textproduct: Gray - Portland

WHAT HAS CHANGED

Aviation section updated for the 12Z TAFs.

KEY MESSAGES

1. At least a couple chances for rain are expected through the weekend. While neither may impact the entire area, some beneficial rainfall is possible.

2. Cool conditions will arrive on Friday and persist through much of next week. Frost is possible some nights, especially across valley locations.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

As the boundary layer continues to moisten with of a frontal wave, I expect that cloud cover as well as marine fog and stratus will continue to expand thru today. The thing to watch will be how quickly marine fog and stratus can expand inland. Hi-res guidance is currently forecast this to occur late afternoon to early evening.

Otherwise attention is mostly on the first rainfall chance as that wave propagates thru southern New England. The sharp northern edge of rainfall will be in the forecast area somewhere, but south of that some beneficial rainfall amounts look likely. There has been a steady ramp up in ensemble QPF amounts for the last couple of days, especially across southern NH. Here forecast soundings indicate some instability and convective rainfall rates are possible. CAM guidance does show some potential for amounts up to 1 inch or so. We will certainly take it. In the central part of the forecast area, like IZG, prospects are more likely 50/50 on getting much in the way of rain. Winds turn northwest and will clear out the rain and any fog, see Key Message 2 Description for more information about winds on Fri.

As we head into the weekend the next rain event looms on Sun. A stout high pressure will be retreating slightly from a position north of the forecast area. Model guidance wants to lift another frontal wave into the area and bring an area of rain with it. Ensemble guidance continues to waffle a bit on placement of this rain leaving it a lower confidence forecast. Given that forcing is weakening as it cross the local area I do like the NBM PoP trending down as it moves east. However it is also showing likely PoP at this range which may be a little high for my tastes right now. But this could very easily turn into another high PoP/low QPF events that have been fairly common from the mid to latter half of the warm season.

KEY MESSAGE 2 DESCRIPTION...

An upper level low will drop south out of Quebec on Friday, sending a surface cold front across the region. A tightening pressure gradient will allow for gusty northwesterly winds with gusts between 30-35 mph likely. Other than some upslope clouds and perhaps a shower, it should be mainly sunny with high temperatures ranging from the 60s across the north with 70s to the south. Friday night will be chilly with low temperatures ranging from the lower to middle 30s across interior valleys with lower 40s elsewhere. Patchy frost is possible, especially across the sheltered valleys.

Mean trofing will prevail across New England Saturday through much of next week with negative H5 height anomalies. This will keep temperatures generally below average with daytime highs into the lower to middle 60s most days with overnight lows into the 30s and 40s. Will need to watch each night closely as we get closer in time for possible frost/freeze conditions.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through 12Z Friday...Fog is expected to clear at LEB and HIE by 13Z this morning. For the rest of the day, MVFR cigs are possible with fog and marine stratus potentially bringing IFR to PWM and RKD as early as this afternoon. Elsewhere, cigs lower to MVFR this afternoon with increasing chances for rain showers, and then ceilings further lower to IFR or lower at most sites through tonight with fog and -SHRA continuing. Showers end west to east overnight, but fog may prolong IFR or lower restrictions at some terminals through daybreak Friday.

Outlook...

Friday: VFR conditions expected. Northwest wind gusts of 25 kt expected.

Saturday: VFR conditions expected.

Sunday and Sunday night: Rain showers and local MVFR or lower conditions possible.

Monday: VFR conditions expected.

MARINE

Winds and seas are generally expected to remain below SCA thresholds through the remainder of the forecast period. However a modest cold front will cross the waters Fri and northwest winds will get gusty during the day. While guidance does not quite show it at this time, I would not be surprised to see a few 25 kt gusts at times. There will also be areas of fog developing ahead of a frontal wave today and that fog may move into bays and inlets towards late afternoon or early evening.

GYX WATCHES/WARNINGS/ADVISORIES

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