Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 231502 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 1102 AM EDT WED JUL 23 2014 .SYNOPSIS... HIGH PRESSURE CENTERED TO OUR SOUTH WILL KEEP HOT AND HUMID AIR IN THE AREA TODAY. A COLD FRONT WILL APPROACH LATE TODAY AND BRING SHOWERS AND STRONG TO POSSIBLY SEVERE THUNDERSTORMS. THE FRONT MOVES ACROSS THE REGION TONIGHT AND EXITS OFFSHORE THURSDAY MORNING. HIGH PRESSURE BUILDS IN FROM THE WEST FRIDAY AND SATURDAY. WET WEATHER WILL ONCE AGAIN BE POSSIBLE LATE IN THE WEEKEND AND EARLY NEXT WEEK AS THE NEXT UPPER TROUGH DIVES IN. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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11 AM UPDATE...HAVE UPDATED THE FORECAST BASED ON LATEST TRENDS IN OBSERVATIONAL DATA. BAND OF SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE WESTERN ME MOUNTAINS THROUGH 18Z. SOME MAY PRODUCE GUSTY WINDS. THE MAIN SHOW IS EXPECTED TO BE MID TO LATE AFTERNOON AS THE UPSTREAM SHORT WAVE TROUGH MOVES INTO THE AREA AND INDUCES HEIGHT FALLS AND FORCING FOR ASCENT. MAIN THREAT WILL BE DAMAGING WINDS LATE THIS AFTERNOON AND EVENING. PREVIOUS DISCUSSION...EARLY THIS MORNING THE BIGGEST WX CONCERN REVOLVES AROUND FOG. A VERY MOIST AIR MASS IN PLACE...WITH DEW POINTS CURRENTLY IN THE UPPER 60S ACROSS SRN ZONES...IS LEADING TO SOME LIGHT FOG AND HAZE ACROSS MOIST OF THE AREA. IN ADDITION...COASTAL FOG/STRATUS IS DEVELOPING ACROSS DOWNEAST ME. AS FAR AS THE LATTER GOES...GENERALLY SW FLOW SHOULD KEEP THIS TO PENOBSCOT BAY EWD FOR NOW. ATTENTION THEN TURNS TOWARDS THIS AFTERNOON...WHERE WIDESPREAD SHRA AND TSTMS ARE FORECAST TO AFFECT THE AREA. DEEP SWLY FLOW WILL CONTINUE THE HOT AND HUMID CONDITIONS ACROSS THE CWFA AGAIN TODAY. EXPECT HIGHS TO CLIMB AOA 90 FOR SRN NH AND INTERIOR ME. A LARGE RESERVOIR OF MOIST AIR LAYS TO THE SW...UP THRU H9 AND H8...SO DEW POINTS WILL LIKELY NOT MIX OUT MUCH THIS AFTERNOON. OF NOTE ON IR SATELLITE THIS MORNING ARE SOME CLOUDS...WHICH REGIONAL ASOS ARE ESTIMATING TO BE BETWEEN 6 AND 8.5 KFT. IF ACCAS IS INDEED FORMING ALREADY...AIR MASS SHOULD BE PLENTY UNSTABLE ALOFT FOR AFTERNOON CAPE VALUES TO CLIMB WELL ABOVE 1000 J/KG. STRONGEST SHEAR WILL BE TIED TO THE FNT ITSELF...SO EXPECT A STEADY INCREASE THRU THE DAY. DURING THE AFTERNOON A SEASONABLY STRONG WIND FIELD AT H8 AND H7 IS FORECAST TO OVERSPREAD THE AREA. KMWN IS ALREADY SUSTAINED WLY AT 40 KTS...SO THIS IS A GOOD SIGN THAT MODEL FORECASTS ARE ON TRACK. WITH PREDOMINANTLY WLY FLOW THRU THE COLUMN...HODOGRAPHS WILL FAVOR MULTI-CELL CLUSTERS WITH OCNL SUPERCELLS. WITH FLOW ALSO PARALLELING THE FORCING ALONG THE FNT...SHOULD SEE DEVELOPMENT GROW INTO A LINEAR FASHION INTO THE EVENING. THAT PARALLEL FLOW WILL ALSO MEAN TRAINING STORMS...SO HEAVY RNFL REMAINS IN THE FORECAST. STEEP LLVL LAPSE RATES...HIGH PWAT AIR...AND SEASONABLY STRONG MID LVL FLOW SUPPORT AT LEAST ISOLD DAMAGING WIND GUSTS. AMPLE INSTABILITY WILL ALSO SUPPORT SOME HAIL THREAT...WITH PLENTY OF CAPE IN THE -10 TO -30 C LAYER. HOWEVER...HIGH FREEZING LVL WILL PRECLUDE THIS FROM BEING A GREATER THREAT. VEERED WINDS WITHIN THE NEAR SURFACE LAYER WILL ALSO PRECLUDE AN ELEVATED TORNADO THREAT. FINALLY...FREQUENT LIGHTNING WILL BE A THREAT WITH THIS LINE OF STORMS...AS EVIDENCED BY ONGOING CONVECTION INVOF LAKE ERIE. SREF AND SPC SSEO GUIDANCE SUGGEST TWO AREAS MORE FAVORED FOR STRONG STORMS. ONE WOULD BE CENTRAL ME...WHERE GREATER SHEAR SHOULD EXIST. THE OTHER BEING SRN NH...WHERE THE GREATEST INSTABILITY WILL OCCUR. HOWEVER...WILL KEEP SEVERE WORDING GOING FOR THE MAJORITY OF THE CWFA AND NOT GET TOO CUTE ATTM. HI-RES MODEL GUIDANCE IS IN GOOD AGREEMENT THIS MORNING ON TIMING...WITH AN EARLY START TO CONVECTION EXPECTED. WITHIN AN HOUR OR SO OF NOON TSTMS SHOULD BE DEVELOPING ACROSS NRN VT AND ADJACENT SRN CANADA. THIS WILL AFFECT NRN PARTS OF THE CWFA BEFORE 18Z. THE LINE OF STORMS SHOULD PROGRESS TO THE COAST BY 00Z.