Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 251057 AAA AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 657 AM EDT TUE AUG 25 2015 .SYNOPSIS... HUMID AND UNSETTLED CONDITIONS WILL CONTINUE THROUGH MID WEEK. ON A COLD FRONT WILL SLOWLY APPROACH FROM THE WEST TODAY...PROVIDING A ROUND OF SHOWERS AND THUNDERSTORMS TODAY. THE FRONT STALLS OVER THE AREA TONIGHT INTO WEDNESDAY AS WEAK LOW PRESSURE TRACKS NORTHEAST ALONG IT...WITH MORE SHOWERS AND THUNDERSTORMS EXPECTED. THE FRONT FINALLY EXITS THE REGION LATE WEDNESDAY. ANOTHER ROUND OF SHOWERS IS POSSIBLE...MAINLY IN THE MOUNTAINS...ON THURSDAY AS A SECOND COLD FRONT PUSHES THROUGH. DIRER AND RELATIVELY COOLER AIR WILL MOVE IN AT THE END OF THE WEEK AS HIGH PRESSURE BUILDS IN. AS THE HIGHS SETTLES SOUTH AND EAST OF US OVER THE WEEKEND...LOOK FOR MAINLY FAIR WEATHER AND A WARMING TREND. && .NEAR TERM /THROUGH TONIGHT/...
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UPDATE...A FEW TWEAKS TO THE CURRENT FORECAST TO ACCOUNT FOR LATEST RADAR TRENDS. A DISORGANIZED CLUSTER OF TSTMS OVER WRN MA IS MOVING SLOWLY NEWD THIS MORNING. THIS AREA OF CONVECTION SHOULD AFFECT SWRN NH IN THE NEXT COUPLE OF HOURS BEFORE DISSIPATING. HAVE INCREASED POP TO LIKELY FOR THIS AREA. PREVIOUS DISCUSSION...THRU MORNING WE WILL SEE PLENTY OF FOG AND LOW CLOUDS. AND LIKE YESTERDAY...AS WE HEAT UP THESE CLOUDS WILL GRADUALLY LIFT AND SCATTER OUT. IT IS THESE BREAKS IN THE OVERCAST THAT WILL BE SO IMPORTANT TO THE AFTERNOON FORECAST. BOUNDARY LAYER IS CHARACTERIZED BY A WARM AND VERY MOIST AIR MASS ENTRENCHED ACROSS THE AREA. DESPITE POOR LAPSE RATES ALOFT...EVEN MARGINAL HEATING OF THIS LOW LEVEL AIR MASS WILL SUPPORT DESTABILIZATION. THIS HEATING IS MOST LIKELY TO OCCUR IN POCKETS...AS ONGOING CONVECTION FROM THIS MORNING SPREADS EXTRA CLOUD COVER INTO THE AREA...AND WHILE MORNING FOG SLOWLY LIFTS. AT THIS HOUR CONVECTION ALLOWING MODELS STRONGLY FAVOR BEST AIR MASS RECOVERY TO OCCUR OVER SRN NH. AS THE DAY WEARS ON...A MODEST...CYCLONICALLY CURVED H5 JET WILL WORK TOWARDS NEW ENGLAND. SHEAR WILL CONSEQUENTLY INCREASE THRU THE DAY...AND PROVIDE MORE THAN ENOUGH TURNING IN THE ATMOSPHERE FOR STORM ORGANIZATION. AS UPPER LOW IS ONLY SLOWLY INCHING EWD...THERE WILL BE A BIT OF A LACK OF FORCING OVERALL...SO STORM COVERAGE SHOULDN/T BE WIDESPREAD. PRIMARY THREAT WILL BE GUSTY WINDS...BOTH VIA WET MICROBURSTS OR AS DEEP SWLY UNIDIRECTIONAL WINDS ALOFT INCREASE LATER IN THE AFTERNOON. GIVEN TENDENCY FOR CONVECTION ALLOWING MODELS TO LEAN TOWARDS SOMEWHAT DISCRETE STORM STRUCTURES LARGE HAIL CANNOT BE RULED OUT...IN ADDITION TO AN ISOLATED TORNADO. THE LATTER IS MITIGATED MAINLY BY THE WEAKER FLOW IN THE LOWEST 3 KM OF THE ATMOSPHERE. THAT BEING SAID...A WARM FRONTAL FEATURE WILL BE DRAPED ACROSS NH DURING THE AFTERNOON...SO NEAR AND JUST N OF THIS BOUNDARY WILL BE A LOCALLY HIGHER TORNADO THREAT. IN ADDITION TO THOSE STORM THREATS...DEEP SWLY FLOW WILL TEND TOWARDS TRAINING OF INDIVIDUAL CELLS. THIS WILL COMPOUND AN ALREADY MOIST ENVIRONMENT FAVORABLE FOR HEAVY RNFL...SO FLASH FLOODING WILL BE JUST AS LIKELY THIS AFTERNOON.
