National Weather Service Raw Text Product

880 
FXUS61 KLWX 050142
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
842 PM EST THU FEB 4 2010

.SYNOPSIS...
HIGH PRESSURE WILL MOVE AWAY FROM THE AREA TONIGHT. A STRONG WINTER
STORM IS EXPECTED TO IMPACT THE REGION FRIDAY INTO SATURDAY. HIGH
PRESSURE MAY RETURN BY MONDAY...BUT ANOTHER STORM WILL AFFECT THE
REGION TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
HIGH PRESSURE RIDGE ALONG THE MID ATLANTIC COAST WILL SHIFT OFFSHORE 
TONIGHT. A LOW PRESSURE SYSTEM IS LOCATED ACROSS EXTREME SOUTHERN 
LOUISIANA...WITH A WARM FRONT ALONG THE GULF COAST. REGIONAL RADAR 
SHOWS COPIOUS AMOUNTS OF PRECIPITATION ASSOCIATED WITH THIS SYSTEM 
ACROSS THE SOUTHEAST. THIS AREA OF PRECIP WILL STEADILY MOVE
NORTHWARD OVERNIGHT...AND BEGIN APPROACHING THE SW CWFA BY
DAYBREAK. 

NOT MANY CHANGES NEEDED TO THE ONGOING FORECAST. HAVE UPDATED THE 
GRIDS TO REFLECT THE CURRENT OBS. POPULATED WITH THE LATEST WIND 
GRIDS FROM THE WRF.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
MID-LVL CONFLUENCE ACRS NEW ENGLAND SHUD SUSTAIN LOW-LVL HIPRES
AND ASSOCIATED COLD AIR IN PLACE FOR MID-ATLC RGN. COMPACT BUT
STRONG SHRTWV TROF WILL MOVE ACRS MS RVR VLY FRI...WITH DEEP MSTR
SPREADING NEWD ON SWLY FLOW.

SFC LOPRES ASSOCIATED WITH THE SHRTWV TROF WILL MOVE ACRS AL AND
GA BFR EMERGING INTO THE ATLC NEAR THE NC/SC BORDER. COASTAL
LOPRES XPCD TO BOMB FRI NGT OVER COASTAL NC BFR DVLPG NNEWD TWD
HAMPTON ROADS AREA OF VA.

RESULT OF THIS MVMT WILL BE A VERY TIGHT PRESSURE GRADIENT AND
ENSUING STRONG NELY WINDS. HIGHEST WINDS XPCD FRI NGT THRU SAT
WITH GUSTS APRCHG 30KT IN COASTAL ZONES.

CONCERNING PCPN...SNOW XPCD TO FORM ACRS CNTRL FOOTHILLS...CNTRL
SHENANDOAH VLY AND SRN PORTIONS OF POTOMAC HIGHLANDS BY DAWN FRI.
SNOW WILL SPREAD NEWD ACRS RMNDR OF FCST AREA THRU FRI MRNG. EARLY
ONSET OF PCPN WILL LIMIT HEATING...AND MAXIMA FRI SHUD BE IN UPR
20S AND LWR 30S MOST AREAS. 

AS UPR WAVE AND COASTAL SYSTEM APRCH...PCPN WILL BCM MDT TO HEAVY
BY LATE AFTN. SNOW TOTALS BY LATE FRI AFTN ARE XPCD TO BE IN 4-6
INCH RNG IN DC METRO AREA...UP TO ONE FOOT IN CNTRL SHENANDOAH VLY
AND CNTRL FOOTHILLS.

HEAVY SNOW XPCD AREAWIDE FRI NGT AS UPR SYSTEM MOVES ACRS. SFC LOW
MOVES NEWD ON SAT...AND SNOW BANDS XPCD TO DVLP ACRS DC/BALTIMORE
METRO AREAS IN DEFORMATION ZONE. ADDITIONAL MDT/HEAVY SNOW PSBL
SAT MRNG BFR ENTIRE SYSTEM MOVES AWAY AND SNOW INTENSITY WANES.