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... LOSS OF DAYTIME HEATING WILL ALLOW THE SEVERE THREAT TO DIMINISH IN THE LATE EVENING...THOUGH SHEAR WILL CONTINUE TO INCREASE FOR A TIME AND MAY OFFSET A RAPID DECLINE IN TSTMS. OTHERWISE THERE WAS LITTLE CHANGE FROM PREVIOUS FORECAST. NW ATLANTIC RIDGING WILL SLOW THE FROPA NEAR THE COAST. THE RESULT WILL BE LINGERING CLOUDS AND PERHAPS AN ISOLD SHRA INTO THU. EXPECT A GRADUAL CLEARING TREND THROUGHOUT THE DAY HOWEVER...WITH TEMPS SOME 10 TO 15 DEGREES COOLER AND NOTICEABLY DRIER AIR. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... FAIR WX TO START THE LONG TERM FCST PERIOD...THEN A PROLONGED PERIOD OF UNSETTLED WX. THE SLOW MOVING SFC LOW AND FRONTAL SYSTEM CONT TO MOVE OUT TO SEA THURSDAY NGT AS HIGH PRESSURE BUILDS IN FROM THE W. THE HIGH SHIFTS OFFSHORE TO OUR S FRIDAY THRU SATURDAY AS FAIR WX DOMINATED WITH MODIFYING TEMPS AS FLOW BECOMES SW AROUND THE OFFSHORE HIGH ON SATURDAY. LOW PRESSURE MOVING TO THE E NE SATURDAY NGT AND SUNDAY PUSHES A WARM FNT N TOWARD THE FCST AREA AS A STRONG UPPER LVL TROF DRIVES EASTWARD THRU THE GREAT LAKES. THIS WILL BRING WARM HUMID AND UNSTABLE AIR AND SHRA/TSTMS TO THE FCST AREA. THE UPPER LVL SYSTEM STALLS AND CUTOFFS OFF OVER THE GREAT LAKES REGION SUNDAY NGT AND MONDAY THEN SLOWLY SHIFTS TO THE E ON TUESDAY. THIS KEEPS A SOUTHERLY FLOW SFC AND ALOFT CONTINUING WARM...HUMID AND UNSTABLE AIR WITH SHRA/TSTMS ACROSS THE REGION. USED A BLEND OF VARIOUS MODELS...HPC GUIDANCE...PREVIOUS FCST FOR PERSISTENCE AND CLIMATOLOGY FOR THE LONG TERM FCST. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... SHORT TERM /THROUGH WEDNESDAY NIGHT/...IN INCREASINGLY MOIST AIR MASS SOME MVFR VALLEY FOG IS POSSIBLE THIS MORNING BEFORE SUNRISE. GENERALLY SW FLOW SHOULD KEEP ANY COASTAL FOG/STRATUS DOWNEAST...POSSIBLY SNEAKING INTO KRKD FOR A COUPLE HOURS. OUTSIDE OF THE MTNS VFR CONDITIONS WILL DOMINATE MOST OF THE DAY. APPROACHING COLD FNT WILL BRING A ROUND OF SHRA AND TSTMS AROUND NOON IN THE N...AND CLOSER TO 00Z ALONG THE COAST. THESE TSTMS MAY BE STRONG TO SEVERE...WITH ISOLD GUSTS GREATER THAN 50 KTS AND LARGE HAIL POSSIBLE...ESPECIALLY INLAND. LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...IFR CONDITIONS WITH SCT SHRA/TSTMS LIKELY TO DEVELOP SATURDAY NGT AND SUNDAY. && .MARINE... SHORT TERM /THROUGH WEDNESDAY NIGHT/...INCREASING SLY FLOW AHEAD OF COLD FNT WITH BUILDING SEAS AND OCNL GUSTS OUTSIDE THE BAYS REACHING MARGINAL SMALL CRAFT INTO THURSDAY NIGHT. OCNL VSBY RESTRICTIONS IN FOG/HAZE LIKELY WITH A ROUND OF STRONG TO SEVERE THUNDERSTORMS LIKELY ON THE NEAR SHORE WATERS WEDNESDAY EVENING. LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...WINDS AND SEAS BELOW SCA LEVELS THURSDAY NGT THRU SATURDAY MORNING THEN SOUTHERLY FLOW INCREASES POSSIBLY PUSHING WINDS AND SEAS TO SCA LEVELS OVER THE OPEN WATERS LATE SATURDAY THRU SUNDAY. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ150-152- 154. && $$ NEAR TERM UPDATE...MLE

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