Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 090831
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
331 AM EST TUE FEB 9 2016

.SYNOPSIS...
MULTIPLE LOW PRESSURES IMPACT THE REGION THROUGH WEDNESDAY BEFORE
PUSHING OFF TO THE NORTHEAST. HIGH PRESSURE BUILDS IN THE WAKE
THROUGH FRIDAY. A QUICK MOVING COLD FRONT SWINGS THROUGH FRIDAY
NIGHT WITH CANADIAN HIGH PRESSURE BUILDING IN FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
A FEW ADJUSTMENTS BEING MADE THIS MORNING WITH THE LATEST MODEL
RUNS CONVERGING ON DCRSG POTENTIAL OF THE HIGHER SNOW TOTALS.
OVERALL...HAVE DROPPED SNOW TOTALS ANYWHERE BETWEEN 1-3 INCHES
ACROSS THE AREA. AS SUCH...HAVE ENOUGH CONFIDENCE TO CANCEL THE
WINTER STORM WARNING...REPLACING WITH A WINTER WX ADVISORY THRU
THIS EVENING. THE WINTER WX ADVISORY ALREADY IN PLACE REMAINS THE
SAME EXCEPT HAVE CANCELLED FOR DC/ARLINGTON/FAIRFAX AND PRINCE
WILLIAM WITH THE INCREASED CONFIDENCE NOW OF LESS THAN 2 INCHES...
ADVISORY CRITERIA. COASTAL FLOOD ADVISORIES ARE IN EFFECT TODAY AS
WELL...PLEASE REFER TO THE COASTAL FLOOD SECTION FOR MORE DETAILS.

THE LIGHT RAIN HAS BEEN SLOW TO TRANSITION TO SNOW OR EVEN A
RAIN/SNOW MIX TONIGHT OUTSIDE OF THE POTOMAC HIGHLANDS. UPPER LVL
TROUGH ACROSS A GOOD PORTION OF THE EASTERN US THE MAIN PLAYER IN
PCPN DEVELOPMENT EARLY THIS MORNING WITH ONE SFC LOW WELL NORTH OVER
THE EASTERN GREAT LAKES...AND A SECOND LOW ORGANIZING OFF THE COAST
OF VA. AS THIS SECOND LOW DEEPENS...PUSHING OFF TO THE NE...
EXPECTING AN INVERTED TROUGH EXTENDING BACK ACROSS MD INTO PA TO
ACT AS A TRIGGER FOR FURTHER PCPN DEVELOPMENT OVER THE EASTERN
HALF OF THE CWA THIS MORNING AND THE AFTN. WITH THE UPPER LVL
TROUGH IN PLACE...A POTENT SHORTWAVE MOVES INTO WESTERN VA...WHICH
WILL ACT AS THE TRIGGER FOR SNOW SHOWERS FOR THE WESTERN HALF OF
THE CWA. AS IT MOVES OVER DELMARVA THIS EVENING...THE PCPN AREA
WILL TRANSITION...LEADING TO DRYING OVER CENTRAL VA.

