textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this forecast package update.

KEY MESSAGES

1. One more day of intense heat today.

2. Isolated strong to severe storms possible this afternoon and evening, mainly over southern New Hampshire (level 1/5 for severe weather).

3. Temperatures start slowly trending down tomorrow with chances for showers and storms. Precipitation chances remain into next week with more seasonable temperatures.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

850 mb temperatures drop a touch but remain +17-20C. Westerly flow should also add a downslope warming boost while negating sea breezes. This will result in widespread 90s outside of the mountains, with upper 90s in the warm spots. Dewpoints will drop a touch from yesterday, but still expecting dangerous heat inidices over 100 degrees.

KEY MESSAGE 2 DESCRIPTION...

As a cold front slowly starts to approach from the west, we will see another day with decent instability and some deep layer shear in the 30 to 40 knot range. While synoptic forcing is forecast to be fairly meager, a weak wave may cross into southern New Hampshire in nearly zonal flow aloft late this afternoon or this evening. An isolated strong to severe storm is possible here. Primary threats include damaging winds and maybe some hail.

KEY MESSAGE 3 DESCRIPTION...

Models have backed off on the progression of the cold front until late today or even Saturday, but regardless, we should begin heading in a more comfortable direction. This still brings one more very warm day Saturday with upper 80s/low 90s, but will mark a downward trend from the peak of the heat. Dewpoints will also be lower on Saturday, keeping heat indices within a few degrees of the air temps.

There remains uncertainty on precipitation coverage this weekend, owing to the frontal passage timing, but it will most likely still be scattered in nature. Right now guidance is beginning to hone in on precip chances Saturday, with drier conditions for Sunday as the front sags south of the region. This should also allow for relief in the form of lower temperatures and dewpoints. Global ensembles continue to trend towards a broad trough following this ridge, which would continue the cooling trend early next week, as well as keeping showers and storms in the forecast. We then may see another warm up midweek as there is surprising agreement already of another ridge taking shape.

AVIATION /06Z FRIDAY THROUGH WEDNESDAY/

Through 06Z Saturday...VFR conditions are generally expected to prevail through this afternoon and evening. We will see some isolated to scattered showers and storms in the afternoon/evening but confidence in placement/timing remains too low to include mention at any specific site for now. If a storm does pass overhead, brief MVFR or IFR conditions will be possible. Any instances of fog this morning or tonight should also be very isolated.

Outlook...

Saturday-Sunday: Isolated to scattered showers and storms could lead to some brief MVFR or IFR conditions Saturday afternoon and evening.

Monday-Wednesday: More showers and storms are also possible Monday through Wednesday, which could lead to localized MVFR or IFR restrictions. Otherwise, VFR conditions are expected to dominate the period.

MARINE

Westerly winds will continue through the day, fighting off the seabreeze. Wind gusts and seas remain below SCA levels through much of next week.

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 Friday for MEZ012-018>020- 023-033. Heat Advisory until 8 PM EDT Friday for MEZ013-014-021-022- 024>028. NH...Extreme Heat Warning until 8 PM EDT Friday for NHZ004>015. MARINE...None.