textproduct: Gray - Portland

WHAT HAS CHANGED

Minor changes to PoPs through tonight to align with observed trends and a minor update to the Aviation section for the 00Z TAFs.

KEY MESSAGES

1. On and off showers tonight lead into a more widespread rainfall Thursday through at least the first half of Friday. While flooding is not forecast, rain rates may be heavy at times Thursday through Thursday evening.

2. Warmer than normal temperatures arrive beginning this weekend, and may be much above normal parts of next week. Local waters however remain very cold and this may be the first real stretch of weather where that is a recreational hazard.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

After a period of rain pushes north through the forecast area today, more showery conditions are expected overnight tonight through the mountains.

As low pressure moves into the eastern Great Lakes overnight, incoming front will tend to orient poleward. This will slow its eastward progression and instead advect moisture in from the New England coast. With daytime heating and LLJ arriving from offshore low to the east, precipitation should break out across southern New England, pushing north. Depending on placement of the occlusion come Thursday, this will be the focal point of moisture advection and resulting moderate rainfall through the day.

There remains some spread in where this lines up, and it will play a big role in amounts for NH during the daytime. A further east translation could lead to greater amounts of NH, where a slower trek would bring much of this rain just to the west. Even with this spread, around a half inch of rainfall seems likely for much of southern and central NH through Thursday daytime.

Into the evening, the center of low pressure shifts more south and east into southern New England. This is when the band of moisture and forcing really compliment each other and could lead to moderate to heavy rainfall rates from the southern ME coast inland towards the White Mountains. Rain processes should be efficient with a 30+ kt LLJ and PWATs over 1 inch, but warm cloud depth is fairly shallow between 6 to 7 kft. Thus not overly concerned about flooding potential with this event, and more look at it as a great opportunity to recharge some drought deficit.

The low will continue to influence conditions (showers) into Friday, but its track east will feature lesser forcing and general improvement in conditions for the eastern forecast area through the day.

KEY MESSAGE 2 DESCRIPTION...

Once upper low pulls away from the region we look to trend fairly quickly to above normal temps. A cold front will approach Sat and southwest winds will strengthen ahead of it. This will transport much warmer air aloft into the forecast area and temps should climb well into the 70s. There does not appear to be much a strong push to drive the front entirely thru the forecast area, but showers and thunderstorms will be possible during the afternoon, especially across the interior. As it stands right now the best shear/CAPE combination appears to be west of the forecast area, but I could see that trending eastward over time and it is something to keep an eye on for severe weather chances. After Sun the real push of warmer air is expected to arrive. There is strong ensemble agreement in temps climbing much above normal and 80s and maybe even a few 90s are possible across parts of the area. If that comes to pass there will be the typical early heat concerns for sensitive populations, but also the hazard of recreation while the inland and ocean waters remain very cold. As this round of heat breaks midweek there will be another chance for thunderstorms and long range machine learning severe weather guidance suggests this as another period to keep an eye on.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Through 00z Friday...Flight restrictions are variable across the area this evening due to SCT to OVC with cloud bases between 500 and 1000 feet. General trend will be towards MVFR/VFR through 06Z to 09Z with CIGs starting to lower thereafter. Low confidence in vis reduction due to fog tonight. Guidance has low probabilities, but the moist environment advecting onshore creates a good environment for this possibility along the coast and interior terminals. There will also be a window of 30-40kt LLWS into early Thurs AM.

More RA/SHRA Thursday, mainly focused south and west of AUG/RKD. Would expect trend to MVFR early morning, with IFR into the daytime for most terminals.

Outlook:

Thursday Night: RA may be heavy at times towards southern coastal ME and southern NH terminals. Would expect IFR vis/cig, with LIFR possible through the evening towards midnight.

Friday: Becoming VFR.

Friday Night: VFR conditions expected.

Saturday: VFR conditions expected. Some local MVFR or lower possible in showers.

Saturday Night: VFR conditions expected.

Sunday: VFR conditions expected.

Sunday Night: VFR conditions expected.

Monday: VFR conditions expected.

MARINE

A period of SCA gusts is forecast through tonight, but a lull is expected as winds shift Thursday. NE winds will then continue overnight through Friday, again building wave heights 4 to 6 ft.

There are two periods of potential SCA conditions coming up in the extended range. Both will occur with the approach of a cold front. Southwest winds will freshen ahead of the fronts, but southwest winds and warm advection this time of year struggles to fully mix down over the surface of the cold Gulf of Maine waters. So I am not sold yet that we reach criteria, but some near 25 kt gusts will be possible both Sat and again next Wed.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ150-152- 154.