Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 301145
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
645 AM EST FRI JAN 30 2015

.SYNOPSIS...
COLD FRONT MOVES THROUGH THIS MORNING WITH HIGH PRESSURE BUILDING
ACROSS THE REGION FOR THE FIRST HALF OF THE WEEKEND. LOW PRESSURE
WILL IMPACT THE AREA LATE SUNDAY INTO MONDAY. COLD HIGH PRESSURE
WILL RETURN FOR THE MIDDLE PORTION OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AS OF 11Z...COLD FRONT PROGRESSING ACROSS THE EASTERN HALF OF THE
CWA...JUST EAST OF THE I-95 CORRIDOR. LIGHT RAIN SHOWERS OUT AHEAD
OF THE FRONT WILL PUSH OFF TO THE NORTH/EAST...WHILE THE NW FLOW
IN THE WAKE IS RESULTING IN UPSLOPING SNOW SHOWERS ALONG THE
ALLEGHENY FRONT. WINTER WEATHER ADVISORY REMAINS IN EFFECT THERE
UNTIL NOON TO ACCOUNT FOR AN ADDITIONAL 1-3 INCHES THIS MORNING.
ADDITIONAL SNOW SHOWERS WILL BE PSBL INTO THIS EVENING WITH THE
REGION POSITIONED UNDER AN UPPER LVL TROUGH...BUT EXPECTING TOTALS
TO BE LIGHT. FOR THE REMAINDER OF THE AREA...HAVE INCLUDED POPS
MAINLY ALONG THE MASON-DIXON LINE AND EXTENDING SOUTH ALONG THE
CHESAPEAKE BAY. STRONG FORCING ALOFT AS A VORT MAX ROUNDS THE BASE
OF THE TROUGH WORKING WITH MOISTURE BEING STREAMED IN FROM THE
GREAT LAKES WITH THE STRONG NW FLOW COULD GENERATE ISO-SCT SNOW
SHOWERS...MAINLY THRU MID AFTN. OVER CENTRAL VA AND TO THE
SOUTH...HAVE INCLUDED FLURRIES WITH LESS FORCING EXPECTED AND WITH
THE DRIER AIR MOVING IN. ANY SNOW THAT OCCURS OUTSIDE THE POTOMAC
HIGHLANDS IS EXPECTED TO BE MINIMAL...LITTLE TO NO ACCUMULATION.

IN ADDITION TO THE PCPN...INCREASING NW FLOW WITH STRONG
CAA...DEVELOPING LLJ ACROSS THE MID ATLANTIC AND TIGHTENING
PRESSURE GRADIENT WILL LEND TO POSSIBLE GUSTS ABV 40 KTS. WIND
ADVISORY REMAINS IN EFFECT FOR TODAY THRU THIS EVENING EXCEPT FOR
PORTIONS OF THE PIEDMONT TO ACCOUNT FOR THIS POTENTIAL. 00Z GFS THE
STRONGER SOLUTION WITH WINDS ALOFT...PLACING A LLJ 50-60 KTS BY 00Z
THIS EVENING. 00Z NAM AND ECMWF THE WEAKER SOLUTIONS...BUT STILL
SHOWING THE POTENTIAL...ESPECIALLY AT THE HIGHER ELEVATIONS...OF
GUSTS INTO THE 40S. TIMING LOOKS TO BE OVER THE WESTERN AREAS
BEGINNING AFTER DAYBREAK THIS MORNING...THEN SPREADING EAST DURING
THE DAY...WITH THE EASTERN AREAS HAVING THE BETTER CHC OF REACHING
WIND ADVISORY CRITERIA LATE AFTN/THIS EVENING.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
SFC HIGH PRESSURE PUSHES EAST OVER THE REGION IN THE WAKE OF THE
COLD FRONT AS RIDGING BUILDS IN ALOFT. MAINLY DRY CONDITIONS TONIGHT
THRU SAT NIGHT WITH THE EXCEPTION OF ANY LINGERING LIGHT UPSLOPING
SNOW SHOWERS FIRST HALF OF TONIGHT. SUBSIDENCE ALOFT WILL RESULT IN
MOSTLY CLEAR CONDITIONS TONIGHT...AND SUNNY CONDITIONS FOR SAT.

THE MAIN CONCERN DURING THIS TIME FRAME WILL BE THE WELL BELOW
NORMAL TEMPS BEING USHERED IN AS 850MB TEMPS DIP BELOW -10 DEGREES
CELSIUS. USING A BLEND OF ADJMET/MOSGUIDE...TEMPS TONIGHT EXPECTED
TO DROP INTO THE TEENS EVERYWHERE EXCEPT POTOMAC HIGHLANDS...WHICH
SHOULD SEE LOWS INTO THE SINGLE DIGITS. THESE TEMPS COMBINED WITH
THE ON GOING NW FLOW WILL PRODUCE WIND CHILLS INTO THE SINGLE
DIGITS. THE POTENTIAL EXISTS FOR NEEDING A WIND CHILL ADVISORY OVER
THE FAR WESTERN PORTIONS OF THE POTOMAC HIGHLANDS WITH WIND CHILLS
DROPPING TO AROUND -12 DEGREES. HOWEVER...HAVE HELD OFF FOR ANY
ISSUANCE AT THIS TIME WITH THE VALUES BEING BORDERLINE WITH THE
CRITERIA AND IT BEING MAINLY AFTER 06Z TONIGHT. ELSEWHERE...THOUGH
IT WILL BE VERY COLD...WIND CHILLS VALUES ARE EXPECTED TO REMAIN ABV
CRITERIA LVLS.