WHILE THERE IS HIGHER CONFIDENCE FOR THE PCPN LOCATION/TIMING...
THERE IS NOW LESS CONFIDENCE OF THE HIGHER QPF AMTS...AND THE SNOW
POTENTIAL LEADING TO HIGHER SNOW AMTS. AS PREVIOUSLY MENTIONED...
BACKED OFF OF SNOW TOTALS BETWEEN 1-3 INCHES FOR A COUPLE OF
REASONS. THE PCPN WAS SLOW TO TRANSITION TO SNOW TONIGHT WITH A
LACK OF HEAVIER BANDS SETTING UP. QPF TOTALS ON THE 00Z RUN ARE
ALSO LOWER. A QUESTION THAT WE HAD BEEN DISCUSSING FOR THE PAST
FEW DAYS WAS THE THERMAL PROFILES AND THE RESULTING PCPN. WHILE
THERE IS PLENTY OF COLD AIR ALOFT...THE LOWEST LAYERS WERE
STRUGGLING TO DROP BELOW FREEZING. HAD THERE BEEN HEAVIER PCPN...
HAD THOUGHT WET BULBING WOULD OCCUR...TRANSITIONING TO THE RAIN TO
SNOW. HOWEVER...TEMPS ARE STILL HOVERING IN THE MID TO UPPER
30S...AND EVEN DEW PTS ARE ABV FREEZING...SUGGESTING IT MAY STILL
BE SOME TIME BEFORE MOST OF THE CWA CHANGES OVER. THINKING THIS
SHOULD OCCUR BETWEEN 10-15Z AS WINDS BECOME MORE NLY...INJECTING
IN LOWER DEW PTS. BUFKIT PROFILES SHOW BOTH WITH THE NAM AND GFS
THAT SOUTHERN MD AND AREAS OF THE PIEDMONT MAY HAVE A SNOWFLAKE OR
TWO...BUT NO ACCUM. MVG NORTH...CULPEPER TO DC AND SOUTH WILL BE
NO MORE THAN AN INCH. THE HIGHEST AMTS ARE STILL THE NORTHEAST
CORNER OF MD...TOPPING OFF UNDER 5 INCHES...BUT THESE MAY STILL BE
OVERDONE...WITH 3-5 INCHES BEING MORE SPARSE THAN WIDESPREAD. ALSO
TO NOTE...THAT WITH THE WARMER TEMPS...THE SNOW MAY FALL FOR A
GOOD WHILE BEFORE ACTUALLY ACCUMULATING.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
HIGHER CONFIDENCE IN THE MIDDLE OF THE WEEK FORECAST AS THE FOCUS
TURNS FROM PCPN THREAT AND MORE INTO THE MUCH COLDER TEMPS. WITH
THE DEPARTING LOW...EXPECTING NW FLOW TO PERSIST THRU THIS
TIME...KEEPING UPSLOPE SNOW SHOWERS IN THE FORECAST THRU THURSDAY.
THE WINTER WX ADVISORY FOR THE ALLEGHENY FRONT IS IN EFFECT THRU
THURS WITH BETWEEN 6 AND 10 INCHES PSBL FROM NOW TILL THEN.
OUTSIDE OF THE UPSLOPE SNOW...AS THE UPPER LVL TROUGH PIVOTS
EAST...ENOUGH ENERGY ALOFT COULD TRIGGER AN ISO SNOW SHOWER ALONG
THE MASON-DIXON...THOUGH WITH THE MUCH DRIER AIRMASS IN PLACE...IT
WILL BE DIFFICULT AND IT MAY END UP BEING MORE JUST FLURRIES.

FOR THE TEMPS...WED WILL BE SLIGHTLY COOLER THAN TODAY...WITH THE
FIRST SURGE OF CAA COMING IN DURING THE DAY...DROPPING LOWS WED
NIGHT INTO THE SINGLE DIGITS AND TEENS. WIND CHILL ADVISORIES MAY BE
NEEDED FOR THE ALLEGHENY FRONT WITH WIND CHILLS DROPPING TO BELOW
-10 DEGREES. THE THREAT WILL BE PSBL AGAIN THURS NIGHT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
ARCTIC AIR WILL BE REINFORCED FRI-SAT BY ANOTHER DISTURBANCE WITHIN
H5 TROF. GDNC SUGGESTING THAT THE LEADING EDGE WL TRACK NORTH OF THE
AREA FRI...ALLOWING SHSN TO BE CAUGHT IN THE MTNS...FOLLOWED BY A
GREATER PUSH LATE FRI NGT/ELY SAT MRNG. NW WINDS AND SGFNT CAA WL
FOLLOW THAT. LTST GDNC SUGGESTING THAT MAXT SAT WL BE IN THE TEENS
PTMC HIGHLANDS/20S ELSW. WIND CHILLS WILL BE A CONCERN THEN...AND WL
ONLY BE AMPLIFIED SAT NGT AS TEMPS FALL INTO THE SINGLE DIGITS--EVEN
IN THE CITIES OF DC/BALT. SUBZERO TEMPS FCST IN THE MTNS. WL HV A
GRADUAL MODERATING TRENDS BY THE START OF THE NEW WEEK...PERHAPS
WITH ANOTHER ROUND OF POTL PCPN.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
IFR/MVFR CIGS CURRENTLY BEING OBSERVED ACROSS THE TAF SITES WITH
LIGHT RAIN IMPACTING ALL BUT KCHO. AS THE PCPN TRANSITIONS TO ALL
SNOW...EXPECTING CIGS TO BECOME IFR OR LIFR AND VIS TO DIMINISH TO
1SM OR LESS. THE TIME FRAME FOR TRANSITIONING IS STILL LOW-MOD
CONFIDENCE...GENERALLY 11-14Z. SNOW PERSISTS THIS MORNING BEFORE
TRANSITIONING BACK TO RAIN AT KDCA AND RAIN/SNOW MIX AT
KIAD/KBWI/KMTN. CIGS/VIS WILL IMPROVE TO MVFR THIS AFTN WITH THIS
TRANSITION. SNOW AMTS WILL BE LESS THAN ONE INCH KCHO/KDCA...1-3
KIAD/KBWI...AND 2-4 KMRB/KMTN.

