Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 221400 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 1000 AM EDT FRI MAY 22 2015 .SYNOPSIS... A COLD FRONT WILL CROSS NEW ENGLAND TODAY...SETTING OFF A FEW SHOWERS ANS THUNDERSTORMS. HIGH PRESSURE THEN BUILDS IN SATURDAY AND SUNDAY. A WARM FRONT WILL APPROACH NEW ENGLAND ON MONDAY...AND CROSS THE AREAS MONDAY NIGHT AND TUESDAY....PROVIDING ANOTHER CHANCE FOR SHOWERS AND STORMS. WARM AND MORE HUMID CONDITIONS ARE EXPECTED MID TO LATE WEEK. && .NEAR TERM /UNTIL 8 PM THIS EVENING/... 950 AM...MINOR ADJUSTMENTS TO 1ST PERIOD GRIDS TO INCORPORATE THE LATEST MESONET. PREV DISC... UPDATE...A FEW MINOR CHANGES TO REFLECT CURRENT OBSERVATIONAL TRENDS. DID INCLUDE SOME SLIGHT CHANCE POP S OF THE MTNS THIS MORNING...AS A BAND OF VERY LIGHT SHOWERS DRIFTS THRU THE AREA ON THE NW SIDE OF WEAK COASTAL LOW PRES. PREVIOUS DISCUSSION...A SEASONABLY STRONG COLD FRONT WILL CROSS THE FORECAST AREA TODAY...USHERING IN SOME VERY CHILLY AIR. PRIOR TO ITS ARRIVAL AREAS E OF THE MTNS SHOULD WARM SUFFICIENTLY TO PROVIDE A LITTLE BIT OF FUEL FOR SHOWERS TO POP UP ALONG THE FRONT. MESOSCALE GUIDANCE IS IN EXCELLENT AGREEMENT THAT A BAND OR CLUSTERS OF SHOWERS WILL DEVELOP QUICKLY ALONG THE MTNS AND RACE EWD TOWARDS THE COAST...ESPECIALLY ACROSS WRN ME. FARTHER S AND W...THE AIR MASS WILL BE QUITE DRY AND SOUNDINGS SUGGEST IT WILL BE DIFFICULT TO SATURATE ENOUGH FOR PCPN. DEEPER MOIST LAYERS WILL RESIDE ACROSS WRN ME...AND WILL SUPPORT LIKELY POP FOR PARTS OF THE MIDCOAST. LOW FREEZING LEVELS WILL ALSO SUPPORT PLENTY OF ICE IN THE CLOUDS...AND CANNOT RULE OUT SOME THUNDER OR SMALL HAIL/GRAUPEL. STEEP LAPSE RATES WILL RESIDE IN THE BOUNDARY LAYER THANKS TO THE DRY AIR MASS...SO SOME OF THESE SHOWERS/TSTMS MAY BE GUSTY. && .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SATURDAY/... TONIGHT THE COLD FRONT WILL BRING H8 TEMPS BETWEEN -4 AND -8 C ACROSS THE FORECAST AREA. THIS IS NEARLY A 3 SIGMA DEPARTURE FROM NORMAL...AND MODEL GUIDANCE HAS EVEN COOLED A LITTLE FROM LAST NIGHT. SOUNDING CLIMATOLOGY SUGGESTS THIS COLD SHOT WILL FALL WELL WITHIN THE LOWEST 10 PERCENT OF OBSERVATIONS FOR THIS TIME OF YEAR. THIS ALL ADDS UP TO A LOW TEMP FORECAST AT LEAST AS COLD AS WED NIGHT...AND PROBABLY A FEW DEGREES COOLER. THAT BEING SAID...MODEL FORECAST SOUNDINGS INDICATE THE BOUNDARY LAYER WILL REMAIN AT LEAST PARTIALLY MIXED AS CAA CONTINUES OVERNIGHT TONIGHT. MAV/MET GUIDANCE CAN OFTEN BE TOO AGGRESSIVE IN DECOUPLING THE BOUNDARY LAYER...THUS FORECASTING MIN TEMPS TOO COLD ESPECIALLY DOWNWIND OF THE MTNS. THE LATEST MAV FOR INSTANCE BRINGS KHIE AND KBML DOWN TO THE UPPER TEENS. TO OFFSET THIS BIAS I HAVE BLENDED IN SOME 2 M TEMPS FROM REGIONAL SCALE MODEL GUIDANCE TO PROVIDE AN ELEMENT CAA MIXED LAYER. OVERALL THIS LOWERED THE PREVIOUS FORECAST A DEGREE OR TWO. THE GRADIENT FLOW MAY BE ENOUGH TO PRECLUDE FROST FOR MOST AREAS...BUT TEMPS REGARDLESS LOOK TO FALL BELOW FREEZING FOR A LARGE PORTION OF THE NRN FORECAST AREA. I EXPANDED THE FREEZE WATCH TO AREAS ON THE BORDERLINE OF 32 DEGREES TO HIGHLIGHT THE POTENTIAL FOR A COLDER FORECAST SOLUTION. THIS IS ESPECIALLY TRUE IF RIDGING CAN MOVE IN FASTER...ALLOWING THE BOUNDARY LAYER TO DECOUPLE. THIS WOULD MOST LIKELY HAPPEN OVER WRN ZONES...SO THE MOST UNCERTAINTY IN THE FORECAST LIES IN THOSE AREAS. IT WILL BE A COOL AND BREEZY DAY SAT IN THE POST-FRONTAL AIR MASS. WILL HAVE TO KEEP AN EYE ON DEW POINT FORECASTS DURING THE DAY. MODEL GUIDANCE IS IN THE LOW TO MID 20S...WHILE BUFKIT SOUNDINGS SHOW THE DEPTH OF MIXED LAYER HINTING AT REALITY BEING CLOSER TO THE LOW TO MID TEENS. THIS WOULD BRING RH VALUES WELL BELOW 25 PERCENT...AND COUPLED WITH WINDS AND RECENT DRYNESS COULD CAUSE SOME FIRE DANGER ISSUES. