textproduct: Gray - Portland

WHAT HAS CHANGED

Added some PoPs in northern zones for the next couple hours as some light showers are arriving early. Otherwise, the forecast remains on track with the bulk of shower and thunderstorm activity expected this afternoon. Also updated the aviation discussion for the 12Z TAFs.

KEY MESSAGES

1. Smoke from wildfires in Ontario meanders back north today into southern NH and southwest Maine.

2. A cold front will bring some scattered showers and thunderstorms this afternoon. These storms could produce strong winds and small hail, mainly across the mountains towards the Maine coast.

3. Seasonable summertime conditions continue through the weekend and into next week, with at least a couple of chances for showers and storms.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

While smoke aloft from wildfires in Ontario dipped south of the forecast area yesterday, the HRRR continues to suggest we will see a return today for at least southern NH and southwest Maine. An approaching cold front and the upper air evolution may lead to the smoke plume dipping south of the area again late today and tonight.

KEY MESSAGE 2 DESCRIPTION...

An upper level shortwave and surface cold front will move through the region today, leading to some scattered showers and thunderstorms. While instability will be limited, we will see some MLCAPE values in the 250 to 500 J/kg range along the cold front. Low level and deep layer shear will be impressive so a few low topped storms here could become strong to marginally severe. Strong winds, small hail, and frequent lightning would be the main threats under the strongest cores.

Most of the CAMs suggest we will see some ongoing storms along the front in southern Quebec later this morning before moving into northern Maine and New Hampshire by early afternoon. While we could see an isolated storm or two ahead of the front, most of the activity will be tied to this boundary. Most of the CAMs weaken these storms as they move further south and towards the Maine coast, eventually diminishing and/or moving out to see by the evening hours.

Highs today are forecast range from the upper 60s/lower 70s north, to the 80s south. Lows tonight will mainly be in the upper 40s to the mid 50s.

Friday should be rather pleasant behind the cold front with dry conditions and highs ranging from the 60s and 70s north, to the low to mid 80s south. Lows will mainly be in the 50s Friday night.

KEY MESSAGE 3 DESCRIPTION...

From this weekend into next week, we will continue to see the ridge over the north-central CONUS break down and retrograde west, as a trough over southeast Canada tightens its grip. This should result in more seasonable temperatures returning to the region for the foreseeable future.

In terms of surface features, a low pressure coming out of the Great Lakes looks to cross through the St. Lawrence Valley Saturday night. This suggests Saturday will be the wetter of the two weekend days. With hi-res guidance just becoming to get into range, can extract a few signals of how things may go. It looks to be a rather strong surface low for midsummer, likely dropping to around 995 mb on closest pass. After some morning showers along the warm front, New England should poke into a highly sheared, moist warm sector ahead of the cold front. There looks to be an apparent severe threat across the interior Northeast. But with a late arrival into New England during the evening hours, and much tamer lapse rates than Tuesday's setup, currently favoring downpours rather than strong- severe storms. Rainfall looks efficient given a moist airmass, but totals should be kept in check given a rather progressive system.

Conditions should clear Sunday morning. Possibly some CAA terrain- induced showers across the high terrain in the north, but generally looks like the more enjoyable day of the weekend. A high pressure crests overhead on Monday bringing more pleasant conditions. Another system looms towards the middle of next week, but ensemble distribution remains massive at this time.

The fly in the ointment for pleasant conditions will continue to be upstream wildfire smoke. Ahead of and behind the weekend system, flow stays pointed towards New England out ahead of the fire source region.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through 12Z Friday...Mainly VFR. WNW winds will increase again this morning, gusting to 20-25 kts by the afternoon. Scattered TSRA will track from the mountains towards the Maine coast this afternoon, bringing the potential for TEMPO restrictions at HIE, LEB, AUG and RKD. PROB30 has been used in the AUG and HIE TAF, but confidence in storms further south is lower. Storm chances diminish in the evening with winds subsiding overnight.

Outlook...

Friday - Saturday Morning: VFR Prevails.

Saturday Afternoon - Sunday Morning: MVFR to IFR possible with widespread showers and storms likely.

Sunday Afternoon - Tuesday: VFR returns and prevails, with scattered afternoon showers possible across northern terminals. Nighttime valley fog will be possible.

MARINE

Winds and seas remain below SCA thresholds through tonight. Offshore winds turn SW today ahead of a cold front. The front crosses this evening shifting winds back offshore Friday.

Fair conditions prevail from Friday into Saturday. A cold front then crosses the waters late Saturday night and Sunday. SCA conditions in westerly flow are possible behind the front late Sunday and into Monday. Broad high pressure returns early next week with fair conditions.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...Air Quality Alert until 11 PM EDT this evening for NHZ001>015. MARINE...None.