textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes at this time.

KEY MESSAGES

1. Rain moves in late this evening and overnight and will be followed by increasing chances for thunderstorms Friday afternoon and early evening, some possibly strong to severe.

2. A moderating trend with multiple chances for showers and storms evolves from the weekend through next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

The rest of this afternoon will be similar to yesterday with temperatures in the 70s to low 80s with periods of mostly cloudy skies. Scattered showers and isolated storms will be mainly confined to the interior, especially the foothills and in and around the mountains. A couple of storms could produce small hail and gusty winds, but these will fade toward sunset with the loss of daytime heating.

Rain will then overspread the area from west to east this evening and overnight with increasing moisture and lift provided by a 500mb shortwave. Models have continue to advertise amounts 0.25" to 0.75" of rain through Friday morning, mainly across the interior, but there may be localized amounts over 1". Outside of rain, patchy fog is possible with the increasing low- level moisture and light winds across the area. This rain should taper off during the morning hours Friday.

Which leads us into the afternoon. A warm front is forecast to have lifted northward through much of the area as low pressure tracks roughly along or just south of the St Lawrence River Valley with the a cold front approaching. Confidence is growing that at least some clearing will occur, especially across NH and far western ME (even more so the southern half of NH and SW ME), allowing destabilization to occur with temperatures reaching the 70s to possibly low 80s and dewpoints in the 60s. Ensemble means are depicting 500-1000 J/kg of SBCAPE across these regions with some deterministic guidance even higher in the 1000-1500 J/kg range. Effective shear is also progged to be 40-50kt, so the ingredients are there for strong to severe storms with damaging winds and hail being the primary hazards with discrete or semi-discrete wells. The directional shear has trended downward but still can't rule out a brief tornado or two. The threat for severe weather is expected to decrease the farther east one goes into western ME, especially toward the Augusta/Midcoast regions where onshore flow and the marine layer will bring in more stability.

Showers and storms will weaken toward sunset and then dissipate into the evening hours. Patchy fog is then expected to develop during the nighttime hours due to light winds and saturated grounds from rain. The mountains may see a few upslope showers and low pressure passing to the south could bring light rain or sprinkles to southernmost NH, otherwise Friday night will be dry.

KEY MESSAGE 2 DESCRIPTION...

Weak troughing lingers across New England through the end of the weekend. A cold pool aloft keeps the chance for afternoon showers and storms both Saturday and Sunday afternoons. With more sunshine in the morning, clouds and showers develop each day with the daytime heating, along with the some isolated thunderstorms. The best chance for these will be across the higher terrain, but they'll be possible everywhere both days.

By early next week the pattern begins to shift. A ridge builds across the Midwest and Great Lakes, bringing hot conditions into the middle of the country and Great Lakes. At the same time, the trough from over the weekend shifts eastward into the Canadian Maritimes and deepens through midweek. This places New England just to the west of the trough, and on the eastern periphery of the building ridge.

This opens the door for some heat to make it's way into New England, but also for daily chances of showers and storms as MCS complexes and leftover convection roll around the periphery of the ridge. Additionally, with the trough sitting just east of New England, it's well within the realm of possibilities that any heat would end up being short lived as the ridge retrogrades further west. So while we likely see some heat next week, there are multiple variables that can limit the extent and the duration of it. These will be the variables we'll be monitoring over the coming days, with this pattern evolution determining the weather for much of next week and into the 4th of July Weekend.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Through 18Z Friday...Mainly VFR today, but can't rule out brief MVFR restrictions at HIE or AUG should a shower or storm pass over. For tonight, expect lowering ceilings as a round of rain moves through. Ceilings could range from LIFR to MVFR with visibility from rain mainly MVFR. Outside of rain, fog could produce locally lower visibilities, primarily at RKD and AUG.

Rain gradually ends from west to east Friday morning with improving visibilities. Ceilings will also lift, especially for the NH terminals with a return to VFR possible. IFR to MVFR restrictions will remain possible through the morning hours at the Maine terminals.

Outlook:

Rest of Friday: Showers and thunderstorms will likely develop and could produce TEMPO IFR to MVFR restrictions. Strong wind gusts and hail will be possible in some thunderstorms, mainly for the NH terminals and possibly PWM.

Friday night: Precipitation comes to an end Friday evening as the low pressure and front shift east. However, with not much wind behind the front, IFR ceilings and fog remain possible.

Saturday through Sunday Night: Mainly VFR, but scattered afternoon showers and storms are possible each afternoon. Night time valley fog is possible.

Monday through Tuesday Night: Mainly VFR prevails.

Wednesday through Thursday night: Mainly VFR prevails, but chances for showers and storms increase. While more likely in the afternoon, these could also occur overnight.

MARINE

SCA conditions are not expected through Friday night. High pressure to the east of the waters and approaching low pressure will keep southerly flow across the waters through Friday...with flow then turning more northwesterly or northerly Friday night. As the low approaches, fog will be possible over parts of the waters from tonight through at least the day Friday but may also linger into Friday night. Rain is likely tonight into Friday morning, and then offshore-moving thunderstorms are possible from late Friday afternoon to early evening, especially from Casco Bay southward to the Seacoast.

Conditions look to remain below SCA levels from this weekend through at least midweek next week with broad high pressure gradually building across the waters through early in the week.

GYX WATCHES/WARNINGS/ADVISORIES

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