Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 020519 AAC AFDGYX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GRAY ME 119 AM EDT SUN AUG 2 2015 .SYNOPSIS... A COLD FRONT WILL EXIT THE REGION THIS EVENING AS SCATTERED SHOWERS AND THUNDERSTORMS COME TO AN END. TEMPERATURES AND HUMIDITY DROP OFF A LITTLE MORE BEHIND THIS FRONT. SUNDAY SHOULD BE MAINLY DRY AS HIGH PRESSURE BUILDS ACROSS NEW ENGLAND. WEAK LOW PRESSURE ALOFT...SITUATED OVER QUEBEC...WILL BRING ANOTHER ROUND SHOWERS OR STORMS MONDAY AFTERNOON INTO MONDAY NIGHT. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1245AM UPDATE... LAST SHOWER DYING OUT OVER CARROLL COUNTY NH...RIGHT ON SCHEDULE. HAVE MADE SOME ADJUSTMENT TO SKY COVER AND NEAR TERM TEMPERATURES BASED ON OVERNIGHT TRENDS...BUT NO SIGNIFICANT CHANGES TO GOING FORECAST AT THIS TIME. 00Z UPDATE... ASIDE FROM A FEW PATCHY MID LEVEL CLOUDS SKIES HAVE CLEARED ACROSS THE FORECAST AREA THIS EVENING. CONVECTION BACK TO THE WEST OVER NORTHERN NEW YORK AND VERMONT STILL HOLDING TOGETHER BUT DIMINISHING AS IT HEADS EAST. HAVE BUMPED UP POPS IN FAR NORTHWEST ZONES FOR THE NEXT 3 TO 4 HOURS FOR ANY CELLS WHICH MIGHT SURVIVE THE TRIP INTO NORTHWEST NEW HAMPSHIRE AND MAINE. ASIDE FROM A FEW TEMP AND TD TWEAKS...NO OTHER CHANGES PLANNED ATTM. PREVIOUS DISCUSSION... SURFACE COLD FRONT AND AN UPPER LEVEL SHORTWAVE WILL BE EXITING TO OUR EAST THIS EVENING. THIS WILL BRING AN END TO ANY REMAINING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. AS SKIES BEGIN TO CLEAR AND WINDS BECOME LIGHT...PATCHY INLAND VALLEY FOG WILL FORM. LOCALLY...THE VISIBILITY MAY DROP DOWN BELOW A MILE IN SOME LOCATIONS. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... EXPECT DRY CONDITIONS SUNDAY MORNING WITH RIDGING OCCURRING ALOFT. HOWEVER...IN THE AFTERNOON...A LARGE SCALE UPPER TROUGH WILL BEGIN TO APPROACH FROM THE NORTHWEST. WITH CYCLONIC FLOW AND COLD AIR ALOFT...DIURNALLY DRIVEN CU WILL FORM - MAINLY OVER NORTHERN AREAS. THERE MAY BE SUFFICIENT MOISTURE FOR A SPRINKLE OR A BRIEF SHOWER...AGAIN...MAINLY CONFINED TO THE FAR NORTH. HOWEVER...HAVE KEPT POPS RELATIVELY LOW FOR THE DAY. A COLD FRONT WILL BEGIN TO APPROACH FROM THE WEST SUNDAY NIGHT. THE CHANCE FOR SHOWERS WILL BE ON THE INCREASE LATE AT NIGHT ALONG THE CANADIAN BORDER. THIS TAKES US TO THE LONG TERM PORTION OF THE DISCUSSION WITH A SLOW MOVING UPPER LEVEL LOW PRESSURE SYSTEM NEAR THE GREAT LAKES REGION. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... WARM MOIST AIR MOVES BACK INTO THE AREA ON MONDAY AHEAD OF AN APPROACHING UPPER LEVEL TROUGH. TEMPERATURES ACROSS THE AREA WARM INTO THE 80S WITH A FEW LOW 90S POSSIBLE IN SOUTHERN NEW HAMPSHIRE. THE INCREASING MOISTURE AT THE SURFACE WILL GENERATE INSTABILITY WHILE THE ADVANCING HEAT ALOFT (700 MB) WILL SERVE AS A CAP TO PREVENT ACCESS TO THAT INSTABILITY UNLESS A FORCING MECHANISM CAN BE FOUND TO OVERCOME THE CAP. AS THE UPPER TROUGH GETS CLOSER TO THE AREA LATER IN THE DAY IT WILL BEGIN ERODING THE CAP AND ALLOW GREATER ACCESS TO THE INSTABILITY IN ADDITION TO PROVIDING UPPER LEVEL LIFT AND PUSHING A SURFACE COLD FRONT EASTWARD. AS A RESULT... EXPECT SHOWERS AND THUNDERSTORMS AS THE TROUGH AND COLD FRONT MOVE THROUGH BUT THIS MAY NOT OCCUR UNTIL LATE IN THE AFTERNOON AND INTO THE OVERNIGHT MONDAY NIGHT. MODELS IN PRETTY GOOD AGREEMENT ON