MORNING FOR MDZ501-
502.
VA...FLOOD WATCH UNTIL 10 AM EST THIS MORNING FOR VAZ025>031-
036>042-050>057.
WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR
VAZ025>031-036-042.
WINTER STORM WARNING UNTIL 7 AM EST THIS MORNING FOR VAZ021.
WV...FLOOD WATCH UNTIL 10 AM EST THIS MORNING FOR WVZ051>053.
WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR
WVZ051>053.
WINTER STORM WARNING UNTIL 7 AM EST THIS MORNING FOR WVZ050-
054-055-501>504.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ530>543.
&&
$$
UPDATE...BAJ
PREV DISC...NWL/SBK/BPP/BAJ
