Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 252039
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
339 PM EST TUE NOV 25 2014

.SYNOPSIS...A WEAK AREA OF HIGH PRESSURE WILL BUILD OVER NEW
ENGLAND TONIGHT. LOW PRESSURE WILL DEVELOP OFF THE MID ATLANTIC
COAST ON WEDNESDAY AND TRACK NORTHEAST TO JUST SOUTH OF CAPE COD
BY WEDNESDAY EVENING. THE COASTAL LOW WILL CONTINUE NORTHEAST INTO
THE MARITIMES WEDNESDAY NIGHT. A TROUGH OF LOW PRESSURE WILL
LINGER OVER THE REGION ON THURSDAY. HIGH PRESSURE WILL BUILD IN
FROM THE WEST ON FRIDAY. A WARM FRONT LIFTS INTO THE REGION FROM
THE SOUTHWEST ON SATURDAY...FOLLOWED BY A COLD FRONTAL PASSAGE ON
SUNDAY NIGHT AND EARLY MONDAY.

&&

.NEAR TERM /TONIGHT/...
NOT MUCH TO TALK ABOUT TONIGHT...AS FOCUS REMAINS ON THE NEXT
COUPLE OF DAYS. CLOUDS WILL GRADUALLY BE ON THE INCREASE TONIGHT
AS A COLD FNT CONTINUES TO OOZE SWD. WILL SEE LITTLE TEMP
ADVECTION WITH THIS FEATURE...BUT IMPORTANTLY FOR WED WE WILL SEE
DEW POINT ADVECTION.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
***SIGNIFICANT COASTAL STORM TO AFFECT HOLIDAY TRAVEL***

MODEL GUIDANCE IS NOW IN EXCELLENT AGREEMENT ON STORM TRACK...WITH
THE ECMWF...GFS...AND NAM...ALL MOVING JUST SLIGHTLY NW OF THE
40N/70W BENCHMARK. THE CMC REMAINS THE ERN OUTLIER...SO HAVE
TROUBLE PUTTING MUCH STOCK IN ITS OUTPUT ATTM.

THIS LEADS TO A FAIRLY CONSISTENT QPF FORECAST AS WELL. THE GFS
AND ECMWF ARE CLOSE TO OR JUST OVER 1 INCH LIQUID FOR COASTAL SWRN
ME. IF YOU TAKE INTO ACCOUNT THE KNOWN BIAS FOR THE NAM TO GIVE
TOO MUCH QPF ON THE COLD SIDE OF LOW PRES SYSTEMS...AND TAKE 2/3
OF ITS QPF...YOU ALSO GET JUST OVER 1 INCH QPF FOR THOSE SAME
AREAS. DIFFERENCES ARISE THE FARTHER NW ONE HEADS FROM THE COAST.
FOR THIS REASON THERE REMAINS A BIT OF UNCERTAINTY IN THE MTNS ON
AMOUNTS.

PCPN HAS SPED UP ON MODEL GUIDANCE...REACHING ALL OF THE SRN HALF
OF THE CWFA BY 18Z. SO THIS FORECAST REPRESENTS A SLIGHTLY BUMP UP
IN TIMING FROM THE PREVIOUS SHIFT. THIS MAKES FOR A TRICKY TEMP
FORECAST. CURRENT THINKING IS THAT HIGHS OCCUR VERY EARLY IN THE
DAY...POSSIBLY EVEN NEAR DAWN FOR SOME SRN NH AREAS. FROM THAT
POINT FORWARD...TEMPS LIKELY FALL DURING THE DAY AS PCPN MOVES
NWD. THIS IS MOSTLY DUE TO THE AFOREMENTIONED DRY ADVECTION
OCCURRING OVERNIGHT TONIGHT. AS PCPN FALLS TEMPS WILL WET BULB
DOWN TO NEAR FREEZING QUICKLY. HI-RES GUIDANCE...INCLUDING THE
NAM12...ARW AND NMM WRF MODELS SHOW THIS IN THEIR 2 M TEMP OUTPUT.
FAVORED A BLEND OF 2 M TEMPS RATHER THAN MOS FOR HOURLY TEMP
TREND.

