Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 230355
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
1055 PM EST MON DEC 22 2014

.SYNOPSIS...
A WEAK ONSHORE FLOW WILL CONTINUE THROUGH TUESDAY. A SIGNIFICANT
LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES WEDNESDAY
INTO THURSDAY. THIS COULD BRING WINDY CONDITIONS AND THE POTENTIAL
FOR HEAVY RAIN AROUND CHRISTMAS EVE INTO EARLY CHRISTMAS MORNING.
ANOTHER LOW PRESSURE SYSTEM WILL APPROACH THE REGION LATE IN THE
WEEKEND POTENTIALLY BRINGING SOME WINTRY WEATHER.

&&

.NEAR TERM /TONIGHT/...
11PM UPDATE...
HAVE INCREASED POP ONE MORE TIME THIS EVENING AS OCEAN EFFECT
RAIN/SNOW STILL GOING STRONG AND EXPANDING AS IT MOVES UP THE
COAST. LIGHT ACCUMULATIONS OF SNOW ARE EXPECTED AWAY FROM THE
COAST. STILL LOOKS LIKE MAINLY A RAIN/SNOW ISSUE DEPENDENT ON
LOCAL SURFACE TEMPERATURES FOR THE NEXT FEW HOURS.

9PM UPDATE...
ONSHORE SOUTHEAST FLOW (AT LEAST ABOVE THE SURFACE ANYWAY) IS
BEING LIFTED ABOVE A COOL SURFACE AIR MASS AND PRODUCING OCEAN
EFFECT TYPE RAIN/SNOW SHOWERS ALONG MOST OF THE MAINE AND NEW
HAMPSHIRE COASTLINE. HAVE UPDATED POP TO REFLECT THE HIGHER
CONFIDENCE IN PRECIPITATION... THOUGH THE OVERALL IDEA OF
PRECIPITATION TYPE HAS NOT CHANGED. IT WILL BE RAIN OR SNOW
DEPENDING ON LOCAL TEMPERATURES FOR THE NEXT SEVERAL HOURS.
HEAVIER... MORE STRAITFORM TYPE PRECIPITATION WILL ARRIVE AFTER
MIDNIGHT OVER SOUTHERN NEW HAMPSHIRE BEFORE SPREADING NORTH AND
THEN EAST TOMORROW.

545PM UPDATE...
HAVE UPDATED THE FORECAST FOR TONIGHT AND TOMORROW PRIMARILY TO
ADJUST PRECIPITATION CHANCES. HAVE INCREASED PRECIPITATION CHANCES
INTO THE 80 TO 100 PERCENT RANGE ACROSS THE ADVISORY AREA TO
INDICATE THE HIGH CONFIDENCE IN PRECIPITATION OCCURRING.
PRECIPITATION ALREADY SHOWING UP ON REGIONAL RADAR AND ALL MODELS
IN AGREEMENT ON PRECIPITATION FALLING IN SOUTHERN NEW HAMPSHIRE
TONIGHT. PRECIPITATION SHIELD WILL FIRST MOVE NORTH TONIGHT THEN
EAST TOMORROW. PRECIPITATION LIKELY BEGINS AS SNOW OR RAIN
DEPENDING ON SURFACE TEMPERATURES... THOUGH WARM AIR BEGINS MOVING
IN ALOFT LATER TONIGHT... ALLOWING FOR A CHANGE OVER TO SLEET AND
FREEZING RAIN IN SOUTHWEST NEW HAMPSHIRE IN AREAS WHICH ARE ABLE
TO FALL BELOW FREEZING AT THE SURFACE. TOTAL ICE AMOUNTS ARE
EXPECTED TO BE LIGHT... BUT ANY ICE ACCUMULATION WILL BE A HAZARD
FOR TRAVEL SO THE ADVISORY WILL CONTINUE. STORM TOTAL SNOW AND ICE
FORECASTS HAVE BEEN UPDATED FOR THE WEB AS WELL TO INCLUDE ONLY
THE CURRENT PRECIPITATION PERIOD THROUGH TUESDAY.

ORIGINAL DISCUSSION...
A PERSISTENT LIGHT ONSHORE FLOW FROM THE EAST COMBINE WITH SOME
WEAK WARM ADVECTION OVERRUNNING ALOFT FROM THE SOUTHWEST WILL
COMBINE TO BRING PERIODS OF LIGHT PRECIPITATION TONIGHT.

