Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201329 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 929 AM EDT SUN JUL 20 2014 .SYNOPSIS... AN UPPER LEVEL DISTURBANCE WILL MOVE THROUGH TODAY BRINGING CLOUDS AND A FEW SPRINKLES. HIGH PRESSURE BECOMES ENTRENCHED OFFSHORE MONDAY THROUGH WEDNESDAY...ALLOWING WARMER AND MORE HUMID AIR TO MOVE IN FROM THE SOUTHWEST. A COLD FRONT APPROACHES LATE WEDNESDAY AND MOVES THROUGH THE REGION THURSDAY...BRINGING A THREAT OF SHOWERS AND THUNDERSTORMS. HIGH PRESSURE BUILDS IN FROM THE WEST FRIDAY AND SATURDAY. && .NEAR TERM /THROUGH TONIGHT/...
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UPDATE... HAVE UPDATED THE GRIDS THIS MORNING TO ACCOUNT FOR SIGNIFICANT CLOUD COVER OVER THE REGION AND AN AREA OF SHOWERS MOVING THROUGH INTERIOR SOUTHWEST MAINE AND CENTRAL NEW HAMPSHIRE. THE LATEST HRRR MODEL RUN HAS A GOOD HANDLE OF THE PRECIP OVER THE NEXT FEW HOURS AS IT HEADS NORTHEAST AND CONTINUES TO WEAKEN WITH TIME. A FEW OTHER SHOWERS WILL CONTINUE TO DEVELOP OVER SOUTHERNMOST NH AND POSSIBLY COASTAL SW ME THIS AFTERNOON. SHOWERS OFF THE SOUTHERN NEW ENGLAND COAST MAY EDGE INTO OUR COASTLINE LATER TODAY. PREV DISC... SHOWERS NOW ENTERING SOUTHWEST NEW HAMPSHIRE... THEREFORE HAVE UPDATED POP TO REFLECT INCREASED CONFIDENCE IN PRECIPITATION. THESE SHOWERS ARE GRADUALLY WEAKENING AS THEY MOVE NORTHEAST... AND ARE ONLY DROPPING A FEW HUNDREDTHS OF AN INCH AT BEST AS THEY MOVE THROUGH. NO OTHER CHANGES MADE AT THIS POINT. ORIGINAL DISCUSSION... ALTHOUGH HIGH PRESSURE EXISTS AT THE SURFACE TODAY... A MID AND UPPER LEVEL TROUGH IS MOVING NORTHEAST OUT OF EASTERN GREAT LAKES AND CENTRAL APPALACHIANS. THE RISING MOTION TO THE EAST OF THIS TROUGH IS WHAT IS BRINGING THE MID/HIGH CLOUDS TO THE AREA. WITHIN THE BROADLY RISING MOTION TO THE EAST OF THE TROUGH AXIS... THERE EXIST SEVERAL VORTICITY MAXIMA WHICH ENHANCE THE RISING MOTION AND LEAD TO A GREATER CHANCE OF SHOWERS. THE TWO MOST PROMINENT OF THESE EARLY THIS MORNING WERE OVER CAPE COD AND OVER THE CATSKILLS IN SOUTHERN NEW YORK STATE. THESE WAVES ARE NOTED ON WATER VAPOR IMAGERY AND MOST MODELS ARE ABLE TO RESOLVE THESE AS WELL. REGIONAL RADAR IMAGERY ALSO SHOWS AREAS OF SHOWERS ASSOCIATED WITH BOTH OF THESE VORTICITY MAXIMA. ALTHOUGH RADAR ECHOES HAVE BEEN FAIRLY IMPRESSIVE... THERE HAVE NOT BEEN VERY MANY REPORTS OF SIGNIFICANT RAINFALL WITH THEM... GENERALLY A FEW HUNDREDTHS OF AN INCH AT BEST. THIS IS DUE TO THE FACT THAT THESE SHOWERS ARE BEING GENERATED IN THE MID LEVELS... 7000 TO 10000 FEET ABOVE THE GROUND. ALTHOUGH THE GOING FORECAST HAS BEEN DRY FOR TODAY... IT IS BECOMING DIFFICULT TO MAINTAIN THIS FORECAST CONSIDERING THE ALREADY EXISTING SHOWERS UPSTREAM OF THE REGION BEING TRACKED ON RADAR. THE AREA OF SHOWERS OVER CAPE COD WILL MOVE MOSTLY OFFSHORE... THOUGH THEY MAY SCRAPE THE MIDCOAST REGION THIS MORNING. THE AREA OF SHOWERS OVER THE CATSKILLS AND HUDSON VALLEY ARE TAKING A MORE DIRECT AIM AT THE HEART OF THE FORECAST AREA... LIKELY MOVING INTO NEW HAMPSHIRE AROUND 8 AM AND INTO WESTERN MAINE LATE THIS MORNING AND THIS AFTERNOON. EXPECT THIS AREA OF SHOWERS TO WEAKEN A BIT AS IT HEADS THIS WAY... BUT LIKELY STILL WILL PRODUCE SHOWERS AS IT ARRIVES. HAVE DECIDED TO INCLUDE SPRINKLES IN THE FORECAST FOR A WIDE PORTION OF THE AREA SINCE MANY AREAS MAY NOT SEE MEASURABLE PRECIPITATION. ALSO INCLUDED UP TO A 30 PERCENT CHANCE OF SHOWERS ACROSS THE AREA WHERE SHOWERS ARE LIKELY TO TRACK. CLOUDS AND SPRINKLES/RAIN SHOWERS WILL KEEP TEMPERATURES COOL TODAY WITH HIGHS ONLY IN THE 70S.