AS THINGS STAND THIS AFTERNOON...GUIDANCE ALSO INDICATES MAINLY N
TO NNE WINDS AT THE SFC. THIS IS COUPLED WITH NWLY AGEOSTROPHIC
FLOW...WHICH WILL ACT TO KEEP WINDS MAINLY OFFSHORE THRU THE
EVENT. FOR THIS REASON I FEEL THAT COASTAL FNT WILL SET UP
OFFSHORE AS WELL...AND MARINE BOUNDARY LAYER WILL NOT BE A
SIGNIFICANT ISSUE. THE BIGGEST DIFFERENTIATOR BETWEEN RA AND SN
WILL BE INITIAL WET BULBING. SO ATTM THE FORECAST IS FOR
SIGNIFICANT SNWFL RIGHT TO THE COAST...ENOUGH TO IMPACT TRAVEL.
WITH MARGINAL TEMPS IT MAY ALSO BE WET AND HEAVY FOR A TIME...AND
SCATTERED POWER OUTAGES ARE POSSIBLE.

THIS LEADS TO ACTUAL FORECAST SNWFL AMOUNTS. IT IS STILL ROUGHLY
24 HOURS AWAY FROM THE BULK OF THE PCPN...SO THERE REMAINS SOME
NUANCES THAT COULD AFFECT SNWFL. FOR SEVERAL DAYS NOW...MODEL
GUIDANCE HAS BEEN CONSISTENT WITH TRACKING MID LEVEL LOW CENTERS
VERY CLOSE TO THE NEW ENGLAND COAST. AT THE SAME TIME...700 MB
HEIGHTS TRY AND CLOSE OFF NEARLY OVERHEAD. THIS FAVORS A STRONG
BAND OF LIFT JUST ON THE COOL SIDE OF THE MID LEVEL LOW TRACK.
DEFORMATION AND FRONTOGENESIS PROGS ON THE ECMWF...GFS...AND
NAM AGREE WITH THIS PLACEMENT...FROM SRN NH TO JUST INLAND FROM
THE COAST OF WRN ME. AS THE MID LEVEL LOWS TAKE THIS TRACK...IT
WILL ALLOW SOME WARMTH ALOFT TO SNEAK NW. IT MAY NOT EVER GET
ABOVE FREEZING AT THESE LEVELS...BUT WARMING TO WITH A COUPLE OF
DEGREES OF FREEZING COULD LEAD TO POOR SN GROWTH FOR A TIME ALONG
THE COAST. SN RATIOS WERE ADJUSTED TO REFLECT THESE EXPECTED
OUTCOMES...LOWERED NEAR THE COAST...AND RAISED JUST INLAND WHERE
STRONGEST DEFORMATION BANDING IS LOCATED. IN ADDITION...WE HAVE
ALSO HAD VERY WARM TEMPS RECENTLY AND WILL START OFF WITH MARGINAL
TEMPS EARLY WED. THIS MAY LEAD TO A FALSE SENSE OF SECURITY
HOWEVER. WHEN STRONGEST LIFT COMES IN...DURING WED AFTERNOON AND
EVENING...FORCING AND SOUNDINGS CONFIRM THAT SN MAY FALL HEAVILY
AT TIMES. WITH RATES POSSIBLY APPROACHING 1 INCH/HR IT WILL NOT
MATTER HOW WARM IT HAS BEEN...AND ACCUMULATION WILL OCCUR ON
ROADWAYS.

