Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 270146 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 946 PM EDT SAT JUL 26 2014 .SYNOPSIS... HIGH PRESSURE CONTINUES TO MOVE EAST TONIGHT... WITH A LOW PRESSURE SYSTEM APPROACHING FROM THE WEST. SHOWERS AND THUNDERSTORMS WILL MOVE INTO THE REGION SUNDAY MORNING WITH MULTIPLE WAVES OF SHOWERS AND THUNDERSTORMS EXPECTED THROUGH TUESDAY WHEN A FRONT FINALLY PUSHES THROUGH THE AREA. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 945 PM...SCALED BACK POPS/SKY JUST A BIT MORE TOWARD DAYBREAK...AS MID-LVL AND UPPR LVL FORCING DONT COME TOGETHER UNTIL 12Z OR AFTER TO OUR WEST. THIS WILL ALLOW FOR A BIT BETTER RAD COOLING IN THE SHELTERED VLYS...AND MINS JUST A TOUCH COOLER THERE. ALSO THINK IT WILL BE CLR ENOUGH TO GET SOME VLY FOG GOING...AND MAYBE WITH SLIGHTLY HIGH TDS IN THE MARINE LYR NEAR THE COAST...MAY SEE SOME FOG THERE AS WELL. 530 PM...BASED ON A PRETTY STRONG CONSENSUS OF THE LATEST MODELS RUNS HAVE BACKED POPS OFF TO JUST SLT CHC IN WRN ZONES TOWARD DAYBREAK. ADJUSTED MINS AND T/TD A BIT AS WELL TO REFLECT EARLIER MINS IN THE N AND W ZONES /CLOSER TO 06Z/ BASED ON THE INCOMING CLOUDS. ALSO MADE SOME UPDATES TO SUNDAY FORECAST. PREVIOUSLY...CUMULUS FIELD HAS EXPANDED A LOT THIS AFTERNOON... BUT HAS NOT PRODUCED MUCH IN THE WAY OF SHOWERS. STILL A SLIGHT CHANCE OF A SHOWER THROUGH THIS EVENING IN THE NORTH WHERE A PASSING SHORTWAVE TROUGH TO THE NORTH OF THE AREA MAY PROVIDE ENOUGH LIFT TO AID A SHOWER OR TWO IN FORMING. MODELS ARE NOW PRETTY CONSISTENT IN DELAYING THE SHORTWAVE TROUGH ALOFT AND SURFACE TROUGH AS THEY BOTH CROSS THE EASTERN GREAT LAKES INTO WESTERN NEW ENGLAND TONIGHT. ALL MAJOR MODELS NOW HOLD OFF ON PRECIPITATION MOVING INTO WESTERN NEW HAMPSHIRE UNTIL AROUND 12Z. THEREFORE RAIN CHANCES TONIGHT ARE LOW ACROSS MOST OF THE AREA AND ONLY INCREASE NEAR SUNRISE. WITH FAIRLY MOIST AIR AROUND... TEMPERATURES ONLY FALL INTO THE 60S TO UPPER 50S TONIGHT. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... 530 PM UPDATE...THE TIMING OF THE WEAK UPPER LVL WAVE AND THE LOW LVL WARM FRONT REMAINS UNCERTAIN FOR SUNDAY...BUT IT LOOKS LIKE THE FRONT SWINGS THRU SW NH IN THE MONRING...AND THEN HEADS NNE ACROSS NH AND INTO THE MTNS OF WRN ME. HAVE ADJUSTED POPS TO COVER THIS AREA WITH THE HIGHEST POPS...AND KEEP POPS CHC/SCT IN THE COASTAL PLAIN OF ME. THE UPPER LVL WAVE DOES LAG A BIT...AND COULD SEE SONME CONVECTION GENERATE IN THE SRN ZONE WARM SECTOR OR ON THE MARINE BOUNDARY DURING THE AFTERNOON...AND THIS WOULD BE THE BEST CHC FOR STRONG STORMS. PREVIOUSLY...SHORTWAVE TROUGH WITH PRONOUNCED LIFT AHEAD OF IT CROSSES THE REGION DURING THE