textproduct: Gray - Portland

WHAT HAS CHANGED

A Frost Advisory has been issued tonight for northern Somerset, Franklin, and Oxford counties in Maine and Coos county in New Hampshire.

KEY MESSAGES

1. Cool high pressure will allow for another round of chilly temperatures tonight.

2. Cool and unsettled conditions are expected on Sunday before temperatures warm into the first half of next week. Cooler temperatures may then return late week with bouts of showers at times.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure will keep the weather fair this afternoon with highs mainly in the lower 60s to the lower 70s. It will be a bit cooler across and north of the mountains, mainly in the lower 50s to the lower 60s.

The high remains in place over the region tonight into Saturday morning so we should have more favorable conditions for radiational cooling. The one caveat is that clouds will be gradually increasing from southwest to northeast through the night. Thus, some areas may have clouds creep in before temperatures can bottom out. Did blend in some NBM 10th percentile to bring lows down, but not as cold as last night. Still feel confident that lows will dip into the low to mid 30s north, so have issued a Frost Advisory for my most northern Maine zones (northern Somerset, Franklin, and Oxford counties) and Coos county in New Hampshire. Elsewhere, expect lows to in the upper 30s to mid 40s.

High pressure will continue to dominate the weather most of Saturday but the center will gradually move east out over the waters by the evening hours. The pressure gradient will tighten modestly as the high slides east, so winds may become a bit breezy in the afternoon out of the south. Gusts to 25 mph will be possible. Highs will mainly be in the 60s.

An upper ridge axis approaches from the west and crosses the western portions of the forecast area Saturday night. Southwestern New Hampshire will start to see some height falls with a transition back into southwest flow aloft. Here, we will see increasing clouds and some low precipitation chances late.

Given the holiday weekend and nice temperatures today and tomorrow, we did send out an SPS inland cold water. Use extreme caution if out on the waters this weekend as most lake temperatures are still only in the mid 50s.

KEY MESSAGE 2 DESCRIPTION...

Surface high pressure will exit to our east on Sunday as low pressure tracks northeastward from the Mid-Atlantic region. This area of low pressure will bring periods of rainfall Sunday into Sunday night before becoming more showery in nature by Monday morning. Temperatures will be below average on Sunday with most readings only into the 50s before temperatures rebound closer to seasonable averages on Monday. Rain will overspread NH on Sunday morning but it likely won't begin until the afternoon in parts of ME, especially for locations east of the Augusta area. Latest ensemble based guidance shows average rainfall of around 1/3rd of an inch, which given the ongoing drought conditions will be very manageable.

Tuesday will feature above average temperatures as westerly flow prevails. Highs into the upper 70s to lower 80s are likely with partly to mostly sunny skies. A s/wv trof axis is progged to drop south from Canada Tuesday night into Wednesday, resulting in an increasing chance for scattered showers. Highs on Wednesday will be similar to those of Tuesday. Cooler conditions are then likely late week as north-northeasterly flow prevails.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through Saturday...VFR conditions prevail. Expect some onshore winds for coastal terminals this afternoon with a sea breeze.

Outlook...

Saturday night: Mainly VFR conditions expected but some MVFR CIGs may begin to creep in late Sat night.

Sunday and Monday: MVFR to IFR CIGS are likely due to -RA along with low ceilings and possible FG. E-SE winds are expected with gusts up to 20 kts possible.

Tuesday: VFR conditions expected.

Tuesday Night: VFR conditions likely but -SHRA may bring some restrictions.

Wednesday: VFR conditions likely but -SHRA may bring some restrictions.

MARINE

High pressure will largely be in control of the region thru weekend. Winds and seas are expected to remain below SCA thresholds. The weak pressure gradient should allow for afternoon sea breezes to develop and turn winds onshore. Winds and seas may approach SCA thresholds Sun night into Mon morning as a longer fetch onshore wind develops ahead of an encroaching warm front. Winds then become offshore by midweek as high pressure builds in from the west.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Frost Advisory from midnight tonight to 8 AM EDT Saturday for MEZ007>009. NH...Frost Advisory from midnight tonight to 8 AM EDT Saturday for NHZ001-002. MARINE...None.