Area Forecast Discussion
Issued by NWS Portland, ME

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KGYX 010955 AAA AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 555 AM EDT SAT AUG 1 2015 .SYNOPSIS... A COLD FRONT WILL CROSS THE AREA TODAY...BRINGING ANOTHER THREAT FOR SHOWERS AND THUNDERSTORMS. TEMPERATURES AND HUMIDITY DROP OFF A LITTLE MORE BEHIND THIS FRONT. SUNDAY SHOULD BE MAINLY DRY AS HIGH PRESSURE BUILDS ACROSS NEW ENGLAND. WEAK LOW PRESSURE ALOFT...SITUATED OVER QUEBEC...WILL BRING ANOTHER ROUND SHOWERS OR STORMS MONDAY AFTERNOON INTO TUESDAY. THE MID TO LATE WEEK PERIOD WILL REMAIN UNSETTLED WITH A FEW ROUNDS OF SHOWERS OR THUNDERSTORMS POSSIBLE. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 553AM UPDATE: WILL DIMINISH EARLY MORNING POPS SOME BASED ON WEAKENING RADAR TREND SEEN WITH INITIAL ECHOES AS THEY ATTEMPT TO WORK THROUGH NORTHERN VERMONT AND OUTRUN ANY MEANINGFUL MUCAPE FROM RECENT RAP ANALYSES. EXPECT THAT WE/LL NEED A LITTLE MORNING SUN AND RESULTANT INSTABILITY TO GET ACTIVITY TO INCREASE IN COVERAGE/INTENSITY. HAVE ALSO LOWERED TEMPS SOME AND INCLUDED SOME FOG THROUGH 12Z BASED ON EARLY MORNING OBSERVATIONS SHOWING LOCALLY DENSE FOG IN THE NORTHERN VALLEYS. HIGH IMPACT WEATHER POTENTIAL: ISOLATED SEVERE THUNDERSTORM POTENTIAL THIS AFTERNOON FOR NORTHERN NH AND NORTHERN MAINE. CURRENT PATTERN: CYCLONIC FLOW THROUGH THE COLUMN HAS FULLY ENVELOPED THE REGION AS OF THIS WRITING WITH EARLY MORNING WATER VAPOR IMAGERY SHOWING VERTICALLY STACKED LOW CENTERED OVER HUDSON BAY. A PARADE OF LOCAL VORTICITY MAXIMA CAN ALSO BE SEEN ROTATING AROUND THIS FEATURE...WITH A BAND OF ENHANCED MOISTURE STRETCHING FROM CENTRAL ONTARIO SOUTH AND EAST ACROSS THE NORTHERN GREAT LAKES...AND JUST STARTING TO SCRAPE NORTHERN NEW ENGLAND. A SHORTWAVE IS COLLOCATED WITH THE LEADING EDGE OF THIS MOISTURE...WITH A SURFACE COLD FRONT SPARKING A FEW SHOWERS /AND EMBEDDED THUNDER/ ACROSS NEW YORK INTO FAR WESTERN NEW ENGLAND. THE INITIAL SHORTWAVE NORTH OF NEW ENGLAND WILL CONTINUE TO RIDE NORTH AND EAST...MAKING WAY FOR ANOTHER WAVE...NOW OVER SOUTHERN ONTARIO...TO PULL EAST AND BE THE FOCUS FOR OUR SENSIBLE WEATHER TODAY. FORECAST CHALLENGES CENTER AROUND PRECIPITATION POTENTIAL WITH THIS FEATURE AS WELL AS THE POTENTIAL FOR ANY STRONG/SEVERE CONVECTION. THROUGH DAYBREAK: SHOWERS SEEN ON REGIONAL 88D MOSAIC CONTINUE TO MAKE A RUN AT NORTHERN NEW HAMPSHIRE. EXPECT THAT WE/LL HAVE TO WAIT FOR THE ACTIVITY IN NEW YORK TO MOVE INTO THE REGION FOR ANY APPRECIABLE PRECIPITATION...WITH PERHAPS A SPRINKLE POSSIBLE OVER COOS COUNTY NH THROUGH DAYBREAK. OTHERWISE...JUST SOME MID LEVEL CLOUDS AND TEMPERATURES RANGING FROM THE LOWER 50S NORTH THROUGH THE LOWER 