Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 011025 AAB
AFDGYX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GRAY ME
625 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 /12Z SATURDAY THROUGH WEDNESDAY/...
SHORT TERM /THROUGH SUNDAY/...A COLD FRONT WILL BRING A ROUND OF
SHOWERS AND THUNDERSTORMS TO THE REGION TODAY WITH QUIETER
CONDITIONS WORKING BACK INTO THE REGION TONIGHT.

A BAND OF LIGHT SHOWERS IS WEAKENING AS IT ARRIVES OVER NH AS OF
THIS WRITING.  OUTSIDE OF SOME THICKENING MID CLOUDINESS...EXPECT A
FAIRLY QUIET MORNING.  SHOWERS AND THUNDERSTORMS WILL INCREASE IN
COVERAGE AND INTENSITY THIS AFTERNOON...WITH THE BEST CHANCES FOR
THUNDER AT HIE/LEB/AUG/RCK WHERE A BRIEF PERIOD OF MVFR/IFR VSBYS IS
POSSIBLE IN A HEAVY DOWNPOUR. WILL INCLUDE VCTS MENTION TO COVER THE
PERIOD MOST LIKELY TO SEE THIS SHRA/TSRA ACTIVITY. THERE IS THE
POTENTIAL FOR A FEW STORMS TO BECOME STRONG TO SEVERE. ACTIVITY WILL
QUICKLY WANE THIS EVENING WITH PARTIAL CLEARING OVERNIGHT. GIVEN
SOME DAYTIME RAINFALL AND ONLY MODEST DRYING OVERNIGHT...EXPECT FOG
WILL ONCE AGAIN IMPACT LEB AND HIE AFTER MIDNIGHT WITH IFR/LIFR
VSBYS.

WINDS: LIGHT WINDS WIL BECOME WEST-SOUTHWESTERLY AND INCREASE TO
10G18KTS FOR THE DAY TODAY BEFORE DIMINISHING TO 5KTS OR LESS FROM
THE NORTHWEST THIS EVENING AND OVERNIGHT TONIGHT.

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.

&&

$$

AVIATION...ARNOTT


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