Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 251917
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
317 PM EDT TUE AUG 25 2015

.SYNOPSIS...
A SLOW MOVING FRONT WILL GRADUALLY PUSH EAST ACROSS THE AREA
THROUGH TONIGHT BRINGING SHOWERS AND THUNDERSTORMS WITH
LOCALLY HEAVY RAINFALL POSSIBLE. ADDITIONAL SHOWERS AND
THUNDERSTORMS ARE POSSIBLE ON WEDNESDAY BEFORE DRIER AIR MOVES
INTO THE REGION THROUGH THE END THE WEEK. SOMEWHAT MORE HUMID
WEATHER WILL RETURN THIS WEEKEND AHEAD OF A COLD FRONT THAT MAY
BRING SOME SHOWERS AND THUNDERSTORMS TO THE REGION BY SUNDAY.

&&

.NEAR TERM /TONIGHT/...
INITIAL AREA OF CONVECTION AND SPILLOVER SHOWERS TO THE NORTH OF
IT HAS MOVED EAST INTO MAINE. THIS WILL CONTINUE TO WEAKEN AS IT
MOVES EAST. ADDITIONAL DEVELOPMENT NOW APPEARS LIKELY OVER NEW
HAMPSHIRE... VERMONT... AND NEW YORK... WITH THIS ACTIVITY
TRACKING EASTWARD INTO NEW HAMPSHIRE WITH TIME. WIND SHEAR
REMAINS FAVORABLE FOR STORM ORGANIZATION INCLUDING SUPERCELLS. SO
STORMS WHICH ARE ABLE TO TAKE THE BEST ADVANTAGE OF THE AVAILABLE
INSTABILITY MAY TAKE ON SUPERCELL STRUCTURE WITH THE THREAT FOR
DAMAGING WINDS... HAIL... AND POTENTIALLY A TORNADO. THIS THREAT
SHOULD DIMINISH THIS EVENING AND FURTHER TOWARD THE EAST.

ACROSS MAINE AND COASTAL NEW HAMPSHIRE... A FRESH BATCH OF MARINE
CLOUDS AND EMBEDDED FOG/DRIZZLE HAS ALREADY MOVED ONSHORE. THIS
WILL LIKELY PERSIST THROUGH THE NIGHT AND SHOULD SERVE TO LIMIT
THE INSTABILITY OVER THIS AREA.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
BY WEDNESDAY MORNING THE SURFACE FRONTAL BOUNDARY WILL BE
POSITIONED NEAR THE MAINE AND NEW HAMPSHIRE STATE LINE WITH A WEAK
SURFACE LOW FORMING ALONG THE FRONT. TO THE EAST OF THE FRONT LOW
CLOUDS... FOG... AND DRIZZLE WILL BE THE RULE IN THE MORNING...
WITH A THREAT FOR LINGERING SHOWERS OR A THUNDERSTORM AS WELL.
BEHIND THE FRONT TO THE WEST... EXPECT DRYING CONDITIONS WITH
DEWPOINTS FINALLY FALLING THROUGH THE 60S INTO THE 50S DURING THE
DAY. THE FRONT WILL GRADUALLY MOVE EAST THROUGH THE DAY... PUSHING
OUT THE LOW LEVEL MOISTURE... CLOUDS... FOG... AND INSTABILITY.
CANNOT RULE OUT A SHOWER OR TWO IN THE MOUNTAINS DURING THE
AFTERNOON EVEN BEHIND THE FRONT AS JUST ENOUGH LOW LEVEL MOISTURE
REMAINS TO POSSIBLY TRIGGER A SHOWER OR TWO. OTHERWISE IT WILL BE
MAINLY DRY BEHIND THE FRONT WITH TEMPERATURES IN THE 70S TO 80S.

EXPECT A COOLER NIGHT WEDNESDAY NIGHT AS DRIER AIR WILL HAVE
FINALLY ARRIVED ACROSS THE ENTIRE REGION. LOWS DROP INTO THE 50S
TO LOW 60S.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
HIGH IMPACT WEATHER POTENTIAL: LOW.