60 OVER SOUTHERN NH. TODAY: ATTENTION TURNS TO UPSTREAM PV ANOMALY MENTIONED ABOVE. THIS FEATURE LOOKS TO SHARPEN AS IT ROUNDS THE BASE OF THE LONGWAVE TROUGH AND PUSH INTO NEW ENGLAND. THIS FEATURE WILL BE ACCOMPANIED BY 50KT JET AT H5 WITH A 1.5PV 85KT SPEED MAX. MODEST HEIGHT FALLS AND INCREASING DPVA WILL WORK IN TANDEM WITH MODEST MOISTURE INCREASE AND GOOD LAPSE RATES THROUGH H5 /GIVEN COOL POOL ALOFT/ TO ALLOW CONVECTION CURRENTLY OVER NEW YORK TO EXPAND AS IT MOVES THROUGH NORTHERN NEW ENGLAND...BEING JOINED LATER BY ADDITIONAL DEVELOPMENT AHEAD OF THE MID LEVEL TROUGH AXIS/WEAK SURFACE FRONT. THUS...EXPECT SHRAS TO EXPAND IN COVERAGE...WITH EMBEDDED THUNDER BECOMING MORE WIDESPREAD AS INSTABILITY GROWS. DEEP LAYER SHEAR IS IMPRESSIVE...APPROACHING 50KTS IN THE 0-6KM LAYER WITH LONG AND STRAIGHT...WEST-EAST ORIENTED HODOGRAPHS FAVORING MORE CELLULAR STRUCTURE TO CELLS GIVEN ORTHOGONAL ORIENTATION OF THE SHEAR TO THE FORCING FEATURE /FRONT/. INSTABILITY WILL BE SOMEWHAT LIMITED GIVEN ONLY MODEST LLEVEL MOISTURE RECOVERY...BUT 1K J/KG MLCAPE APPEARS POSSIBLE TO ATTAIN OVER FAR NORTHERN NH / NW MAINE CLOSER TO THE BEST MID LEVEL LAPSE RATES. SEVERE WEATHER THREATS: PROFILES HAVE AN INVERTED-V LOOK TO THEM...WHICH...WITH STRONG WINDS ALOFT SUGGEST A DAMAGING WIND THREAT...ALTHOUGH MORE LOCALIZED GIVEN THE MORE CELLULAR NATURE TO THE CONVECTION. WET BULB ZERO HEIGHTS 8-9KFT HIGHLIGHT A HAIL THREAT AS WELL. TOR THREAT VERY LOW GIVEN THE AFOREMENTIONED INVERTED-V PROFILES. OVERALL THREAT WILL BE TIED PRIMARILY TO INSTABILITY...AND THEREFORE WILL BE GREATEST OVER FAR NORTHERN NH AND NW MAINE...WHICH IS RIGHT IN LINE WITH THE NEW SWODY1 FROM SPC. WILL INCLUDE ENHANCED WORDING IN THESE LOCATIONS...WITH LESS THUNDER EMPHASIS FURTHER SOUTH. AND...WHILE THE ACTIVITY FURTHER SOUTH WILL LIKELY NOT BE SEVERE...WILL MENTION GUSTY WINDS HERE AS WELL GIVEN INVERTED-V NATURE TO THE PROFILES. TEMPERATURES: THE INCREASE IN CLOUD COVER WILL SPELL A COOLER DAY...PARTICULARLY OVER NORTHERN AREAS WHERE CONVECTION WILL BE MOST WIDESPREAD. HERE...HIGHS WILL REMAIN IN THE 70S. DOWNSLOPE WESTERLIES WILL PROMOTE HIGHS WELL INTO THE 80S OVER SOUTHEASTERN NH AND EXTREME SW MAINE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... HIGH IMPACT WEATHER POTENTIAL: NONE. PATTERN/IMPLICATIONS: WESTERLY FLOW ALOFT WILL CONTINUE THROUGH THE SHORT TERM FORECAST PERIOD ALONG THE SOUTHERN PERIPHERY OF LONGWAVE TROUGH CENTERED OVER HUDSON BAY. OUR WEATHER WILL BE AT THE MERCY OF SHORTWAVES ROTATING AROUND THIS FEATURE...WITH A RELATIVE LULL LIKELY FOR TONIGHT-SUNDAY BEHIND THE STRONGER WAVE ON SATURDAY AND PRECEDING ANOTHER STRONG WAVE ON MONDAY. DESPITE RELATIVELY LOW HEIGHTS IN THE TROUGH...LLEVEL