textproduct: Gray - Portland

WHAT HAS CHANGED

Northern Grafton County has been converted to a Freeze Warning tonight. Otherwise no significant changes with this forecast update.

KEY MESSAGES

1. High pressure allows for cold night tonight followed by fair weather Friday. Frost and Freeze headlines are in effect across the mountains and foothills.

2. High pressure will dominate the remainder of the forecast. Some rain will push into the area to end the weekend, but the question is how far northeast does the rain make it before sliding out to sea.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A cool and dry airmass is in place as high pressure continues to build in from southeast Canada tonight. Highs clouds over the southern half of the area will gradually clear overnight along with diminishing winds. This will allow for favorable radiational cooling with northern valleys dropping below freezing and areas along the foothills and western New Hampshire dropping into the mid 30s. Frost and Freeze headlines remain in effect for tonight. Enough flow along the coastal plain will keep lows in the upper 30s to low 40s.

High pressure provides fair weather on Friday. Light and variable winds will turn onshore Friday afternoon. Highs will generally be in the 60s with some interior locations climbing into the low 70s. High pressure will allow for another cool night although increasing clouds from the southwest may halt radiational cooling the second half of the night. Some frost will be possible across the north where clouds are last to arrive.

KEY MESSAGE 2 DESCRIPTION...

By Saturday, a mid to upper level ridge will be located to our west with surface high pressure located to the north over Quebec. This pattern will lead to mostly dry conditions through the day, but an approaching trough could lead to at least low chances (20 to 40 percent) of some light rain over southwest New Hampshire by late Saturday night. Some of the guidance has rain moving in earlier than others but I am skeptical of the earlier solutions as most models suggest we will be seeing height rises or neutral heights until Sunday.

On Sunday, a surface low will also deepen off the coast of New Jersey before lifting into the Gulf of Maine by Monday morning. Thus, we will see increasing chances of rain through the day on Sunday and Sunday night before a gradual decrease in coverage from west to east on Monday. The best synoptic forcing should move through Sunday night into Monday morning which is when we will likely see the heaviest rain. Even then, amounts are expected to be fairly light. The latest NBM currently suggests medium to high probabilities (40 to 80 percent) for a quarter inch of rain or more across the southern half of New Hampshire and the foothills/interior of Maine. However, when we increase that threshold to a half inch, the QPF probabilities decrease into the low to medium (20 to 50 percent) range. Thus, confidence is fairly high that we will see widespread totals in the quarter to half inch range, but confidence for higher amounts are pretty low at this time.

Sunday and Memorial Day do not look to be a washout by any means, but keep an eye on the skies if you have plans outside as there will be some widespread light to moderate rain floating around.

After rain moves out on Monday, the rest of the week looks fairly dry but models do have a weak wave and cold front moving through the Tuesday night through early Thursday period, but confidence in location/timing remains low. Otherwise, expect high pressure to dominate the pattern.

Regarding temperatures, we will start out with highs mainly in the 60s on Saturday, but a few lower 70 aren't out of the question. We will then cool down on Sunday with widespread rain and cloud cover in the area. Highs will mainly be in the 50s. High pressure will then lead to a gradual warmup through the rest of the week. By Tuesday, we will have widespread highs back in the 70s. A weak disturbance could lead to some cooler temperatures midweek, but large NBM temperatures spread suggests some timing differences.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Through Friday...VFR prevails tonight through Friday. Light and variable winds will become light onshore winds for coastal terminals Friday afternoon.

Outlook...

Friday night: VFR conditions expected.

Saturday and Saturday night: VFR conditions expected to prevail much of the time, though some MVFR CIGs may begin to creep in late Sat night.

Sunday and Monday: Periods of MVFR or lower as CIGs lower and areas of rain move thru the region.

Tuesday: Gradual improvement to VFR expected.

MARINE

High pressure continues to build in tonight and will settle over New England through Saturday. This will keep winds and seas below SCA thresholds.

Winds may approach SCA criteria on the coastal waters Tuesday and Wednesday as southerly fetch builds. Winds then become offshore behind a stronger cold front Wed evening. High pressure builds in from the west mid to late week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Freeze Warning from 11 PM this evening to 8 AM EDT Friday for MEZ007-008. Frost Advisory from 11 PM this evening to 8 AM EDT Friday for MEZ009-012-013-033. NH...Freeze Warning from 11 PM this evening to 8 AM EDT Friday for NHZ001>003. Frost Advisory from 11 PM this evening to 8 AM EDT Friday for NHZ004>007-011. MARINE...None.