THE PCPN WILL TAPER OFF COMPLETELY BY TONIGHT WITH VFR CONDITIONS
THEN EXPECTED TONIGHT THRU THURSDAY. WINDS DURING THE TAF PERIOD
WILL BE NE LESS THAN 10 KTS...BCMG NW AND INCRSG THIS AFTN...WITH
GUSTS PSBL TONIGHT. GUSTY NW WINDS WILL CONTINUE WED-THURS.

VFR MOST LKLY FRI-SAT. WINDS SAT CUD GUST NW 20-25 KT.

&&

.MARINE...
SUB-SCA CONDITIONS ON ALL WATERS THROUGH TODAY. INCRSG NW
WINDS TONIGHT WILL PRODUCE OCNL SCA GUSTS ON THE CHESAPEAKE
BAY...BCMG MORE PERSISTENT AND WIDESPREAD THURSDAY AND THURSDAY
NIGHT.

WINDS FRIDAY WL BE ON THE LGT SIDE...AS WE/LL BE IN A WK HIPRES RDG
AHD OF ANOTHER TROF AXIS. THAT AXIS/REINFORCING FNT WL CROSS WATERS
BEFORE SAT AM. SCA CONDS XPCTD DURING THE DAY...AND MOST LKLY
LINGERING THRU THE NGT.

&&

.TIDES/COASTAL FLOODING...
WATER LEVELS SHOT UP TO 2.5 FEET ABOVE ASTRO NORMALS OVERNIGHT...
WHICH IS SIGNIFICANTLY ABOVE ANY GUIDANCE FORECAST...EXCEPT PERHAPS
CBOFS.  ITS ON PACE TO EXCEED MINOR FLOOD THRESHOLDS AT JUST ABOUT
ALL TIDE SITES ON THE WESTERN SHORE OF THE BAY.  HAVRE DE GRACE WILL
BE TOUGH TO ACHIEVE...BUT CORRELATIONS SUGGEST THAT MINOR FLOODING
SHOULD OCCUR SOUTH OF THERE NEAR EDGEWOOD. THEREFORE...HV EXPANDED
CF ADVISORY TO THE ENTIRE SHORELINE.  HAVE ALSO ADDED CHARLES CO TO
ACCOUNT FOR POTENTIAL EFFECTS ON/NEAR COBB ISLAND. PINEY POINT AND
ANNAPOLIS MAY EACH COME CLOSE TO MDT /WRNG/ LVL...BUT WILL HOLD OFF
FOR NOW.

WINDS WILL GRADUALLY BE SWINGING AROUND TO THE NW THIS AFTN AND
EVENTUALLY WEST TONIGHT.  HOWEVER AM NOT SURE HOW STRONG THEY WILL
BE...AND ITS THEREFORE IN DOUBT WHETHER THEY WILL HAVE A BLOWOUT
EFFECT. IN ADDITION...THE PM TIDE CYCLE IS THE HIGHER OF THE TWO
ASTRONOMICALLY...SO EVEN IF THERE IS A PINCH OF RELIEF...IT WILL BE
COMPENSATED.  FOR THAT REASON...HAVE EXTENDED THESE ADVISORIES FOR A
2ND TIDE CYCLE.

LATEST HEC-RAS GUIDANCE SUGGESTS THAT MINOR THRESHOLD WILL BE
ACHIEVED AT SW DC/ALEXANDRIA AS WELL. ITS UNCLEAR WHETHER THE BIG
SLUG WILL MAKE IT ALL THE WAY UP. WASD2 SEEMS TO BE TRACKING WELL SO
FAR...BUT THERE ARE THE FIRST INDICATIONS AT ALEXANDRIA THAT THE LOW
TIDE WONT BE NEARLY AS LOW AS MODELED. THAT COULD PLAY INTO THE REST
OF THE POTOMAC SHORELINE...WHICH IS SOMETHING THAT WILL BE MONITORED.
&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY UNTIL 10 AM EST THIS MORNING FOR DCZ001.
MD...WINTER WEATHER ADVISORY UNTIL 6 PM EST WEDNESDAY FOR MDZ501.
     WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR
     MDZ003>006-011-013-014-502>508.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ011-
     014-016>018-508.
VA...WINTER WEATHER ADVISORY UNTIL 6 PM EST WEDNESDAY FOR VAZ503.
     WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR VAZ027-
     028-030-031-501-504>507.
     COASTAL FLOOD ADVISORY UNTIL 10 AM EST THIS MORNING FOR VAZ054.
WV...WINTER WEATHER ADVISORY UNTIL 6 PM EST WEDNESDAY FOR WVZ501-
     503-505.
     WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR
     WVZ050>053-055-502-504-506.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST
     WEDNESDAY FOR ANZ533-534-537-541-543.

&&

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


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