TEMPERATURES WILL REMAIN NEAR NORMAL PROMOTING SURFACE TEMPERATURES NOT TOO FAR FROM SEASONAL NORMS. TONIGHT: ANY AFTERNOON CONVECTIVE ACTIVITY SHOULD VERY QUICKLY WANE WITH PARTIAL CLEARING...ALTHOUGH WITH DEEPER MOISTURE POOL CLOSER TO THE REGION...DO EXPECT SOME MID LEVEL CLOUDINESS TO HANG AROUND THROUGH THE NIGHT. LOWS LOOK NOT ALL THAT DISSIMILAR TO TONIGHT WITH MODEST COOLING TO THE LLEVEL AIRMASS BEHIND DEPARTING COLD FRONT. GIVEN AT LEAST SOME RAIN ACROSS THE REGION...AND ONLY MODEST COOLING BEHIND THE DEPARTING COLD FRONT...SOME PATCHY VALLEY FOG LOOKS TO BE A GOOD BET. SUNDAY: DEEP CYCLONIC FLOW CONTINUES ACROSS THE REGION AND WHILE THERE WILL BE LITTLE IN THE WAY OF SYNOPTIC FORCING FOR ASCENT...MID LEVEL COLD POOL /T5S NEAR -15C/ AND DECENT MOISTURE ALONG SOUTHERN PERIPHERY OF THE HUDSON BAY VORTEX WILL LIKELY ALLOW SOME AFTERNOON SHOWERS TO SPARK OVER THE MOUNTAINS. ACTIVITY LOOKS WEAKER AND FAR LESS WIDESPREAD THAN ON SATURDAY...SO REALLY NOT A BAD DAY EVEN UP NORTH. OVER SOUTHERN NH/SOUTHWEST MAINE...EXPECT A DIURNAL INCREASE IN CLOUDS...BUT NO PRECIPITATION. TEMPS ALOFT WILL BE ABOUT 2C COOLER THAN ON SATURDAY...BUT WITH LIKELY A BIT MORE SUN...SO HIGH TEMPERATURES LOOK SIMILAR TO THE DAY PREVIOUS...PERHAPS A DEGREE/TWO COOLER FOR SOUTHEAST NH AND SW MAINE. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... HIGH IMPACT WEATHER IN THE EXTENDED WILL BE THREAT OF STRONG TO SEVERE THUNDERSTORMS MONDAY AFTERNOON INTO MONDAY NIGHT. 500MB PATTERN IS TRENDING TOWARD A MODIFIED +PNA PATTERN WITH CLOSED LOW STARTING OUR OVER HUDSON AROUND 60N AND EVENTUALLY SHIFT SWD INTO SRN QUEBEC BY MID WEEK BEFORE SHIFTING THE NE AND WEAKENING AS IT RUNS INTO N ATLANTIC RIDGING. THIS WILL PULL SOME COOLER AIR SWD BY MID TO LATE THIS WEEK...AND WILL KEEP THINGS SOMEWHAT UNSETTLED AS IT PRODUCES CYCLONIC FLOW ALOFT. TOWARD NEXT WEEKEND THE CORE OF THE JET WILL SHIFT BACK TO THE N...AND COULD SEE THINGS START TO WARM AGAIN. SUN NIGHT WILL START WITH BUILDING 500MB RIDGING OVER ME AN THE CANADIAN MARITIMES WHICH WILL ALLOW FLOW TO SHIFT TO THE SW ANDTAP INTO WARM AIR...SFC AND MID-LVL JUST TO OUR SW. AFTER AN MAINLY CLEAR AND SEASONABLY COOL SUN NIGHT MONDAY WILL WARM UP WITH SHRA/TSRA MOVING INTO NW ZONES IN THE AFTERNOON. AS THE 500 MB CLOSED LOW DEEPENS TO THE WEST AND HEIGHTS FALL WILL SEE DECENT INSTABILITY DEVELOP ALONG WITH INCREASED FLOW ALOFT. NAM IS SUGGESTING BORDERLINE EML MOVING IN OVER THE COASTAL PLAIN BY LATE MON AFT INTO MON EVE...WHICH WOULD AID IN THE FORMATION OF SEVER STORMS. AT ANY RATE THUNDERSTORMS...WILL BE A GOOD BET AWAY FROM THE COAST MON AFTERNOON INTO EVENING. ANOTHER WEAK WAVE SWINGS AROUND THE CLOSED LOW ON TUE...SO ANOTHER ROUND