A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR SOUTHWEST NH FOR
SOME VERY LIGHT SNOW OR MIXED PRECIPITATION TONIGHT INTO EARLY
TUESDAY BEFORE CHANGING TO RAIN TOWARD MORNING AS THE BOUNDARY
LAYER TEMPERATURES WARM BACK ABOVE FREEZING. ELSEWHERE ACROSS
CENTRAL AND NORTHERN NH AND WESTERN MAINE ANY LIGHT PRECIPITATION
WILL BE IN THE FORM OF SNOW. TOWARD AND ALONG THE COASTAL AREAS
BOUNDARY LAYER TEMPERATURES WILL BE MARGINAL DUE TO THE ONSHORE
FLOW SO THE PRECIPITATION MAY BE IN THE FORM OF LIGHT RAIN.

USED A BLEND OF THE MODELS FOR POPS AND OVERNIGHT TEMPERATURES.
STAYED WITH RFCQPF VALUES WHICH CONFIRMED ONLY VERY LIGHT AMOUNTS
OF QPF EXPECTED OVERNIGHT.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
OVER SOUTHERN AREAS OF NH AND MAINE, LOW LEVEL TEMPERATURES WILL
SLOWLY WARM ABOVE FREEZING SO ANY AREAS OF LIGHT SNOW OR MIXED
PRECIPITATION SHOULD CONVERT TO RAIN AS THE DAY PROGRESSES. OVER
NORTHERN AREAS, SOME LIGHT SNOW WILL CONTINUE BUT NO ACCUMULATIONS
EXPECTED. OF NOTE: BUFKIT SHOWS NICELY THE VERY SHALLOW INVERSIONS
ACROSS NH AND SOUTHERN MAINE TUESDAY MORNING BUT WITH TIME THEY
GET WIPED OUT DURING THE DAY. ALL AREAS CHANGE TO RAIN TUESDAY NIGHT
AS THE WARM ADVECTION ALOFT FROM THE SOUTH AND SOUTHWEST
CONTINUES WHILE AT THE SAME TIME THE LOW LEVEL ONSHORE FLOW
STRENGTHENS. QPF AMOUNTS WILL REMAIN LIGHT THROUGH TUESDAY NIGHT
AS PER RFCQPF. STAYED CLOSE TO A SUPERBLEND OF MODELS FOR
TEMPERATURES WHICH SEEMED TO APPEAR RATHER REPRESENTATIVE FOR THE
SCENARIO.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
THE WEDNESDAY THROUGH THURSDAY MORNING PERIOD CONTINUES TO LOOK
LIKE A WET ONE. COLD AIR DAMMING WILL LIKELY HOLD TOUGH AT THE
SURFACE ON WEDNESDAY...HOLDING TEMPERATURES IN THE 30S. HAVE
LOWERED HIGHS FOR WEDNESDAY IN STEP WITH MESOSCALE GUIDANCE BUT
THEY MAY NEED TO BE LOWERED A LITTLE MORE MOVING FORWARD. IN A
NUTSHELL...A COLD RAIN IS EXPECTED WEDNESDAY WITH SOME ICING
POSSIBLE IN THE MORNING ACROSS THE NORTHERN MOUNTAINS.

THE WARM FRONT TO OUT SOUTH LOOKS TO PUSH NORTHWARD WEDNESDAY
NIGHT AS A STRONG SHORT WAVE TROUGH APPROACHES FROM THE SOUTHWEST.
THE COLD SURFACE AIR WILL BE TOUGH TO DISLODGE BUT IT LOOKS LIKE
THE WARM FRONT SHOULD MAKE IT INTO SOUTHERN NH WEDNESDAY
NIGHT...THEN CONTINUE TO PUSH NORTH THURSDAY BEFORE COLD
FRONT/OCCLUSION MOVES THROUGH. IT/S POSSIBLE THAT
MANCHESTER/NASHUA NH CORRIDOR COULD BE 55-60 DEGREES LATER
WEDNESDAY NIGHT WHILE AT THE SAME TIME CONCORD IS IN THE 30S.
SHOULD BE A TIGHT GRADIENT.

THE RAINFALL FROM THIS SYSTEM DOES NOT LOOK LIKE IT WILL BE AS
HEAVY AS WAS ADVERTISED BY THE MODELS THE PREVIOUS SEVERAL DAYS.
THIS LIKELY DUE TO THE ABSENCE OF A STRONG SOUTHEASTERLY INFLOW
BELT JUST ABOVE THE SURFACE. INSTEAD...IT/S MAINLY DEEP LAYER
SOUTHERLY/SOUTHWESTERLY FLOW JUST ABOVE THE BOUNDARY LAYER WHICH
SHOULD KEEP STORM TOTAL RAINFALL AMOUNTS IN THE 1-2.25 INCH
RANGE. THIS SHOULD KEEP ANY FLOODING PROBLEMS TO THE URBAN/POOR
DRAINAGE KIND...WITH THE RIVERS REMAINING OK. THE HEAVIEST
RAINFALL IS EXPECTED WEDNESDAY AFTERNOON INTO THURSDAY MORNING. A
RUMBLE OF THUNDER CANNOT BE RULED OUT AS MARGINAL INSTABILITY
DEVELOPS ABOVE THE COOL BOUNDARY LAYER.

