Area Forecast Discussion
Issued by NWS Portland, ME

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239 FXUS61 KGYX 221247 AFDGYX Area Forecast Discussion National Weather Service Gray ME 847 AM EDT Fri Mar 22 2019 .SYNOPSIS...
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Low pressure will deepen and track north to coastal Maine late today. Precipitation will continue to spread across the area through morning. This will bring snow and rain at the start to many locations, except for the higher elevations which will likely see snow all day. The snow and rain will briefly change to snow through midday...especially away from the coast. The low will make its closest approach late today, which will end the widespread precipitation as drier air aloft moves overhead. Colder air and gusty winds move in from the west tonight and Saturday. Snow showers will break out across much of New Hampshire and western Maine, with moderate accumulations possible in the higher terrain. After a brief warm up on Sunday, a cold front will cross the region Monday. Cold but fair weather follows for Tuesday and Wednesday, with a warming trend for the end of the week.
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&& .NEAR TERM /UNTIL 7 PM THIS EVENING/...
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845 AM...the 12z GYX RAOB shows colder profile and thus expect more snow closer to the coast and along the coastal plain. As this is a transition season storm...there are likely to be wide variations in snow amounts based on elevation as well as precipitation intensity. The winter weather advisory area has been expanded further south and east to account for more snow then rain with this ESTF update. Winds over coastal waters in advance of the low continue to strengthen and Gales for the outer waters began a short time ago with strong SCA for the bays. Prev disc... 625 AM Update...Forecast on track so far early this morning. Have raised total snowfall for the coastal plain a bit based on newest forecast sounding information and trends in upstream obs. Area of strong UVVs just offshore of northeast MA continues to move northward at this time and will be affecting the our CWA this morning. A flip to snow (where it starts as rain) can be expected away from the immediate coast for a few hours (and even for an hour or two at the coast is possible). Snow could oscillate with rain for a time this morning as well in spots...all depending on UVVs and cooling of the column. Warnings and advisories remain the same but could be expanded a bit depending on trends over the next 1-3 hours. Previously... Tricky, changeable forecast today. Low pressure currently centered south of Long Island NY will move north-northeastward and into the Gulf of Maine this afternoon. At the same time, deepening mid level low will also move to a position just off the maine coast by this afternoon. The most concern at this time is the expected slug of heavy precipitation that is forecast (by consensus of mesoscale models) to move northward and through the region this morning into the early afternoon hours. This slug of precipitation will be forced by a tightening zone of frontogenesis extending to the northeast of the deepening mid level low (back-bent mid level warm front). Since much of the model suite has cooled in the column (current obs are showing a cooler/drier draw of air coming in from the north), this makes the precip type forecast tricky outside of high elevations since the temperature trace may be straddling the 0c isotherm for several hours this morning through about midday, even close to the coast. Therefore, even areas outside of the advisory/warning area could flip to heavy wet snow for a time. As such, have increased snow accums a bit at lower elevations on the coastal plain away from the immediate coast. This will be dependent on getting into some really intense upward motion, but it`s possible. After the heavier band of precipitation moves through early afternoon, SFC temperatures will rise, and any snow will go back over to rain. In the mountains, have issued a winter storm warning for heavy wet snow as accumulating snowfall is expected to occur today and well into tonight. This should get zone averages above 6 inches in the warning area. Highest elevations could see a foot or more. South of the warning area, have issued a winter weather advisory for 3-6" of heavy wet snow - with highest amounts in highest elevations. Power outages will be possible due to the potential for downed branches in the advisory and warning area. Precipitation will be considerably lighter this afternoon in many areas with dry lot moving on in. Winds will increase from the west this afternoon, especially across southern zones. Overall, a forecast where near-term updates to follow trends will likely be needed today as just a degree colder/warmer in the column will likely mean a big difference in ptypes. Some areas may waver from rain to heavy wet snow and back again as the temperatures profile wiggles around the 0c isotherm.