DAY SUNDAY. THIS WILL LIKELY BRING WITH IT WIDESPREAD SHOWERS AND A FEW EMBEDDED THUNDERSTORMS. OVERALL INSTABILITY LOOKS FAIRLY WEAK... BUT WIND SHEAR WOULD BE SUPPORTIVE OF ORGANIZED STORMS IF INSTABILITY WERE HIGHER. INCREASINGLY SOUTHERLY/SOUTHEASTERLY SURFACE WINDS AHEAD OF THE SURFACE TROUGH ALSO ADD SOME DIRECTIONAL SHEAR IN THE LOW LEVELS WHICH WOULD BE MORE FAVORABLE FOR SOME WEAK SPIN UPS BUT THE THREAT IS NOT VERY HIGH. THINK THAT WITH THE STRONG LIFT ALONG AND AHEAD OF THE SHORTWAVE TROUGH... WILL LIKELY SEE A LARGE AREA OF RAIN SHOWERS WHICH WILL TEND TO PREVENT THE SUN FROM ADDING MUCH HEAT TO THE SURFACE TO INCREASE INSTABILITY... AND THE NUMEROUS SHOWERS WILL LIKELY INHIBIT ANY ONE STORM FROM ACCESSING ENOUGH OF THE AVAILABLE INSTABILITY TO BECOME SEVERE. SURFACE TROUGH GETS HUNG UP IN THE MOUNTAINS OF VERMONT AND NEW HAMPSHIRE WHILE UPPER LEVEL SHORTWAVE TROUGH MOVES OFF TO THE EAST. THERE MAY BE A BREAK IN THE RAIN LATER SUNDAY AND SUNDAY NIGHT AS SUBSIDENCE BEHIND THE WAVE ACTS TO PREVENT PRECIPITATION. HOWEVER... IF THE SHOWERS AND CLOUDS MOVE OUT EARLY ENOUGH... THERE COULD BE ENOUGH SUN TO DESTABILIZE THE ATMOSPHERE AGAIN ESPECIALLY OVER NEW HAMPSHIRE SUNDAY AFTERNOON. IF THIS OCCURS... THERE COULD BE ANOTHER AREA OF THUNDERSTORMS DEVELOPING... WITH A BETTER CHANCE OF BECOMING STRONG/SEVERE. CURRENT STORM PREDICTION CENTER OUTLOOK HAS THE SOUTHERN HALF OF NEW HAMPSHIRE IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS ON SUNDAY. UPPER TROUGH BEGINS TO CUT OFF OVER THE EASTERN GREAT LAKES TONIGHT... WITH A MORE DISTINCT SURFACE LOW AND FRONTAL SYSTEM DEVELOPING OVER SOUTHERN NEW ENGLAND... REMINISCENT OF A WINTER-LIKE SYNOPTIC SYSTEM WITH A SHARPENING WARM FRONT OVER THE GULF OF MAINE AND RAIN SPREADING NORTH ABOVE THIS FRONT. RAIN CHANCES INCREASE TOWARD MORNING FROM SOUTH TO NORTH. STILL A CHANCE FOR AN ISOLATED THUNDERSTORM BUT THIS WILL PRIMARILY BE JUST A RAIN EVENT. && .LONG TERM /MONDAY THROUGH SATURDAY/... A PERIOD OF UNSETTLED WEATHER WILL LAST THRU ALMOST THE ENTIRE LONG TERM FORECAST PERIOD... ESPECIALLY ON MONDAY. THE UPPER LEVEL PATTERN SHOWS A CUTOFF LOW OVER EASTERN CANADA WELL TO OUR N ON MONDAY. A STRONG SHORT WAVE TROUGH DRIVES SE THRU THE NORTHERN TIER OF STATES THEN TO THE NE ACROSS NEW ENGLAND AS IT ROTATES AROUND ON THE SOUTHERN PERIPHERY OF THE LARGER CUTOFF LOW. A SURFACE LOW STRENGTHENS AND MOVES NE THRU NEW ENGLAND ON MONDAY GENERATING SHOWERS/THUNDERSTORMS ACROSS THE FORECAST AREA. A TRAILING COLD FRONT S OF THE LOW BECOMES STALLED OVER THE EASTERN SEABOARD DUE TO THE UPPER LEVEL CUTOFF LOW PROVIDING A BROAD SW FLOW ALOFT OVER THE EASTERN U.S. WHICH NEARLY PARALLELS