textproduct: Gray - Portland

WHAT HAS CHANGED

Updated Aviation section for the 12Z TAFs.

With the very warm temperatures across the area today, some of the CAMS are suggesting enough instability for a few showers over portions of western and southern NH this afternoon, but dry air aloft is expected to keep coverage low. Can't completely rule out a storm based on forecast soundings from the NAM/RAP, but the dry air aloft may be too much to overcome. However, should a storm develop, gusty winds are possible.

KEY MESSAGES

1. Outdoor recreation is bound to be in high demand and area inland and ocean waters remain very cold today. Slightly cooler weather is expected at the coast on Monday as winds go onshore. The far interior remains in the 70s with even some lower 80s possible in southwestern NH.

2. Above normal temperatures continue Tuesday into mid week which should feature the warmest days of the year so far. With the heat also comes the chance for scattered showers and thunderstorms on Tuesday and Wednesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Any showers early this morning should be gone by sunrise allowing for another warm day today. High pressure crests over New England tonight allowing for a decent night for radiational cooling, especially in the mountain valleys where lows may dip into the upper 30s in spots. The main issue will be gusts today with 25 to 30 MPH possible. Area lakes will be wavy.

On Monday, SFC high pressure will move just offshore. This will set up sort of an in-situ warm front which with onshore flow to its east will keep the coastal plain cooler than Sunday. This will especially be true late afternoon and evening when the coldest surface push moves onshore with the help of a seabreeze circulation. Western zones remain warm. There may be a few showers or a brief thunderstorm during the afternoon hours in the mountains as a wave moves eastward north of warm front.

With the abundantly warm weather today, it is important to recognize that lake and ocean water temperatures have not warmed up. Ocean sea-surface temperatures are still in the lower to mid- 40s, with lake temperatures only around 50F. Lake and ocean temperatures this cold pose a significant hazard to swimmers, boaters and beachgoers. Hypothermia and cold shock can occur in these water temperatures.

KEY MESSAGE 2 DESCRIPTION...

Mid/upper level ridging starts to flatten a bit Monday night as a wave moves over the top. Most of the forcing should remain north of our area, but a few showers will be possible across the mountains overnight.

Progressive ridging will pop back up early Tuesday but will be followed by some modest height falls in the late afternoon and into the evening. While synoptic forcing remains a bit nebulous, there should be enough lift to see some isolated to scattered thunderstorms. The best chances will be over northern New Hampshire and the northern portions of the western Maine mountains, but a backdoor front/surface trough could lead to some storms over the Interior and Midcoast as well. The NAM and GFS differ in their estimation of how much instability we will see. The NAM suggests we could see up to 2000 J/kg MUCAPE but the GFS is more in the 1000 to 1500 J/kg range. The European ensemble spits out medium to high chances for MUCAPE greater than 1000 J/kg in the afternoon. The GEFS and GEPS are less bullish. With deep layer shear forecast as high as 30 to 35 knots, this parameter space could potentially be enough for some strong to marginally severe storms in the afternoon and into the early evening. CSU Machine Learning guidance also continues to highlight Tuesday for low severe weather probabilities.

A cold front then moves across the region on Wednesday which could lead to another round of thunderstorms, potentially a bit more widespread than Tuesday. The magnitude of strong to severe storm potential on Wednesday will heavily depend on the frontal timing. The later the front moves through, the more afternoon instability and better chance for stronger storms. There has been a trend over the past couple of days for the front to move through earlier in the day which would keep the stronger thunderstorm potential confined to southern New Hampshire, the Interior/Foothills of Maine, and potentially into portions of the Midcoast. CSU Machine Learning guidance has backed off on probabilities on Wednesday as well. Still, it will be another day to monitor the potential for strong to marginally severe storms, especially if the frontal passage slows down over the next few rounds of guidance. After storms move out on Wednesday we should see mainly dry conditions through the rest of the week and into the early part of the weekend.

Regarding temperatures, Tuesday and Wednesday look likely to be our warmest days of the year so far for most (if not all) locations. Highs on Tuesday will generally range from the upper 70s and lower 80s north, to the upper 80s and lower 90s south. Some coastal areas will be a little bit cooler with an onshore component to the winds. With the cold front moving through on Wednesday, highs will be a touch cooler north (70s) but still very warm south and along the coast ahead of the cold front (mid 80s to lower 90s). We will then cool down through the end of the week and into the weekend with widespread highs in the 50s north, to the 60s south. A few lower 70s will remain possible over southern New Hampshire.

AVIATION /09Z SUNDAY THROUGH THURSDAY/

Through 12Z Monday...VFR is expected for all terminals today with westerly wind gusts of 20 to 30 kt, possibly up to 35 kt. A couple of showers may develop this afternoon across central and southern NH, but chances are too low for TAF inclusion at this time. Winds diminish this evening, and VFR prevails tonight.

Outlook: Monday: Lighter winds and VFR on Monday as winds go onshore.

Tuesday: AM VFR, PM MVFR possible due to showers/thunderstorms.

Wednesday: AM VFR, PM MVFR possible due to showers/thunderstorms.

Thursday: VFR Likely.

MARINE

Southwesterly SCA-level winds will subside early this morning, but seas may remain at or above 5 ft for the coastal waters until later this morning or early afternoon. Light and variable winds are expected to turn east tonight and will continue through Monday.

Southerly winds build up to near SCA levels during the day Tuesday, but slowly start weakening Tuesday night and into Wednesday. Below-SCA level winds and seas will continue through the remainder of next week. Seas are forecast to generally be in the 2-5ft range Tuesday through the rest of the work week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Beach Hazards Statement through this evening for MEZ023>028. NH...Beach Hazards Statement through this evening for NHZ014. MARINE...Small Craft Advisory until 3 PM EDT this afternoon for ANZ150- 152. Small Craft Advisory until 10 AM EDT this morning for ANZ154.