Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 260759 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 359 AM EDT SUN APR 26 2015 .SYNOPSIS... UPPER LEVEL LOW PRESSURE WILL CONTINUE TO WOBBLE AROUND OVER MAINE AND THE CANADIAN MARITIMES THROUGH MIDWEEK....WITH THE COOL AND SHOWERY WEATHER CONTINUING. THE LOW WILL FINALLY SHIFT EAST ALLOWING HIGH PRESSURE TO BUILD IN FOR THE SECOND HALF OF THE WORK WEEK. LOW PRESSURE PASSES SOUTH OF THE AREA THURSDAY...WITH HIGH PRESSURE BUILDING BACK IN BEHIND IT. && .NEAR TERM /TODAY/... PESKY UPPER LOW REMAINS OVER THE WESTERN ATLANTIC WITH ITS AXIS STRETCHING BACK TO THE WEST OVER NORTHERN NEW ENGLAND. THE SHORT STORY IS THAT THE PRESENCE OF THIS UPPER LOW WILL KEEP SHOWERY WEATHER IN THE FORECAST TODAY THROUGH MONDAY. BUT THERE IS MORE TO THIS STORY. THE BROADER UPPER CAN BE THOUGHT OF AS A WHEEL... AN OBLONG SHAPED ONE... BUT YES A WHEEL. THIS WHEEL IS CURRENTLY CENTERED SOMEWHERE OFF THE SOUTHEAST COAST OF NOVA SCOTIA. SPOKES WITHIN THE WHEEL ROTATE AROUND THE WHEEL CENTER. EMBEDDED SHORTWAVE TROUGHS CAN BE THOUGHT OF AS THE SPOKES OF THE WHEEL. HOWEVER... NOT ALL SPOKES ARE CREATED EQUAL. SOME ARE LARGER OR MORE POTENT THAN OTHERS. AND THE STRENGTH AND TIMING OF EACH OF THESE SPOKES DETERMINES WHETHER THEY WILL PASS BY WITHOUT BEING NOTICED OR WHETHER THEY WILL CAUSE BIGGER SNAGS (YOUR PICNIC GETS RAINED OUT). THE NEXT SPOKE TO COME THROUGH OUR AREA WILL BE ARRIVING FROM THE NORTH THIS MORNING MOVING OUT OF QUEBEC AND NORTHERN MAINE. WHILE THIS SPOKE IS FAIRLY WEAK IT WILL BE MOVING THROUGH NEW HAMPSHIRE AND WESTERN MAINE DURING THE MIDDLE OF THE DAY... PERFECT TIMING FOR TRIGGERING SHOWERS. THE BEST CHANCE OF SHOWERS WILL BE ALONG THE NEW HAMPSHIRE AND MAINE STATE LINE. WEAK WIND FLOW TODAY WILL ALLOW A SEA BREEZE TO DEVELOP NEAR THE COAST. AS THIS PUSHES INLAND IT WILL CUT OFF SURFACE BASED INSTABILITY BUT MAY NOT BE ENOUGH TO PREVENT PLACES LIKE PORTLAND FROM GETTING WET EVENTUALLY. && .SHORT TERM /TONIGHT THROUGH MONDAY/... CONTINUING WITH THE SPOKES ANALOGY FROM THE PREVIOUS SECTION... THE NEXT SPOKE WILL MOVE SOUTHWEST THROUGH THE FORECAST AREA TONIGHT... CROSSING THROUGH THE CENTER OF THE AREA AFTER MIDNIGHT AND NEARING THE MASSACHUSETTS LINE IN THE MORNING ON MONDAY. THIS SPOKE IS STRONGER THAN THE LAST ONE (STRONG ENOUGH TO BEGIN PULLING THE CENTER OF THE WHEEL ITSELF BACK WESTWARD) BUT WILL BE MOVING THROUGH DURING THE OVERNIGHT HOURS WHEN THERE IS NO DIURNAL INSTABILITY TO WORK WITH. IN SPITE OF THE LACK OF INSTABILITY... THERE WILL STILL LIKELY BE ENOUGH LIFT TO TRIGGER SOME SHOWERS DURING THE OVERNIGHT PERIOD. FINALLY THE CENTER OF THE WHEEL ITSELF WILL SPIN SOUTHWEST OUT OF NOVA SCOTIA AND INTO THE GULF OF MAINE DURING THE DAY MONDAY. THE COMBINATION OF LIFT AND DIURNAL INSTABILITY WILL LEAD TO MORE WIDESPREAD SHOWERS ESPECIALLY OVER MAINE AND EASTERN NEW HAMPSHIRE. WITH MORE SHOWERS EXPECTED IT WILL ALSO BE A LITTLE BIT COOLER ON MONDAY THAN IT WILL BE TODAY. