textproduct: Gray - Portland

WHAT HAS CHANGED

The threat for severe storms has ended across the region with the loss of daytime heating and instability. A few showers and rumbles of thunder will remain possible for a few more hours though, mainly from the foothills and points north. Other than making some minor adjustments to near term trends and adjusting the aviation section for the 00Z TAF package, no significant changes were made at this time.

KEY MESSAGES

1. A couple of strong to severe thunderstorms are possible this afternoon into early evening as a front moves across the region. Damaging winds and hail will be the primary hazards.

2. Mostly dry weather with seasonal temperatures is expected Friday and Saturday as high pressure builds toward New England.

3.An unsettled pattern returns with rain Sunday night into Monday morning, with shower and thunderstorm chances returning for the latter half of the week. Seasonable temperatures are expected through the period.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Showers and thunderstorms will continue to develop this afternoon as a front approaches from the northwest. Convergence isn't all that great along the boundary, which should help keep coverage more scattered in nature. Still, effective shear of 30-35 kt and MLCAPE of 500-1000 J/kg could allow some storm organization and a couple of strong to severe storms. Damaging winds will be the primary hazard, but lowering freezing levels to around 8000-9000 ft and some steepening of lapse rates aloft will also bring a threat of hail.

Convection will diminish toward sunset, but some of the CAMS are advertising another push of convection approaching from the north this evening that could bring additional storms in and around the mountains...so we'll have to be mindful of that. Otherwise, upsloping may allow a few showers overnight in the mountains, while skies clear out to the south as drier air moves in behind the front. With the clearing skies and light winds, expect valley fog to develop in some areas, especially along the CT River. Overnight lows will be mainly in the 50s.

KEY MESSAGE 2 DESCRIPTION... Friday will be a mostly dry and somewhat breezy day as high pressure begins to build in from the northwest behind today's cold front. Upslope flow may continue a few showers in the mountains early in the day, and a 500mb shortwave crossing the eastern Great Lakes and into southern New England was allow a shower or storm to clip southwestern NH...but the vast majority of the area will not see any precipitation. High temperatures will range from the low-mid 70s north to upper 70s-low 80s south.

Canadian high pressure further builds in from the northwest Friday night with good conditions for radiational cooling and a seasonably cool night. Low temperatures in the normally cooler and valley locations have a good chance of seeing lows in the 40s while others see temps in the 50s. Valley fog will again be possible.

The high builds overhead Saturday, keeping the first part of the weekend dry with lighter winds and comfortable humidity. Highs will be similar to those for Friday with temps in the upper 70s-low 80s for southern areas and low-mid 70s in the north. Good radiational cooling Saturday night could again bring lows down into the 40s to lower 50s.

KEY MESSAGE 3 DESCRIPTION...

Looking ahead toward the second half of the weekend, Sunday looks very seasonable due to high pressure nudging into our area for the day with temperatures approaching the low 80s away from the coast, but elsewhere, expect temperatures should stick to the mid to upper 70s. Like for most of the summer, a sea breeze will likely kick in during the afternoon hours, dropping temperatures a bit, near and along the immediate coastline. Clouds will be on the increase towards the latter half of the day due to an approaching system looking to bring rainfall for our region during the overnight hours. PoPs look relatively low for the majority of the day, however, they will start to increase as the weekend wanes. Most global models have Sunday nights' batch of rain move out by the start of the work week on Monday, although some showers could linger throughout the late morning hours. These models also show the low pressure center, which delivers our rainfall, to move south of us, delivering the heaviest batch of rain to the north of the storm center, putting it right into our CWA. Most models have around one half to an inch or so of rainfall,for our CWA. For the remainder of the day on Monday, scattered showers look to be present in the mountainous areas in the afternoon hours with temperatures in the mid 70s away from the immediate coastline, with a few pockets of upper 60s for northern Coos, Franklin, and Somerset counties.

Tuesday has high pressure sneaking closer to our area, delivering calm conditions with temperatures in the mid to upper 70s, resulting in seasonable conditions for this time of year. This high pressure system looks to dominate till the middle of the day on Wednesday, with diurnal shower and thunderstorm chances returning to our area during the afternoon hours. Thursday holds the potential for another system to approach with shower and thunderstorm chances once again. Long-range models, although subject to change, have a steady amount of precip returning to our area for most, if not all of the day on Thursday. The amount of rainfall is uncertain at this time being this far out, but some indications are there for around a half an inch of rainfall again, further lowering any ongoing drought concerns for our area.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Through 00Z Saturday...Mostly VFR, except IFR or lower possible due to fog at HIE and LEB late tonight through early Friday morning. VFR conditions are then expected on Friday with NW wind gusts up to 25 kts possible. No LLWS is anticipated through the period.

Outlook...

Friday night: Mostly VFR with IFR or lower again possible at HIE and LEB should valley fog develop.

Saturday-Saturday night: VFR.

Sunday: VFR, increasing clouds with SHRA arriving west to east.

Sunday Night: MVFR/IFR cigs in RA. Some TS possible.

Monday: Decreasing RA coverage, improvement towards VFR likely for points outside of the mountains.

Monday night and Tuesday: VFR. No sig wx.

MARINE

Through Saturday night...Winds and seas are expected to remain below SCA levels. A cold front crosses the waters this evening with winds turning northwesterly behind the front tonight. Winds stay out of the northwest through Friday night but could be more westerly at times for a period Friday afternoon.

Low pressure will move up the St Lawrence Valley Sunday night and Monday morning with a warm front passing over the waters Monday. An uptick in southerly winds is expected, but may fall just short of SCA criteria for the coastal waters. High pressure then returns over the waters for the middle of the week.

GYX WATCHES/WARNINGS/ADVISORIES

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