Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 021340 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 940 AM EDT SUN AUG 2 2015 .SYNOPSIS... LOOK FOR TODAY TO BE MAINLY DRY AND SUNNY...WITH LOW HUMIDITIES AND HIGHS IN THE 80S...ALTHOUGH A LITTLE COOLER IN THE MOUNTAINS AND AT THE BEACHES. PERSISTENT LOW PRESSURE ALOFT...SITUATED OVER QUEBEC...WILL BRING THE THREAT OF SHOWERS AND THUNDERSTORMS MONDAY INTO TUESDAY. A FEW STORMS COULD BE STRONG MONDAY AFTERNOON AND EVENING. COOLER AIR MOVES IN FOR THE MID TO LATE WEEK...AND IT WILL BE MAINLY DRY...ALTHOUGH SCATTERED SHOWERS WILL BE POSSIBLE IN THE MOUNTAINS WEDNESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... UPDATE... MAINLY CLEAR SKIES CONTINUE DURING THE MID/LATE MORNING HOURS ACROSS NORTHERN NEW ENGLAND. SOME CLOUD COVER WILL SPILL INTO THE NORTHERN MOUNTAIN AREAS WHICH IN CLOSEST PROXIMITY TO MODEST WARM AIR ADVECTION ALOFT. HAVE MADE MINOR ADJUSTMENTS TO DEW POINT AND WIND FORECASTS...OTHERWISE VERY LITTLE IN THE WAY OF CHANGES THIS MORNING. ANY CHANCE FOR SEVERE WEATHER CONDITIONS TOMORROW APPEARS TO BE LIMITED TO VERY LATE IN THE DAY OR MONDAY NIGHT. PREV DISC... 610AM UPDATE: SPED UP CLEARING EARLY THIS MORNING BASED ON RADAR TRENDS WHICH SHOWS ACCAS OVER CENTRAL MAINE QUICKLY PULLING EAST. OTHERWISE...JUST SOME MINOR CHANGES TO BRING NEAR TERM GRIDS IN LINE WITH EARLY MORNING OBSERVATIONS. HIGH IMPACT WEATHER POTENTIAL: NONE. CURRENT PATTERN: EARLY MORNING WATER VAPOR IMAGERY REVEALS CYCLONIC SWIRL THAT CONTINUES TO BE CENTERED OVER SOUTHERN HUDSON BAY...WITH SPOKES OF ENERGY/MOISTURE ROTATING AROUND THIS FEATURE. MORE SIGNIFICANT WAVES HAVE BEEN ARRIVING ABOUT EVERY 48 HOURS...WITH TODAY BEING A LULL PERIOD BETWEEN THESE STRONGER DISTURBANCES. NORTHERN NEW ENGLAND FINDS ITSELF IN A POST-FRONTAL FLOW REGIME EARLY THIS MORNING WITH A GRADUAL DECREASE IN MOISTURE /PWATS FALLING BELOW 1 INCH/ ONGOING. MID LEVEL FORCING IS IN THE PROCESS OF CHANGING SIGN AS WEAK SHORTWAVE OVERHEAD AS OF 06Z CONTINUES TO ROTATE EAST. THIS HAS BEEN RESPONSIBLE FOR AN AREA OF SHRAS...THAT HAS FALLEN APART OVER THE PAST FEW HOURS AS MOISTURE/FORCING WANE. NEXT WEAK SHORTWAVE IS WELL WEST OF THE REGION NEAR GEORGIAN BAY AND WILL ROTATE INTO THE REGION THIS MORNING. THIS FEATURE WILL PROVIDE THE FORECAST CHALLENGE FOR TODAY...DETERMINING WHETHER IT WILL BE ABLE TO POP A FEW SHRAS TODAY DESPITE THE DRIER LLEVEL AIRMASS. THROUGH DAYBREAK: OUTSIDE OF VALLEY FOG...PARTLY TO MOSTLY CLEAR CONDITIONS SHOULD CONTINUE THROUGH DAYBREAK WITH VERY COMFORTABLE SLEEPING CONDITIONS AS TEMPERATURES FALL THROUGH THE 50S NORTH AND INTO THE LOWER 60S OVER SOUTHERN NH/SW MAINE. TODAY: TEMPERATURES ALOFT WILL CONTINUE TO BE COOL...ESPECIALLY TO START THE DAY...WITH A WEAK SHORTWAVE MOVING ALONG THE US/CANADIAN BORDER