textproduct: Gray - Portland

WHAT HAS CHANGED

Not much has changed for the general forecast package. Rain may come in two rounds on Sunday, one during the first part of the day and one more in the evening/night.

KEY MESSAGES

1. Seasonable weather to begin Memorial Day Weekend with wet weather closing it out.

2. A fairly unsettled but unimpactful 2nd half of the week is expected, with cooler temperatures and showery weather likely.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

An upper level ridge axis will gradually approach from the west through the day, eventually crossing the forecast area tonight through Sunday. This will mean dry conditions through the rest of today and most of tonight, but high clouds will be on the increase through the day as high pressure slides east and out over the waters by this evening. A modest tightening of the pressure gradient will keep some breezy southerly winds in the forecast this afternoon and again on Sunday.

As the ridge axis moves east, locations will transition into southwest flow aloft as the next trough starts it's approach. This will lead to increasing precipitation chances either late tonight or early Sunday morning as shortwave energy moves through the flow. This first round of rain will gradually spread southwest to northeast through the day with high chances of precipitation (70 to 100 percent) at some point during the day for almost all of New Hampshire and western Maine. This will mainly be a stratiform rain with some moderate patches embedded. Some locations could see a break in precipitation in the mid to late afternoon before the core of the trough approaches in the evening/night time hours. CAMs seem to suggest this next round could be more convective with some heavier embedded downpours, especially southern New Hampshire and southwest Maine where RAP forecasts suggest 100 J/kg of MUCAPE or so. A stray rumble of thunder or two here is not out of the question. Most of the rain will then move out of the area on the morning of Memorial Day/Monday, but a few showers may linger into the afternoon. Certainly not a washout by any means with some clearing by the afternoon. As a side note, Mount Washington and some of the higher peaks could see a little bit of snow mixing in at times on Sunday.

For total rainfall amounts, we still aren't expecting anything too impactful. The highest totals will likely be over the southern half of New Hampshire and locations along and south of the foothills/interior of Maine where we could see a broad range of a quarter to half inch. Any areas that see heavier showers could see some locally higher amounts.

Regarding temperatures, expect widespread highs in the 60s but we cool down into the 50s on Sunday with widespread cloud cover and rain expected. The cool down will be short lived, however as we warm back into mid 60s to mid 70s south of the mountains on Monday. Highs will be in the upper 50s to mid 60s around and north of the mountains. Even during warmer period stretches this holiday weekend, keep in mind that water temperatures still range from the upper 40s to mid 50s so just remember that cold water temperatures can quickly cause hypothermia to anyone immersed in the water.

KEY MESSAGE 2 DESCRIPTION...

Through the 2nd half of next week, a 500mb ridge builds in the central US. The amplification of this ridge is likely to push an upper-level low southward into the Canadian Maritimes. This will allow for an unsettled and cooler end of next week.

Wednesday morning, a surface low moves southeastward across the region. Instability exists with minimal energy and an early frontal passage time should allow for more showery weather across the area rather than thunderstorm activity. The cold front moves across by the end of the day, allowing for even cooler temperatures to arrive on Thursday. Temperatures on Wednesday will range from upper 60s in the north, to lower 80s across southern NH.

Just like Wednesday, some instability may also exist on Thursday but temperatures will be too cold to generate enough diurnal heating to produce convection. Thursday should start dry but become more unsettled by the end of the day. Thus, more showery and rainy weather is likely Thursday evening with rain chances a bit higher over Maine. Conditions generally look to become drier through the weekend as a weak high pressure system tries to squeeze into the northeast. High temperatures look to be in the mid-60s along the coast through the remainder of the week, near 70F elsewhere.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

VFR conditions expected to prevail thru the night. Gradually from southwest to northeast light rain will creep across the forecast area. This will be followed by MVFR CIGs a few hours later. Eventually IFR conditions develop rapidly near sunset. There could be a little bit of a break in rain in the afternoon.

Outlook...

Sunday night and Monday: Widespread MVFR/IFR continue as more rain moves into the forecast area. Fog will become possible by Monday. Near the coast southeasterly surface gusts of 20 kt are possible.

Monday night: VFR Expected.

Tuesday: VFR Expected.

Tuesday night: VFR Expected.

Wednesday: MVFR possible due to showers.

Wednesday night: MVFR possible due to showers.

Thursday: MVFR possible due to showers.

Thursday night: MVFR possible due to showers.

MARINE

High pressure remains in control of the coastal waters through Sunday. Sea breeze is likely during the afternoon under the weak pressure gradient. As a warm front lifts across the waters Monday, onshore winds will increase and marginal SCA conditions are possible as southerly flow builds seas to near 5 feet. The period will be approaching 10 seconds, so fairly marginal, but may pose an increasing rip current risk bordering on high surf. Winds then become offshore by midweek as high pressure builds in from the west.

Light and variable winds are expected through the remainder of next week. Seas of 4-6ft are expected Tuesday morning, but will decrease to 2-4ft by Wednesday morning. Seas of 2-4ft expected beyond Wednesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.