textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes to the forecast with this update.

KEY MESSAGES

1. Wet weather moves in early this morning and continues through Memorial Day.

2. Warmer than normal Tuesday and Wednesday with shower chances Tuesday night and Wednesday with isolated thunder. Late week and weekend remains uncertain with unsettled weather possible.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure continues to be hard to dislodge with the leading edge of precip largely stationary thru the night. However delayed the rain will not be denied, and the column will gradually saturate thru sunrise. Some light rain/showers will break out across parts of the Upper Valley into southwestern NH before then, reaching the Portland area by midday, and late afternoon farther northeast. As the day wears on the mid level warm advection and frontogenesis will weaken, so there is a general expectation that precip will become more showery, lighter, and more confined to the near coastal areas. By the time precip winds down later today most areas south of the mtns are expected to be around 0.25 to 0.5 inches total. Amounts will be lighter in the mtns and northeast towards Moosehead Lake. Tonight the warm advection flow continues in the dry slot so I am expecting that areas of fog and low cloud will develop, and latest runs of the HRRR are already hinting at that. Some of that fog may be dense near the coast, and drizzle will remain possible in the low clouds into Mon. Then as the cold front approaches Mon another area of rain will develop along and ahead of it. CAM guidance is starting to show some more impressive rainfall rates. Thru the day 0.5 to 1 inch of rain is more likely the outcome across the forecast area, so rainier than today but not something that should cause flooding issues. By the late afternoon some clearing from the west is possible, but maybe too late to salvage much of the day.

KEY MESSAGE 2 DESCRIPTION...

Tuesday looks to be the warmest day of the week as temperatures rebound well into the 70s to mid 80s depending on location. Wednesday with be a bit cooler but still pretty warm. Tuesday night a short wave trough will move in from the northwest with increasing chances for showers and possible thunder. Heights will continue to fall on Wednesday and this will likely aid in scattered showers and perhaps a few thunderstorms.

Various sources of guidance begin to diverge with respect to the upper air pattern over Quebec on Thursday. Most ensemble guidance shows upper level low pressure diving into New England or at least nearby sometime between later Thursday and Saturday. This may portend to unsettled weather. However, timing and amplitude has to come into better agreement for us to have more confidence in the late week and weekend forecast.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

VFR conditions expected to prevail thru sunrise for most locations. However early this morning and gradually from southwest to northeast light rain will creep across the forecast area. This will be followed by MVFR CIGs a few hours later. Even with a break in rainfall during the afternoon eventually IFR conditions are expected to develop rapidly near sunset. Areas of fog will be possible near the coast tonight into Mon.

Outlook...

Monday: Areas of IFR may improve slightly during the day but more rain will move in and local IFR may continue into the afternoon. Near the coast southeasterly surface gusts of 20 kt are possible. Some late day improvement in CIGs is anticipated.

Monday night: VFR conditions expected.

Tuesday: VFR conditions expected.

Tuesday night: MVFR possible in the mountains with showers and isolated thunder.

Wednesday: MVFR possible due to showers and possible thunder.

Wednesday night: MVFR possible due to showers.

Thursday: MVFR possible due to showers, mainly in the mountains.

Thursday night: MVFR possible due to showers.

MARINE

High pressure continues its slow retreat today and southeast or east southeast winds will slowly increase overnight into Mon. While wind gusts will generally stay below 25 kt for most of the waters, seas are forecast to build to 5 or 6 ft Mon. Current forecasts are for periods to be in the high single digits, so seas may approach high surf advisory criteria.

Generally relatively light winds are expected Tuesday through the remainder of next week. Seas of 3-6ft 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...Small Craft Advisory from 2 AM Monday to 8 AM EDT Tuesday for ANZ150-152-154.