-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 042350
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
650 PM EST WED MAR 4 2015

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION TONIGHT. ASSOCIATED
PRECIPITATION WILL CONTINUE INTO THURSDAY AS SNOWFALL DUE TO THE
PASSAGE OF A CORE OF STRONGER WINDS IN THE JET STREAM. HIGH
PRESSURE BUILDS OVERHEAD FRIDAY...THEN PERSISTS THROUGH THE
WEEKEND.

&&

.NEAR TERM /THROUGH THURSDAY/...
...UPDATE...
A DENSE FOG ADVISORY HAS BEEN ISSUED FOR PORTIONS OF
THE WASHINGTON DC METRO AREA...ALL OF THE BALTIMORE METRO AREA AND
WESTWARD TO FREDERICK COUNTY MD. VISIBILITIES HAVE DROPPED TO ONE
QUARTER MILE AT NUMEROUS LOCATIONS IN THIS AREA...AND WILL
PROBABLY PERSIST UNTIL A COLD FRONT MOVES THROUGH THIS EVENING AND
NW WINDS DEVELOP.

...PREVIOUS DISCUSSION...
THE TWO SFC BNDRYS OF THIS MRNG SEEM TO
HV COMBINED INTO ONE... STRETCHING FM INVOF MRB- BNA- SHV. GIVEN
THE LACK OF FORCING...PCPN HAS BEEN SLOW IN ADVCG EWD TDA.
HWVR...LTST RADAR COMPOSITE DEPICTS PCPN /ALL RAIN/ ACRS NRN CWFA.
ANTICIPATE PCPN TO OVERSPREAD THE REST OF THE AREA TAFTN.

DUE TO IN-SITU WEDGE...ITS BEEN TOUGH TO GET TEMPS OUT OF THE 40S
TDA. W99 HAS BEEN THE ONE EXCEPTION. THE ARRIVAL OF RAFL WL PUT AN
END TO ANY ADDTL TEMP RISE.

LTST GDNC CYCLE REVEALS A DECENT AMT OF CONSISTENCY SYNOPTICALLY.
HV SUBTLE THERMAL TIMING CHGS...WHICH IS XPCTD. BUT FROM AN
ENSEMBLE VIEWPOINT...GDNC CONFIRMING THAT GOING FCST ON TRACK...
AND HV NOT ADJUSTED MUCH. THE END RESULT IS TO COVERT THE SRN
FRINGE OF THE CWFA FROM A WATCH TO A LOW END WARNING. PTYPES IN
THIS AREA A BIT OF A CONCERN.

AS ALREADY MENTIONED...IT WL BE RAINING AT THE BGNG OF THE TNGT
PD. AS THE CDFNT WORKS SWD...COLDER AIR WL BE DRAINING SOUTH...
WHILE BAROCLINICITY AND THE UPR JET WL PROVIDE FORCING FOR CONTD
PCPN GENERATION. THE MSTR FEED WL COME FROM THE WRN GLFMEX AS
WELL AS THE PACIFIC. PWAT FM RNK 12Z RAOB WAS 250 PCT OF NORMAL.
CERTAINLY PLENTY OF MSTR IN PLAY.

AM KEEPING FCST CONSISTENT IN TRANSITIONING FROM RA TO SNW W/ A
SHORT PD OF PL IN BTWN. EXACT TIMING OF EACH STILL MAY NEED TO BE
ADJUSTED BY AN HR OR TWO EITHER WAY. BTTM LINE...BY SUNRISE XPCTG
ALL SNOW BY SUNRISE TMRW N OF SHD-DCA-NAK. HV A SNPL OR PLRA MIX
TO THE S.