THIS MORNING BEFORE HEADING EAST OF THE REGION THIS AFTERNOON WITH BUILDING HEIGHTS/TEMPS ALOFT. THUS...THE BEST JUXTAPOSITION OF POTENTIAL INSTABILITY AND FORCING FOR ASCENT WILL OCCUR FROM LATE MORNING THROUGH EARLY AFTERNOON WITH A FEW HUNDRED J/KG OF CAPE REALIZED OVER THE MOUNTAINS. IT IS AT THIS TIME WE/LL CONTINUE A SLIGHT CHANCE OF A SHOWER FOR THIS AREA. OUTSIDE OF THE MOUNTAINS...REALLY DON/T EXPECT ALL THAT MUCH CU DEVELOPMENT SO A MOSTLY SUNNY DAY LOOKS TO BE IN STORE. IT LOOKS LIKE A TERRIFIC EARLY AUGUST DAY WITH T8S IN THE +10-13C RANGE SUGGESTING HIGHS IN THE MID/UPPER 70S NORTH TO MID/UPPER 80S ACROSS SOUTHEAST NH AND SOUTHWEST MAIN AWAY FROM THE COAST. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... HIGH IMPACT WEATHER POTENTIAL: RISK OF SEVERE THUNDERSTORMS MID-LATE AFTERNOON MONDAY. PATTERN/IMPLICATIONS: A SLIGHT MODIFICATION TO THE PATTERN DURING THE SHORT TERM FORECAST PORTENDS A POTENTIALLY MORE ACTIVE PERIOD OF THE FORECAST AS HUDSON BAY LOW SETTLES SOUTH SOME INTO NORTHERN ONTARIO...SHIFTING THE FLOW ALOFT ACROSS NEW ENGLAND TO MORE SOUTHWESTERLY. THIS WILL HELP DRAW A BETTER MOISTURE PLUME NORTH AND EAST INTO THE REGION...WHICH...COMBINED WITH THE IMPLIED INCREASED DYNAMICAL FORCING AS PRIMARY RIBBON OF SHORTWAVE ENERGY NEARS THE REGION WITH SOUTHWARD SINKING MID LEVEL LOW TO THE NORTH AND WEST. THUS...INSTABILITY AND MOISTURE WILL BE IN PLACE WITH AT LEAST SOME SUPPORT FOR ASCENT ALOFT. THE PRIMARY FORECAST CHALLENGE THIS PERIOD LIES IN IDENTIFYING WHEN/WHERE POTENTIAL CONVECTIVE DEVELOPMENT WILL OCCUR /IE WHERE/S THE TRIGGER/ AND HOW ROBUST THIS ACTIVITY WILL BE. TONIGHT: SYNOPTICALLY QUIESCENT TONIGHT AS FLOW ALOFT BACKS AHEAD OF THE NEXT SIGNIFICANT MID LEVEL SHORTWAVE. THIS SHOULD KEEP DEEP MOISTURE WEST OF THE REGION WITH A MOSTLY CLEAR NIGHT IN STORE. INCREASING GRADIENT WILL LIKELY CAUSE MANY LOCATIONS TO REMAIN COUPLED OVERNIGHT /OR RE-COUPLE AFTER GOING CALM FOR A TIME IN THE EVENING/ WITH THIS EFFECT LIKELY NOT ALLOWING FOG TO BE MUCH MORE THAN PATCHY/ISOLATED DESPITE INCREASING MOISTURE ALOFT. WITH INCREASING MOISTURE...AND A RE-COUPLING OF THE BOUNDARY LAYER FLOW DUE TO THE STRENGTHENING GRADIENT...EXPECT A WARMER NIGHT THAN IS ONGOING ATTM...WITH LOWS LIKELY IN THE UPPER 50S TO MID 60S. MONDAY: POTENT MID LEVEL SHORTWAVE ROTATING OUT OF THE BASE OF TROUGH TO OUR WEST WILL RIDE NORTH AND EAST TO THE WEST OF OUR REGION FOR THE DAY ON MONDAY. THIS MID LEVEL FORCING WILL BE COUPLED WITH FORCING ASSOCIATED WITH RIGHT ENTRANCE REGION TO 100+KT 1.5PVU JET CENTERED OVER SOUTHERN QUEBEC. CLOSER TO THE SURFACE...A WAVE OF LOW PRESSURE AHEAD OF THE SHORTWAVE WILL START THE DAY OVER SOUTHWEST QUEBEC AND RIDE NORTH AND EAST DURING THE DAY...DRAGGING A SURFACE COLD FRONT TOWARDS THE REGION LATE IN THE DAY. GIVEN