WILL ALSO HAVE TO WATCH OUT FOR GUSTY WINDS LATE WEDNESDAY NIGHT
AND THURSDAY MORNING WHERE WE WARM SECTOR...AS THE LOW LEVEL JET
COULD MIX DOWN. THIS WOULD BE ESPECIALLY POSSIBLE IN CONVECTION.

OTHERWISE...FAIR WEATHER RETURNS THURSDAY AFTERNOON AND NIGHT.
ECMWF HAS BEEN ADVERTISING A SNOWSTORM LATE IN THE WEEKEND OVER
THE LAST FEW RUNS...SO WE/LL HAVE TO CONTINUE TO MONITOR THAT
POTENTIAL.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
SHORT TERM...MVFR CONDITIONS EXPECTED TONIGHT THROUGH TUESDAY AND
MAY BECOME IFR AT TIMES IN ANY LIGHT PRECIPITATION. CONDITIONS TO
BECOME WIDESPREAD IFR TUESDAY NIGHT.

LONG TERM...EXTENDED PERIOD OF FLIGHT RESTRICTIONS WEDNESDAY INTO
THURSDAY MORNING. LOOK FOR IFR OR LOWER DURING THIS TIME. EXPECT
IMPROVEMENT TO VFR THURSDAY AFTERNOON...WHICH SHOULD HOLD THRU
SATURDAY.

&&

.MARINE...
SHORT TERM...WINDS WILL REMAIN BELOW SCA CRITERIA TONIGHT THROUGH
TUESDAY NIGHT BUT THE CONTINUED EASTERLY FETCH WILL ALLOW SEAS TO
BUILD ABOVE 5 FT OVER THE OUTER WATERS BEGINNING THIS EVENING AND
CONTINUING THROUGH TUESDAY NIGHT AS PER THE SWAN NAMSWAN GUIDANCE
SUGGESTS.

LONG TERM...MODELS CONTINUE TO BACK OFF THE STRONG WINDS WEDNESDAY
INTO THURSDAY...BUT STILL A PERIOD OF GALES POSSIBLE IN THE S
FLOW LATE WEDNESDAY AND WEDNESDAY NIGHT...BUT MORE LIKELY IN
STRONG W FLOW THURSDAY INTO THURSDAY NIGHT.

&&

.HYDROLOGY...
MODELS CONTINUE TO BACK OFF ON RAINFALL TOTALS FOR THE CHRISTMAS
EVE/EARLY CHRISTMAS MORNING EVENT...BUT ARE STILL AROUND 2 INCHES.
IN ANY CASE...WHILE THE THREAT OF FLOODING IS LOWER...IT STILL
REMAINS A POSSIBILITY WEDNESDAY NIGHT INTO THURSDAY...MAINLY THE
URBAN AND POOR DRAINAGE VARIETY. RIVER FLOODING DOESN/T LOOK LIKE
A BIG THREAT AT THIS TIME SINCE IT LOOKS LIKE TEMPERATURES WON/T
GET UP HIGH ENOUGH IN THE MOUNTAINS TO ALLOW FOR SUBSTANTIAL
MELTING OF SNOW.

&&

.TIDES/COASTAL FLOODING...
ASTRONOMICAL TIDES ARE AT THEIR PEAK FOR THE MONTH. THIS...IN
COMBINATION WITH STRONG SOUTHERLY WINDS LATE WEDNESDAY INTO EARLY
THURSDAY WILL LIKELY ALLOW FOR SOME STORM SURGE. THERE IS SOME
POTENTIAL FOR MINOR COASTAL FLOODING OR SPLASH OVER AND BEACH
EROSION AROUND THE TIMES OF HIGH TIDE WEDNESDAY NIGHT INTO EARLY
THURSDAY AFTERNOON.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...NONE.
NH...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 8 AM EST
     TUESDAY FOR NHZ007-008-011-015.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 AM EST
     WEDNESDAY FOR ANZ150-152-154.

&&

$$

NEAR TERM UPDATE... KIMBLE



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