Area Forecast Discussion
Issued by NWS Portland, ME

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660 FXUS61 KGYX 231132 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 632 AM EST Thu Feb 23 2017 .SYNOPSIS... Low pressure moving east through southern Canada will allow a mild southwesterly flow to continue today. Highs will climb into the 50s for most of the area with lower 60s across southern New Hampshire. A weak cold front will try and push south across the area this evening with a few rain showers before returning north as a warm front by late Friday. A strong cold front and more widespread showers will move across the region Saturday night followed by a drier and colder air mass for Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Update...Tweaked forecast slightly to account for latest observational trends. A band of moisture convergence along the coast is allowing for some enhanced stratus/fog from PWM NEwd. This is a narrow band...possibly tied to frictional convergence at the land/sea boundary...because PWM has low ceilings while here at the office skies are mostly clear even off to the E with only patchy valley fog. Daytime heating will help to mix out this low clouds near the coast. Previous discussion...Biggest question today is just how warm it will get across the forecast area. Currently the warm front is more or less sharpening in place across the Northeast...and is forecast to move more rapidly thru the area this morning as we mix out. That last bit is the we mix out. Recent warm wx has led to significant model guidance struggles regarding just how deep the boundary layer gets during the day over snow pack. Many models failed to even produce a mixed layer over the forecast area yesterday...yet we managed to climb well into the 50s for much of the area. 23.00z KGYX raob showed a residual mixed layer extending up to around H9. Given stronger low level flow today and some partial sun possible I see no reason why mixing to near H9 again is not possible. For max temps I have blended the mixed down H9 temps with MOS guidance and ignored the raw and hi-res model output. This gives me fairly widespread 60s across Srn NH...with 50s elsewhere...which looks on track for this afternoon. There is a little more bust potential in areas that see more clouds than not...especially the temps could come under forecast values in those areas if things break wrong. A s/wv trof crossing Srn Canada will send a cold front into the region early this evening. It is currently forcing a line of thunderstorms across Lake Huron...impressive for Feb. That line will be weaker by the time it arrives in our forecast area...but convective nonetheless. The line is forecast to move thru the mtns and central NH before decaying further as the best forcing continues NE and away from our area.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... The front washes out over the area tonight...and allows moisture to pool S of it. I expect a little more widespread fog/stratus as a result...and a very mild night overall. Early Fri as the front tries to lift back N...there could be some light precip along it. Given the large dry slot ahead of the next s/wv trof I think models are over-forecasting QPF. However Sly upslope flow could lead to more concentrated light rain or drizzle in the mtns. S of the front will see another mild Feb day...though not quite as warm as today. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The models are in decent agreement on the longwave pattern through late next week. While we`ll see some brief intrusions of colder air into the region...ridging and above normal temperatures are expected to dominate the extended period. In the dailies...we begin the period with an impulse and associated surface low over the upper Mississippi Valley. A warm front will extend eastward into northern New England where light rain, drizzle and fog will be ongoing. The warm front will gradually lift north across the area on Saturday as the impulse pushes a surface low northward across the Great Lakes. A glance at the forecast soundings for Saturday makes me question how far north the surface warm front will make it...and hence forecast high temperatures for the day. The surface low will drive a strong cold/occluded front across the area Saturday night with more seasonable air and upslope snow showers to follow for Sunday. Another quick moving impulse will race eastward along the U.S. Canadian border and drive a second cold front across the area on Monday accompanied by a second round of upslope snow showers. A weak ridge follows for Monday night into Tuesday. By Tuesday night, warmer air returns in broad west- southwest flow aloft. Both clouds and pops will increase in warm air advection ahead of a disturbance expected to track to our north and west down the Saint Lawrence mid week. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... Short Term...Main concern for the first part of today is development of fog/stratus. A large area of marine fog/stratus has developed off Srn New England coast this morning...but forecast motion is generally E and not N. However weak onshore flow along the coast may bring patchy at RKD...especially thru morning. Otherwise moisture lifting Nwd is expected to remain mid to high level thru today. Tonight into Fri...warm air and greater moisture will advect in and likely lead to more widespread low clouds. IFR or lower is possible at Srn NH and coastal Wrn ME terminals. There is also the possibility for LLWS tonight as warm front lifts thru the area. SW flow around 2000 ft is forecast in the 35 to 40 kt range and light surface winds could lead to shear values around 30 kts. Long Term... Fri night - SAT...MVFR in -ra with areas of IFR in drizzle and fog. SE sfc wnd Sat gusting to 25 kt at coastal terminals. Sun...Sct MVFR in mtn -shsn. NW sfc wnd gusting to 25 kt. Mon...Sct MVFR in mtn -shsn. && .MARINE... Short Term...SW flow will develop over the waters today as a warm front lifts thru the area. With WAA over cold SSTs I expect that winds will not be as strong as modeled. A few gusts near SCA thresholds are possible along with seas building to near 5 ft. However at this time this looks to occur mainly after 00z...and will give the day shift another look at new data. There should also be some developing fog/stratus over the waters as warm/moist air moves Nwd into the region thru Fri. Long Term... Sat - Mon...SCA`s likely...wth gusts approaching gale outside the bays. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Legro SHORT TERM...Legro LONG TERM...Schwibs AVIATION...Legro/Schwibs MARINE...Legro/Schwibs is the U.S. government's official web portal to all federal, state and local government web resources and services.