&&

.SHORT TERM /THURSDAY NIGHT/...
WL TAKE THE TRANSITION TO SNW FM SHD-DCA-NAK AT THE START OF PD
SWD TO EDGE OF CWFA BY MID MRNG. UVV ALIGNS VERY WELL W/ SNOW
GROWTH REGION A CPL HRS BHD TRANSITION TO SNOW. SCREAMING MESSAGE
HERE...EVEN THOUGH IT MAY NOT LOOK BAD UPON WAKING UP...XPCT CONDS
TO GET WORSE DURING THE DAY. WL HV THE RRQ OF 160 KT UPR JET...
SNOW GROWTH REGION...AND FGEN FORCING ALL CROSSING CWFA DURING THE
MIDDAY HRS-- A LTL ERLR TO THE N AND LATER CENTRAL VA/SRN MD. THAT
IS WHEN THE BULK OF THE FCSTD SNOW WL ACCUMULATE. SMALL TWEAKS
HERE CUD HV BIG IMPACTS ON STORM TTLS. DID NOT MASSAGE FCST AS ANY
CHGS WUD BE MINOR WRT PSBL FCST ERRORS.

GDNC HOLDS ONTO PL A BIT LONGER IN SRN MD. ULTIMATELY THAT WL
IMPACT SNW TTLS...POTENTIALLY BY CUTTING THEM DOWN. CURRENT FCST
REPRESENTS BEST ASSESSMENT AT THIS TIME. RECOGNIZE THAT THIS
ASPECT OF THE FCST SUBJECT TO MORE SIZABLE ERRORS THAN THE REST
OF THE CWFA.

BACK EDGE OF SNOW SHUD MV SE BY LATE DAY. ADDED A CHC SNW ELY
EVENING TO ACCNT FOR LINGERING ACTIVITY/TIMING DIFFS. AFTER THAT
ITLL ALL BE A TEMP FCST. TEMPS WL ALREADY BE DROPPING DUE TO CAA
DURING THE DAY THU...AND THAT DROP WL ONLY BE ENHANCED AT NGT W/
THE LOSS OF DAYLIGHT. USED MOS MEAN W/ A SMALL CONTRIBUTION FM
PRVS FCST FOR MIN-T. WL HV PLENTY OF LOWS INTHE SINGLE DIGITS AND
TEENS...AND WL NEED TO BE CONSIDERING SUBZERO WIND CHILL FACTOR
BY DAWN FRI MRNG.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
NOT MUCH HAS CHANGED FROM PREVIOUS FORECASTS FOR THE EXTENDED
PERIOD. AFTER AN EXTREMELY COLD START FRIDAY MORNING...TEMPERATURES
WILL BE VERY SLOW TO RISE THROUGH FRIDAY...WITH WEAK CAA AND
RESIDUAL SNOW PACK. VERY WEAK SOUTHERLY FLOW COMMENCES LATE FRIDAY
NIGHT...BUT THE SNOWPACK AND STRONG RADIATIONAL COOLING WILL KEEP
NIGHTTIME LOWS WELL BELOW NORMAL.

WARMING BEGINS SATURDAY...AND DESPITE THE PASSAGE OF A WEAK COLD
FRONT SATURDAY NIGHT...TEMPERATURES WILL SLOWLY WARM THROUGH THE
REST OF THE WEEKEND AND THROUGH THE EARLY/MIDDLE PART OF NEXT WEEK.
FOR NOW KEPT THE EXTENDED POP FREE DUE TO LARGE MODEL DIVERGENCE.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
STILL HV VFR CIGS ACRS THE TERMINALS ATTM. RESTRICTIONS COMING FM
VSBYS. THAT SHUD CHG AS RA OVERSPREADS TERMINALS BY DARK. HV CONDS
DROPPING TO IFR AFTR MIDNIGHT WHEN RA MIXES WITH PL AND THEN SNOW.
ALL TERMINALS WL HV JUST SNW BEFORE THE START OF THE MRNG PUSH
TMRW. THE LOWEST CONDS WL OCCUR DURING THE MIDDAY OF THE DAY WHEN
THE SNOW WL BE HEAVIEST.

CONDS WL BE IMPRVG MID-LT AFTN. VFR PSBL BY THU EVNG...AND LKLY BY
THU NGT.

EXPECT VFR CONDITIONS FRIDAY AS WINDS CALM AND CEILINGS RISE. VFR
CONDITIONS EXPECTED THROUGH THE REST OF THE WEEKEND.

&&

.MARINE...
ASIDE FM TPLM2...ALL WNDS AOB 10 KT ATTM. STILL HV SLY FLOW. THE
TRANSITION TO NNWLY FLOW WL OCCUR THIS EVNG AS CDFNT CROSSES
WATERS. WNDS WL INCREASE THEREAFTR...W/ SCA CONDS FOR THE LATTER
PART OF THE NGT INTO THU NGT.

