Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 031151 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 751 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/...
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745 AM UPDATE: QUICK UPDATE FOR THE CT RIVER VALLEY DENSE RIVER VALLEY FOG...VISIBILE 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.
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&& .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 /12Z 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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