FXUS61 KLWX 090320
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1020 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/...
SNOW AND SLEET ARE MORE WIDESPREAD AND LASTING LONGER THAN EARLIER
THOUGHT. ONE BAND OF MAINLY SNOW ACROSS NORTHERN MARYLAND WILL
LEAVE 1 TO 2 INCHES OF SNOW. ALSO HAVE AREAS NEAR THE BLUE RIDGE
NOT INCLUDED IN PREVIOUS ADVISORY THAT WILL RECEIEVE SNOW/SLEET
ACCUMS AND HAVE HAD REPORTS OF ROAD PROBLEMS. WITH THIS ACTIVITY
LASTING SEVERAL MORE HOURS...WILL THROW UP ADVISORY.
PREV...
ADDED RAIN/SLEET MIX FOR REST OF THE EVENING ALONG I-95 AND WEST.
UPPER 30S EXPECTED AT SFC ACROSS BALT-DC METRO AREA AS PRECIP
SHIELD MOVES IN. NO ADDED IMPACT WITH THIS UPDATE...SELY FLOW
INCREASES INCREASING THE SFC TEMPERATURES AND RAIN INTENSITY AFTER
MIDNIGHT.
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.
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 /03Z WEDNESDAY THROUGH SUNDAY/...
CIGS/VSBYS WILL BE REDUCED IN RAINFALL /WITH SOME SLEET MIXED IN
ACROSS THE TERMINALS THIS EVENING BEFORE ALL RAIN/ 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 TO AROUND 30 KT...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 UNTIL 10 AM EST WEDNESDAY FOR DCZ001.
MD...FLOOD WATCH UNTIL 10 AM EST WEDNESDAY FOR MDZ003>007-009>011-
013-014-016>018.
WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR
MDZ003>007-009-010.
WINTER STORM WARNING UNTIL 7 AM EST WEDNESDAY FOR MDZ501-502.
VA...FLOOD WATCH UNTIL 10 AM EST WEDNESDAY FOR VAZ025>031-036>042-
050>057.
WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR
VAZ025>031-036-042.
WINTER STORM WARNING UNTIL 7 AM EST WEDNESDAY FOR VAZ021.
WV...FLOOD WATCH UNTIL 10 AM EST WEDNESDAY FOR WVZ051>053.
WINTER WEATHER ADVISORY UNTIL 7 AM EST WEDNESDAY FOR
WVZ051>053.
WINTER STORM WARNING UNTIL 7 AM EST WEDNESDAY FOR WVZ050-054-
055-501>504.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ530>532-
535-536-538>540.
SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR ANZ533-534-
537-541>543.
&&
$$
