Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 252042 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 442 PM EDT Sun Jun 25 2017 .SYNOPSIS... A series of upper level disturbances will cross the area this week, bringing chances for showers or thunderstorms, especially in the mountains. Otherwise temperatures will be near normal with lower humidity into mid week. Warmer and more humid conditions move in at the end of the week, with a chance of showers and thunderstorms Thu night into Friday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Update...I have tweaked PoP grids to better reflect current radar trends. There are several areas of showers/storms across the Northeast at this hour. One of those is moving across central parts of the forecast area. Higher dBZ returns are just barely edging above the freezing level...so thunder is a possibility but I do not expect frequent lightning until those echoes can reach much higher into the colder air aloft. The large dew point depressions will continue to make gusty winds a possibility...with kgyx 88D showing around 30 kts in this area of showers/storms. Other storms may slip S out of Canada and affect Nrn zones...and additional storms over central NY may also hold together and reach parts of NH after sunset. Previous discussion...Upper level trough will support scattered showers and thunderstorms into this evening. Best dynamics will be in the north and mountains, where we have the highest pops. There may be a couple storms with gusty winds and small hail, but as of early this afternoon, the convection appears to be relatively unorganized. Temperatures will drop through the 50s tonight for overnight lows. This will allow for some patchy fog to develop as dew points remain in the lower 50s.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... A short wave will be digging eastward over the central Great Lakes on Monday, too far to the west to affect our weather. Despite the lack of a true focusing mechanism, a broad upper level trough over the region will trigger more diurnally driven showers and perhaps a thunderstorm. Precipitation will mainly be confined to western portions of the forecast area. With temperatures cooling aloft, look for high temperatures to be a little cooler on Monday, mainly in the 70s in most areas. Upper level trough will remain to our west Monday night. However, pops will gradually be on the decrease during the night. Patchy late night fog a possibility once again. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Models continue to show a flattening 500 MB pattern with time as wrn Atlantic ridging begins to strengthen a little bit. After higher amplitude trough swings through the region mid week, will then trend toward warmer more humid conditions at the surface, possibly sitting beneath the core of the 500 mb jet a loft, with frequent passage of fast moving weak waves, and a more active pattern for thunderstorms late this week and into next weekend. Of course, the models have been struggling in the extended period, and we are dealing with large scale models trying to resolve mesoscale convection, so confidence remains low in the day to day pops and features, as well as localized wind direction, which will affect whether flow is onshore or or offshore, although, with persistent W-SW flow aloft, should allow for mainly warmer conditions. On Tuesday, a 500 mb wave moves through the SW flow ahead of the main trough to our west, and this will being a chance of showers, and maybe some thunder. Will still be dealing with cooler airmass, so TSRA are possible, but should not be widespread, but strong sun should generate at least some instability, and partly to moistly clouds skies in the afternoon. Best forcing is to the north, so best chance for any precip will be there. Highs will range from around 70 in the mountains, to the mid to upper 70s in the south. Should see the threat of showers diminish Tue evening, with lows generally in the 50s. Wednesday will see the trough axis move across the CWA with cold pool aloft, so again, SHRA/TSRA will be possible, more widespread in the mountains. Highs will be similar to Tue, generally in the 70s. Wed night looks mostly dry, and Thursday will start to see warmer air move in, with highs climbing back to the mid 70s to low 80s, but cooler on the coast as a sea breeze develops. Models show, what looks like convective system tracking eastward out of the Great Lakes late in the day and crossing the region Thu night. showing strong 925-850 mb jet with some shear in that level. Both Euro and GFS have been fairly consistent with this feature in this time frame, especially across the north, so good bet for some rain, especially Thu night. And some thunder is likely. After this confidence gets lower for timing of showers and storms, Still we look to get into 850 temps fluctuating around 15 C aloft, and tend to sit beneath the strongest 850 temp gradient through the weekend. So, dependent on sfc features, it could be warm and humid in this timeframe, with the coast likely running cooler most days. We will probably not see showers and storms every forecast period, but forecasting the timing this far out is sketchy at best. As we get closer, should be able to time the waves better. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... Short Term...Mainly VFR conditions with the possibility of convection lowering the ceilings and visibilities briefly into the MVFR category, mainly in the north and mountains. Most of the convection will occur during the afternoon hours Monday. Long Term...VFR should be predominant, with tempo flight restrictions in showers and storms, especially in the mountains. && .MARINE... Short Term...Winds and seas to remain below SCA thresholds in the near/short term portion of the forecast. Long Term...Winds/seas remain below SCA through Thu. May need SCA in SW winds Thu night into Fri. && .TIDES/COASTAL FLOODING... Very high astronomical tides continue tonight. Water levels will likely reach the 12 foot flood stage in Portland Harbor. Will issue another statement for tonight. High astronomical tides finally begin to drop for tomorrow night. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Beach Hazards Statement until 8 PM EDT this evening for MEZ023>028. NH...Beach Hazards Statement until 8 PM EDT this evening for NHZ014. MARINE...None. && $$ NEAR TERM...Legro

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