Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 311331 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 931 AM EDT FRI JUL 31 2015 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD IN FROM THE WEST TODAY...PROVIDING A DAY WITH VERY LITTLE CHANCE OF SHOWERS OR THUNDERSTORMS FOR A CHANGE. IT WILL STILL BE WARM TODAY...BUT NOTICEABLY LESS HUMID THAN PREVIOUS DAYS. A WEAK COLD FRONT WILL CROSS THE AREA SATURDAY...BRINGING ANOTHER THREAT FOR SHOWERS AND THUNDERSTORMS. BEHIND THIS FRONT WE WILL SEE ANOTHER DROP IN TEMPERATURES AND HUMIDITY. WEAK LOW PRESSURE ALOFT...SITUATED OVER QUEBEC...WILL BRING A THREAT FOR SHOWERS OR STORMS MONDAY AND TUESDAY. COOLER AIR MOVES FOR THE MIDDLE TO END OF NEXT WEEK.
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&& .NEAR TERM /UNTIL 8 PM THIS EVENING/...
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925 AM...QUIET DAY ON TAP WITH WESTERLY FLOW ALLOWING EVEN THE COAST TO WARM WELL INTO THE 80S TODAY. ONLY MINOR ADJUSTMENTS FOR THIS ESTF UPDATE TO REFLECT THE 13Z MESONET IN 1ST PERIOD GRIDS. PREV DISC... UPDATE: LOWERED SKY COVER SOMEWHAT AND ALLOWED PATCHY FOG TO CONTINUE THROUGH 12Z BASED ON EARLY MORNING OBSERVATIONS. OTHERWISE...NO OTHER CHANGES NEEDED TO THE GOING FORECAST. PREVIOUS DISCUSSION BELOW... HIGH IMPACT WEATHER POTENTIAL: PATCHY DENSE FOG THROUGH EARLY MORNING...THEN NIL. CURRENT PATTERN: HUDSON BAY LOW HAS BECOME RE-ESTABLISHED AS OF THIS WRITING AS POTENT SHORTWAVE AND ASSOCIATED SURFACE LOW HAVE BECOME VERTICALLY-STACKED AND STATIONARY IN THIS REGION. SOUTH OF THIS FEATURE A COLD FRONT IS DRAPED FROM QUEBEC SOUTHWEST ALONG THE EAST COAST OF THE UNITED STATES. BEHIND THIS FEATURE...EARLY MORNING WATER VAPOR IMAGERY REVEALS SUBSTANTIAL MIDLEVEL DRYING IS TAKING PLACE...WITH LLEVEL DRYING OCCURRING JUST A TAD SLOWER IN A BROAD SUBSIDENT REGIME. LOOKING UPSTREAM...ADDITIONAL LOW-MID LEVEL MOISTURE CAN BE SEEN ASSOCIATED WITH A WEAK SHORTWAVE OVER THE NORTHERN GREAT LAKES PINWHEELING EAST. IN THE POST-FRONTAL AIRMASS...A GENERALLY QUIET DAY IS EXPECTED TODAY...WITH FORECAST CONCERNS CENTERED AROUND THE AFOREMENTIONED UPSTREAM SHORTWAVE AND IT/S IMPLICATIONS FOR CLOUD/SHOWER POTENTIAL THIS AFTERNOON. FOG: A HANDFUL OF LOCATIONS HAVE SEEN VSBYS DROP BELOW A MILE EARLY THIS MORNING. EXPECT VSBYS TO IMPROVE TOWARDS DAYBREAK AS LLEVEL DRY ADVECTION CONTINUES...WITH DEWPOINTS FALLING THROUGH THE 60S AND INTO THE UPPER 50S. CLOUDS/PRECIP: MID LEVEL SHORTWAVE NOW CROSSING FROM ONTARIO INTO WESTERN QUEBEC WILL RACE RAPIDLY EAST-NORTHEAST TODAY WITH AN UPTICK IN QG FORCING FOR ASCENT SPREADING ACROSS NORTHERN NH AND NW MAINE EARLY...BUT THEN CONTINUING EAST WITH OUR REGION IN ANTICYCLONIC DPVA FOR THE AFTERNOON. MODEL SOUNDINGS SHOW A NON-ZERO BUILDUP OF CAPE DURING THE AFTERNOON WITH THE RELATIVELY COOL TEMPERATURES ALOFT... HOWEVER...SUBSTANTIAL CAPPING WILL BE IN PLACE IN THE H6-7 LAYER. THUS...HAVE A HARD TIME SEEING MUCH IF ANY SHRA ACTIVITY DEVELOPING...WITH PERHAPS A SPRINKLE IN THE MOUNTAINS DURING THE AFTERNOON. A MUCH BETTER BET IS SOME INCREASE IN CLOUDINESS BY AFTERNOON. GIVEN THE LOWER DEWPOINTS...IT WILL BE VERY PLEASANT DAY TO END JULY. TEMPERATURES: H8 TEMPS ARE SLOWLY DROPPING IN THE POST-FRONTAL AIRMASS...BUT WILL REMAIN IN THE MID TEENS...SUPPORTING HIGHS WELL INTO THE 80S PARTICULARLY IN THE DOWNSLOPE REGIMES...WITH LESS IMPACTS FROM ANY SEA-BREEZES GIVEN DECENT WESTERLY GRADIENT.