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&& .SHORT TERM /WEDNESDAY/... COLD FRONT WILL VERY SLOWLY PROGRESS ACROSS THE AREA OVERNIGHT...SO THE THREAT FOR SHOWERS WILL LINGER ACROSS ERN ZONES WELL INTO THE NIGHT. AGAIN GIVEN THE DEEP SWLY FLOW...THE TENDENCY FOR TRAINING WILL CONTINUE AS WELL...AND HEAVY RNFL IS A POSSIBILITY. ONSHORE FLOW WILL CONTINUE...ESPECIALLY ACROSS ME...AND ALLOW FOG/STRATUS TO REDEVELOP TONIGHT AHEAD OF THE FRONT. THE EXTENT OF LOW CLOUDS WILL DEPEND ON HOW FAR E THE FRONT CAN ADVANCE...BUT GENERAL MODEL CONSENSUS IS THAT ERN ZONES REMAIN DOWNSTREAM OF THE BOUNDARY UNTIL WED. AGAIN WILL KEEP HIGHEST POP IN THE ERN ZONES TO ACCOUNT FOR SLOW FRONTAL MOVEMENT. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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HIGH IMPACT WEATHER: NONE. OVERALL 500MB PATTERN TREND IS TO TREND AWAY FROM MORE AMPLIFIED BLOCKY PATTERN AT THE START OF THE FORECAST PERIOD...TO LARGE SCALE RIDGING BUILDING OVER THE ERN 2/3 OF THE CONUS AND TROUGHING NEAR THE WEST COAST BY EARLY NEXT WEEK. INITIALLY...LARGE CLOSED LOW SOUTH OF JAMES BAY WILL LIFT NE THU AND FRI...WITH ZONAL FLOW TAKING OVER THE WEEKEND...AND FINALLY THAT RIDGE STARTS TO BUILD IN EARLY NEXT WEEK. 850MB TEMPS WILL INCREASE FROM 8-10C AT THE END OF WEEK TO 12-15C MON AND TUE. SENSIBLE WEATHER WILL START WITH SHRA/TSRA SHIFTING EWD AND OUT OF THE CWA WED EVENING...WITH A SLIGHT DROP IN RH/TEMPS WED NIGHT. ANOTHER WAVE WILL ROTATE AROUND THE LOW ALOFT ON THU AND PUSH ANOTHER COLD FRONT THRU ON THU...AND COULD SET OFF A SCT SHRA...AND EVEN A TSRA...WHICH WILL PROBABLY BE LIMITED TO THE NRN ZONES...WHICH WILL BE CLOSER TO THE BEST DYNAMICS...WHILE THE COASTAL SHOULD STAY DRY IN DOWNSLOPE. BEYOND THAT LOOK FOR MAINLY DRY AND GENERALLY FAIR WEATHER FRI-MON...ALTHOUGH A WEAK 500MB WAVE PASSING N OF THE CWA COULD PRODUCE A FEW SHRA IN THE MTNS SAT NIGHT OR SUN. TEMPS WILL START NEAR NORMAL THU AND FRI...AT LEAST FOR MAXES...OVERNIGHT LOWS MAY CONTINUE TO RUN SLIGHTLY ABV NORMAL WED NIGHT INTO THU NIGHT BEFORE THE DRIEST AIR MOVES IN FRI...WITH HIGHS IN THE 70S TO AROUND 80...AND LOWS IN THE 50S TO AROUND 60. THE COOLEST NIGHT WILL PROBABLY BE FRI NIGHT INTO SAT MORNING WITH LOWS DROPPING INTO THE 50S EVERYWHERE...AND MAYBE A FEW UPPER 40S IN THE MTN VLYS. TEMPS WILL GRADUALLY WARM OVER THE WEEKEND AS WARMER AIR MOVES IN ALOFT ON THE ZONAL FLOW...WITH HIGHS REACHING INTO THE 80S IN MOST SPOTS BY MONDAY.
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&& .AVIATION /12Z TUESDAY THROUGH SATURDAY/... SHORT TERM...AREAS OF LIFR IN FOG AND DRIZZLE WILL PERSIST THRU MORNING ACROSS EXTREME COASTAL NH AND MUCH OF WRN ME. EXPECT VERY GRADUAL IMPROVEMENT TODAY...BUT WITH COLD FRONT EDGING CLOSER THERE WILL BE MORE AREAS OF MVFR THAN YESTERDAY AFTERNOON. SHRA AND TSRA WILL ALSO CONTINUE TO FORM ALONG THE FRONT AND BECOME MORE WIDESPREAD WITH DAYTIME HEATING. SHRA ARE LOOKING MORE LIKELY AT NH TERMINALS THAN WRN ME AT THIS TIME...THOUGH EVENTUALLY RNFL WILL WORK THRU BOTH STATES. TIMING AND LOCATION OF TSRA REMAINS SOMEWHAT UNCERTAIN AT THIS HOUR...SO WILL START WITH A PROB30 FOR NOW. FOG/STRATUS WILL MOVE BACK INTO THE COAST AFTER 00Z TONIGHT...ESPECIALLY ACROSS WRN ME. LONG TERM...SOME AREAS OF FOG AND LOW CLOUDS WILL BE POSSIBLE WED NIGHT...BUT PROBABLY NOT AS PREVALENT NOR AS IMPACTFUL AS THE LAST FEW NIGHTS. AFTER THAT...THU-SAT WILL FEATURE MAINLY VFR...WITH THE EXCEPTION OF VLY FOG EACH NIGHT. && .MARINE... SHORT TERM...WINDS AND SEAS EXPECTED TO REMAIN BELOW SCA THRESHOLDS THRU WED. WIDESPREAD FOG AND LOW CLOUDS WILL PERSIST THRU MORNING TODAY...SCATTERING OUT THIS AFTERNOON. IT SHOULD RETURN AGAIN TONIGHT...MAINLY CONFINED TO COASTAL ME WATERS. LONG TERM...MAY SEE SOME LINGERING LIGHT FOG WED NIGHT...BUT OTHERWISE SEAS/WINDS WILL BE COMFORTABLY BLO SCA LVLS THU-SAT. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ NEAR TERM...LEGRO SHORT TERM...LEGRO LONG TERM...CEMPA AVIATION...CEMPA/LEGRO MARINE...CEMPA/LEGRO

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