Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 291420 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 1020 AM EDT SAT AUG 29 2015 .SYNOPSIS... HIGH PRESSURE WILL GENERALLY REMAIN IN CONTROL OF THE WEATHER ACROSS THE REGION THROUGH THIS WEEKEND AND AT LEAST THE FIRST HALF OF NEXT WEEK...WITH AN EXTENDED PERIOD OF QUIET WEATHER EXPECTED. A SERIES OF WEAK COLD FRONTS WILL TRY TO PUSH THROUGH THE REGION SUNDAY AND MONDAY WITH NO MORE THAN AN ISOLATED SHOWER EXPECTED. CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE TOWARDS THE END OF THE WEEK. TEMPERATURES WILL REMAIN WELL ABOVE SEASONAL NORMS THROUGH THE PERIOD...WITH GRADUALLY INCREASING HUMIDITY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1020 AM UPDATE...LITTLE CHANGE TO THE GOING FORECAST. JUST A FEW MINOR ADJUSTMENTS TO TEMPERATURES AND SKY COVER BASED ON LATEST TRENDS IN OBSERVATIONAL DATA. OVERALL...A FINE DAY WEATHERWISE IS EXPECTED. 0545 UPDATE...UPDATED GRIDS TO ACCOUNT FOR CURRENT CONDITIONS. NO SIGNIFICANT CHANGES. ANOTHER NICE LATE SUMMER DAY TODAY AFTER ANY VALLEY FOG BURNS OFF. WITH THE RIDGE OF HIGH PRESSURE SLIDING OFF THE COAST TODAY, WARM ADVECTION ALOFT ON THE BACK SIDE OF THE RIDGE WILL PRODUCE CIRRUS...BUT OTHERWISE...EXPECT MOSTLY SUNNY SKIES ACROSS THE REGION. TEMPERATURES THIS AFTERNOON WILL REACH THE 70S TO LOWER 80S. A SEA BREEZE WILL LIMIT TEMPS ALONG THE COAST TO THE 70S. OTHER AREAS WILL HAVE LIGHT WINDS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... HIGH CLOUDS WILL CONTINUE TO INCREASE ACROSS THE REGION OVERNIGHT AS A WEAK FRONTAL BOUNDARY APPROACHES THE REGION. SKIES WILL BECOME CLOUDY OVERNIGHT WITH ONLY A SLIGHT CHANCE OF ANY SHOWERS AS THE FRONTAL BOUNDARY MOVES THROUGH THE REGION EARLY SUNDAY. BEHIND THE FRONT...SKIES SHOULD BECOME PARTLY SUNNY DURING THE DAY SUNDAY. CLOUDS SUNDAY MORNING SHOULD HELP TO LIMIT VALLEY FOG. HIGH TEMPS SUNDAY AFTERNOON WILL BE IN THE 70S AND 80S WITH COOLEST TEMPS IN THE NORTH AND MOUNTAINS...AND ALONG THE COAST. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... WARM AND QUIET... HIGH IMPACT WEATHER POTENTIAL: NIL. PATTERN SUMMARY: AN EARLY MORNING LOOK AT THE PATTERN ACROSS NOAM REVEALS A LONGWAVE TROUGH OVER THE EASTERN PACIFIC WITH A WEAKER DOWNSTREAM LONGWAVE TROUGH CENTERED ACROSS EASTERN CANADA. A PATTERN REALIGNMENT IS EXPECTED DURING THE LONG TERM FORECAST PERIOD AS JET ENERGY CURRENTLY OVER THE BERING SEA DROPS INTO THE WESTERN TROUGH HELPING TO