Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 222251 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 551 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/... 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 ME, 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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