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&& .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SATURDAY/... HIGH IMPACT WEATHER POTENTIAL: THREAT FOR AN ISOLATED SEVERE STORM PARTICULARLY NORTHERN AREAS ON SATURDAY. PATTERN/IMPLICATIONS: CYCLONIC FLOW ALOFT WILL DOMINATE THE PATTERN THROUGHOUT MUCH OF THE COLUMN THROUGH THE SHORT TERM FORECAST PERIOD WITH ONE PRIMARY DISTURBANCE IN THIS CYCLONIC FLOW PUSHING INTO THE AREA ON SATURDAY. FORECAST CHALLENGES PRIMARILY CENTER ON THIS FEATURE...AND IT/S ABILITY TO BRING SHOWERS AND THUNDERSTORMS TO THE REGION. FRIDAY NIGHT: GOOD FLOW OFF THE DECK AND A DRIER EVENING AIRMASS SUGGESTS MUCH LESS FOG POTENTIAL OVERNIGHT...ESPECIALLY AFTER A DAY THAT SHOULD BE FREE FROM RAIN. EXPECT SOME INCREASING MID AND UPPER LEVEL CLOUDINESS FROM UPSTREAM SHORTWAVE LATE...WITH A PARTLY CLOUDY NIGHT ON TAP THROUGHOUT THE REGION. WITH THE DRIER LLEVEL AIRMASS...A COOLER NIGHT LOOKS TO BE IN STORE...WITH LOWS RANGING FROM THE MID 50S NORTH TO THE LOWER 60S COASTAL AREAS AND SOUTHERN NEW HAMPSHIRE. SATURDAY: ROBUST SHORTWAVE ROTATES INTO THE REGION ON SATURDAY WITH ASSOCIATED MID LEVEL HEIGHT FALLS OVERSPREADING THE REGION. THIS QG FORCING WILL BE WORKING WITH MODESTLY INCREASED MOISTURE AS COMPARED TO FRIDAY AS PWATS MOVE BACK TO AROUND ONE INCH /RIGHT AROUND NORMAL FOR THE FIRST DAY OF AUGUST/. LOW AND MID LEVEL LAPSE RATES ARE DECENT...ASSISTED BY MID LEVEL COOL POOL TO THE NORTH OF THE REGION. THUS...FULLY EXPECT SHOWERS TO EXPAND ACROSS THE REGION DURING THE MORNING AS DAYTIME HEATING LEADS TO GROWING LLEVEL INSTABILITY. AS FOR THE THUNDER THREAT...INSTABILITY IS MARGINAL AS SURFACE DEWPOINTS STRUGGLE BACK TO THE 60 DEGREE MARK. IN ADDITION...THERE IS PLENTY OF DRY AIR ALOFT...WHICH...WHEN COMBINED WITH STOUT DEEP SHEAR /0-6KM BULK SHEAR 40-50 KTS/ COULD POTENTIALLY PORTEND A HOSTILE ENVIRONMENT DUE TO ENTRAINMENT. THAT SAID...WITH ENOUGH INSTABILITY...ANY STORMS THAT DEVELOP WOULD HAVE ACCESS TO AMPLE SHEAR AND LOWER FREEZING LEVELS THAN OF LATE...AND THUS A CONDITIONAL SEVERE THREAT. BEST MOISTURE RESIDES FURTHER NORTH...WHICH AGREES WELL WITH SPC/S INTRODUCTION OF A MARGINAL RISK OVER COOS COUNTY NH AND MUCH OF NORTHERN MAINE. WILL INTRODUCE MENTION OF THIS POTENTIAL IN THE MORNING HAZARDOUS WEATHER OUTLOOK. TEMPERATURES WILL LIKELY BE A TAD COOLER THAN ON FRIDAY...PARTICULARLY FURTHER NORTH WHERE THE GREATEST CLOUD COVER AND PRECIPITATION COVERAGE IS EXPECTED. EXPECT TEMPERATURES TO RANGE FROM THE 70S IN THE MOUNTAINS THE LOWER/MIDDLE 80S OVER SOUTHWEST MAINE AND SOUTHERN NEW HAMPSHIRE. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... 