OF SHRA AND TSRA POSSIBLE...AS THE COOLER AIR WILL WORK IN BEHIND THIS WAVE TUESDAY. WED THRU FRI WILL BE PARTLY SUNNY...BUT COLD AIR ALOFT COULD PRODUCE SCT SHRA...MAYBE A TSRA EACH DAY...ESPECIALLY IN THE MTNS. TEMPERATURES WILL START OUT ON THE WARM SIDE MONDAY...AS HIGHS WILL SURGE BACK INTO THE 85-90 RANGE IN MANY INLAND SPOTS...BUT SHOULD BE A FEW DEGREES COOLER ON THE COAST...AND ESPECIALLY THE MID-COAST WHERE SW FLOW INCREASES. IT WILL BE A WARM AND MUGGY MON NIGHT...WITH TEMPS AND HUMIDITY ON THE HIGHER SIDE TUE...BUT MORE CLOUDS WILL KEEP TEMPS DOWN A FEW DEGREES. ONCE THE FRONT COMES THRU IN THE AFTERNOON LOOK FOR OVERNIGHT LOWS TO DROP TO AROUND NORMAL...LOW-MID 50S N...TO THE LOW 60S IN SRN NH...WITH HIGHS RUNNING IN THE LOW 70S TO AROUND 80 THRU THE REST OF THE WEEK. && .AVIATION /10Z SATURDAY THROUGH WEDNESDAY/... SHORT TERM /THROUGH 06Z SAT/...GENERALLY VFR WITH SOME INCREASING MID LEVEL CLOUDINESS THROUGH DAYBREAK /ESPECIALLY NORTH/...WITH SOME PATCHY GROUND FOG AT HIE BRINGING OCCASIONAL MVFR VSBYS. FOR THE DAY ON SATURDAY...A MID LEVEL DISTURBANCE MOVING INTO THE REGION WILL RESULT IN INCREASING CLOUDS WITH SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS DEVELOPING ACROSS NORTHERN NEW HAMPSHIRE AND NORTHWESTERN MAINE DURING THE LATE MORNING HOURS AND CONTINUING THROUGH THE AFTERNOON...WITH MORE ISOLATED ACTIVITY FURTHER SOUTH. THERE WILL LIKELY BE A FEW TEMPORARY PERIODS OF MVFR VSBYS/CIGS... WITH IFR VSBYS POSSIBLE IN A FEW DOWNPOURS...BUT THE DAY WILL REMAIN LARGELY VFR. LEB/HIE/AUG/RKD STAND THE BEST CHANCE OF SEEING STORMS...WHICH COULD BE POTENTIALLY STRONG. ANY CONVECTION WILL QUICKLY WANE DURING THE EVENING WITH PARTIAL CLEARING EXPECTED. WINDS: CALM-LIGHT/VARIABLE WINDS THROUGH DAYBREAK WILL BECOME WEST- SOUTHWESTERLY 10G18KTS FOR THE DAY ON SATURDAY BEFORE BECOMING LIGHT WEST-NORTHWESTERLY /5KTS OR LESS/ SATURDAY EVENING. EXPECT VFR CONDITIONS ON SUNDAY...WITH A DIURNAL INCREASE IN CUMULUS COVERAGE...AND PERHAPS A SPRINKLE/SHOWER AT HIE. LONG TERM...MAINLY VFR SUN NIGHT THROUGH TUESDAY...WITH VLY FOG POSSIBLE EACH NIGHT. SCT SHRA/TSRA WILL IMPACT MOST OF THE TERMINALS LATE MON AND MON NIGHT. && .MARINE... SHORT TERM...EXPECT WAVES AND SOUTHERLY WINDS TO REMAIN BELOW SMALL CRAFT LEVELS THROUGH SUNDAY DESPITE INCREASING SOMEWHAT DURING THE DAY TODAY AHEAD OF A COLD FRONT. LONG TERM...PERSISTENT SW FLOW SUNDAY AND MONDAY COULD BRING HIGHER SWELLS TO THE COASTLINE MONDAY AND MONDAY NIGHT....AND A SURGE OF SW WINDS COULD APPROACH SCA LVLS FOR A SHORT PERIOD MON NIGHT. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...ARNOTT SHORT TERM... LONG TERM... AVIATION... MARINE...

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.