textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes for this forecast package.

KEY MESSAGES

1. A very warm day with lingering humidity is expected today. Warm conditions continue into the beginning of the work week with various chances for showers and storms.

2. A series of fronts will bring a chance for afternoon and evening showers and thunderstorms, as well as a gradual cool down from midweek into the weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

More valley and marine fog will be possible early this morning. Areas outside of the mountains should clear up fairly quickly this morning with fog lifting around 13z or so.

Persistent low amplitude troughing will remain in place over the region which will help keep the pattern a bit unsettled. As a cold front approaches today, a weak short wave will move across the area, leading to some low chances of showers and thunderstorms, mainly over the higher terrain.

Temperatures will once again be very warm ahead of the cold front with highs ranging from the upper 70s and lower 80s north, to the upper 80s and a few lower 90s south/along the coast. Dewpoints will start to decrease as the front moves across the area but we will still see values in the mid 60s to lower 70s ahead of the boundary. Thus, we could still some heat index values in the lower 90s across southeast New Hampshire and coastal Maine. A reading or two in the mid 90s will be possible in the vicinity of the Midcoast. Lows will then be a little bit cooler than in previous nights behind the front, ranging from upper 50s north to the low/mid 60s south.

Monday remains warm to hot, but dewpoints will be lower behind the front which will keep the heat index values subdued. Still, highs will range from the mid/upper 70s north, to the mid to upper 80s south. By Monday afternoon a weak surface low will deepen near the New Hampshire/Maine border as next shortwave moves into the region. This will lead to better chances of scattered showers and storms late Monday into Tuesday morning. The best chances (40 to 70 percent) will once again be across northern New Hampshire and the western Maine mountains. Instability and shear will be marginal, but some models do suggest the potential for some enhanced DCAPE so some gusty winds are not out of the question with this activity.

Chances for showers and storms may linger into Tuesday morning but should be on their way out through the day as high pressure moves in late. High temperatures will be a touch cooler on Tuesday, ranging from the low/mid 70s north to the mid 80s south (a few upper 80s will be possible over southeast New Hampshire and coastal Maine).

KEY MESSAGE 2 DESCRIPTION...

Broad troughing dominates the 500 mb pattern into the first part of the weekend. Wednesday looks to feature more zonal flow making for a drier day and starting a cooling trend. The trough axis moves eastward on Thursday along with forcing from a front. The brief period of southwesterly flow advects some moisture into the region making this the next best chance for widespread showers and storms.

The trough axis moves to the east of the area late week with some ensembles bringing the upper low into the region as well. The resulting northwesterly flow should continue to dry out our airmass and bring cooler temperatures, but if an upper low is nearby upslope clouds and showers would be possible. Most ensemble members begin to build high pressure into the region by Saturday, but depending on the track and progressiveness of the upper low the mountains may still see some clouds and showers.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through 12z Monday...Fog and low stratus will continue to dissipate over the early morning hours. West breeze today with less SHRA coverage than Sat. These remain mostly through the NH/ME mountains. VFR conditions prevail tonight with drier conditions as breeze subsides. Valley fog is likely again at HIE and LEB after midnight.

Outlook:

Monday-Monday night: VFR conditions during the morning through much of the afternoon. Scattered MVFR or lower conditions in late day and evening thunderstorms.

Tuesday-Tuesday night: Mainly VFR conditions outside of any possible SHRA/TSRA.

Wednesday-Wednesday night: Mainly VFR conditions.

Thursday: TEMPO MVFR possible in showers and thunderstorms.

MARINE

Mainly fair conditions continue as a weak cold front crosses the waters today. Some marine fog and visibility restrictions continue east of Casco Bay ahead of this front. Clearing and fair conditions follow by tonight.

Winds and seas will largely remain below SCA criteria through next week as a series of generally weak cold fronts cross the waters.

GYX WATCHES/WARNINGS/ADVISORIES

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