Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 181233 AFDGYX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAY ME 833 AM EDT SAT APR 18 2015 .SYNOPSIS... A COLD FRONT WILL SAG SOUTH INTO THE AREA THIS MORNING. WEAK LOW PRESSURE NORTH OF THE GREAT LAKES WILL RIDE SOUTHEAST ALONG THIS FRONT ACCOMPANIED BY INCREASING CLOUDS AND SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM. HIGH PRESSURE FOLLOWS THIS SYSTEM TONIGHT AND SUNDAY. ANOTHER SYSTEM WILL APPROACH THE REGION ON MONDAY AND TUESDAY. THIS SYSTEM LOOKS STRONGER...AND WILL LIKELY BRING SIGNIFICANT RAINFALL TO THE AREA ALONG WITH THE POTENTIAL FOR COASTAL FLOODING. UNSETTLED WEATHER LOOKS TO DOMINATE MID TO LATE WEEK. && .NEAR TERM /TODAY/... 830AM UPDATE... HAVE UPDATED THE FORECAST TO RAISE HIGH TEMPERATURES IN AREAS ALREADY APPROACHING OR EXCEEDING FORECAST HIGHS AT PORTSMOUTH AND PORTLAND. HAVE ALSO ADJUSTED HOURLY PRECIPITATION CHANCES. PRECIPITATION IS LIKELY TO ARRIVE AFTER 18Z AS SHOWN BY ALL THE HIGH RESOLUTION MODELS. HAVE ALSO INCREASED MAGNITUDE OF PRECIPITATION CHANCES OVER MUCH OF THE AREA TO COME MORE IN ALIGNMENT WITH MODEL CONSENSUS AND CURRENT FORECAST EXPECTATIONS. WITH COOLING ALOFT DURING THE DAY... ENOUGH INSTABILITY MAY BE PRESENT FOR ISOLATED THUNDERSTORMS PRIMARILY ALONG AND SOUTH OF THE SURFACE LOW TRACK. ORIGINAL DISCUSSION... AT 06Z...A COLD FRONT EXTENDED FROM CASCO BAY NORTHWESTWARD TO A WEAK 1010 MILLIBAR LOW VICINITY OF THE QUEBEC- ONTARIO BORDER. GOES IMAGERY SHOWED PATCHY LOW AND MID CLOUD ALONG THIS BOUNDARY ACROSS THE FORECAST AREA. THE SURFACE LOW WILL RIDE SOUTHEAST ALONG THIS FRONTAL BOUNDARY AND CROSS THE FORECAST AREA THIS AFTERNOON. CLOUDS WILL INCREASE AHEAD OF THIS DISTURBANCE TODAY WITH THE BEST CHANCE OF SHOWERS AND ISOLATED THUNDER ALONG AND TO THE NORTH OF THE BOUNDARY. THE WARMEST READINGS TODAY WILL BE FOUND ACROSS SOUTHERN INTERIOR NEW HAMPSHIRE AND THE LOWER CONNECTICUT VALLEY WITH TEMPERATURES IN THE 60S...WHILE ONSHORE FLOW ALONG WITH CLOUDS AND SHOWERS NORTH OF THE BOUNDARY LIMIT HIGHS TO THE UPPER 40S AND 50S. && .SHORT TERM /TONIGHT AND SUNDAY/... SHOWERS AND CLOUDS SHOULD QUICKLY EXIT BY EARLY EVENING AS SURFACE WAVE AND UPPER SUPPORT RACES OFFSHORE. SURFACE HIGH PRESSURE WILL BUILD EAST ACROSS THE AREA TONIGHT AND SUNDAY WITH DRY WEATHER AND SEASONABLE TEMPERATURES TO ROUND OUT THE WEEKEND. