textproduct: Gray - Portland

WHAT HAS CHANGED

Cancelled a portion of the Small Craft Advisory that was set to expire at 8am. Winds and seas here have since fallen below criteria. Otherwise, no significant changes to the going forecast.

KEY MESSAGES

1. Expect mainly dry and warmer weather through Wednesday but a cold front could lead to a few showers and a rumble of thunder or two tonight or Wednesday.

2. A cooler and more unsettled pattern develops the second half of this week, peaking next weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure settles in across most of the northeast this morning with light winds mainly out of west or southwest. We should see some fog in the early morning given the light winds, recent rainfall, and dewpoints in the low to mid 50s - particularly in the valleys.

East coast high pressure will sag south this afternoon as a low amplitude upper level ridge axis moves across the forecast area. A shortwave will flatten the ridge a bit as a surface low moves into central Quebec this afternoon/evening. A cold front will extend south southwest from this low and start to approach the northeast CONUS tonight. Most of the synoptic forcing will just clip our area, mainly remaining north of the International Border and over northern Maine, but a few isolated to scattered showers will be possible along the higher terrain ahead of the cold front in the afternoon or evening. A few rumbles of thunder will also be possible but instability will be limited. Any showers and storms should diminish fairly quickly with the loss of daytime heating.

The cold front will cross the region tonight into Wednesday. A few early day showers and storms will be possible on Wednesday if they can form in time along the front before it moves out to sea. The latest NAM Nest suggests we could see 500 to 1000 J/kg of MUCAPE along the frontal boundary late morning/early in the afternoon across far southern New Hampshire. With 30 to 40 knots of deep layer shear in the forecast, there could be a brief window for a stronger storm or two here. A few isolated showers will remain possible across the mountains the rest of the day.

Regarding temperatures, it will be much warmer today as a warm front lifts north across the area. Highs will mainly range from the mid 70s north to the low to mid 80s south. It will be quite mild tonight as well with lows only dipping into the lower 50s to the lower 60s. With the cold front moving through, locations across and north of the mountains will see some slightly cooler temperatures on Wednesday, but the rest of the forecast area will see another round of highs in the low to mid 80s. Wednesday night lows will range from the mid 40s north to the mid 50s south.

KEY MESSAGE 2 DESCRIPTION...

After a couple of warm days, longwave troughing develops over the eastern CONUS, cooling temperatures down to near or below seasonal normals for highs through at least this weekend. Ensembles are suggesting a rather anomalous blocking pattern developing by this weekend. Upstream ridging over Hudson Bay, combined with troughing over the SW CONUS, will resemble an omega block pattern. This is likely to result in persistent troughing over the Northeast U.S. for the foreseeable future.

Daily diurnal shower chances are likely, fueled by a persistent cold pool aloft. Both 850 mb and 500 mb temperatures will be anomalously cold for this time of year, peaking this weekend. In fact, freezing levels may be at or below 850 mb, which is rather impressive for the end of May. This cold pool aloft will have arctic origins due to northerly flow aloft. Deterministic guidance is hinting at a more organized low pressure arriving from Canada that could bring more in the way of widespread rainfall. While model agreement in a track from north to south through New England is rather impressive, timing and spatial differences remain notable at this time. Details will become clear in the coming days, but unfortunately a cold and wet trend has become apparent for at least part of next weekend. In fact, cannot rule out graupel or mountain snow given such cold temperatures expected aloft.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Through 12z Wednesday...Fog dissipates early, leading to widespread VFR today through Wednesday morning. WSW breeze picks up later this morning, with a weak sea breeze bringing an onshore wind shift to PWM/PSM around 18z this afternoon. Drier airmass should keep fog at bay tonight, with some lowered cigs, perhaps MVFR, towards the mountains. A couple hours of LLWS possible tonight as a 40kt lower jet passes through the region.

Outlook:

Wednesday: MVFR or localized IFR restrictions may return with showers and thunderstorms. The best chances will be over LEB and HIE. VFR expected Wednesday night.

Thursday-Friday: Scattered showers and a few storms could lead to brief periods of MVFR to IFR restrictions, mainly during the afternoon and early evening hours each day. Otherwise, mainly VFR expected.

Friday night-Saturday: Potential for more widespread rainfall and IFR restrictions, but uncertainty remains.

MARINE

Light westerly winds are expected to continue through the morning and afternoon. An SCA is in effect for elevated seas of 3-6ft through this same timeframe. Winds will become southwesterly and strengthen to near SCA-levels this evening. Elevated seas and winds start to subside by Wednesday morning.

Thursday-Monday...Winds will likely be primarily out of the north Thursday into Friday with low pressure to the east or southeast of the Gulf on Maine. Conditions will mostly remain below SCA levels during this time but can't rule out a brief period of 25 kt gusts Thursday night. A more organized low pressure dropping southward out of Canada may then bring a higher chance of SCA level winds and seas over the weekend.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ150- 152.