FXUS61 KLWX 081451
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
951 AM EST TUE DEC 8 2009
.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE MID ATLANTIC COAST TODAY. LOW
PRESSURE WILL TRACK THROUGH THE MIDWEST AND INTO THE GREAT LAKES
TONIGHT AND WEDNESDAY...BRINGING A GOOD CHANCE FOR FREEZING
RAIN. HIGH PRESSURE WILL BUILD OVERHEAD FOR THE SECOND HALF OF THE
WEEK AND WILL USHER IN A VERY COLD AIRMASS.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
MAKING A FEW UPDATES TO THE PACKAGE THIS MORNING...MAINLY FOR
HEADLINES. THE FIRST PERIOD FORECAST LOOKED GOOD AND MADE VERY FEW
CHANGES...EXCEPT TO THE MAX T GRID. OTHERWISE...JUST UPDATED THE
WIND/WIND GUSTS GRIDS.
WILL GO AHEAD AND ISSUE A FLOOD WATCH EAST OF THE BLUE RIDGE
MOUNTAINS FOR OVERNIGHT. MODELS ARE PROGGING A GOOD ONE TO TWO
INCHES OF RAINFALL ACROSS THIS AREA...WITH SOME LOCALLY HIGHER
AMOUNTS TO AROUND 3 INCHES...MAINLY ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
WILL UPGRADE THE WINTER STORM WATCH TO A WARNING FOR
ALLEGANY...GRANT...MINERAL..HAMPSHIRE AND HARDY COUNTIES. THIS
AREA SHOULD SEE AROUND ONE QUARTER OF AN INCH OF ICE ACCUMULATIONS
OVERNIGHT. FOR THE REMAINDER OF THE WATCH AREA...WILL MAKE
DECISIONS AFTER 12Z GUIDANCE COMES IN.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
THE WARM FRONT WILL CONTINUE TO BUILD TOWARD THE REGION TONIGHT
AS THE SURFACE LOW TRACKS TOWARD THE GREAT LAKES. LOW-LEVEL COLD
AIR LIKELY WILL REMAIN IN PLACE AS A COASTAL LOW DEVELOPS ALONG
THE WARM FRONT. WARM AND MOIST AIR WILL CONTINUE TO OVERRUN THE
COLD AIR...BRINGING RAIN AND WINTRY PRECIPITATION TO THE CWA
TONIGHT. THE MAIN QUESTION IS HOW MUCH LOW-LEVEL COLD AIR WILL
EXIST FOR WINTRY PRECIPITATION.
CURRENT THOUGHT IS THAT MOST OF THE PRECIPITATION WILL FALL IN
THE FORM OF RAIN FROM WASHINGTON AND BALTIMORE TO THE SOUTH AND
EAST. SINCE THERE IS NOT AN ABUNDANT AMOUNT OF COLD AIR WITH THE
SURFACE HIGH...TEMPS WILL LIKELY REMAIN ABOVE FREEZING FOR MOST OF
THE EVENT. HOWEVER...PRECIP IN THE CITIES MAY MIX WITH SNOW AND
SLEET AT THE ONSET.
ACROSS THE NORTHERN AND WESTERN SUBURBS...WINTRY PRECIPITATION IS
LIKELY AT THE ONSET BEFORE WARMER AIR ARRIVES OVERNIGHT...CAUSING
PRECIPITATION TO CHANGE OVER TO RAIN. ANY SNOW/ICE ACCUMULATIONS
SHOULD BE LIGHT ACROSS THE IMMEDIATE NORTHERN AND WESTERN
SUBURBS...BUT COLD AIR WILL LIKELY HANG ON LONG ENOUGH FOR A
PROLONGED PERIOD OF ICING CLOSER TO THE MASON-DIXON LINE AND BLUE
RIDGE MOUNTAINS.
ALONG AND WEST OF THE BLUE RIDGE MOUNTAINS...LOW-LEVEL COLD AIR IS
EXPECTED TO REMAIN FOR MOST OF THE NIGHT. PRECIPITATION LIKELY
WILL BEGIN MAINLY AS SNOW AND SLEET BEFORE CHANGING TO FREEZING
RAIN OVERNIGHT. THE BEST CHANCE FOR SNOW/SLEET ACCUMULATIONS WILL
BE ACROSS EASTERN WEST VIRGINIA INTO THE POTOMAC HIGHLANDS.
THE BIGGEST THREAT FROM THIS STORM STILL APPEARS TO BE ICE
ACCUMULATION FROM FREEZING RAIN. SIGNIFICANT ICE ACCUMULATIONS ARE
POSSIBLE FROM THE BLUE RIDGE AND CATOCTIN MOUNTAINS WESTWARD. A
WINTER STORM WARNING SHOULD BE EVALUATED CLOSELY FOR THESE AREAS
DURING THE NEXT SHIFT.
HAVE ALSO LOOKED AT THE POSSIBILITY OF FLOODING OVERNIGHT.
PRECIPITABLE WATER WILL BE OVER TWO STANDARD DEVIATIONS ABOVE
NORMAL. THE STRONG DYNAMICS WITH THIS SYSTEM ALONG WITH THE
COPIOUS AMOUNTS OF MOISTURE WILL BRING MODERATE RAIN TO THE AREA
WHERE TEMPERATURES ARE ABOVE FREEZING. HOWEVER...QPFS REMAIN
BELOW FLOOD GUIDANCE ACROSS THESE AREAS...SO A FLOOD WATCH WAS
NOT ISSUED WITH THIS PACKAGE.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
FZRA MAY LINGER ACRS SHELTERED VLYS IN FAR WRN ZONES...BUT A RAPID
TRANSITION TO RAIN DURG MID-MRNG XPCD. DECRG CVRG OF PCPN W OF
BLUE RDG MTNS XPCD BY WED AFTN AS DRY AIR ALOFT INVADES. PCPN MAY
CONT INTO WED AFTN ACRS ERN ZONES BFR TROF AXIS MOVES THRU AND
CDFNT PASSES THRU FCST AREA.
