textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes to the forecast were needed.

KEY MESSAGES

1. Hot and humid into this evening with a couple of strong to severe storms possible. Not quite as hot Saturday as temperatures and humidity trend downward slightly.

2. Cooler, more comfortable air filters into the region later this weekend and early next week before temperatures possibly rebound into late week. Rain chances are greatest across southern New Hampshire Monday afternoon into Tuesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Similar to the past couple of days, very hot and humid conditions continue into early this evening with not much in the way of clouds this afternoon during peak heating. Fortunately and unfortunately, there is again a bit of breeze out of the W/WNW, but this will also keep the seabreeze from bringing relief to most of the coastline.

As far chances for thunderstorms this afternoon and evening, CAMs aren't showing much activity developing or making into NH and western ME, but keep in mind these have not had a good track record the last couple of days. So with the same airmass (although slightly drier and less unstable today) in place, I think we could again see a few storms, whether they develop upstream and move into the area or simply develop over NH or western ME. These will be capable of becoming of strong to severe, with damaging winds the main hazard, but hail is also possible. If storms do occur, the more favorable parameters for severe weather will be across southern NH, where a Marginal Risk (level 1/5) is in place but can't rule out a severe storm elsewhere. Most convection should dissipate or move out of the area by midnight or shortly after, but an additional storm or two is possible overnight with some elevated CAPE remaining and weak waves moving overhead. Temperatures remain very warm again tonight with upper 60s to low 70s.

Saturday will be a hot day but not to the levels of the last few days as a shortwave trough moves into southeastern Canada and sends a weak cold front through northern New England, which will begin to begin to suppress the strong upper ridge to farther to the south. Temperatures aloft (+16C to +19C) support reaching highs mostly in the upper 80s to low 90s, but dewpoints are expected to come down into the lower 60s (and maybe even upper 50s) in the afternoon both due to deeper mixing and some drier air behind the front. This will bring in lower humidity and not make it feel as oppressive out, but heat indices could still approach 95F across portions of southern NH and maybe the ME coast. It's possible a Heat Advisory may be needed in parts of southern NH but will let the next shift take another look as it looks pretty marginal. As instability builds during the afternoon, expect at least some development of showers/storms but have chance limited to 20-30% across the board.

Temperatures return to move comfortable levels Saturday night. Lows will be mostly in the 60s, but 50s are possible in an around the mountains.

KEY MESSAGE 2 DESCRIPTION...

Broad low pressure over the Canadian Maritimes continue to push east on Sunday, bringing a plume of drier continental air into northern New England for the second half of the weekend into early next week. The drier airmass should keep showers to the south of the forecast area, but can't rule out some shower activity pushing north into southern NH through the Sunday evening hours. Daytime temps will run about 5 degrees cooler than Saturday, topping out in the mid to upper 80s across the coast and interior. Upper 70s seem like a good bet for the mountains. Perhaps more noticeable would be the lower dewpoint temps, resulting in RH values in the 20 to 30 percent range, some welcome relief after a hot week.

As the upper trough moves east, SW flow ahead of a wave out of the Great Lakes will move to replace the exiting dry airmass Monday. The absence of former anomalously warm temperatures aloft and increase in cloud cover will present cooler temperatures Monday and Tuesday. These two days feature a large spread in forecast temperatures, with temps greater than 85 unlikely for most of the CWA. The aforementioned wave will undergo some strengthening, but overall will remain broad and on the weaker side. It should be enough to force a stratiform rain shield through New England Monday afternoon into Tuesday. Unfortunately, cluster analysis reveals there is still equal weights amongst global models on how far north or south this sets up. At time of writing, the better chance for greater than a quarter inch of QPF is across southern NH from Monday evening through Tuesday.

Once this system clears east Tuesday night, temperatures again warm towards the upper 80s for late week. Also possible will be a cold front nearing the region into Friday. Depending on timing, this could bring the chance of some thunderstorms to the area Thursday evening or even for the day on Friday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday...Mostly VFR. Similar to yesterday, a couple of storms could bring TEMPO IFR restrictions this afternoon through late evening. Although the chance is low, have added VCSH mention for the NH terminals as chances appear somewhat higher there.

Outlook:

Rest of Saturday: Mainly VFR. TEMPO IFR to MVFR restrictions possible if a shower or storm passes over any terminal in the afternoon, but chances appear low.

Saturday night: VFR with light winds, except valley fog may develop at LEB and HIE.

Sunday and Sunday Night: VFR likely w/ no sig wx.

Monday: Increasing rain chances and clouds south to north in the afternoon. Patchy MVFR cigs across southern NH possible, otherwise VFR.

Monday Night: Continued rain chances across southern NH. MVFR possible.

Tuesday: Rain departs east, with improving cig in the late afternoon. VFR likely.

Wednesday: VFR likely under high pressure in the region.

MARINE

Conditions will continue to remain below SCA levels through Saturday night. The waters will see primarily a west to southwest flow through Saturday before turning north to northwest behind a weak frontal boundary Saturday evening and Saturday night. .

High pressure over the waters Sunday will move east through Tuesday. Broad low pres exiting the Great Lakes will move over New England Monday night into Tuesday. This exits east Tuesday night, with high pressure moving into New England Wednesday.

CLIMATE

High temperature records at long term climate sites...

July 3rd

AUG 94 (2002)

PWM 95 (2002) CON 102 (1966)

GYX WATCHES/WARNINGS/ADVISORIES

ME...Air Quality Alert until midnight EDT Sunday night for MEZ007>009-012>014-018>028-033. Extreme Heat Warning until 8 PM EDT this evening for MEZ012- 018>020-023-033. Heat Advisory until 8 PM EDT this evening for MEZ013-014-021- 022-024>028. NH...Extreme Heat Warning until 8 PM EDT this evening for NHZ004>015. MARINE...None.