GIVE IT A KICK EASTWARD WHILE THE DOWNSTREAM TROUGH OVER CANADA FOLDS BENEATH RIDGING IN THE VICINITY OF GREENLAND...HELPING TO REINFORCE THE -NAO AND ASSOCIATED BLOCKING IN THIS REGION. DETERMINISTIC AND ENSEMBLE GUIDANCES IS IN GOOD AGREEMENT THAT THE RESULT ACROSS NOAM WILL BE THE DEVELOPMENT OF A STABLE TROUGH/RIDGE/TROUGH PATTERN WITH THIS PATTERN AMPLIFYING AS THE WEEK CONTINUES. INTERESTINGLY, THIS PLACES NEW ENGLAND INITIALLY UNDER BUILDING HEIGHTS AS THE EASTERN CANADIAN TROUGH PUSHES EAST...BUT WITH HEIGHTS LATER FALLING AS THE NORTHWESTERN ATLANTIC TROUGH AMPLIFIES. THIS PATTERN SPELLS LITTLE IN THE WAY OF NOTABLE WEATHER THROUGH THE WEEK WITH DEEP-LAYER RIDGING IN CONTROL FOR NEARLY ALL OF THE PERIOD. FORECAST CHALLENGES WILL CENTER AROUND ANY MINOR PRECIPITATION CHANCES ASSOCIATED WITH POTENTIAL BACK DOOR COLD FRONT MONDAY-MONDAY NIGHT AND POTENTIAL RIDGE-ROLLER ACTIVITY LATE IN THE WEEK. A FURTHER CONCERN IS JUST HOW WARM WE WILL GET AS HEAT DOME BUILDS OVER THE UPPER MIDWEST AND CENTRAL CANADA AND GRADUALLY PUSHES EAST. GUIDANCE TRENDS/CONFIDENCE: EARLY MORNING DETERMINISTIC AND ENSEMBLE GUIDANCE IS IN GOOD AGREEMENT ON THE LONGWAVE FEATURES THROUGH THE LONG TERM FORECAST PERIOD...WITH AGREEMENT STRONGEST ON DETAILS OF THE WESTERN TROUGH. THERE CONTINUES TO BE DISCREPANCIES IN THE STRENGTH AND PLACEMENT OF AMPLIFYING TROUGH OVER THE NORTHWEST ATLANTIC WITH THE GFS STILL MORE ROBUST THAN THE ECMWF...ESPECIALLY DURING THE SECOND HALF OF THE WEEK. THIS REDUCES CONFIDENCE PRIMARILY IN THE DEGREE OF LATE WEEK HEAT WE WILL ACHIEVE. INTERESTINGLY...THE GUIDANCE CONSENSUS IS FAR MORE BULLISH WITH BACKDOOR COLD FRONT MONDAY NIGHT-TUESDAY...WITH THE CONSENSUS CLOSE TO THE GFS SOLUTION FROM 24 HOURS AGO. THE DETAILS... A COLD FRONT DROPS INTO THE REGION ON MONDAY AS STRONG SHORTWAVE BRUSHES THE REGION AS IT AMPLIFIES OVER THE CANADIAN MARITIMES. MOISTURE IS NOT TERRIBLY IMPRESSIVE WITH THIS FEATURE...WITH MID/UPPER LEVEL FORCING WELL TO OUR EAST. GIVEN THAT WE/LL ALREADY BE IN A NORTHWESTERLY FLOW REGIME AFTER SUNDAY/S WEAK FRONTAL PASSAGE...SEE LITTLE THREAT OF ANY PRECIPITATION WITH THIS FEATURE OVER SOUTHERN AREAS...AND WILL RESTRICT SCHC/LOW CHANCE POP MENTION TO THE MOUNTAINS AND FAR NORTHERN AREAS. HIGH PRESSURE BUILDS INTO THE REGION BEHIND THE DEPARTING COLD FRONT MONDAY NIGHT AND TUESDAY BRINGING WITH IT A DRIER AIRMASS WHICH SUGGESTS A TERRIFIC DAY WITH PLENTY OF SUNSHINE. QUIET WEATHER LOOKS TO