Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 260200 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1000 PM EDT Wed Apr 25 2018 .SYNOPSIS...
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Low pressure over the mid Atlantic coast will move north through the area overnight and early Thursday with a good soaking rain. This system will slowly exit the region late Thursday allowing clearing Thursday night into early Friday. Another area of low pressure will move into the region late Fri and Friday night. Some instability showers are possibly mainly in the afternoon and evening Saturday. A cold front with cooler drier air arrives on Sunday. A warming trend is expected to begin early next week.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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10 PM Update...Rain continues to push northward across the forecast area at this time. It will taper off from south to north over the next couple of hours leaving light rain/showers, drizzle and fog for a couple of hours. Thereafter another resurgence of heavier rain should take place as a short wave trough approaches from the west. This activity will continue into or through the morning hours Thursday. As such, the flood watches remain up for the mountains and foothills. In addition, a rumble or two of thunder will be possible tonight into Thursday morning as mid level lapse rates steepen with the approach of the upper low. 6 PM Update...Have updated PoPs and winds a little bit based on latest observations as well as mesoscale model output. Heaviest slug of rain is moving into southern zones now, and should mainly be north and east of the forecast area around or just after midnight (except for the mid coast of Maine). Fog and drizzle should end up filling in behind this slug of rain and last through the overnight. As the main short wave trough impinges on the area early Thursday morning, showery precipitation should develop and sweep across the forecast area, as the air mass becomes weakly unstable. Cannot rule out isolated thunder at that time. Previously... Most of the precip with this event will fall through this evening as decent slug of rain, currently congealing over SE MA, will move NNE across areas along and just inland of the coast. This is in response to tightening WAA at mid-lvls, which is also developing a low level jet in the region. Models are in some agreement that some places near the coast could see close to an inch of rain or so between 22-06Z or so. So, the +RA wording was put into the forecast for the evening. Could see some localized areas of urban and poor drainage flooding, but overall not anticipating anything significant. The surge of decent SE upslope flow overnight, will also produce enhanced amounts in these areas of the mtns, and this will drain into some rivers and tributaries that are already running high due to snowmelt, so, the flood watch will be held as it is. The rain will lighten up some after midnight, but should continue thru most of the night before it tapers off to showers anywhere but maybe srn NH. Temps will fall off a little bit tonight, but lows will mostly be in the mid to upper 40s.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Could see another surge of steady rain move across ern zones Thu morning, but other areas will be more showery, although clouds and fog will linger through at least the first part of the morning, until winds shift to the west. Should see showers end around midday in srn NH and far SW ME, but clouds will linger through a good part of the day, with some breaks of sun late. Most everywhere else will see a chance of showers thru the afternoon, with mainly cloudy skies. Highs will generally be in the mid to upper 50s in the mtns and eastern zones, where clouds and rain will hang around longer, to 60-65 in SW ME and srn NH, where it will be drier, with a greater chance of some sun, and downslope W flow. Should see showers ending early Thu evening everywhere with clearing overnight. Winds will diminish a bit and allow temps to cool, with lows upper 30s to mid 40s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Models indicate another short wave trof moving across the southern jet stream will lift northeast to the mid Atlantic region Fri forming another area of low pres along the mid Atlantic coast that will move north into the area with a similar track as its predecessor. This will mean another round of rain or showers will overspread the area late Fri through Fri night. QPF amounts may be in the 1/2-1 inch range. The system will be a fast mover and move into the maritimes by Sat with a dry slot of air to arrive for Sat with a cyclonic flow aloft remaining. The combination of some heating on Sat with the cyclonic flow aloft may allow some scattered afternoon showers to develop. On Sunday the cold trof aloft over the Great Lakes progresses east and allows a cooler northwest flow to develop Sunday with more instability showers expected due to steepening lapse rates with any daytime surface heating. Winds may become gusty due to the strong northwest winds aloft mixing down to the surface. Temps will be cool through Sunday. Early next week a progressive large upper ridge will build east and become further amplified by Wed with a much warmer southwest flow to develop with dry conditions. Bottom line is a major warm up is looking like a reality beginning early next week and continuing through at least mid week. With a broad west to southwest flow expected Tue-Wed, guidance temps will likely be forecast too low for days 6-7. For now stayed close to guidance temps to match surrounding forecast areas. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Short Term...Conds will drop to IFR or lower everywhere this evening and stay there into early Thu. Some improvement to VFR possible by afternoon at KCON/KMHT/KPSM/KPWM, with MVFR lingering thru the afternoon elsewhere. VFR expected everywhere Thu night. Long Term...VFR early Fri with conditions lowering to MVFR/IFR late Fri into Sat in rain showers. VFR conditions return Sunday with gusty NW winds in the afternoon. && .MARINE... Short Term...SCA up for both winds and seas tonight, as SE winds gust to 30 kts or so. Seas stay up Thu into Thu night, although winds will shift to W and diminish, so will likely need to convert SCA to haz seas versions during the day Thu, and extend it thru at least Thu night. Long Term...Seas over the outer waters will remain aoa 5 ft F Fri into Sat so SCA`s for seas will likely be needed even though winds will remain light for that time frame. On Sun winds shift to westerly and continue into early next week and should remain generally below SCA conditions. && .HYDROLOGY... Expect continued snow melt to combine with about an inch or so of rainfall to bring further rises to all rivers, but especially the headwaters that drain eastward out of the mountains toward the Atlantic. These are the areas most likely to see minor flooding, and some locations are currently forecast by the RFC to reach minor flooding. Because of this, we have kept a flood Watch going covering the most likely impacted areas, including the upper Saco River as well as tributaries of the Androscoggin River. Flooding cannot be ruled out on the upper Pemigewasset River as well as along the Kennebec. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch through Thursday afternoon for MEZ007>009-012>014- 021. NH...Flood Watch through Thursday afternoon for NHZ001>006. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ151-153. Small Craft Advisory until 8 PM EDT Thursday for ANZ150-152- 154. && $$ NEAR TERM...EKSTER

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