Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 031348
AFDGYX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAY ME
948 AM EDT FRI JUL 3 2015

.SYNOPSIS...
HIGH PRESSURE BUILDS IN TODAY AND MOVES OFFSHORE ON SATURDAY. LOW
PRESSURE PASSES SOUTH OF THE REGION AND MAY BRING A FEW SHOWERS
TO NEW ENGLAND ON SATURDAY. HIGH PRESSURE BUILDS IN SUNDAY THROUGH
TUESDAY. A FRONTAL SYSTEM BRINGS RAIN TO THE REGION BY MIDWEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
945 AM UPDATE: MINOR TWEAKS TO TEMPERATURES...OTHERWISE NO OTHER
CHANGES NEEDED AT THIS TIME.

745 AM UPDATE: QUICK UPDATE FOR THE CT RIVER VALLEY DENSE RIVER
VALLEY FOG...VISIBLE SAT IMAGERY SHOWS IT NICELY. NO OTHER
CHANGES AT THIS TIME.


730AM UPDATE...
SOME CLOUDS MOVING IN FROM THE NORTH WITH THE UPPER TROUGH. HAVE
UPDATED THE FORECAST TO INCREASE CLOUD COVER SLIGHTLY WITH THIS.
OTHERWISE NO SIGNIFICANT CHANGES NEEDED.

ORIGINAL DISCUSSION...
UPPER TROUGH AXIS SHIFTS EAST THIS MORNING WITH MID AND HIGH LEVEL
CLOUDS EXITING TO THE EAST. BENEATH THE SUBSIDENT FLOW ON THE BACK
SIDE OF THE TROUGH... SURFACE HIGH PRESSURE CONTINUES TO BUILD
INTO THE REGION. SHOULD BE A FEW DEGREES WARMER TODAY AS WARMER
AIR BUILDS IN FROM THE WEST COMBINED WITH STRONG SURFACE HEATING.
MOST AREAS WILL BE IN THE 70S FOR HIGHS WHILE SOME LOW 80S ARE
EXPECTED IN SOUTHEAST NEW HAMPSHIRE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
UPPER RIDGE AXIS SHIFTS ACROSS THE AREA TONIGHT WITH SURFACE HIGH
PRESSURE SHIFTING EAST AS WELL. A LITTLE BETTER LOW LEVEL MOISTURE
SHOULD KEEP TEMPERATURES FROM FALLING AS FAR TONIGHT AS THEY DID
LAST NIGHT. 50S WILL BE WIDESPREAD WITH SOME 40S IN SHELTERED
VALLEYS.

INDEPENDENCE DAY IS A UNIQUE HOLIDAY IN THAT IT IS ONE IN WHICH
THERE IS A GREAT AMOUNT OF OUTDOOR ACTIVITIES TIED TO THE HOLIDAY.
THE FOURTH OF JULY OCCURS ON A SATURDAY ONLY ONCE EVERY 5 OR 6
YEARS. WITH THE HOLIDAY OCCURRING ON A SATURDAY THIS YEAR... IT
CAN BE ASSUMED THAT OUTDOOR ACTIVITIES WILL BE PARTICULARLY
IMPORTANT TO MANY PEOPLE.

A HANDFUL OF DAYS A YEAR THE FORECAST MODELS LEAD FORECASTERS IN
ONE FORECAST DIRECTION FOR QUITE SOME TIME AND THEN SUDDENLY SHIFT
WITHIN THE FINAL DAY OR TWO TO BRING A SURPRISE CHANGE IN THE
FORECAST. WHILE THIS DOES NOT HAPPEN ALL THAT OFTEN... IT CAN BE A
PARTICULAR PAIN FOR FORECASTERS WHO PRIDE THEMSELVES ON TRYING TO
PRODUCE A HIGH QUALITY AND CONSISTENT FORECAST THAT USERS CAN RELY
ON FROM DAY TO DAY.

UNFORTUNATELY... MODEL FORECASTS HAVE SUDDENLY SHIFTED JUST IN
TIME FOR THE FOURTH OF JULY. THE TIMING OF THIS COULD NOT BE MUCH
WORSE. WHILE FOR MANY DAYS FORECASTS HAVE CONSISTENTLY CALLED FOR
AN UPPER TROUGH TO MOVE THROUGH THE GREAT LAKES AND INTO NEW
ENGLAND ON SATURDAY... THE SURFACE LOW ASSOCIATED WITH THIS TROUGH
HAS INCREASINGLY BEEN FORECAST TO MOVE WELL SOUTH OF NEW
ENGLAND... LEADING TO A DRY INDEPENDENCE DAY FORECAST. THIS DRY
FORECAST HAS NOW COME INTO QUESTION. EACH OF THE MAJOR MODELS NOW
FORECAST RAIN FOR AT LEAST SOME PARTS OF THE FORECAST AREA ON
SATURDAY... MAINLY OVER SOUTHERN NEW HAMPSHIRE AND POTENTIALLY
INTO SOUTHWEST MAINE.