SCA LIKELY EXTENDS INTO FRIDAY BEFORE HIGH PRESSURE BUILDS OVERHEAD.
DO NOT ANTICIPATE MARINE CONCERNS THROUGH THE REMAINDER OF THE
WEEKEND.

&&

.HYDROLOGY...
RAIN IS ONGOING ACROSS THE NORTHERN HALF OF THE FORECAST AREA...AND
WILL SPREAD SOUTHWARD THIS EVENING. PRIOR TO THE CHANGEOVER TO
WINTRY PRECIPITATION...ADDITIONAL RAIN WILL BE BETWEEN 1/4 AND 1
INCH. WITH NO DIRECT SUNSHINE...SNOWMELT HAS BEEN SLOW BUT STEADY.

THE ONLY STREAM REACTIONS THROUGH MID AFTERNOON HAVE BEEN IN THE
NORTH BRANCH POTOMAC...NORTH FORK SOUTH BRANCH POTOMAC...AND WILLS
CREEK BASINS. THE NORTH BRANCH POTOMAC AT KITZMILLER HAS RISEN ABOVE
ACTION STAGE AND WILL BE MONITORED FOR POSSIBLE FLOODING ALL NIGHT.
OTHER STREAMS IN THOSE BASINS ARE SHOWING SOME ICE EFFECTS AND HAVE
RISEN QUITE A BIT...BUT ARE STILL WELL BELOW BANKFULL.

POOR DRAINAGE FLOODING AND PONDING ARE LIKELY WHERE NORMAL DRAINAGE
PATTERNS ARE DISTURBED BY SNOWPACK AND/OR ICE. HOWEVER...LOCALIZED
MINOR OUT-OF-BANK FLOODING OF STREAMS CANNOT BE RULED OUT...
ESPECIALLY IN NRN MD AND THE HIGHLANDS.&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST
     THURSDAY FOR DCZ001.
MD...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR MDZ003-501-502.
     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR MDZ004>006-011-503>508.
     WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST
     THURSDAY FOR MDZ013-014-016-018.
     WINTER STORM WARNING FROM 3 AM TO 10 PM EST THURSDAY FOR
     MDZ017.
VA...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR VAZ028-503-504.
     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR VAZ025>027-029>031-040-501-505>508.
     WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST
     THURSDAY FOR VAZ038-039-050>055-502.
     WINTER STORM WARNING FROM 3 AM TO 10 PM EST THURSDAY FOR
     VAZ036-037-056-057.
WV...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR WVZ050>052-055-501>506.
     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR WVZ053.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM THURSDAY TO 6 AM EST FRIDAY FOR
     ANZ530>543.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST
     THURSDAY FOR DCZ001.
     DENSE FOG ADVISORY UNTIL 10 PM EST THIS EVENING FOR DCZ001.
MD...WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR MDZ003-501-
     502.
     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR MDZ004>006-011-503>508.
     WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST
     THURSDAY FOR MDZ013-014-016-018.
     WINTER STORM WARNING FROM 3 AM TO 10 PM EST THURSDAY FOR
     MDZ017.
     DENSE FOG ADVISORY UNTIL 10 PM EST THIS EVENING FOR MDZ004>006-
     011-013-014-503>508.
VA...WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR VAZ028-503-
     504.
     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR VAZ025>027-029>031-040-501-505>508.
     WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST
     THURSDAY FOR VAZ038-039-050>055-502.
     WINTER STORM WARNING FROM 3 AM TO 10 PM EST THURSDAY FOR
     VAZ036-037-056-057.
     DENSE FOG ADVISORY UNTIL 10 PM EST THIS EVENING FOR VAZ053-054.
WV...WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR WVZ050>052-
     055-501>506.
     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     THURSDAY FOR WVZ053.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM THURSDAY TO 6 AM EST FRIDAY FOR
     ANZ530>543.

&&

$$
SYNOPSIS...HTS
NEAR TERM...HTS/KCS
SHORT TERM...HTS
LONG TERM...MSE
AVIATION...MSE/HTS
MARINE...MSE/HTS
HYDROLOGY...