Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 290144 AFDGYX Area Forecast Discussion National Weather Service Gray ME 944 PM EDT Sun May 28 2017 .SYNOPSIS... Weak high pressure over the area will slowly shift east tonight. The next system over the eastern Great Lakes will lift north into Quebec tonight and will send a front towards the region. An area of showers will slowly cross New Hampshire and western Maine on Memorial Day. Warmer weather returns by the mid to latter part of the week but with the chance of showers each day. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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945 PM Update...Have adjusted sky cover and temperature grids for the next few hours. Overall, a tranquil evening with stratus continuing to work inland which may eventually portend to fog. 650 PM Update...Little change to the going forecast. A pleasant evening remains in the cards for most areas, with some stratus and fog expected to creep inland by late evening. Previously... The center of high pressure has moved off the coast and allowing a developing onshore southeast flow to develop. This will allow stratus currently over the southwest coast from psm-pwm to expand west and north by later tonight as the maritime air mass slowly moves inland and saturates the lower levels. Over western areas of inland NH and ME afternoon clouds developed due to differential heating to full sun across those areas. These clouds should generally remain tonight as the approaching weak trough will help enhance cloud formation by later this evening. Guidance temps of lows in the upper 40s to lower 50s looks good.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Models generally agree on lifting a weakening trof northeast across the area Monday bringing with it scattered showers and a moist damp east to southeast onshore flow...although it will be light. Qpf amounts will be light as the system weakens. Models generally agree on bringing the main surface low well to the southeast of Cape Cod and also the heavier precipitation associated with it. Temps will be very cool Monday with highs only in the lower to mid 50s. Monday night the system will slowly exit the area by lingering scattered showers are expected. Temps will be cool with overnight lows generally in the mid 40s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... 500 mb omega blocking along and north of the US/CAN border continues to be the main weather player through this week into next weekend. Main feature for Nw England will be closed low currently to our west, which will track slowly eastward to the Maritimes by the weekend, which brings a chance of showers most days. Models in fair agreement on the larger scale trends, but confidence on timing of waves that rotate around the closed low diminishes as we move further out in time. Initially, ridging in the center of the omega block will keep sfc low well to our south, but will also allow SE onshore flow to linger into Tuesday, so temps will be cooler Tuesday, with highs mostly in the upper 50s on the coast to the mid 60 inland. Also expect a fair amount of clouds, and the htreat of showers, especially mid to late afternoon into Tuesday evening as wave rotates around the low to our west, and will eventually drag the occlusion across the CWA late Tue night. Lows will be in the upper 40s to low 50s. On wed, the flow will shift to W-SW and this should allow for warmer air air to mix down, and keep the sea breezes at bay except maybe right at the beaches. Some sun is likely esecially on the coastal plain in the downslope, and highs should warm into the 70-75 range in all but the mountains and the mid coast, which will be in the mid-upper 60s. Another wave will rotate through Wed afternoon/evening and may see enough sfc warming and 500 mb height falls to produce some TSRA in the afternoon. After this wave clears, flow aloft becomes a little more zonal on Thu, and this may be the best chance of a dry day with highs 70-75 again on the coastal plain, and mid-upper 60s in the mtns/foothills. Another wave approaches Friday and brings a threat for showers back into the forecast. The weekend remains questionable for showers at this point, but it will likely not be a washout, as the persistent W flow south of the closed low should keep things drier, if not necessarily warm. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Short Term...Areas of IFR conditions from KPSM-KPWM will spread thru AUG and RKD by later tonight...confidence is low on timing. Further inland VFR conditions will become MVFR tonight and possibly IFR at times in developing showers from S-N Monday morning and into the afternoon. Monday night conditions will be variable MVFR to IFR as a moist maritime air mass sits over the area with a prolonged light onshore flow. Long Term...Tuesday will start MVFR-IFR, lowest close to the coast, but should improve a bit in the afternoon. Beyond that look for VFR Wed-Fri, with tempo reductions in MVFR in SHRA. Some TSRA possible Wed afternoon. && .MARINE... Short Term...A flow ahead of the next system will have a weak southeast flow tonight becoming east Monday and through Monday night. Winds and seas to remain below SCA thresholds thru Mon night. Long Term...SE flow Tue shifts to W Wed-Friday, and should remain blo SCA levels through the period. && .TIDES/COASTAL FLOODING... The astronomical high tide in Portland is 11.6 feet MLLW at 2:10 AM Monday. Winds will be light but onshore through the night with low seas...but will help keep tides at least a half foot above the predicted upcoming high tide. Tides currently are about 8 tenths above their predicted levels so will once again issue a coastal flood statement to indicated some high water conditions that may exceed their minimal benchmark levels for isolated minor flooding at time of the early morning high tide late tonight. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$

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