THE NAM IS INDICATING A SIGNIFICANT AMOUNT OF MID AND UPPER LEVEL
LIFT WITH THE UPPER TROUGH LEADING TO SOME LIGHT RAIN OVER NEW
HAMPSHIRE DURING THE DAY ON SATURDAY. THIS IS NOT ASSOCIATED
DIRECTLY WITH THE OFFSHORE SURFACE LOW... AND PRECIPITATION
AMOUNTS WOULD LIKELY BE TOO LIGHT TO COMPLETELY RUIN MOST OUTDOOR
EVENTS. THE GFS USES THIS MID LEVEL LIFT TO NOW DEVELOP A MORE
ROBUST SURFACE LOW AND TRACK IT FAIRLY CLOSE TO THE SOUTHERN NEW
ENGLAND COASTLINE. THE PRECIPITATION WHICH WOULD THEN DEVELOP
WOULD SPREAD THROUGH MASSACHUSETTS AND UP INTO SOUTHERN NEW
HAMPSHIRE AND POSSIBLY INTO SOUTHWEST MAINE. THIS WOULD BE A
LITTLE HEAVIER RAIN BUT STILL MAYBE NOT A COMPLETE WASH OUT. FOR
ITS PART THE ECMWF GENERALLY AGREES WITH THE GFS THOUGH THERE IS
SOME TIMING DIFFERENCE AND LESS OVERALL QPF. THE CMC ALSO
DEVELOPS A STRONGER SURFACE LOW BUT KEEPS THE PRECIPITATION SOUTH
OF THE NEW HAMPSHIRE STATE LINE.

WHAT DOES ALL THIS MEAN? THERE IS NOW SIGNIFICANTLY MORE
UNCERTAINTY REGARDING THE INDEPENDENCE DAY FORECAST. WHEN THE MAV
AND MET BOTH SUGGEST 70 TO 80 POP IT IS USUALLY TOUGH TO ARGUE
WITH. BUT CONSIDERING THIS IS THE FIRST RUN WHICH HAS SHOWN SUCH A
HIGH CHANCE OF PRECIPITATION... IT HAS BEEN DECIDED THAT IT WOULD
BE BETTER TO RAISE THE POP A LITTLE BIT AND WAIT FOR A LITTLE MORE
RUN TO RUN CONSISTENCY ON THIS NEW SOLUTION BEFORE JUMPING FULLY
ON BOARD WITH IT. FOR NOW... WILL GO WITH 20 TO 30 PERCENT CHANCE
OF RAIN OVER SOUTHERN NEW HAMPSHIRE AND SOUTHWEST MAINE DURING THE
DAY ON SATURDAY. IF MODELS CONTINUE TO SHOW A LIKELY RAIN EVENT ON
SATURDAY... THE NEXT FORECAST SHIFT CAN HAVE MORE CONFIDENCE IN
GOING WITH THIS DRAMATIC CHANGE IN THE FORECAST. AT THIS POINT
INDEPENDENCE DAY DOES NOT LOOK LIKE A TOTAL WASH OUT EVEN IF IT
DOES RAIN AT SOME POINT. BUT IT IS WORTH COMING BACK TO CHECK
FUTURE FORECASTS AS THE CONFIDENCE LEVEL ON THIS FORECAST CAN
SEEMINGLY ONLY GO UP FROM HERE.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
A NORTHERN STREAM SHORT WAVE TROUGH AXIS WILL BE JUST TO OUR WEST
EARLY SUNDAY MORNING KEEPING THE CHANCE OF A FEW UPSLOPE SHOWERS
AROUND ACROSS THE FAR NORTHERN COUNTIES. BERMUDA HIGH THEN EXPANDS
TO ENVELOPE THE NORTHEAST MONDAY AND TUESDAY. THE NEXT SYSTEM OF
NOTE WILL PASS TO OUR NORTH AND DRAG A COLD FRONT ACROSS THE
REGION TUESDAY INTO WEDNESDAY. SHOWERS SHOULD BE LIGHT WITH ONLY
WEAK TO MODERATE FORCING BUT SURFACE HEATING WILL BE ENOUGH EACH
DAY TO SEE THUNDERSTORMS DURING THE AFTERNOON HOURS. TRANSIENT
HIGH PRESSURE BUILDS IN THURSDAY BUT QUICK MOVING SYSTEMS AND
CYCLONIC FLOW ALOFT MAKES IT PRUDENT TO KEEP AT LEAST A SLIGHT
CHANCE OF PRECIPITATION IN EACH DAY. OVERALL TEMPERATURES WILL BE
AT OR ABOVE NORMAL.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
SHORT TERM...VFR CONDITIONS EXPECTED THROUGH SATURDAY. ALTHOUGH
SOME LIGHT RAIN IS POSSIBLE IN SOUTHERN AREAS ON SATURDAY THE
CEILING AND VISIBILITY MAY NOT BE IMPACTED MUCH.

LONG TERM...PREVAILING VFR CONDITIONS SUNDAY THROUGH TUESDAY WITH
HIGH PRESSURE BUILDING IN FROM THE SOUTH.

&&

.MARINE...
SHORT TERM...HIGH PRESSURE LEADS TO LIGHT WINDS AND DECREASING
SEAS THROUGH SATURDAY.

LONG TERM...NO CONCERNS. A COUPLE OF WEAK FRONTAL SYSTEMS CROSS
THE REGION THIS COMING WEEK BUT NONE ARE STRONG ENOUGH TO DISTURB
THE WATERS.

&&

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

&&

$$




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