THE WARMING AIRMASS ALOFT...AGREE WITH THE PREVIOUS FORECASTER THAT THIS LOOKS TO BE A LATER IN THE DAY EVENT...WITH THE AIRMASS REMAINING CAPPED IN THE MORNING WELL AHEAD OF THE SURFACE COLD FRONT. THUS...WILL RESTRICT ANYTHING BUT SCHC POPS UNTIL AFTERNOON WITH LIKELIES HOLDING OFF UNTIL THE VERY END OF THIS FORECAST PERIOD LATE MONDAY AFTERNOON. SEVERE THREAT: DEEP SHEAR IS AMPLE /0-6KM VALUES NEAR 40KTS/ WITH MLCAPES REACHING THE 750-1250 J/KG RANGE WITH THE MODEST INFLUX OF LLEVEL MOISTURE. A GOOD BIT OF THE SHEAR OCCURS IN THE 0-3KM LAYER. ORIENTATION OF THE SHEAR VECTOR SW-NE IS FAIRLY CLOSE TO THAT OF THE FORCING BOUNDARY...SO EXPECT CELLS THAT CONGEAL INTO LINEAR SEGMENTS AS THEY TRAVEL FROM WEST TO EAST. SO...CERTAINLY A WIND THREAT...WITH DEEP SHEAR SUFFICIENT FOR UPDRAFT ROTATION AND THUS SOME HAIL CONCERN. WILL CONTINUE INCLUDING ENHANCED WORDING IN THE FORECAST FOR THE AFTERNOON. AM A LITTLE CONCERNED THAT IF WE SEE ACTIVITY DELAY MUCH MORE INTO THE EVENING THAT WANING INSTABILITY MAY LIMIT THE SEVERE THREAT...BUT THIS PERIOD IS CERTAINLY WORTH WATCHING AND AGREE WITH SPC DAY 2 MARGINAL AND SLIGHT RISK AREAS FOR THE CWA. IMPRESSIVE WARM ADVECTION WILL TAKE T8S TOWARDS +17-18C...WHICH SHOULD ALLOW MUCH OF SOUTHERN NH AND SW MAINE AWAY FROM THE COAST TO MAKE A GOOD RUN AT 90F. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... HIGH IMPACT WEATHER: STRONG TO SEVERE STORMS WILL BE POSSIBLE MONDAY EVENING...AND AGAIN ON TUESDAY AFTERNOON. THE MAIN THREAT WILL BE DAMAGING WINDS...ALTHOUGH LARGE HAIL IS ALSO POSSIBLE. 500 MB PATTERN CONTINUES TO SHOW INCURSION OF AIR FROM THE POLAR JET TRAPPED IN CLOSED LOW THAT WILL BE OVER JAMES BAY BY MONDAY NIGHT...AND WILL THEN WORK EWD INTO QUEBEC BY MID WEEK...WHERETHE CLOSED LOW WILL HANG OUT FOR A FEW DAYS AND PROVIDE WITH COOLER AIR...NORMAL TO SLIGHTLY BELOW NORMAL INTO SATURDAY. A PEEK AHEAD INTO EARLY NEXT WEEK SHOWS TROUGH BREAKING DOWN AND WARMER AIR MOVING BACK IN. MONDAY EVENING STARTS OFF STORMY AS WEAK FRONTAL BOUNDARY APPROACHES AND 500 MB WAVE BRINGS INCREASED WINDS AND STRONGER WINDS ALOFT AS THE EVENING PROGRESSES. ANY STORMS MON EVENING PERHAPS WILL INTO MONDAY NIGHT COULD PRODUCE STRONG WINDS AND HAIL AS LINGERING LOW LEVEL MOISTURE MAINTAINS INSTABILITY. THIS FIRST WAVE SHEARS OUT IN THE SW FLOW AND STALLS THE SFC FRONT OVER THE CWA LATE MON NIGHT AND TUE. A SECOND WAVE MOVES THROUGH ON TUESDAY...AND WILL BRING ANOTHER CHANCE FOR SEVERE WEATHER...ALTHOUGH OVERALL COVERAGE OF SHRA/TSRA WILL NOT BE AS WIDESPREAD. THE 500 MB CLOSED LOW WILL SLOWLY FILL AND LIFT NE WED-FRI...AND PROXIMITY OF ASSOC COLD POOL...ESPECIALLY ON WED...WILL BRING A THREAT FOR SHRA IN THE MTNS. THIS WILL ALSO BRING THE COOLER AIR AND LOWER RH WITH TDS MAINLY IN THE 50S WED-FRI. SAT AND THE WEEKEND ARE A BIT