500 MB CONTINUES TO TEND BACK TOWARD A MORE +PNA PATTERN...ALTHOUGH SKEWING MORE TOWARDS AN OMEGA BLOCK BY MID TO LATE WEEK WITH TROUGHING FIRMLY ENSCONCED OVER JAMES BAY AND NRN QUEBEC. THIS TREND WILL LEAD TO AN UNSETTLED PATTERN THROUGH THE PERIOD...WITH THE THREAT FOR SHRA/TSRA...HIGHEST IN THE NORTHERN ZONES. HOWEVER...FAST FLOW WILL KEEP THINGS MOVING AND PREVENT ANY SIGNIFICANT RAIN EVENTS. SUNDAY WILL SEE PARTLY SUNNY SKIES AND CHANCE FOR SHRA/TSRA IN THE MTNS. MON AFTERNOON INTO TUE LOOK LIKE THE BEST CHC FOR CWA WIDE SHRA/TSRA AS TROUGHING SAGS S...AND PULLS A COLD FRONT THROUGH NRN NEW ENGLAND. WED /THU WILL KEEP US ON THE COOLER SIDE OF THE FRONT...AS IT STALLS ACROSS THE MID ATLANTIC. SOME MTNS SHOWERS WILL BE POSSIBLE AS UPPR LVL TROUGH AND ASSOCIATED COLD POOL WILL BE JUST TO THE N OF THE CWA. TEMPERATURE WILL SUNDAY WILL BE NEAR NORMAL WITH HIGHS IN THE MID 70S TO MID 80...BUT WILL CLIMB BACK ABOVE NORMAL ON MONDAY WITH HIGHS IN THE 80S...AND APPROACHING 90 AGAIN IN INTERIOR SRN NH. OVERNIGHT LOWS SAT AND SUN NIGHT WILL RANGE FROM THE UPPER 50S TO MID 60S...AND MONDAY NIGHT WILL BE MORE MUGGY WITH LOWS IN THE 60S TO AROUND 70. TEMPS MAY FALL TO SLIGHTLY BELOW NORMAL BY MID TO LATE WEEK. STAYED CLOSER TO THE EURO THOUGH AS THE GFS IS PROBABLY OVERDOING THE COOL AIR INCURSION LATE IN THE WEEK. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... SHORT TERM...VFR CONDITIONS EXPECTED TO DOMINATE THE COMING TAF PERIOD. EXPECT FEW/SCT CU TO DEVELOP DURING THE DAY TODAY...WITH A TRANSITION TO MORE MID LEVEL CLOUDINESS TONIGHT AHEAD OF AN APPROACHING MID LEVEL DISTURBANCE. ONLY THREAT FOR RESTRICTIONS THROUGH DAYBREAK SATURDAY WILL BE IN THE FORM ON FOG TONIGHT AT LEB/HIE. FOG WILL BE LESS WIDESPREAD AND DENSE THAN IT WAS THIS MORNING GIVEN DRIER LLEVEL AIRMASS...MODERATE WINDS ALOFT...AND NO RAIN DURING THE AFTERNOON HOURS. THUS...WILL ONLY CARRY SOME MVFR RESTRICTIONS IN THE HOURS LEADING TO DAYBREAK AT THESE SITES. WINDS: WESTERLY WINDS WILL INCREASE TO 10G18KTS FOR THE DAY TODAY BEFORE DIMINISHING TO 5KTS OR LESS TONIGHT. A MID LEVEL DISTURBANCE WILL BRING SCATTERED SHOWERS AND THUNDERSTORMS ON SATURDAY...PARTICULARLY FOR OUR NORTHERN NH TERMINALS. BRIEF MVFR/IFR RESTRICTIONS POSSIBLE IN ANY OF THESE SHOWERS AND STORMS WITH CONDITIONS REMAINING VFR ELSEWHERE. LONG TERM...MAINLY VFR SAT NIGHT THROUGH TUESDAY... WITH VLY FOG POSSIBLE EACH NIGHT. SCT SHRA/TSRA WILL IMPACT MOST OF THE TERMINALS LATE MON AND MON NIGHT. && .MARINE... SHORT TERM /THROUGH SATURDAY/...WINDS/WAVES LOOK TO REMAIN BELOW SMALL CRAFT LEVELS THROUGH THE SHORT TERM FORECAST PERIOD UNDER GENERALLY LIGHT SOUTHWESTERLY WINDS. LONG TERM....PERSISTENT SW FLOW SUNDAY AND MONDAY COULD BRING SWELL TO 5 FT OR SO BY SUNDAY NIGHT....WHICH WOULD LINGER THROUGH MON NIGHT. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ ES

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