BY SATURDAY...WILL SEE GRADUAL WARMING AS THE HIGH NUDGES ACROSS THE
AREA...WITH RETURN FLOW SETTING UP AND INJECTING IN WARMER AIR.
DESPITE THE WARMING...TEMPS STILL EXPECTED TO REMAIN BELOW NORMAL
THRU AT LEAST SAT NIGHT. 00Z MODEL SUITE IN PRETTY GOOD AGREEMENT OF
ANY PCPN MOVING INTO THE REGION WITH THE NEXT LOW PRESSURE SYSTEM
HOLDING OFF TILL AFTER 12Z SUNDAY AND HAVE THUS A DRY FORECAST THRU
THIS TIME PERIOD.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
WHAT WAS ONCE LOOKING LIKE A POTL SNOWSTORM SUN-MON ISNT QUITE SO
CLEAR ANYMORE...AS 00Z GDNC--INCL THE ECMWF--HAS TRENDED WARMER.
LOPRES PROGGED TO CROSS THE MS RIVER MIDDAY SUN /ALREADY CONTAINING
GREATER THAN DESIRED PLACEMENT SPREAD/ AND ARRIVES IN CWFA SUN NGT.
THE TRACK OF THIS LOW LOOKING TO BE SOMEWHERE N OF THE VA/NC BRDR
BUT S OF THE MASON-DIXON LINE. THAT IN TURN BUMPS THE TRACK OF THE
H8 LOW ACRS PA...PERMITTING WARM AIR TO PENETRATE REGION ALOFT.
THEREFORE...ALL SORTS OF PTYPE ISSUES EMERGE.

GFS BUFKIT SNDGS SUGGEST THAT PCPN WL START AS SNW SUNDAY BUT CHG TO
JUST RA SUN EVE FOR A LARGE PORTION OF THE VA SHEN VLY...ALL OF
METRO DC...AND EVEN PART OF METRO BALT. AM NOT READY TO GO THAT WARM
JUST YET...BUT NEED TO ENTERTAIN PSBLTYS OF PARTIAL MELTING OR EVEN
COMPLETE MELTING AND REFREEZING SINCE WET BULBS LKLY WL BE BELOW
32F. DO BELIEVE THAT SUNDAYS PCPN SHUD BE MAINLY SNOW WHERE IT ISNT
TOO WARM. GRIDS EMPHASIZING AFTN...AS THE MRNG HRS SHUD BE DEDICATED
TO SATURATION. WL HV A MIXED BAG FOR SUN NGT. MADE THE OVNGT HRS
MESSIER..THINKING THAT SFC COLD AIR CUD SEEP SWD ON BACK SIDE OF
LOW. BY 12Z MON...LOPRES WL BE OFFSHORE. AT THAT POINT...PTYPE
BECOMES MORE CERTAIN AGAIN AS ENUF COLD AIR SHUD DRAIN DOWN THRUT
THE COLUMN TO SUPPORT PCPN CHGG BACK TO SNW BEFORE ENDING.

GIVEN LTST TRENDS THERES TOO MUCH UNCERTAINTY IN THE OUTCOME TO
SUPPORT WATCHES. IN FACT WL BE ADJUSTING HWO FM ACCUM SNW TO A MORE
GENERIC WINTER WX. OVERALL...HV LWR THAN TYPICAL FCST CONFIDENCE.

NEXT WEEK WL START COLD AS THE CSTL LOW STRENGTHENS...DRAGGING DOWN
COLD AIR. H8 TEMPS SHUD BE DROPPING TO -10 TO -14C. AT THAT RATE
MON-TUE MAXT WL HV TROUBLE RISING ABV FRZG...AND MIN-T MAY DIP BELOW
0 DEGF ACRS NRN MD AND IN THE PTMC HIGHLANDS.

GFS SUGGESTING THAT ANOTHER SRN STREAM LOW WL FLLW MIDWEEK HIPRES
FOR A POTL STORMY THU. ITS STILL TBD IF WE WL RECEIVE THE LOW OR IT
WL PASS S OF CWFA. WL BE KEEPING POPS LOW AS THERES A LOT OF WX TO
GET THROUGH FIRST.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
HIGH CONFIDENCE VFR CONDITIONS THROUGH SAT.