INSTBY INCRS ON WRN SLOPES LATE THIS AFTN AND EARLY THIS EVE AS
MUCH COLDER AMS ARRIVES. UPSLP SNOW SHOWERS PSBL DURG THIS TIME.
VERY COLD AIR /MODIFIED ARCTIC AMS/ ENTERS MID-ATLC BY THU IN WAKE
OF SHRTWV TROF...WITH MAXIMA SHARPLY COLDER LATE IN THE WEEK. HAVE
UNDERCUT GUIDANCE BY SVRL DEG F FOR MAXIMA. WDSPRD MINIMA LOW TENS
TO MID 20S XPCD THU NGT.
COLD AIR WILL RMN IN PLACE THIS WEEKEND AS A LOW AMPLITUDE SHRTWV
TROF MOVES THRU QUASI-ZONAL FLOW AND DVLPS COASTAL LOPRES. HAVE
INCRD POPS SAT-SUN...WITH HIGHEST VALUES ACRS SRN ZONES. SNOW PSBL
XCPT IN FAR SERN SECTIONS OF FCST AREA.
MODEL SIGNATURES SUGGEST ANOTHER ROUND OF ARCTIC AIR WILL BE
DISLODGED INTO CNTRL AND SRN PLNS THIS WEEKEND AS SHRTWV TROF
MOVES ACRS NRN CONUS. A MODIFIED VERSION OF THIS AMS WILL ARRIVE
IN MID-ATLC RGN BY EARLY NEXT WEEK AS UPR LOW MOVES THRU NEW
ENGLAND.
&&
.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
HIGH PRESSURE WILL MOVE OFF THE COAST TODAY WHILE LOW PRESSURE
BUILDS INTO THE PLAINS. THE WARM FRONT ASSOCIATED WITH THIS LOW WILL
TRACK TOWARD THE TERMINALS TODAY. CIGS/VSBYS WILL DETERIORATE LATER
THIS AFTERNOON INTO TONIGHT AS PRECIPITATION OVERSPREADS THE
TERMINALS AHEAD OF THE WARM FRONT. THERE WILL BE ENOUGH LOW-LEVEL
COLD AIR FOR SNOW/SLEET EARLY THIS EVENING AND POSSIBLE FZRA LATER
THIS EVENING INTO THE OVERNIGHT HOURS...ESPECIALLY NEAR KMRB.
FARTHER EAST...ANY MIXED PRECIPITATION THIS EVENING WILL CHANGE TO
RAIN OVERNIGHT.
RAIN CONTS WED MRNG AND DECRS IN CVRG BY WED AFTN. VFR CONDITIONS
XPCD THU-FRI NGT. NEXT PSBLTY OF PCPN WILL BE THIS WEEKEND...WHEN
LOW CIGS/VSBYS COULD OCCUR AMID SNOW.
&&
.MARINE...
HIGH PRESSURE GRADUALLY WILL MOVE OFF THE COAST TODAY. A WARM
FRONT WILL APPROACH THE WATERS TONIGHT FROM THE SOUTH AND EAST. A
WAVE OF LOW PRESSURE WILL DEVELOP ALONG THIS FRONT AS IT MOVES
OVER THE WATERS OVERNIGHT. AN INCREASING PRESSURE GRADIENT AHEAD
OF THE FRONT WILL RESULT IN SCA WINDS TONIGHT. THE STRONGEST WINDS
ARE EXPECTED ACROSS THE LOWER TIDAL POTOMAC AND MIDDLE PORTION OF
THE BAY...WHERE WIND GUSTS AROUND 30 KNOTS ARE POSSIBLE OVERNIGHT.
BRIEF LULL XPCD IN ADZY THRESHOLD WINDS DURG WED MRNG...BUT GUSTS
20-30 KT SHUD RESUME BY WED AFTN. CDFNT ARRIVES EARLY WED EVE...
WITH GUSTY WLY WINDS XPCD IN ITS WAKE ACRS CHSPK BAY AND TIDAL
POTOMAC. ADZY THRESHOLD WINDS PSBL WED NGT-FRI.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLOOD WATCH FROM THIS EVENING THROUGH WEDNESDAY MORNING FOR
DCZ001.
MD...FLOOD WATCH FROM THIS EVENING THROUGH WEDNESDAY MORNING FOR
MDZ004>007-009>011-013-014-016>018.
WINTER STORM WATCH FROM 7 PM EST THIS EVENING THROUGH
WEDNESDAY MORNING FOR MDZ003>005-009.
WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR MDZ501-502.
VA...FLOOD WATCH FROM THIS EVENING THROUGH WEDNESDAY MORNING FOR
VAZ036>042-050>057.
WINTER STORM WATCH FROM 7 PM EST THIS EVENING THROUGH
WEDNESDAY MORNING FOR VAZ025>031-036>042.
WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 AM EST
WEDNESDAY FOR VAZ021.
WV...WINTER STORM WATCH FROM 7 PM EST THIS EVENING 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.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EST
WEDNESDAY FOR ANZ530>532-538>540.
SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 6 PM EST
WEDNESDAY FOR ANZ533-534-537-541>543.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST
WEDNESDAY FOR ANZ535-536.
&&
$$
UPDATE...LISTEMAA
