Area Forecast Discussion
Issued by NWS Portland, ME

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295 FXUS61 KGYX 211452 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1052 AM EDT Sat Oct 21 2017 .SYNOPSIS... High pressure will shift offshore today allowing for another warming trend to commence. High pressure will hold off the coast through Sunday as a weak warm front holds steady across southern New England on Sunday. A slow moving cold front will approach from the west on Monday and will move across New England Tuesday night and Wednesday. Low pressure will then develop along this front and move into the Gulf of Maine Thursday. Fair weather should move in over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Update...The nocturnal inversion is slowly breaking with daytime heating...but lack of wind to assist is delaying the temp rise so far. I have adjusted the next couple of hours to better reflect this trend...but otherwise I expect temps will make it into the 70s across Srn NH and well into the 60s elsewhere. Some upstream mid to high level moisture also moved into the area this morning and with the help of a mtn top inversion well above the nocturnal boundary layer produce some upward propagating mtn wave clouds. As that inversion continues to mix out this morning those clouds across mainly Somerset Co right now will scatter out. ORIGINAL DISCUSSION... After a chilly start in some spots, we should see a good warm up today. Southerly flow transports warm air back into the region, with temperatures reaching the 70s for most places and mid 70s for the warmest. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... High pressure shifts offshore tonight, though it will still be a pretty calm night across the area with good cooling expected. Greater moisture in place should keep temperatures from falling much below 40, and as a result some fog can be expected by morning especially in valley locations. It will be another warm day on Sunday as high pressure offshore brings a southerly flow into the area. There will be some additional moisture moving in from the Gulf of Maine on Sunday, so dewpoints should rise into the 50s while temperatures reach the upper 60s and low 70s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Not too many changes to the extended as the same general theme exists in the latest deterministic and ensemble guidance as deep layer ridging early on gives way to troughing midweek. Large deep layer high pressure will be centered just off the New England coast on Monday, with southerly return flow bringing in warmth and more moisture. Some lower clouds may work in later in the day, but it should remain dry. On Tuesday, long wave troughing will approach from the west as the ridging gradually moves out to sea. This will result in increasingly southerly meridional deep layer flow during the day. Increasing moisture will come with it, and this will result in an increasing chance of rain as the day progresses. It is however expected to be light. Forcing for ascent increases Tuesday evening and night as the trough and attendant SFC cold front approaches from the west. There should be a south-north oriented band of heavy rain that moves into western zones ahead of this front Tuesday night as the low level jet kicks up and fuels the prefrontal environment with high PWAT air. A few thunderstorms will be possible as well as weak instability develops, at least aloft. Speaking of the low level jet, with the boundary layer expected to be relatively warm and moist, a percentage of the low level jet should be able mix down Tuesday night into Wednesday. Would not be surprised to see a few 40 MPH gusts during this time, especially in convection, and especially if a few thunderstorms develop or at least a narrow prefrontal fine line. There many be some localized flooding during this time, but most of the area is parched so we don`t expect any widespread flooding problems. We need the rain. The main question later Wed into Thu is whether or not a secondary wave of low pressure develops along the front and moves across our area - delivering another round of heavy rainfall. Model solutions are somewhat divergent on this idea at this time due to differences in amplitude and speed of the approaching trough. Plenty of time to iron things out there - but there is somewhat of a chance that the frontal rains Tue night-Wed could be the main show. However, the latest 00z ECMWF is less progressive and at least delivers a few more inches of rain to coastal and eastern zones. Either way, improvement is foreseen Fri into the weekend. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Short Term...VFR conditions expected with light winds as high pressure drifts east across the area. Should see some fog develop in the valleys by Sunday morning as greater low level moisture will exist. Long Term...VFR Monday. Mon night into Tue...deep moisture and WAA over the waters may bring stratus into coastal terminals. Tue night and Wed should feature widespread IFR in rain along with LLWS. && .MARINE... Short Term...Light winds and relatively low seas expected as high pressure crests over the waters. Long Term...High pressure in control of the region will keep winds and seas below SCA thresholds thru Mon. Developing return flow Mon into Tue will gradually build seas outside the bays towards 5 ft Tue. Low level winds increase later Tue and especially overnight into Wed. There will be a small window for gale force gusts outside the bays...and seas will build to near 10 ft. Persistent Sly flow thru the remainder of the week will keep seas above 5 ft even as winds begin to diminish. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Legro

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