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... MID/UPPER TROUGH AXIS MOVES EAST ACROSS THE AREA TONIGHT... WITH CLEARING EXPECTED AS IT DOES SO. THE CLEARING SKY WILL ALLOW BETTER RADIATIONAL COOLING CONDITIONS TONIGHT THAN HAVE BEEN SEEN THE PAST FEW NIGHTS... SO FOG WILL LIKELY BE MORE WIDESPREAD. HAVE INCLUDED PATCHY FOG BY MORNING OVER ALL LAND AREAS... BUT HAVE INCLUDED GREATER FOG WORDING (INCLUDING DENSE FOG) IN FAVORED VALLEY AREAS ESPECIALLY THE LOWER CONNECTICUT RIVER VALLEY. TEMPERATURES WILL BOTTOM OUT IN THE LOW/MID 50S. MONDAY WILL BE MOSTLY SUNNY BUT DO EXPECT SOME AFTERNOON CUMULUS ESPECIALLY OVER THE MOUNTAINS. SOME OF THESE CLOUDS MAY GROW TO FORM SHOWERS BY THE AFTERNOON... SO HAVE INCLUDED A CHANCE OF SHOWERS IN THE MOUNTAINS. THE REST OF THE AREA WILL LIKELY STAY DRY. HIGHS REACH THE UPPER 70S AND LOW 80S. && .LONG TERM /TUESDAY THROUGH SATURDAY/... 00Z GFS/EURO NOW IN AGREEMENT THAT SHORT WAVE TROUGH DIGS TO OUR W TUESDAY AND WEDNESDAY AND CROSSES NORTHERN NEW ENGLAND ON THURSDAY... LEAVING BEHIND A SLIGHTLY MORE AMPLIFIED OMEGA BLOCK WITH TROUGHING ALOFT JUST TO OUR WEST... AND RIDGE STILL HOLDING OVER THE WESTERN ATLANTIC. INITIALLY THE DEEPENING TROUGH WILL ALLOW THE RIDGE TO OUR EAST TO AMPLIFY AND BRING IN WARM AND HUMID AIR... WITH TUESDAY SEEING MOST EVERYONE GETTING INTO THE 80S... AND THE HOT SPOTS INTO THE MID TO UPPER 80S. BY WEDNESDAY... SHOULD SEE A FEW SPOTS IN IN SOUTHERN NH AND INTERIOR SW ME HIT 90. BOTH DAYS WILL FEATURE SW FLOW... WHICH WILL LIMIT HIGHS TO THE LOW TO MID 80S ALONG THE COAST FROM CASCO BAY SOUTH... AND HIGHS WILL BE ONLY 75 TO 80 ON THE MID COAST. SHOULD SEE ENOUGH SURFACE INSTABILITY... COMBINED WITH HEIGHT FALLS AT 500 MB ACROSS THE NORTH TO DEVELOP SOME THUNDERSTORMS IN THE MOUNTAINS AND FOOTHILLS DURING THE AFTERNOON... WHICH COULD APPROACH THE COAST BY EVENING. AS THE FRONT AND UPPER LEVEL TROUGH SWING THROUGH ON THURSDAY... LOOK FOR ANOTHER ROUND OF SHOWERS/THUNDERSTORMS ON THURSDAY... WHICH LOOKS TO BE THE BEST CHANCE OF RAIN THIS WEEK. SHOWERS COULD LINGER INTO THURSDAY NIGHT... BUT NW FLOW WILL KICK IN BY FRIDAY WITH SOME DRIER AIR AND HIGHS CLOSER TO NORMAL. SURFACE HIGH BUILDS FROM THE WEST ON SATURDAY FOR A FAIR AND SEASONABLY WARM DAY. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/... SHORT TERM...ANY MORNING FOG THIS MORNING DISSIPATE BY 13Z. EVEN THOUGH A FEW SHOWERS ARE POSSIBLE... VFR CONDITIONS ARE EXPECTED AS SHOWERS ARE COMING OUT OF A 7000 TO 10000 FT CLOUD LAYER. EXPECT CLEARING SKIES THIS EVENING WHICH WILL MAKE FOG MORE LIKELY TONIGHT ESPECIALLY AT LEB AND HIE. LONG TERM...COASTAL STRATUS/FOG POSSIBLE MONDAY NIGHT. SCATTERED THUNDERSTORMS POSSIBLE INLAND WEDNESDAY AFTERNOON/EVENING... WITH MORE WIDESPREAD SHOWERS/THUNDERSTORMS ON THURSDAY. && .MARINE... SHORT TERM...LIGHT WINDS AND SEAS EXPECTED. LONG TERM...SCA MAY BE NEEDED FOR INCREASING SW FLOW LATE WEDNESDAY INTO THURSDAY. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$

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