textproduct: Gray - Portland

WHAT HAS CHANGED

As of 720 PM, we continue to watch showers and thunderstorms across upstate NY that continue to move eastward. There severe stuff will weaken and remain to our south as backdoor front has pushed southward into extreme SW NH. However, southern and central NH are likely in for periods of heavy downpours and a few thunderstorms later this evening with sufficient elevated instability in place. Otherwise, drizzle and fog is expected. No changes to to the winter weather advisory for tonight in the far north where some snow and ice is expected.

Previously...

QPF and ice amounts have come down slightly for this evening, but it is still enough to make for slippery travel so Winter Weather Advisories remain unchanged. QPF and chance of thunder has increased slightly this evening in the south as some heavier showers are expected.

PoPs have been dropped significantly for Wednesday as the front clears early and it ends up being a mostly dry day.

KEY MESSAGES

1. Slippery travel possible with mixed precipitation arriving tonight in the Western Maine Mountains. Winter Weather Advisories remain in effect. Heavier rain, and possibly a rumble of thunder, will accompany this second round of precipitation for southern New Hampshire and southwestern Maine.

2. Rain tapers off Wednesday as a frontal boundary moves south of the area making for a drier day. Warmer temperatures briefly make it back into the region as well.

3. Low pressure brings another chance for a wintry mix Thursday into early Friday over portions the area. There is higher confidence from foothills northward seeing a wintry mix with less certainty to the south.

4. Above normal temperatures likely for most of the area Friday into the weekend with widespread precipitation likely going into Sunday. Mostly rain is expected.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... The current lull in steady precipitation this afternoon will come to an end this evening as a second round enters the region. PWATs have been juicy with 0.82" on the 12Z GYX sounding, and SPC mesoanalysis currently showing one inch amounts across southern New Hampshire and far western Maine. This is going to be the area that is going to see some heavier rain and some rumbles of thunder. There was enough instability this morning for a few lightning strikes in southern New Hampshire, and models show MUCAPE a little greater this evening with values 500-800 J/kg. The overnight runs of the HRRR were a little bullish in my opinion on the thunderstorm threat for an area that isn't going to see much if any clearing, but this mornings runs have looked more reasonable. This instability will be mostly elevated, so no storms are expected to be strong. The rain has been, and will continue to be, fast moving so impactful flooding is not a concern, but nuisance low land flooding and ponding on roads is likely to occur in heavier showers. Heavy rain also appears likely in the mountains with this second round, and this runoff combined with 0.75" to an inch of snowmelt runoff may lead to some modest river rises in the more sensitive rivers, but flooding is not a high concern here either.

The northern Maine mountains saw some snow this morning, but now these locations have warmed to freezing or just below freezing with temperatures continuing to warm aloft. QPF has come down a bit in the north for this evening with this mornings suite of model runs, but light icing of a tenth to two tenths of an inch is still anticipated with a wintry mix, so no changes to the Winter Weather Advisory was made. Be prepared so potentially slick travel in this area overnight.

KEY MESSAGE 2 DESCRIPTION... Showers linger on the coast and in the mountains early Wednesday, but hi-res models have come into agreement on a drier day as a whole with the front clearing early and stalling further to our south. Clouds will remain abundant with 500mb troughing, but at the surface we will begin to see some height rises as strong high pressure begins to make its approach from the north west. Weak southwest flow is present during the morning and afternoon which is going to allow some warmer temperatures in the area at least south of the mountains. Southern New Hampshire and far southwestern Maine have the best chance of seeing a return of upper 50s and low 60s. The remainder of southern and central Maine may only top out in the upper 40s and low 50s, and then locations north of the mountains will be the first to see the flip to northerly flow and likely end up in the upper 30s and low 40s. Northerly flow prevails areawide through the night dropping temperatures into the upper 20s and low 30s south of the mountains, and into the low to mid-20s across the north.

KEY MESSAGE 3 DESCRIPTION... Mid-level warm front lifts back northward through the area Thursday into Thursday night with question to how far north the surface front makes it. The expectation is to remain generally cool and cloudy (northern areas may be less cloudy early in the day), and interestingly the CAD signal is not quite as strong as looked earlier with a slight veering of the low-level winds, so the surface boundary may end up getting a little farther north with slightly warmer temps as a result. Isentropic lift will allow precip to develop Thursday morning in the afternoon with a mixed bag possible across the area. Highest confidence would be for light wintry precip north of the foothills where surface temps remain colder with FZRA/IP both possible as temps aloft warm. To the south, it's still possible, but the potential looks to be a lower with surface temps coming in slightly milder.

