textproduct: Gray - Portland

WHAT HAS CHANGED

Based on trends from the past few days, went just a touch cooler for highs today and Friday. Widespread heat headlines still look to be in good shape. Showers and thunderstorms will continue to diminish through the morning.

KEY MESSAGES

1. Heat continues to build and then lingers into at least Friday. Overall the heat remains on track, with minor tweaks to temperatures and heat indices over the next few days.

2. Isolated strong to severe storms possible today (Level 1/5 for severe weather).

3. The ridge responsible for the extreme heat breaks down late Friday through the weekend allowing for a down trend in temperatures. Chances for showers and storms remain in the forecast into midweek.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

The heat will be peaking today-Friday. 850 mb temperatures will be +18-21C. Westerly flow both days should also add a downslope warming boost while negating sea breezes. This will result in widespread 90s outside of the mountains. 100 degree highs are possible in southeast New Hampshire if full surface heating can be attained. With dew points still hanging in the upper 60s-low 70s, this will result in dangerous heat inidices of 105-110+.

Nighttime will bring very limited relief with lows only dropping into the 70s outside of the mountains tonight, with a chance the valleys in southeast NH struggle to fall below 80.

KEY MESSAGE 2 DESCRIPTION...

Another opportunity for storms is in the forecast today, namely "ridge rollers" rounding the top of the anomalous ridge centered over the Eastern U.S. Shear and forcing will once again be on the weak side, which will limit organization. Dewpoints will be a bit lower than today, while it also looks like yesterday's elevated mixed layer will be pushing offshore. Thus, CAPE is expected to be lower, but mean hi-res guidance is still showing a healthy 1500-2500 J/Kg. Given this set of ingredients, would expect damaging winds to be the main threat.

Finally, convection will be a for us attaining the highest potential temperatures tomorrow. There is a low probability that more concentrated storm coverage could cut down on peak temperatures locally, as well as the chance for remnant cloud debris from overnight convection to limit surface heating slightly.

KEY MESSAGE 3 DESCRIPTION...

Models have backed off on the progression of the cold front until later on Friday or even Saturday, but regardless, we should begin heading in a more comfortable direction. This still brings one more very warm day with highs in the upper 80s to low 90s Saturday, but will mark a downward trend from the peak of the heat. Dew points 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 also given it will still be scattered in nature most likely. Right now guidance is beginning to hone in on precip chances Saturday, while Sunday's threat may push south of the forecast area with a sagging front. Details should sharpen in the next 24 hours as hi-res guidance begins to arrive.

Global ensembles continue to trend toward the transition to 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 THURSDAY THROUGH TUESDAY/

VFR should prevail at most terminals through tonight, but some brief restrictions are possible with any showers or storms that move overhead today and tonight. Valley fog or low stratus is also likely at LEB and HIE this morning. Some shallow marine fog is also possible at RKD this morning.

Outlook... Friday-Monday: Generally VFR conditions are expected during daylight hours with TEMPO MVFR conditions possible each afternoon in showers and thunderstorms.

MARINE

High pressure remains centered south of New England for the next couple days. Seas up to 5ft are possible across the far eastern waters late tonight in southwest flow. Some patches of marine fog are possible near the MidCoast shoreline this morning. High pressure settles south of the waters late week keeping winds and seas below SCA levels into midweek next week.

CLIMATE

High temperature records at long term climate sites...

July2nd 3rd

AUG 93 (1963) 94 (2002)

PWM 98 (1941) 95 (2002) CON 98 (1966) 102 (1966)

GYX WATCHES/WARNINGS/ADVISORIES

ME...Heat Advisory until 8 PM EDT this evening for MEZ007>009. Extreme Heat Warning until 8 PM EDT Friday for MEZ012-018>020- 023-033. Heat Advisory from 11 AM this morning to 8 PM EDT Friday for MEZ013-014. Extreme Heat Warning from 11 AM this morning to 8 PM EDT this evening for MEZ021-022-024>028. NH...Heat Advisory until 8 PM EDT this evening for NHZ001>003. Extreme Heat Warning until 8 PM EDT Friday for NHZ004>015. Air Quality Alert from 10 AM this morning to 10 PM EDT this evening for NHZ013-014. MARINE...None.