textproduct: Gray - Portland

WHAT HAS CHANGED

Confidence continues to increase in the potential for significant heat in the Wednesday through Friday timeframe.

KEY MESSAGES

1. Pleasant conditions, with a few passing showers this afternoon/evening, continue through Monday.

2. Hot and Humid conditions arrive this week, with near record breaking heat increasingly likely for mid to late week. Any preparations, such as installing air conditioning units, would best be completed early this week before the hottest conditions begin on Wednesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Daytime cumulus will continue this afternoon, with deeper structures supporting a brief shower or rumble of thunder. These seem most likely across interior and mountain areas through early evening before daytime heating subsides. Like last evening, there is the chance for an isolated shower to continue through the late evening and overnight hours, but these should be few and far between.

Fog bank that had been in vicinity of the bays/harbors yesterday and overnight has retreated 20 to 30 miles off the coast. This should be a good buffer to keep prevent additional widespread dense fog tonight. But, with little shift in airmass, can't rule out some fog development along the coast and Midcoast later this evening and overnight.

Monday continues warmer, but a drier atmospheric column should keep showers at bay. Temperatures climb into the mid to upper 80s outside of the mountains, but an afternoon sea breeze should offer some relief along the coast.

KEY MESSAGE 2 DESCRIPTION...

The warming trend continues on Tuesday with widespread highs in the 80s across the interior. Along the coast, onshore flow likely keeps highs mainly in the 70s for one more day.

By Wednesday, the significant heat likely arrives into at least New Hampshire and western Maine as highs warm into the 90s. What makes this heat event notable is just how much moisture will accompany the heat. Dew points likely push into the low to mid 70s on Wednesday, pushing heat indices into the triple digits where temps reach the 90s. These high dew points continue through at least Friday.

One possible limiting factor for the heat remains the potential for rounds of convection originating near the Great Lakes, and riding around the ridge into New England. Should these arrive during the midday timeframe, they would serve to limit the heating potential. But arriving at any other time of the day, they will likely only serve to increase dew points. We'll likely have to wait until Tuesday to have a better handle on how these will effect temperatures in the Wednesday through Friday time frames, as the differences will be localized and variable.

Outside of any convection, the heat looks most likely to peak on Thursday and Friday. Modeled 850mb temps of 22-24C support the potential for near record high temps of 97-102 degrees, barring any hinderance from convection or sea breezes. It would be a misuse of time to tinker with which side of 100 temperatures will reach in the Thursday and Friday timeframe at this point in time. The main message remains that heat and humidity hazardous to health is increasingly likely as heat indices push 110 degrees by Thursday.

Additionally, the trend over the last few model runs has been for an increasing chance of the heat to continue into at least Friday of Saturday. The models first trended warmer for Wednesday and Thursday over the last few days, and now look to be trending this way for Friday and Saturday as well. We will continue to watch the progression of this, with a trough and cooler conditions situated just to our east across Atlantic Canada.

Across the Northeast US as a whole, this heat wave is shaping up to look similar to some of the more notable events from history, such as the 1911 and 1966 heat waves. For northern New England, there remains some uncertainty on how high temps will climb with convection and potential sea breezes offering opportunities for some relief. But record breaking or not it's going to be hot, and individuals sensitive to heat and those working or playing in the heat should take precautions to limit exposure to it mid to late this week.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Through 18z Monday...Mostly VFR expected except for valley locations that see another night of FG w/ LIFR vis/cig. Fog shouldn't be as widespread along the ME/NH coast tonight, but can't rule out dips to 3 or 4SM with 1SM towards RKD. SHRA and possible TS through early evening, mostly for interior ME and central/northern NH terminals.

Outlook:

Monday Night: Chance for the return of fog along the coast hinges on how robust it is over the coastal waters through Monday. It is likely this does not return until after 00z.

Tuesday - Friday: Mainly VFR prevails at most terminals, but rounds of showers and storms will be possible each day. Marine fog will be possible at RKD.

MARINE

Marine stratus or fog seems likely to remain around the coastal waters for much of the coming week in between systems.

High pressure gradually settles south of the waters by midweek. Mainly fair conditions prevail, but some seas to near 5ft are possible Tuesday night in southwesterly flow.

CLIMATE

High temperature records at long term climate sites...

July 1st2nd3rd

AUG929394

PWM939895 CON9998102

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.