THE NOW STALLING FRONT. WEAK LOW PRESSURE ALSO FORMS ALONG THIS FRONT AND TRACKS N NE ALONG THE BOUNDARY ON TUESDAY. THE UPPER LEVEL TROUGH REMAINS OVER THE EASTERN U.S. WEDNESDAY THRU SATURDAY WITH A SOUTHERLY FLOW ALOFT AND THE FRONT REMAINING STALLED NEAR OR JUST OFF THE COAST WITH WEAK LOW PRESSURE AREAS MOVING N ALONG THE SURFACE BOUNDARY. THIS WILL KEEP THE UNSETTLED WEATHER GOING WITH THE RISK OF SHOWER/THUNDERSTORM ACTIVITY. HOWEVER... WITHOUT A SIGNIFICANT MAIN FOCUS FOR PRECIPITATION WILL ONLY GO WITH NO MORE THAN SLIGHT CHANCE OR CHANCE POPS FOR WEDNESDAY THRU SATURDAY...MAINLY DURING THE DAYLIGHT HOURS WHEN THERE IS A BETTER CHANCE FOR CONVECTION TO DEVELOP WITH SURFACE HEATING. USED A BLEND OF VARIOUS MODELS...HPC GUIDANCE...PREVIOUS FORECAST... PERSISTENCE AND CLIMATOLOGY FOR THE LONG TERM FORECAST. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... SHORT TERM...RAIN WILL SPREAD INTO THE AREA BY SUNDAY MORNING WITH MVFR CONDITIONS EXPECTED (AND IFR POSSIBLE) MAINLY TOWARD THE COAST. THERE IS ALSO A CHANCE FOR LOW CLOUDS AND FOG TO MOVE IN OFF THE GULF OF MAINE TONIGHT... THOUGH THIS WAS NOT SEEN AS LIKELY ENOUGH TO INCLUDE IN THE TAFS. COULD SEE AN EMBEDDED THUNDERSTORM ON SUNDAY AS SHOWERS MOVE ACROSS THE AREA. MAY SEE A BREAK IN THE RAIN UNTIL EARLY MONDAY MORNING... BUT MVFR CONDITIONS WILL REMAIN POSSIBLE THROUGH THE DAY SUNDAY... LIKELY DROPPING TO IFR BY MONDAY MORNING ESPECIALLY NEAR THE COAST. LONG TERM /MONDAY THROUGH THURSDAY/...AN EXTENDED PERIOD OF UNSETTLE WEATHER. BEST CHANCE OF SHOWERS/THUNDERSTORMS AND IFR CONDITIONS ON MONDAY THEN STILL A THREAT OF SHOWERS/THUNDERSTORMS AND MVFR OR POSSIBLY IFR CONDITIONS TUESDAY THRU THURSDAY MAINLY DURING THE DAYTIME HOURS. && .MARINE... SHORT TERM...SOUTHERLY WINDS WILL INCREASE ON SUNDAY AS THE PRESSURE GRADIENT STRENGTHENS BETWEEN HIGH PRESSURE TO THE EAST AND A TROUGH OF LOW PRESSURE TO THE WEST. WINDS WILL GUST TO AROUND 20 KT. WAVE HEIGHTS WILL BE BUILDING... BUT PROBABLY NOT TO THE HEIGHTS ADVERTISED BY THE MODELS. STILL COULD SEE SOME 5 FT WAVES BY SUNDAY AFTERNOON AND A SMALL CRAFT ADVISORY MAY BE NEEDED. LONG TERM /MONDAY THROUGH THURSDAY/...S SW FLOW AHEAD OF AN APPROACHING LOW AND TRAILING COLD FRONT MAY GENERATE SCA WIND GUSTS OVER THE OPEN WATERS MONDAY AND MONDAY NIGHT. PROLONGED ONSHORE FLOW WILL LIKELY PUSH SEAS TO SCA LEVELS AS WELL. THE FRONT STALLS NEAR OR JUST E OF THE WATERS TUESDAY THRU THURSDAY KEEPING WINDS BELOW SCA LEVELS AND ALLOWING THE ROUGH SEAS TO SUBSIDE. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...CEMPA SHORT TERM... LONG TERM... AVIATION... MARINE...

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