HOLDING PRECIPITATION OFF UNTIL LATE AFTERNOON AT THE EARLIEST. THE NAM IS ACTUALLY THE FASTEST OF ALL THE MODELS IN SPITE OF ITS NORMAL SLOW BIAS... TRIGGERING STORMS AROUND MID AFTERNOON. WITH THE INSTABILITY PRESENT (1000 OR MORE CAPE) ON TUESDAY THERE WILL ALSO BE A SUBSTANTIAL AMOUNT OF WIND SHEAR. MID LEVEL WINDS WILL BE OUT OF THE SOUTHWEST AT ABOUT 45 OR 50 KT WHILE SURFACE WINDS ARE LIGHT OUT OF THE SOUTH. THIS WOULD BE PLENTY SUFFICIENT FOR SUPERCELLS OR A MORE ORGANIZED DAMAGING WIND THREAT. THIS IS IN AGREEMENT WITH THE STORM PREDICTION CENTER`S OUTLOOK FOR MONDAY ALSO. HAVE INCLUDED DAMAGING WINDS WITH THE THUNDERSTORMS ON MONDAY TO HIGHLIGHT THIS THREAT WHICH WILL BE GREATEST OVER NEW HAMPSHIRE AND FAR WESTERN MAINE. UPPER LEVEL TROUGH AXIS AND SURFACE FRONTAL BOUNDARY SHOULD CLEAR THE AREA BY EARLY TUESDAY MORNING... HOWEVER SOME INSTABILITY STILL EXISTS BEHIND IT AND AN ISOLATED SHOWER OR STORM CANNOT BE RULED OUT AS THE PRIMARY UPPER LOW AND TROUGH AXIS MOVE ACROSS THE AREA. COOL HIGH PRESSURE BUILDS IN FROM THE WEST AND NORTHWEST WEDNESDAY THROUGH FRIDAY. EXPECT A LITTLE COOLER TEMPERATURES... ALTHOUGH AN OFFSHORE WIND WILL STILL ALLOW COASTAL AREAS TO GET INTO THE UPPER 70S AND LOW 80S. THE NEXT UPPER TROUGH WILL MOVE THROUGH THE GREAT LAKES ON SATURDAY AND TRIGGER CYCLOGENESIS OFF THE MID ATLANTIC COAST INTO SUNDAY. AN AREA OF RAIN WILL LIKELY FORM AND TRACK THROUGH SOUTHERN NEW ENGLAND AND POSSIBLY INTO SOUTHERN PARTS OF MAINE AND NEW HAMPSHIRE BUT SEEMS MORE LIKELY TO STAY JUST SOUTH OF OUR AREA AT THIS POINT. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... SHORT TERM...VFR THROUGH THE COMING TAF PERIOD OUTSIDE OF MORNING VALLEY FOG DEVELOPMENT AS A COLD FRONT PUSHES EAST OF THE REGION WITH SLIGHT DRYING OF THE LLEVEL AIRMASS TODAY. CLOUD COVER OVER NORTHERN AREAS MAY HELP KEEP FOG FROM GETTING TOO OUT OF HAND THROUGH DAYBREAK...BUT STILL FEEL SOME IFR VSBYS ARE POSSIBLE AT HIE/LEB...AND EVENT RKD...BUT HAVE SCALED BACK THE FOG JUST A BIT FROM PREVIOUS TAF PACKAGE. EXPECT JUST A FEW CU ALONG WITH SCATTERED MID CLOUDS /GREATEST COVERAGE FURTHEST NORTH/ FOR THE DAY SUNDAY...WITH THIS CONTINUING THROUGH SUNDAY EVENING. WINDS: LIGHT/VARIABLE WINDS WILL BECOME WESTERLY 5-10KTS THIS MORNING...TURNING MORE SOUTHWEST /PARTICULARLY COASTAL SITES/ THIS AFTERNOON. WINDS AGAIN GO LIGHT/VARIABLE TONIGHT. LONG TERM...EARLY MORNING MARINE FOG OR LOW CLOUDS IS POSSIBLE ALONG THE MAINE COASTLINE MONDAY MORNING. SHOULD SEE VFR CONDITIONS AREAWIDE BY LATE MORNING. SHOWERS AND THUNDERSTORMS CROSS THE AREA FROM WEST TO EAST LATE AFTERNOON THROUGH THE OVERNIGHT HOURS. THEN EXPECT VFR CONDITIONS OUTSIDE OF NOCTURNAL FOG IN THE NEW HAMPSHIRE VALLEYS FOR THE REST OF THE WORK WEEK. && .MARINE... SHORT TERM...EXPECT WAVES AND WINDS TO REMAIN BELOW SMALL CRAFT LEVELS THROUGH SUNDAY. HOWEVER...SEAS WILL BEGIN TO INCREASE LATE SUNDAY NIGHT IN AHEAD OF AN APPROACHING COLD FRONT. LONG TERM...SOUTHERLY FLOW ON MONDAY SHOULD STAY BELOW ADVISORY LEVELS BUT WAVE HEIGHTS COULD EVENTUALLY BUILD TO AROUND 5 FEET ESPECIALLY OVER EASTERN WATERS. A COLD FRONT MOVES WEST TO EAST ACROSS THE GULF OF MAINE ON TUESDAY WITH LIGHTER WINDS BEHIND IT. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ NEAR TERM...ARNOTT AVIATION...ARNOTT

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