Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 212358 AFDGYX Area Forecast Discussion National Weather Service Gray ME 658 PM EST Sun Jan 21 2018 .SYNOPSIS... A stalled frontal boundary across southern New England will gradually lift north as a warm front late tonight through Monday night. Low pressure will track northeast out of the Great Lakes and into the St Lawrence Valley on Tuesday and will drive a cold front through the region late in the day. Low pressure will continue northeast into the maritimes Tuesday night. High pressure will slowly build in from the west Wednesday through Friday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 7 pm Update: Input latest mesonet data with only a few minor tweaks needed. Previous forecast looks good going forward to the overnight hours. Previous Discussion: Clouds will be on the increase overnight as weak over-running sets up along a stalled frontal boundary draped across southern New England. With the exception of a stray flurry in the mountains...expect a dry night with lows dropping back into the mid teens to mid 20s north and mid 20s to near 30 in the south. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Frontal boundary will begin to lift north on Monday bringing over-running precip into western zones in the afternoon. Precipitation will likely be in the form of light rain or snow in southern New Hampshire with occasional light snow elsewhere. Expect little if any accumulation through evening with QPF generally less than a tenth of an inch. Highs will range through the 30s in the south and mid 20s to mid 30s north. Warm front will continue to lift north Monday night producing occasional light snow in northern zones and a mix of sleet...snow and eventually freezing rain in southern sections. Once again only looking for light amounts of QPF with just an inch or two of accumulation in the north and light accumulations of snow sleet and ice in the south. Southern New Hampshire will hover around freezing overnight with the remainder of the forecast area ranging through the 20s. With this generally being a 3rd and 4th period event will let the mid shift decide on timing and areal extent of any needed advisories. && .LONG TERM /TUESDAY THROUGH SUNDAY/... ***Mixed precipitation expected Tuesday*** Focus of the extended remains on the Mon night/Tue system moving out of the Great Lakes. 21.12z GFS and ECMWF remain insistent on primary low pressure moving into Ontario...and weak secondary development occurring and running thru the heart of New England. There is not much climatological support for this type of I hesitate to warm the surface as much as those models indicate. We are now in long ranges of some hi-res guidance...which show a much colder and cold air dammed scenario. I prefer this evolution...especially given the high pressure building across the top of the advancing system. I leaned heavily on the hi-res NAM 2 m temps for general pattern Tue. Aloft I used a multi-model blend for max wet bulb temp in order to determine ptype. Relatively early on in the event...warmer air aloft will be moving in from the SW. So I expect snow will be rather brief outside of the Wrn ME mtns. Behind the mid level warm front we end up in the warm sector without much precip occurring. There could be some drizzle or freezing drizzle that occurs at this time...but confidence is low. That warm air aloft marches steadily the heavier precip arrives around 12z. I expect a mix of snow in the mtns...sleet and freezing rain S...and rain near the coast and parts of far Srn and SWrn NH. The cold air damming signal lets up around I expect more of a transition to rain at that point and a mix in the mtns. Overall no one winter ptype looks to amount to significant in all likelihood a winter wx advisory will handle it. The preference is to let the next shift get another look at hi-res guidance...which will have a better handle on low level temp fields. It is still worth noting that 12z raobs across the Wrn CONUS show H5 heights are higher than modeled ahead of the developing wave. This has tended to favor stronger high pressure to the NE of the storm in the ensemble systems. It is something to watch for regarding cooling trends. Also of concern is any run off going into area rivers. There remain ice jams...and water levels rising may lead to renewed flooding. A flood watch has been issued for the areas most at risk for this. Beyond the early week system...CAA midweek gradually gives way to moderating and mild temps. The multi-model consensus blend was used for this portion of the forecast...with the focus being on the mixed precip event. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Short Term...VFR this evening with MVFR/IFR ceilings developing after midnight. IFR/LIFR ceilings Monday through Monday with IFR/LIFR ceilings/vsby Monday night. Long Term...Widespread IFR conditions are likely as mid level warm front moves thru and WAA continues aloft. Precip will increase in intensity after 12z Tue...with some FZRA and PL possible at all terminals. Coastal terminals are expected to warm up first to RA...but it is possible that models are warming the surface too quickly. Widespread LLWS is expected as LLJ increases to 50 kts around 2000 ft. Flow becomes Wly Wed...returning S of the mtns to VFR. HIE will hang on to MVFR CIGs and VCSH for much of the day. && .MARINE... Short Term...SCA`s may be needed late Monday afternoon and Monday night. Long Term...Gale force winds are possible Tue ahead of approaching low pressure...especially outside of the bays. A gale watch has been issued for the outer waters into Tue night. SCA conditions likely for the bays. SCA conditions are expected to continue for much of the rest of the CAA Wly flow. && .HYDROLOGY... A flood watch has been issued as some run off and river rises are expected and ice jams remain in place along several rivers. This may lead to minor flooding as ice jams break up and reform downstream. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch from Tuesday morning through late Tuesday night for MEZ012-018>028. NH...Flood Watch from Tuesday morning through late Tuesday night for NHZ003>015. MARINE...Gale Watch from Tuesday morning through late Tuesday night for ANZ150-152-154. && $$ Marine is the U.S. government's official web portal to all federal, state and local government web resources and services.