OF A QUESTION MARK AS WAVE TRAVELING OUT OF THE NRN PLAINS AND ACROSS THE MIDWEST ON FRIDAY AND TRIES TO DIG A TROUGH ACROSS THE MID ATLANTIC...AND TRIES TO DEVELOP A WEAK COASTAL LOW. RIGHT NOW...MODELS DIFFER ON TIMING AND EXACT TRACK...BUT CONFIDENCE IS ALSO LOW BECAUSE THIS WAVE LOOKS TO BE ASSOCIATED WITH CONVECTIVE SYSTEM AND MODEL SCALING ERRORS MAY BE COMING INTO PLAY...SO ONLY GOING WITH LOW CHC POPS FOR NOW. TEMPERATURE WILL START OUT ABOVE NORMAL MON NIGHT...WITH WARM AND HUMID CONDITIONS AND LOWS IN THE 60S TO NEAR 70 IN A FEW SPOTS. STILL WARM AND HUMID TUE...ALTHOUGH NOT AS WARM AS MONDAY WITH MORE CLOUDS AND WEAKER S-SW FLOW. HIGHS WILL BE IN THE UPPER 70S TO MID 80S. THE COOLER AIR FILTERS IN TUE NIGHT...WITH HIGHS WED- FRI RANGING FORM 70 IN THE COOLER MTN SPOTS TO AROUND 80 IN URBAN SRN NH...WITH OVERNIGHT LOWS IN THE 50S TO AROUND 60. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... SHORT TERM...VFR CONDITIONS EXPECTED TO DOMINATE THE COMING TAF PERIOD...AS A WEAK RIDGE OF HIGH PRESSURE BUILDS INTO THE REGION FOR THE NEXT 24 HOURS. HAVE DEALT WITH A LITTLE FOG AT LEB...BUT THIS SHOULD BE LIFTED AS OF THE BEGINNING OF THE NEW TAF CYCLE. FOR THE DAY TODAY EXPECT SOME CU TO DEVELOP /PARTICULARLY NORTH/...BUT REMAIN FEW-SCT. CLOUDS SHOULD CLEAR THIS EVENING. FOG WILL LIKELY DEVELOP AGAIN LATE TONIGHT HIE/LEB...WITH OTHER LOCATIONS REMAINING VFR. WINDS: WEST-SOUTHWEST WINDS WILL INCREASE TO AROUND 10KTS FOR THE DAY TODAY BEFORE DIMINISHING TO 5KTS OR LESS TONIGHT FROM THE SOUTHWEST. LLWS: WILL HAVE TO WATCH FOR POTENTIAL LLWS ISSUES SUNDAY NIGHT AS 1- 1.5KFT WINDS INCREASE TO 30KTS FROM THE SOUTHWEST. WITH VERY MARGINAL VALUES...WILL NOT INCLUDE IN THIS TAF PACKAGE AS THIS IS IN THE 18-24 HOUR FORECAST PERIOD...BUT SOMETHING FOR LATER SHIFTS TO CONSIDER. A POTENT COLD FRONT WILL MOVE INTO THE REGION ON MONDAY WITH SCATTERED-NUMEROUS SHOWERS AND THUNDERSTORMS DEVELOPING BY MID- LATE AFTERNOON WITH LOCAL RESTRICTIONS LIKELY. SOME OF THESE STORMS MAY BE STRONG TO SEVERE. LONG TERM...SHOWERS AND STORMS MONDAY NIGHT WILL LOWER CONDS TO MVFR OR IFR AT TIMES AND PATCHY FOG CAN BE EXPECTED AFTER MIDNIGHT INTO EARLY TUE MORNING. ALTHOUGH ROUND OF SHRA/TSRA POSSIBLE TUE AFTERNOON...SHOULD SEE MAIN VFR TUE-THU...WITH THE USUAL CAVEAT FOR VLY FOG AT KHIE/KLEB...AND WE ARE GETTING INTO THAT TIME OF YEAR WHERE IT BECOMES MORE FREQUENT AT KCON AS WELL. && .MARINE... SHORT TERM...WINDS WAVES BELOW SCA LEVELS THROUGH EARLY MONDAY. LONG TERM...SOUTHERLY FLOW WILL APPROACH SCA LVLS LATE MON AND MON NIGHT...ALTHOUGH SHOULD STAY BLOW 25 KTS. WAVE HEIGHTS COULD EVENTUALLY BUILD TO AROUND 5 FEET ESPECIALLY OVER EASTERN WATERS MON NIGHT INTO TUE. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$

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