textproduct: Gray - Portland

WHAT HAS CHANGED

There has been a slight reduction in snow amounts for the mountains and foothills for tonight into Wednesday. Ice amounts have also come down slightly across southern and coastal areas due to the possibility of more sleet mixing in, but slick travel is still expected across the region tonight and Wednesday morning.

KEY MESSAGES

- Key Message 1: Widespread wintry precipitation expected this evening through Wednesday and is expected to bring slick travel and impact the Wednesday morning commute. Precipitation tapers off by Wednesday afternoon.

- Key Message 2: Patchy freezing drizzle is possible Friday morning before temperatures warm up Friday as low pressure tracks north of the region bringing mainly light rain.

- Key Message 3: Accumulating wintry precipitation is possible Saturday night through Sunday as the next low pressure system tracks across northern New England. Areas south of the foothills likely see more in the way of rain than wintry precipitation with this system.

DISCUSSION

KEY MESSAGE 1 Discussion...

00Z Update... The 00Z KGYX RAOB report shows significant dry air aloft, which is allowing for a lot of the current radar returns to be simply virga based on ASOS/AWOS obs and webcam imagery. This dry air will erode though over the coming hours with snow developing over NH within the next few hours before spreading into western ME. Other than slowing the onset of precip, the inherited fcst remains in good shape.

Previously... The weather will remain quiet this afternoon before wintry precipitation returns...but fortunately after this evening's commute. Precipitation, mostly in the form of snow, will then overspread the area this evening as lift and moisture increase with low pressure approaching from the Great Lakes, and based on latest guidance this will be in the 7-9pm timeframe across NH and then into western ME between 9pm and midnight. It should be noted that portions of southern NH could see precip start as freezing rain or sleet.

As the night goes on, temperatures at the surface will remain subfreezing with CAD and a developing low over the Gulf of Maine, but warming aloft is expected to allow a change to or at the very least mix of freezing rain and/or sleet across southern NH and the Maine coast through Wednesday morning. It's uncertain exactly how far inland the freezing rain or sleet make it, but the expectation is still for precip stay mainly snow from the foothills northward. There may be even a brief period of plain rain along the immediate coastline, but the main takeaway is that regardless of ptype, the Wednesday morning commute looks messy across all of NH and western ME. No changes to the current Winter Weather Advisories.

Guidance has come down slight but remains fairly consistent in QPF being fairly light with this system and mostly in the 0.20" to 0.40" range which will yield 2-4" of snow to where ptype stays all or mostly snow. To the south, expecting mainly a coating to 2" of snow, a few hundredths to a tenth of an inch of flat ice, except a stripe of higher ice amounts of a tenth or two of an inch of inch ice may occur across southern NH and into far southwestern ME. This decrease is mainly due to the possibility of more sleet mixing in and the slightly downward trend in overall QPF.

The steady precipitation will begin tapering off from west to east from late morning and into the afternoon south mountains, although there still may be a few snow showers after. Skies will then start to clear out south of the mountains Wednesday night, but upslope flow will keep mountains mostly cloudy with a chance of snow showers. Overnight lows will be mostly in the 20s.

Key Message 2 Discussion...

Heights build over the Northeast Thursday with a mid level ridge axis cresting over the region Friday morning. Deep southwest flow will advect moisture and warm air into the region with T8s climbing to +3C to +5C Friday morning. BUFKIT profiles show a strong inversion Friday morning with surface temperatures below freezing. Subtle lift within a shallow moist layer beneath the inversion will bring the potential for patchy freezing drizzle Friday morning that could create a glaze of ice and slick travel for the morning commute.

Surface temperatures will climb into the upper 30s to low 40s by mid day Friday as steady precipitation breaks out across the area. By this time, rain will be the most likely precipitation type, although a brief wintry mix cannot be ruled out in the mountains before the highest summits climb above freezing Friday afternoon. QPF will be light with this system with the latest NBM bringing only around a tenth of a inch with up to a quarter inch in the mountains. Therefore there are no impacts expected from rainfall or melting snow, although some river ice movement is possible.

Key Message 3 Discussion...

A cold front crosses the Friday night with high pressure building to the north of the area Saturday. This high pressure will be in a favorable position for cold air damming ahead of the next system that approaches from the Great Lakes. The big forecast question at this time is how much cold air can work back into the area before precipitation likely breaks out by Saturday evening. Ensembles generally agree that temperatures will remain above freezing across southern NH and the coastal plain of Maine resulting in mostly rain event for these areas into Sunday. From the foothills northward precipitation types become more complex given the potential CAD and several ensemble members suggesting a secondary low more form in the Gulf of Maine. Have mainly stuck with the NBM which brings mostly snow from the mountains northward, however it should be noted that several ensemble members suggest that a change to rain is possible well north of the Canadian Border. Across the interior/foothills precipitation may waver between snow/mix/rain depending on the development of a secondary low in the Gulf of Maine. Precipitation tapers off Sunday afternoon with a shot of much colder air building in to start the work week. The main take away is that difficult travel will be possible Saturday night through Sunday mainly from the foothills northward.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

00Z TAF Update... Other than pushing back the start time of restrictions at most TAF sites, the overall thinking for tonight through tomorrow remains on track. SN will overspread the region over the next several hours from west to east with deteriorating flight restrictions thereafter. A period of mixed wintry precip is likely for southern sites Wed morning.

Previously... -Expect a range of MVFR to VFR conditions this afternoon before conditions deteriorate to IFR or LIFR this evening and tonight as wintry precipitation overspreads the area. Precipitation is expected to be mainly snow initially (except could start as FZRA at PSM and MHT) before the rest of southern NH and coastal sites see a change to freezing rain and/or sleet overnight into Wednesday morning. Coastal sites may even see a brief period of plain rain. HIE and LEB are expected to stay as snow. The steady precipitation is expected to end from west to east Wednesday morning and afternoon with a few rain or snow showers remaining. Ceilings may a take a little longer to improve, but conditions return to VFR Wednesday evening into Wednesday night. The exception is HIE with a continued chance of MVFR ceilings and snow showers.

-Active weather is likely Friday through Sunday. Low cigs and patchy freezing drizzle will likely bring periods of at least IFR Friday morning. Some improvement to MVFR is possible as cigs lift and light rain overspreads the area Friday afternoon. The airspace likely remains overcast Friday night as rain ends before the next round of rain/wintry precipitation moves in Saturday afternoon through Sunday.

MARINE

-Weak low pressure or troughing remains across the waters today with another weak low developing and moving across the Gulf of Maine tonight and Wednesday with a mix of precipitation types possible. Northwest winds may reach SCA levels on the backside of this low Wednesday evening into Wednesday night.

-Southerly winds increase Friday ahead of a cold front with SCAs likely needed by Friday afternoon. Active weather is expected to continue through the weekend as another low pressure system crosses the waters Sunday with offshore Gales possible Sunday afternoon.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory until 1 PM EST Wednesday for MEZ007>009-012>014-033. Winter Weather Advisory until 10 AM EST Wednesday for MEZ018>028. NH...Winter Weather Advisory until 1 PM EST Wednesday for NHZ001>004. Winter Weather Advisory until 10 AM EST Wednesday for NHZ005>015. MARINE...None.