FXUS61 KLWX 082049
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
349 PM EST TUE DEC 8 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 WEDNESDAY MORNING/...
QUICK UPDATE TO INCLUDE NELSON COUNTY IN WINTER WX ADZY /EFFECTIVE
NOW/ DUE TO MTN OBS /INCL WINTERGREEN/ BELOW FREEZING ATTM WITH
RADAR ECHOES FILLING IN ACROSS THE COUNTY.
PREVIOUS DISCUSSION...
SURFACE LOW PRESSURE ACROSS MISSOURI WILL MOVE INTO THE GREAT
LAKES OVERNIGHT...WHILE A WARM FRONT OVER THE CAROLINAS WILL
ADVANCE TOWARDS THE SOUTHERN CWFA. REGIONAL RADAR SHOWS WIDESPREAD
PRECIPITATION WITH THIS SYSTEM STRETCHING FROM SW VA...ALL THE WAY
BACK INTO THE GULF STATES.
TEMPERATURES ALOFT WILL BE WARM ENOUGH FOR ALL RAIN...BUT
FREEZING/SUB FREEZING TEMPS AT THE SURFACE ARE POSSIBLE WEST OF THE
BLUE RIDGE OVERNIGHT. THE COLDEST SURFACE TEMPS (AT OR BELOW 32
DEGREES) WILL BE ACROSS THE POTOMAC/ALLEGHENY HIGHLANDS AND THE
CENTRAL SHENANDOAH VALLEY OVERNIGHT. ACCUMULATING ICE WILL BE LIKELY
IN THIS AREA...WITH UP TO A QUARTER OF A INCH LIKELY ACROSS THE
HIGHER ELEVATIONS OUT WEST AND A TENTH OF AN INCH OR LESS ACROSS THE
CENTRAL SHENANDOAH VALLEY (AUGUSTA/ROCKINGHAM).
MODELS HAVE ALSO SHOWN AN INCREASING TREND FOR QPF THE LAST COUPLE
OF RUNS...WITH THE HIGHEST AMOUNTS MAINLY EAST OF THE BLUE RIDGE
MOUNTAINS. ONE TO TWO INCHES OF RAINFALL IS LIKELY ACROSS THE FLOOD
WATCH AREA...WITH SOME LOCALLY HIGHER AMOUNTS ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
A NON DIURNAL TREND IN TEMPS IS EXPECTED OVERNIGHT. EARLY MIN TEMPS
ARE LIKELY IN THE EAST...WHILE TEMPS HOVERING NEAR FREEZING ARE
LIKELY IN THE WEST. TEMPS IN THE EAST ARE EXPECTED TO RISE OVERNIGHT
AS LOW PRESSURE DEVELOPS ACROSS SE VIRGINIA.
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 WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
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 /WEDNESDAY 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 /21Z TUESDAY THROUGH SUNDAY/...
CIGS/VSBYS WILL BE REDUCED IN RAINFALL FOR MOST TERMINAL SITES
OVERNIGHT WITH IFR CIGS/VSBYS ANTICIPATED. CIGS/VSBYS ARE NOT
EXPECTED TO IMPROVE UNTIL LATER IN THE DAY ON WEDNESDAY. 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 GRADUALLY PICK UP DURING THE LATE
MORNING/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...
NLY WINDS THIS AFTN WILL SWITCH TO E/SE THIS EVE IN ADVANCE OF LOW
PRESSURE MOVING THROUGH OHIO VALLEY. OVNGT THESE WINDS WILL INCREASE
AND SLY CHANNELING WILL ALLOW FOR SCA CRITERIA WINDS SPEEDS. SFC
LOW DVLPS JUST S OF THE REGION...WITH COULD ENHANCE WINDS
FURTHER...WITH GALE CONDS NOT OUT OF THE QUESTION FOR A FEW HOURS
TONIGHT ACRS LOWER PORTIONS OF THE MD CHESAPEAKE. WINDS SHUD SUBSIDE
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 FROM 1 AM EST WEDNESDAY THROUGH WEDNESDAY MORNING
FOR DCZ001.
MD...FLOOD WATCH FROM 1 AM EST WEDNESDAY THROUGH WEDNESDAY MORNING
FOR MDZ003>007-009>011-013-014-016>018.
WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR MDZ501-502.
WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR MDZ003.
VA...FLOOD WATCH FROM 1 AM EST WEDNESDAY THROUGH WEDNESDAY MORNING
FOR VAZ025>031-036>042-050>057.
WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR VAZ036.
WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR VAZ021.
WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR VAZ025>028.
WV...FLOOD WATCH FROM 1 AM EST WEDNESDAY THROUGH WEDNESDAY MORNING
FOR WVZ051>053.
WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR WVZ050-054-055-501>504.
WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR WVZ051-052.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST
THURSDAY FOR ANZ530>532-535-536-538>540.
SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 6 AM EST
THURSDAY FOR ANZ533-534-537-541>543.
&&
$$
UPDATE...BAJ
PREV DISC...NWL/SBK