ONCE AGAIN...THE CONDITIONS WILL BE QUICKLY DETERIORATING AND
EXPECTED TO BE THE WORST WED AFTERNOON AND EVENING...COINCIDING
WITH THE BUSIEST TRAVEL TIMES. TRAVELERS SHOULD BE AT THEIR
DESTINATIONS BY WED AFTERNOON IF AT ALL POSSIBLE.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
A SURFACE RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD IN FROM THE
WEST ON THANKSGIVING AS THE STORM DEPARTS INTO THE MARITIMES.
HOWEVER....A LARGE SCALE...UPPER LEVEL TROUGH WILL REMAIN TO OUR
WEST. 12Z MODEL SUITE IS IN GOOD AGREEMENT AT THIS TIME WITH THESE
LARGE SCALE FEATURES. HOWEVER...THE NEW EURO RUN DEPICTS A NEARLY
STATIONARY INVERTED TROUGH ALONG THE SOUTHWEST COAST OF MAINE
THURSDAY INTO FRIDAY. THE SCENARIO WOULD KEEP SCATTERED SNOW
SHOWERS IN THE PORTLAND AREA FOR THE END OF THE WORKWEEK. OTHER
MODELS ARE NOT PICKING UP ON THIS NORLUN TROUGH TYPE FEATURE.
WILL SEE IF THIS FEATURE REMAINS ON THE FOLLOWUP MODEL RUNS.

THEREAFTER...VERY QUIET WITH A BRIEF WARM UP ON SUNDAY FOLLOWED BY
A STRONG COLD FRONT ON MONDAY. MODELS DIVERGE AS TO WHETHER A WAVE
OF LOW PRESSURE WILL FORM ALONG THIS FRONT...AFFECTING NEW
ENGLAND. A LARGE AND CHILLY CANADIAN HIGH PRESSURE SYSTEM WILL
FOLLOW.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
SHORT TERM...VFR CONDITIONS PREVAIL THRU EARLY WED. CONDITIONS
RAPIDLY DETERIORATE FROM S TO N THRU WED AFTERNOON. CONDITIONS
WILL QUICKLY DROP TO IFR AND LOWER BY EVENING. COULD SEE SOME
BRIEF MIXING WITH RA AT KPSM AND KPWM...BEFORE A TRANSITION TO ALL
SNWFL. WINDS ALONG THE COAST WILL BE GUSTY FROM THE NNE...AROUND
25-30 KTS. CONDITIONS QUICKLY IMPROVE TO MVFR OR VFR THU AS LOW
PRES PULLS AWAY.

LONG TERM...MAINLY VFR CONDITIONS ACROSS THE REGION IN THE LONG
TERM. THERE MAY BE LOCALIZED MVFR CONDITIONS IN SCT SNOW SHOWERS
ALONG THE COAST THURSDAY INTO FRIDAY. MVFR CONDITIONS WITH A
FRONTAL PASSAGE NEXT MONDAY.

&&

.MARINE...
SHORT TERM...GALE WARNINGS IN EFFECT STARTING WED AFTERNOON.
COASTAL STORM WILL QUICKLY MOVE ACROSS THE GULF OF ME...WITH A
BRIEF PERIOD OF GALE FORCE GUSTS. SCA WILL LIKELY BE NEEDED
FOLLOWING THE LOW PRES.

LONG TERM...WINDS WILL LIKELY REACH SCA CRITERIA LATE IN THE
WEEKEND AND INTO EARLY NEXT WEEK.  A SW WIND WILL VEER TO THE NW.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...WINTER STORM WARNING FROM 10 AM WEDNESDAY TO 7 AM EST THURSDAY
     FOR MEZ012>014-018>028.
     WINTER WEATHER ADVISORY FROM 1 PM WEDNESDAY TO 7 AM EST
     THURSDAY FOR MEZ007>009.
NH...WINTER STORM WARNING FROM 10 AM WEDNESDAY TO 7 AM EST THURSDAY
     FOR NHZ002>010-013-014.
     WINTER WEATHER ADVISORY FROM 1 PM WEDNESDAY TO 7 AM EST
     THURSDAY FOR NHZ001.
MARINE...GALE WARNING FROM 5 PM WEDNESDAY TO 7 AM EST THURSDAY FOR
     ANZ150>154.

&&

$$

LEGRO/JC


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