PATTERN SUMMARY: THE LONG TERM PERIOD BEGINS WITH A PERSISTENT
TROUGH/RIDGE/TROUGH PATTERN EXTENDING FROM THE EASTERN PACIFIC
THROUGH THE EASTERN PART OF NORTH AMERICA.   THERE IS MODEST
AGREEMENT THAT THE EASTERN PACIFIC TROUGH WILL DEEPEN THROUGH THE
END OF THIS WEEK...WITH BUILDING DOWNSTREAM HEIGHTS CAUSING THE
DOWNSTREAM TROUGHING OVER THE NORTHEASTERN UNITED STATES TO FLATTEN.
HEADING THROUGH THIS WEEKEND INTO EARLY NEXT WEEK...THE EASTERN
PACIFIC TROUGH BECOMES MORE MOBILE...WITH DOWNSTREAM RIDGING FURTHER
STRENGTHENING ACROSS EASTERN NORTH AMERICA.  THIS PATTERN EVOLUTION
ARGUES FOR A RELATIVELY QUIET START TO THE FORECAST PERIOD...WITH A
DRIER AIRMASS IN PLACE COURTESY OF NEARBY TROUGH.  BEYOND THIS...AS
THE TROUGH LIFTS OUT AND WESTERLY FLOW ALOFT STRENGTHENS...ATTENTION
WILL TURN TO WEAK DISTURBANCES IN THE MID LEVEL FLOW INTERACTING
WITH AN INCREASINGLY WARM AND MOIST BOUNDARY LAYER.  THIS WILL
INCREASE THE THREAT OF SHOWER/THUNDERSTORM ACTIVITY...WITH MODEST
MID LEVEL FLOW SUGGESTING AT LEAST SOME SEVERE WEATHER RISK.

GUIDANCE TRENDS/CONFIDENCE:  MODEL AGREEMENT IS STRONG THROUGH THE
END OF THE WEEK...WITH PRETTY SUBSTANTIAL DIFFERENCES APPEARING THIS
WEEKEND INTO EARLY NEXT WEEK...EVEN WITH THE LOCATION OF THE LARGE
SCALE PATTERNS.  MOST OF THESE DIFFERENCES ARE WITH THE PLACEMENT
AND DEPTH OF THE EASTERN PACIFIC TROUGH...WITH THE ECMWF MUCH FASTER
TO MOVE THIS FEATURE EAST THAN THE GEFS/GGEM.  WHILE THIS LOWERS
CONFIDENCE FOR THE SECOND HALF OF THE FORECAST...THE OVERALL IDEA OF
BUILDING HEIGHTS IN THE EAST IS WELL AGREED UPON.

THE DETAILS...

MID LEVEL TROUGHING STILL IN PLACE AS THE LONG TERM FORECAST PERIOD
OPENS ON THURSDAY.  WHILE THE COLUMN WILL HAVE DRIED A DECENT BIT
FROM 24 HOURS PREVIOUS...COOL TEMPS ALOFT /T5S AROUND -16C/ SHOULD
BE ABLE TO COAX A FEW SHOWERS TO DEVELOP DURING THE AFTERNOON
HOURS...PARTICULARLY IN THE MOUNTAINS...WHICH IS CAPTURED WELL BY
RECENT GEFS/SREF ENSEMBLE PRECIPITATION PERCENTILES.  THUS...WILL
CONTINUE WITH CHANCE POPS IN THIS AREA.

GENERALLY QUIET WEATHER FOR THE FRIDAY-SATURDAY PERIOD AS SURFACE
RIDGING BUILDS INTO THE REGION ALONG WITH SUBSTANTIAL DRYING OF THE
COLUMN AS PWATS FALL BACK BELOW ONE INCH FOR THURSDAY NIGHT THROUGH
EARLY SATURDAY.  FRONT NORTH OF THE REGION WILL NEAR THE CANADIAN
BORDER TOWARDS EVENING...JUST CLOSE ENOUGH TO WARRANT SOME LOW POPS
FROM THE MOUNTAINS NORTH...WITH MOST LOCATIONS LIKELY REMAINING DRY.