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... DEEP-LAYER RIDGING WILL HOLD OVER THE REGION SUNDAY NIGHT AND WILL PROVIDE THE AREA WITH FAIR WEATHER. THINGS START TO CHANGE ON MONDAY AS A LARGE AND DEEPENING UPPER LEVEL LOW PRESSURE SYSTEM STARTS TO DIVE SOUTHEASTWARD ACROSS THE GREAT LAKES. IN RESPONSE TO THIS...SURFACE LOW PRESSURE WILL DEVELOP NEAR THE DELMARVA COAST BY LATER MONDAY. THIS LOW WILL CONTINUE TO DEEPEN AS IT MOVES NORTHEASTWARD INTO THE GULF OF MAINE ON TUESDAY. THE MAIN THREAT WITH LOW PRESSURE SYSTEM WILL BE THE POTENTIAL FOR HEAVY RAIN. A LONG FETCH OF STRONG SOUTHEASTERLY INFLOW ABOVE THE BOUNDARY LAYER WILL BRING IN COPIOUS MOISTURE WHICH SHOULD OVERRUN A COASTAL FRONT AS WELL AS UPSLOPE IN INTO THE NH MOUNTAINS. 1 TO 2 INCHES OF RAIN IS EXPECTED AS A BASIN AVERAGE MONDAY NIGHT AND TUESDAY. HOWEVER...GIVEN THE LONG FETCH OF INFLOW IT WOULD NOT BE SURPRISING TO SEE A FEW AREAS APPROACH 3 INCHES. THIS WOULD OBVIOUSLY POSE FLOODING CONCERNS WHEN WORKING IN TANDEM WITH RECENT SNOW MELT. ACROSS THE WESTERN MAINE MOUNTAINS...ESPECIALLY THE HIGHER ELEVATIONS WITHIN...THE COLUMN MAY BE COLD ENOUGH FOR SEVERAL INCHES OF WET SNOW MONDAY NIGHT. COASTAL FLOODING MAY BECOME A CONCERN MONDAY NIGHT AS OFFSHORE EASTERLY GALES AND BUILDING SEAS WORK IN TANDEM WITH HIGH ASTRONOMICAL TIDES. AS FAR AS WINDS GO OVER LAND...SOME 30 MPH GUSTS WILL BE POSSIBLE. HOWEVER...THE STRONGEST WINDS SHOULD REMAIN ON THE IMMEDIATE COAST ALONG AND EAST OF THE COASTAL FRONT. THE HEAVIEST RAIN SHOULD MOVE OUT TUESDAY MORNING. HOWEVER...MUCH OF THE REST OF THE WEEK LOOKS UNSETTLED WITH SEVERAL POSSIBLE WEAK LOW PRESSURE SYSTEMS CONTINUING TO AFFECT THE REGION. && .AVIATION /13Z SATURDAY THROUGH WEDNESDAY/... SHORT TERM...AREAS OF MVFR BETWEEN 16 AND 22Z TODAY MAINLY NORTH OF A KLEB TO KPSM LINE IN SHOWERS AND ISOLATED THUNDER OTHERWISE VFR CONDITIONS EXPECTED. LONG TERM...IFR OR LOWER IN RAIN LATER MONDAY THROUGH TUESDAY. SOME IMPROVEMENT FORESEEN TUESDAY NIGHT AND WEDNESDAY. && .MARINE... SHORT TERM...QUIET WEATHER ON THE WATERS WITH WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT CRITERIA. LONG TERM...EASTERLY GALES WILL BE POSSIBLE MONDAY NIGHT INTO TUESDAY ALONG WITH RAPIDLY BUILDING SEAS AS LOW PRESSURE MOVES INTO OUR REGION. && .FIRE WEATHER... EXTREME SOUTHWESTERN PORTIONS OF THE FORECAST AREA MAY SEE MINIMUM RELATIVE HUMIDITY VALUES THIS AFTERNOON NEAR 30 PERCENT. HOWEVER...THE LACK OF GUSTY WINDS AND POSSIBLE PRECIPITATION SHOULD KEEP CONDITIONS FROM REACHING RED FLAG CRITERIA. AN SPS WILL BE ISSUED FOR NHZ007/008/011/015 TO ADDRESS CONDITIONS POSSIBLY APPROACHING RED FLAG FOR A BRIEF TIME THIS AFTERNOON. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...NONE. NH...NONE. MARINE...NONE. && $$ NEAR TERM UPDATE... KIMBLE

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