textproduct: Gray - Portland

WHAT HAS CHANGED

Little change to the going forecast at this time.

KEY MESSAGES

1. Showers, possibly heavy at times through the the morning before becoming lighter during the afternoon hours. A few thunderstorms possible.

2. Low-impact weather expected mid to late week, with a couple chances for light rain.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A warm front will gradually lift northward through the forecast area early this morning. The modest forcing for ascent coupled with PWATS climbing to around 1.75 inches will aid in showers, possibly heavy at times. A thunderstorm is possible. Latest CAMs have been a bit inconsistent with the potential for a 1 to 3 inch band of rain early this morning across the mountain zones. Heavier amounts would be possible. However, the inconsistencies in the latest guidance is leading to less confidence in the occurrence of this. We'll monitor this for a localized flash flood but appears as though the most focused forcing will be to the north of the CWA.

As today progresses, low pressure will develop to our south and pass northeastward into the Gulf of Maine tonight. This will aid in turning our winds toward a more northerly component which will also aid in lowering PWATS as the mid levels dry out. This will result in a more spotty nature to the showers and possibly portend to drizzle at times along with some fog on the coastal plain.

It's not out of the question that the CT River valley destabilizes by late this afternoon which could aid in thunderstorm development for a couple of hours before sunset.

Tonight will feature areas of fog and drizzle with low clouds.

Gradual improvement is foreseen Tuesday, especially during the afternoon hours.

KEY MESSAGE 2 DESCRIPTION...

Tuesday, low level moisture may still be entrenched along the coast and interior. It will depend on proximity to a low as it exits southern New England and pivots towards/just outside of the Gulf of Maine. Would expect northerly flow behind the low to whittle this away, but just 10 kts at 850mb won't make it quick.

Guidance has been initiating some diurnal showers or storms Tuesday afternoon across portions of the interior where this moisture overlaps enough daytime heating. Model profiles show moisture in the lower levels, but also feature a very dry mid to upper level. It is possible warm air aloft also advects in, creating a cap and ultimately limiting a unstable layer. As a result, went with lower precip chances at this range. Not ruling out showers and storms, but think they could be more isolated in nature given the prominent dry air aloft and ceiling on instability.

Warmer for Wednesday as southerly flow kicks in ahead of an elongated cold front. Highs should bump up into the low 80s, a few degrees warmer than Tuesday. While the approaching front will carry precipitation with it, lift is in question as the parent surface low is well north, east of Hudson Bay. Thus precip into New England may be dependent on daytime instability if timing aligns.

A southern stream disturbance may pass just to the south Thursday, exiting across the Gulf of Maine or open Atlantic. This could bring NW periphery showers, but we could also see a deep enough dry layer to negate much of this. High pressure then looks to return to the region late week, perhaps in time for a sunny start to next weekend.

AVIATION /01Z MONDAY THROUGH FRIDAY/

TONIGHT THROUGH TUESDAY...VFR conditions will degrade to IFR early on across the CT river valley with MVFR elsewhere in showers. Conditions further degrade by afternoon as low clouds and fog are expected with showers. Widespread IFR conditions are expected tonight in fog and low clouds. Gradual improvement is foreseen from west to east Tuesday morning.

OUTLOOK:

Tuesday night and Wednesday: VFR, no sig wx.

Wednesday Night: SHRA possible for the mountains, MVFR/VFR.

Thursday: SHRA possible along the coast, mainly VFR.

Friday: VFR, no sig wx.

MARINE

A brief period of SCA-magnitude winds are possible this morning but for the most part should stay below 25 knots. Seas should mostly remain below SCA levels through this timeframe, with seas of 2-4ft expected. Some 5ft waves can not be ruled out in the open waters over 25 miles offshore.

Winds and seas likely remain below SCA levels through the rest of the week. A cold front approaches the waters midweek, as a wave of low pressure passes south of New England and into the Gulf of Maine or open Atlantic. High pressure could return late week.

GYX WATCHES/WARNINGS/ADVISORIES

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