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&& .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM SATURDAY/... Snow to continue in the mountains tonight, with upslope contributions from NW flow becoming more dominant as the night goes on. In addition, it`s possible that the coastal plain sees a period of accumulating snow once again tonight as lobe of vorticity moves across the region (remnants of merging northern stream wave). Winds will increase as the night progresses due to tightening pressure gradient. Drier air moves in on Saturday. Aside from gusty west winds, we should see a decent amount of sunshine. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Models to continue to advertise a break of the +PNA pattern by early to mid-week, but not before we get a shot colder air for early to mid week as the trough is already in place before the flow becomes less amplified. The good news it will at least be dry after Monday and thru the rest of the week. Warming trend expected Thu-Fri as New England sits in the anticyclonic flow N of a closed low off the SE coast. The models have been struggling with srn stream closed lows, though, so not high confidence. Sat night should see NW flow break down as sfc high begins to work in briefly, and winds will diminish,as will mtn SHSN. Lows will drop into the teens N, to the mid 20s S, and some colder spots could decouple late with rad cooling for part of the night. The high shifts offshore Sunday with a Sw flow picking up and temps warming to 40-45 in the N, and 50-55 in srn and interior SW ME. Given the onshore flow, the ME coast is likely to stay in the mid to upper 40s. Sunday night and Monday will see the passage of cold front as srn stream energy phases to the south and drags [polar vortex toward Labrador. We will be on the equatorward of the cold air, so it will turn colder, and Tue-Wed will likely run below normal, but highs Tuesday, which will be the coldest day will range from around 30 in the N, to the mid to upper 30s in the south, and overnight lows will run from around 10-20 both Monday and Tue night. The cold air shifts out fairly quickly, and Wed will be a few degrees warmer than Tue, but still on the cool side for late March. Thu and Fri, will see the area under the influence of SW flow with warmer temps, in the 40s and 50s, with warmest air interior sections of the south, as onshore flow keeps the coast cooler. && .AVIATION /13Z FRIDAY THROUGH TUESDAY/... Short Term...IFR conditions expected today in rain and snow. Rain mainly at the coast, with snow in the interior. Conditions improve on the coastal plain and across southern NH tonight with low conditions continuing in the mountains. VFR returns Saturday with gusty west winds. Long Term...Mainly VFR Sat night thru Tuesday. KHIE could see some SHSN late Sun night early Monday. && .MARINE...
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Short Term...SCA conditions likely today with some gale gusts possible this morning. Westerly gales later tonight and Saturday as low pressure moves off into the Maritimes. Will keep a gale watch going for the bays as confidence in wind speeds remains a little low at this time. Long Term...SCA winds may linger through Sat night, but should subside below SCA on Sunday, and stay below SCA levels through Tuesday. .HYDROLOGY... Warming temperatures and rainfall may produce sufficient runoff to cause rises on rivers and streams late today through Saturday. At this time QPF looks to be less than an inch and a half...with a good portion of that being snow in the mountains. Even so, some ice breakup will be possible, especially central and southern ME.
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&& .TIDES/COASTAL FLOODING... Winds and seas begin to build right around the time of high tide tonight. However, the vast majority of increased storm surge of around a foot will occur around or shortly before the time of the midday high tide on Friday. With high astronomical tides already in place, minor coastal flooding is possible from Portland and points south during this tidal cycle. Most likely we remain below 13 ft at Portland, so a coastal flood advisory has been issued from there south. Some splash over or erosion may occur northward to Penobscot Bay and a coastal flood statement has been issued. 00Z wave models suggest long period waves arrive Friday night into Saturday. Therefore, with high astronomical tides still in place, there is the possibility for beach erosion and splash- over to continue for subsequent tides. This additional splash- over has been indicated in wave run-up output. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Weather Advisory until midnight EDT tonight for MEZ012- 013. Winter Weather Advisory until 2 PM EDT this afternoon for MEZ018>022. Winter Storm Warning until 8 AM EDT Saturday for MEZ007>009. Coastal Flood Advisory until 3 PM EDT this afternoon for MEZ023-024. NH...Winter Weather Advisory until midnight EDT tonight for NHZ003>007. Winter Weather Advisory until 2 PM EDT this afternoon for NHZ008>010. Winter Storm Warning until 8 AM EDT Saturday for NHZ001-002. Coastal Flood Advisory until 3 PM EDT this afternoon for NHZ014. MARINE...Gale Watch from late tonight through Saturday evening for ANZ151-153. Small Craft Advisory until 5 AM EDT Saturday for ANZ151-153. Gale Warning until 8 PM EDT Saturday for ANZ150-152-154.
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