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... MODEL GUIDANCE IS GOOD AGREEMENT ON ANOTHER SHORTWAVE PINWHEELING AROUND THE UPPER LOW PRESSURE AND CROSSING THE FORECAST AREA MONDAY EVENING. THIS LOOKS TO BE THE LAST GASP FOR CONTROL OF OUR WEATHER...AS THE UPPER LOW PRESSURE WILL BEGIN TO MOVE OUT TO SEA BY MID WEEK. WHILE WE WILL TEND TOWARDS RISING HEIGHTS AND HIGH PRESSURE FOR THE LATTER HALF OF THE WEEK...THERE IS SOME UNCERTAINTY REGARDING THE EVOLUTION OF THE UPPER AIR PATTERN. WESTERN RIDGE LOOKS TO REESTABLISH ITSELF...HELPING TO KEEP HEIGHTS DOWN ALONG THE EAST COAST. THIS WILL SUPPORT CYCLOGENESIS ALONG THE EASTERN SEABOARD. HOW FAR N IS LOW CONFIDENCE AT THIS TIME...BECAUSE MUCH WILL DEPEND ON HOW SOUTHERN SHORTWAVE INTERACTS WITH NORTHERN STREAM FEATURE DIVING OUT OF THE HUDSON BAY REGION. THE GFS DEPICTS AGGRESSIVE PHASING AND A MUCH FARTHER N SOLUTION...WHERE THE ECMWF AND CMC FAVOR A DELAY AND MORE S AND E SOLUTION. AT THIS TIME I WILL FAVOR A CHANCE FOR SHOWERS WITH THE PASSAGE OF THE NORTHERN STREAM SHORTWAVE. RIDGING TRIES TO BECOME MORE PROMINENT HEADING THRU THE WEEKEND. && .AVIATION /07Z SUNDAY THROUGH THURSDAY/... SHORT TERM...GENERALLY VFR CONDITIONS BUT THERE IS A BETTER CHANCE FOR SHOWERS THIS AFTERNOON OVER WESTERN MAINE AND EASTERN NEW HAMPSHIRE. EXPECT AN EVEN BETTER CHANCE OF SHOWERS AND POTENTIALLY MVFR OR IFR CONDITIONS AT TIMES ON MONDAY. LONG TERM...GENERALLY VFR CONDITIONS EXPECTED TO PREVAIL IN THE EXTENDED. UPPER LOW PRESSURE WILL REMAIN NEARBY THRU ABOUT WEDNESDAY...SO CANNOT RULE OUT AFTERNOON MVFR CEILINGS OR VISIBILITY IN SCATTERED SHOWERS. GIVEN THE SMALL AREAL COVERAGE...ANY POTENTIAL MVFR IS FAIRLY LOW CONFIDENCE. BEYOND MIDWEEK WILL TEND TOWARDS RISING HEIGHTS AND HIGH PRESSURE...SO SHOWER CHANCES SHOULD DIMINISH. && .MARINE... SHORT TERM...WEAK PRESSURE GRADIENT WILL LEAD TO VERY LIGHT WINDS AND NEARLY CALM SEAS. WIND FLOW WILL LIKELY BE DOMINATED BY SEA BREEZE CIRCULATIONS ESPECIALLY TODAY. BY MONDAY LOW PRESSURE WILL BE MOVING SOUTHWEST INTO THE GULF OF MAINE AND WILL ALLOW NORTHERLY WINDS TO STRENGTHEN A BIT BY MONDAY EVENING. LONG TERM...SCA CONDITIONS ARE POSSIBLE LATER IN THE WORK WEEK DEPENDING ON HOW CLOSE TO THE GULF OF MAINE LOW PRESSURE TRACKS. && .FIRE WEATHER... GENERALLY COOL AND SHOWERY WEATHER WILL MAKE DANGEROUS FIRE WEATHER CONDITIONS UNLIKELY FOR THE NEXT SEVERAL DAYS. EXPECT A SEA BREEZE ALONG THE COAST THIS AFTERNOON. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ NEAR TERM...KIMBLE SHORT TERM...KIMBLE LONG TERM...LEGRO AVIATION...KIMBLE/LEGRO MARINE...KIMBLE/LEGRO

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