MAIN CONCERN TODAY STRONG NW FLOW. GUSTS START TIME +/- 1-2
HRS...GENERALLY IN THE 20S THIS MORNING...THEN INCREASING 30-40
KTS THIS AFTN/EVENING. WINDS WILL GRADUALLY DIMINISH
TONIGHT...WITH GUSTS PSBL THOUGH THROUGH THE NIGHT. KCHO COULD SEE
GUSTS ENDING AS EARLY AS 06Z. ISO SNOW SHOWER PSBL KMRB BUT TOO
LOW CONFIDENCE TO INCLUDE...ESP WITH LITTLE IMPACT TO CONDITIONS.

DECREASING WNW FLOW SAT WITH WINDS BCMG W SAT NIGHT. PSBL LOWERING
CIGS LATE SAT NIGHT AS THE NEXT LOW PRESSURE SYSTEM APPROACHES.

FLGT RESTRICTIONS APLENTY SUN AS LOPRES CROSSES TERMINALS. THE
AFTN-NIGHT TIME HRS SHUD BE MOST AFFECTED. PTYPE ISSUES EXIST. ITS
NO LONGER A CLEAR-CUT SNOW EVENT. THE LOW WL BE PULLING OFFSHORE
MON. CONDS WL IMPRV THRU THE DAY...BUT SHUD HV SOME STRONG NW WIND
GUSTS.

VFR TUE UNDER HIPRES.

&&

.MARINE...
GALE WARNING IN EFFECT FOR TODAY THRU TONIGHT. GALES MAY START AS
EARLY AS MID MORNING...BUT BETTER CHC THIS AFTN/EVENING TIME
PERIOD. COULD SEE LINGERING GALES PAST DAYBREAK SAT MORNING...BUT
HAVE HELD AT 09Z FOR NOW TO ACCOUNT FOR UNCERTAINTY THEREAFTER.
HIGH CONFIDENCE SCA CONDITIONS WILL SET IN SAT MORNING FOR
CHESAPEAKE BAY...AND PSBL OVER THE TIDAL POTOMAC. SUB-SCA
CONDITIONS EVERYWHERE FOR SAT NIGHT.

LOPRES APPRCHS WATERS SUN DAY AND CROSSES SUN NGT. TRACK OF LOW WL
PERMIT A MIXED BAG OF PTYPES AT NIGHT BEFORE CHGG BACK TO SNOW UPON
EXIT MON. ALSO ON MON SHUD BE STIFF NW WINDS AS THE STORM
STRENGTHENS AS IT PULLS AWAY. AT LEAST SCA PSBL. WUDNT COMPLETELY
RULE OUT GLW...CONTINGENT UPON DETAILS THAT ARE STILL A LTL MURKY.
HIPRES WL RETURN BY TUE.

&&

.TIDES/COASTAL FLOODING...
WATER LEVELS RUNNING A FOOT AND A HALF ABV ASTRO NORMS WITH THE
OVNGT TIDE CYCLE. THX TO A QUARTER MOON...TIDES ARE AT THEIR LOW
POINT ASTRONOMICALLY...AND WE/RE ABLE TO ABSORB THE EXCESS WITHOUT
ISSUE. SITES IN THE NRN CHSPK BAY AREA REACHING CAUTIONS STAGES
THOUGH.

WINDS WL BE TURNING NW BHD A COLD FRONT DURING THE DAYLIHGT HRS.
THIS WILL SUPPORT BLOW OUT TIDES. THEREFORE...WATER LEVELS WL
RETURN TO NORMAL EITHER LATER TODAY OR TONIGHT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WIND ADVISORY FROM NOON TODAY TO MIDNIGHT EST TONIGHT FOR
     DCZ001.
MD...WIND ADVISORY FROM 10 AM THIS MORNING TO MIDNIGHT EST TONIGHT
     FOR MDZ003-501-502.
     WIND ADVISORY FROM NOON TODAY TO MIDNIGHT EST TONIGHT FOR
     MDZ004>006-011-013-014-016>018-503>508.
     WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR MDZ501.
VA...WIND ADVISORY FROM 10 AM THIS MORNING TO MIDNIGHT EST TONIGHT
     FOR VAZ025>031-503-504-507-508.
     WIND ADVISORY FROM NOON TODAY TO MIDNIGHT EST TONIGHT FOR
     VAZ040-051>055-057-501-502-505-506.
     WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR VAZ503.
WV...WIND ADVISORY FROM 10 AM THIS MORNING TO MIDNIGHT EST TONIGHT
     FOR WVZ050>053-055-501>506.
     WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR WVZ501-503-
     505.
MARINE...GALE WARNING UNTIL 4 AM EST SATURDAY FOR ANZ530>543.

&&

$$
SYNOPSIS...SEARS/HTS
NEAR TERM...SEARS
SHORT TERM...SEARS
LONG TERM...HTS
AVIATION...SEARS/HTS
MARINE...SEARS/HTS
TIDES/COASTAL FLOODING...HTS






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