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... 500MB PATTERN TRANSITIONS TO BLOCKY SUMMER-LIKE PATTERN NEXT WEEK AS RIDGING DEVELOPS OVER THE ERN CONUS AND WRN ATLANTIC AND 500MB JET RETREATS WELL POLEWARD. THIS WILL LEAD TO WARM AND MORE HUMID CONDITIONS MOVING IN...WITH POTENTIAL FOR SCT TSRA AT TIMES AS WE ARE ON THE SRN PERIPHERY OF IMPULSES MOVING BY IN THE STRONGER 500 MB TO OUR N. SUNDAY LOOKS TO BE A SEASONABLY FAIR DAY WITH HIGHS MAINLY IN THE 70S AND A DECENT WEST WIND WILL KEEP THE COOLER MARINE AIR MAINLY OFFSHORE...EXCEPT MAYBE AT THE BEACHES. SUNDAY NIGHT LOOKS CLEAR AND MORE MILD THAN PREVIOUS NIGHTS WITH LOWS IN THE MID 40S N...TO MID 50S S. DECENT WAA BEGINS TO DEVELOP TO OUR WEST ON MONDAY...AND SHOULD CLOUDS OVERSPREAD WRN ZONES AT LEAST DURING THE AFTERNOON...BUT THINKING ANY RAIN/SHOWERS WILL HOLD OFF UNTIL MON NIGHT. THE SW FLOW SHOULD WARM TEMPS INLAND WELL INTO THE MID-UPPER 70S...BUT WILL COOL THE COAST DOWN...ESPECIALLY THE MID COAST. DECENT MID-LVL WAA MOVES THROUGH MON NIGHT INTO TUE MORNING...AND SHOULD PRODUCE A PERIOD OF RAIN OR SOME CONVECTIVE SHOWERS DURING THIS TIMEFRAME. TDS RISE QUICKLY BEHIND THIS WARM FRONT SHOOTING UP INTO THE MID 50S TO LOW 60S. WED-FRI WILL BE WARM AND HUMID...WITH HIGHS GENERALLY RUNNING 80-85 INLAND...AND IN THE 70S ON THE COAST. SOME WAVES WILL INEVITABLY MOVE OVER THE TOP OF THE RIDGE...SO THERE WILL BE THE THREAT OF SHRA/TSRA...BUT TIMING THIS FAR OUT IS A GUESS AT BEST. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... SHORT TERM...VFR EXPECTED TO PREVAIL THRU SAT. COLD FRONT CROSSING THE FORECAST AREA WILL KICK OFF SCATTERED SHOWERS...ESPECIALLY ACROSS INTERIOR WRN ME. SOME OF THESE SHOWERS MAY CONTAIN SOME THUNDER...THOUGH THE PROBABILITY IS LOW. AT ALL TERMINALS NW WIND GUSTS TO 25 KTS ARE POSSIBLE BEHIND THE FRONT. GUSTY WINDS CONTINUE AGAIN SAT. LONG TERM...VFR EXPECTED SAT NIGHT THROUGH MONDAY. FLIGHT RESTRICTIONS ARE EXPECTED MON NIGHT INTO AT LEAST TUE MORNING IS SHRA AND LOW CLOUDS. && .MARINE... SHORT TERM...COLD FRONT WILL CROSS THE WATERS TODAY...WITH STRONG CAA TO FOLLOW BEHIND IT. WINDS WILL GUST ABOVE 25 KTS LATE TONIGHT INTO SAT MORNING. SEAS WILL BUILD TO NEAR 5 FT ON THE OUTER WATERS BEFORE SLOWLY DIMINISHING SAT. LONG TERM...WEST WINDS SUNDAY SHIFT TO SW ON MONDAY...AND WILL GUST TO AROUND 20 KT BOTH DAYS BUT ARE EXPECTED TO BE SUB-SCA LVLS. IN GENERAL WINDS WILL REMAIN BLO SCA THROUGH THE MIDDLE OF NEXT WEEK. SOME SEAS WELL OFFSHORE COULD REACH 5 FT LATE MON AND TUE. && .FIRE WEATHER... DRY AIR MASS WILL MOVE INTO THE AREA TODAY. COOLER TEMPERATURES WILL KEEP RELATIVE HUMIDITY VALUES GENERALLY AROUND 25 PERCENT. LOWER RELATIVE HUMIDITIES MAY BE POSSIBLE NEAR THE COAST...WHERE TEMPERATURES MAY CLIMB INTO THE LOWER 70S. AS COLD FRONT CROSSES THE AREA WINDS WILL BECOME GUSTY FROM THE WEST NORTHWEST. AIR MASS WILL BECOME WINDIER AND DRIER ON SATURDAY. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...FREEZE WATCH FROM 9 PM EDT THIS EVENING THROUGH SATURDAY MORNING FOR MEZ007>009-012-013. NH...FREEZE WATCH FROM 9 PM EDT THIS EVENING THROUGH SATURDAY MORNING FOR NHZ001>009-011. MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 11 AM EDT SATURDAY FOR ANZ150>154. && $$ ES

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