WINTER STORM WRNG FOR HEAVY SNOW CONTS THRU SAT EVE. HAVE ADJUSTED
SNOW TOTALS SLGTLY FROM PREV ISSUANCE...BUT SYNOPTIC EVOLUTION IS
SIMILAR TO PREV FCST. SOME VARIABILITY IN SNOW TOTALS FCST FOR SRN
MD AND ADJACENT PORTIONS OF VA WOULD BE PSBL IF SLEET DVLPS LATE
FRI NGT AS WARM AIR BRIEFLY WRAPS INTO SYSTEM. ATTM HAVE RETAINED
PRIMARILY SNOW FCST /WITH SNOW AND SLEET MIX INCLUDED IN GRIDS/...
BUT A PROLONGED PD OF SLEET COULD REDUCE TOTALS IN THIS AREA.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
MAIN FOCUS OF EXTENDED PDS IS A STRONG CLOSED UPR LOW THAT MOVES
ACRS NRN CONUS TUE-WED AND DISLODGES ARCTIC ORIGIN AIR INTO OH
VLY. THIS SYSTEM MAY PROMOTE A ROUND OF LIGHT SNOW ACRS MUCH OF
FCST AREA TUE...WITH UPSLP FLOW AND A SEQUENCE OF SHRTWV TROFS IN
WAKE OF CLIPPER SYSTEM XPCD TO SUSTAIN SHSN FOR WRN SLOPES IN VERY
COLD AIR.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS THROUGH THE OVERNIGHT HRS WITH NEAR CALM WINDS. A 
RAPID CHANGE IN CONDITIONS WILL SPREAD NORTHEAST FRI MRNG. AREAS IN 
N-CNTRL VA SUCH AS KCHO WILL SEE LIGHT-MOD SNOW SOON AFTER 
SUNRISE...AND LATE MORNING FOR DC AREA THEN MIDDAY FOR BALT.  BANDS 
OF HEAVY/WET SNOW WITH IFR CONDITIONS SET IN ONLY A COUPLE HOURS 
AFTER ONSET /IFR LATE MORNING FOR CHO...EARLY AFTERNOON FOR 
DC-BALT/. 

HEAVIEST SNOW/LIFR CONDITIONS FRIDAY NIGHT NELY FLOW IN THE 15 TO 20 
KT RANGE WITH GUST POTENTIAL IN THE 25 KT RANGE. WRAP AROUND SNOW 
AND STRONG NELY WINDS CONTINUE THROUGH SATURDAY AFTERNOON.


SUB-VFR CONDITIONS XPCD TO PERSIST THRU SAT EVE AS LOPRES MOVES
NEWD AND DEFORMATION ZONE DVLPS. PCPN ENDS QUICKLY SAT EVE...WITH
IMPROVED AVIATION CONDITIONS THRU MON.

&&

.MARINE...
LIGHT FLOW WILL CONTINUE ACROSS THE CWFA OVERNIGHT. WINDS WILL BEGIN 
TO PICK UP SLIGHTLY TOWARDS DAWN OUT OF THE SOUTH/SOUTHEAST...BUT 
ARE STILL EXPECTED TO REMAIN 10 KT OR BELOW FOR TOMORROW MORNING. 

PRESSURE GRADIENT TIGHTENS ACRS WATERS BY LATE FRI AFTN AS LOPRES
DEEPENS RAPIDLY OFF CAROLINA COAST. SMALL CRAFT ADZY THRESHOLD
WINDS XPCD FOR SRN PORTIONS OF CHSPK BAY AND TIDAL POTOMAC FRI
AFTN. GALE WRNG HAS BEEN ISSUED FOR MUCH OF MD CHSPK BAY AND LWR
TIDAL POTOMAC FRI NGT THRU SAT...WITH SMALL CRAFT ADZY POSTED FOR
RMNDR OF WATERS DURG THIS TIME.

SMALL CRAFT ADZYS MAY BE NEEDED LATE NEXT WEEK AS A CDFNT WITH
ARCTIC ORIGINS MOVES THRU MID-ATLC.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER STORM WARNING FROM 10 AM FRIDAY TO 10 PM EST SATURDAY 
     FOR DCZ001.
MD...WINTER STORM WARNING FROM 10 AM FRIDAY TO 10 PM EST SATURDAY 
     FOR MDZ003>007-009>011-013-014-016>018-501-502.
VA...WINTER STORM WARNING FROM 10 AM FRIDAY TO 10 PM EST SATURDAY 
     FOR VAZ028-031-042-052>057-501-502.
     WINTER STORM WARNING FROM 6 AM FRIDAY TO 10 PM EST SATURDAY 
     FOR VAZ021-025>027-029-030-036>040-050-051.
WV...WINTER STORM WARNING FROM 10 AM FRIDAY TO 10 PM EST SATURDAY 
     FOR WVZ050>053-503-504.
     WINTER STORM WARNING FROM 6 AM FRIDAY TO 10 PM EST SATURDAY 
     FOR WVZ054-055-501-502.
MARINE...GALE WARNING FROM 6 PM FRIDAY TO 6 PM EST SATURDAY FOR 
     ANZ530>534-537>543.
     SMALL CRAFT ADVISORY FROM 2 PM TO 6 PM EST FRIDAY FOR ANZ533-
     534-537-541>543.
     SMALL CRAFT ADVISORY FROM 6 PM FRIDAY TO 6 PM EST SATURDAY FOR 
     ANZ535-536.

&&

$$
UPDATE...LISTEMAA/JACKSON