The bigger push of moisture comes in late Thursday through early Friday, with the higher amounts focused from the foothills northward. Potential for wintry precip remains highest the mountains and northern zones with less certainty with southward extent.

For what it's worth there are some model solution not showing much in the way of QPF for southern areas, so that will also have to be looked at.

KEY MESSAGE 4 DESCRIPTION...

Any precipitation early Friday will continue to lift to the north with models showing not much else in the way of precip the rest of the day other than a few showers as the cold front approaches. Skies stay mostly cloud in the morning, but NH and maybe far western ME look to see some clearing by the afternoon as mixing starts, which will also bring in some down some gusty winds from aloft. These areas should be able to reach the 60s for highs. Farther east into western ME, the marine layer may keep things cloudier and cooler, especially toward the Kennebec and Midcoast regions. The front crosses Friday night with little in the way of precipitation expected.

Above normal temperatures continue into the weekend, but precipitation chances will be increasing, especially Sunday. Friday's cold front lifts back north as a warm front on Saturday, and then Sunday will have increasing south to southwest flow as a cold front approaches from the west. Warmest temperatures will be across southern NH with 60s possible each day, but western ME is less certain, especially the farther east one goes as any onshore component will bring the marine layer in to keep things cooler. Some showers are possible Saturday, but the higher precipitation chances look to come Sunday and Sunday night as the cold front draws nearer to northern New England. The clouds/precip may also keep temps a bit cooler. Precipitation type will most likely be rain with the exception of the higher peaks.

The cold front will likely cross through Sunday night or Monday, so Monday may or may not be dry depending on the time of the FROPA. With an earlier FROPA, Monday would be a cooler and breezy day with mainly just upslope showers. Conversely, the slower solution would be cloudier with higher shower chances remaining for the rest of the area. High pressure should then bring drier conditions for at least some of Tuesday. There's indications there could be increasing chances for showers late in the day, but these may also hold off until beyond the forecast period.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Through 18Z Wednesday...Rain picks up again around 00Z Wednesday which will maintain MVFR ceilings and visibilities through about 03Z Wedensday. Thunderstorms are possible in this time period as well, particularly at MHT and PSM, but confidence is not high enough to include in the TAFs at this time. After this ceilings will lower to IFR with some IFR visibilities expected in heavier rain. Rain begins to taper off around 09Z Wednesday but conditions will stay IFR as fog forms. Improvement will start after 12Z Wednesday with most terminals VFR after 15Z Wednesday.

Outlook... Wednesday Afternoon: VFR conditions prevail.

Wednesday Night: Terminals may begin to see MVFR as precipitation moves back into the region.

Thursday-Thursday night...LIFR to IFR restrictions and widespread precipitation possible. Mostly rain is expected, except a wintry mix is possible at HIE and AUG.

Friday: Lingering low ceilings, drizzle, or fog possible in the morning with gradual improvement to VFR, especially in NH. Improvement is more questionable in western ME with AUG and RKD possible holding on to low ceilings all day.

Saturday: VFR possible early in the day with restrictions possible later in the day. Confidence is low.

Saturday night-Sunday: Increasing chances for fog, low ceilings, and precipitation with IFR possible as a cold front approaches. Precipitation type is expected to be rain.

MARINE

SCA conditions return tonight as low pressure moves over the waters. This is mainly for building wave heights as wind gusts are expected to generally stay below 25 knots. Northwesterly winds flip to southwesterly winds as a front crosses the waters Wednesday morning. The front then lifts back north flipping winds back northeasterly for Wednesday afternoon and evening.

Thursday-Early Next Week...Easterly flow Thursday will become more southerly Thursday night into early Friday as a warm front lifts to the north. South to southwest flow then likely increases to SCA levels on Friday ahead of a cold front that looks to cross the waters Friday night. Another cold front approaches on Sunday as low pressure tracks north of the region. South to southwest winds again increase to SCA levels, and there may gusts to gale force ahead of the front. SCA conditions probably continue into Monday or Monday night as winds turn west to northwest behind the front, but high pressure should bring subsiding winds and seas by Tuesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory until 8 AM EDT Wednesday for MEZ007>009. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ150>152- 154.