PERSIST THROUGH WEDNESDAY AS HEIGHTS ALOFT SURGE SIGNIFICANTLY. AS FLOW TRAJECTORIES ALOFT BECOME MORE WESTERLY...WE/LL SEE AN INCREASE IN LLEVEL HUMIDITY WITH MORE CLOUDS THAN TUESDAY...BUT IT SHOULD REMAIN DRY. CONFIDENCE DECREASES AS WE REACH THE END OF THE FORECAST PERIOD THURSDAY-FRIDAY...DEPENDING ON THE DEGREE OF DOWNSTREAM TROUGH AMPLIFICATION. REGARDLESS OF MODEL SOLUTION...LITTLE IN THE WAY OF ORGANIZED DYNAMICAL FORCING IS APPARENT WITH SPRAWLING RIDGE EXTENDING WELL NORTH INTO CANADA. HOWEVER...PRECIPITATION CHANCES LIKELY RETURN BACK TO NEAR OR A LITTLE ABOVE CLIMATOLOGY /20 PERCENT/ WITH SOME POTENTIAL FOR EITHER CONVECTIVE ACTIVITY RIDING OVER THE CREST OF THE RIDGE TO THE WEST...OR SOME THREAT OF ADDITIONAL BACK DOOR COLD FRONT ACTIVITY /VERY AGGRESSIVE IN THE NEW 29.00Z GFS/. TEMPERATURES: VERY SUMMERY PATTERN IN PLACE THROUGH THE LONG TERM FORECAST PERIOD AS HEIGHTS BUILD TO +1-2SIGMA WITH T8S FOLLOWING SUIT. BACKDOOR COLD FRONT INTRODUCES SOME UNCERTAINTY FOR TUESDAY...WITH GFS/ECMWF ENSEMBLE MOS PRODUCTS REVEALING 10-15 DEGREE SPREADS FROM THE BOTTOM TO TOP MEMBERS. GUIDANCE CONSENSUS IS LIKELY THE BEST WAY TO GO HERE...GIVING A NOD TO THE RECENT TRENDS TO THE MORE BULLISH GFS. BEYOND THIS...VERY WARM CONDITIONS SHOULD RETURN...BUT WILL TEMPER HIGHS IN THIS FORECAST PACKAGE GIVEN UNCERTAINTY IN THE DEGREE OF DOWNSTREAM TROUGH AMPLIFICATION /GFS MUCH MORE ROBUST HERE THAN THE ECMWF/...WHICH HAS THE POTENTIAL TO BRING HIGHS BACK CLOSER TO NORMAL. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... SHORT TERM...MAINLY VFR CONDITIONS EXPECTED...EXCEPT IFR CONDITIONS POSSIBLE EARLY THIS MORNING AND AGAIN SUNDAY MORNING. LONG TERM...WIDESPREAD MVFR/IFR RESTRICTIONS ARE NOT EXPECTED THROUGH THE LONG TERM FORECAST PERIOD. OUTSIDE OF POTENTIAL BACKDOOR COLD FRONT ON MONDAY NIGHT...LIGHT WIND REGIME WITH GRADUALLY BUILDING HUMIDITY INDICATES DAILY MORNING FOG CONCERNS AT HIE/LEB. && .MARINE... SHORT TERM...WINDS AND SEAS EXPECTED TO REMAIN BELOW SCA CRITERIA. PATCHY FOG MAY LIMIT VISIBILITIES TONIGHT. LONG TERM...WINDS AND WAVES LOOK TO REMAIN BELOW SMALL CRAFT LEVELS THROUGH THE LONG TERM FORECAST PERIOD AS HIGH PRESSURE DOMINATES CONDITIONS ALONG THE EAST COAST. STRONGEST WINDS THROUGH THE PERIOD /15-20KTS/ APPEAR TO BE MONDAY/MONDAY NIGHT ASSOCIATED WITH A BACKDOOR COLD FRONTAL PASSAGE. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$

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