AFOREMENTIONED COLD FRONT LOOKS TO PUSH THROUGH THE REGION ON
SUNDAY...BUT REALLY WASHES OUT AS IT DOES SO.  THIS RESULTS IN A
VERY WEAK SIGNAL FOR PRECIPITATION CHANCES WITH NO MORE THAN SLIGHT
CHANCE TO CHANCE POPS FOR A FEW SHOWERS AND THUNDERSTORMS WARRANTED
PRIMARILY FROM THE MOUNTAINS NORTH.

FOR THE END OF THE LONG TERM FORECAST PERIOD MONDAY AND TUESDAY...
MODEL AGREEMENT DECREASES...BUT IN GENERAL...HEIGHTS ALOFT CONTINUE
TO BUILD AS THE WEAK FRONTAL BOUNDARY FROM SUNDAY PUSHES OFF THE
COAST. THERE CONTINUE TO BE SOME VERY WEAK SIGNALS FOR ISOLATED
SHOWER/STORM ACTIVITY /WITH SOME RIPPLES IN THE AMPLIFYING
FLOW/...BUT GIVEN PATTERN RECOGNITION...WILL LEAN MORE TOWARDS A DRY
FORECAST AT THIS RANGE GIVEN LITTLE COMPELLING SUPPORT FOR
PRECIPITATION FROM THE GUIDANCE.

TEMPERATURES:  THURSDAY AND FRIDAY EXPECT TEMPERATURES CLOSE TO
SEASONAL NORMALS AS TROUGH LIFTS OUT OF THE REGION. WITH BUILDING
HEIGHTS...EXPECT TEMPERATURES TO WARM AS WE REACH THIS WEEKEND AND
MOVE INTO EARLY NEXT WEEK...REACHING 5-7F ABOVE SEASONAL NORMALS.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
SHORT TERM...ONSHORE FLOW CONTINUES TO BRING IN ROUNDS OF LOW
LEVEL CLOUDS AND FOG FROM PORTSMOUTH TO ROCKLAND. EXPECT THIS TO
PRIMARILY BE THE CASE THROUGH WEDNESDAY MORNING WITH IFR OR LIFR
CONDITIONS BEING THE RULE. THUNDERSTORM DEVELOPMENT THIS AFTERNOON
REMAINS POSSIBLE ACROSS MOST OF NEW HAMPSHIRE... THOUGH CONFIDENCE
IN AFFECTING ANY ONE TAF SITE IS TOO LOW TO MENTION IN 18Z TAF
ISSUANCE. EXPECT IMPROVING CONDITIONS FROM WEST TO EAST DURING THE
DAY WEDNESDAY.

LONG TERM...LONG TERM PERIOD SHOULD BE LARGELY VFR...WITH MORNING
FOG CONCERNS THURSDAY THROUGH SATURDAY MORNINGS FOR LEB-HIE...WITH
ANY POTENTIAL RESTRICTIONS FROM SHOWERS/THUNDERSTORMS LIKELY NOT
RETURNING TO THE FORECAST UNTIL SUNDAY.

&&

.MARINE...
SHORT TERM...MOIST SOUTHEAST FLOW PROMOTES THE DEVELOPMENT OF FOG
THROUGH TONIGHT. FRONT SLOWLY PUSHES ACROSS THE GULF OF MAINE ON
WEDNESDAY AND BRINGS DRIER AIR IN TO GET RID OF THE FOG.

LONG TERM...WINDS AND WAVES LOOK TO REMAIN WELL BELOW SCA LEVELS
THROUGH THE LONG TERM FORECAST PERIOD.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...NONE.
NH...NONE.
MARINE...NONE.

&&

$$

SYNOPSIS...ARNOTT
NEAR TERM...KIMBLE
SHORT TERM...KIMBLE
LONG TERM...ARNOTT
AVIATION...ARNOTT/KIMBLE
MARINE...ARNOTT/KIMBLE


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