textproduct: Gray - Portland

WHAT HAS CHANGED

Raised PoPs some for northern NH and the western ME mountains for this morning.

KEY MESSAGES

1. Cooler today in ME with easterly winds, but still very warm across much of NH. A few showers possible this morning in central and northern NH including the western ME mountains.

2. Tuesday and Wednesday should feature the warmest temperatures of the year thus far with chances of isolated to scattered thunderstorms, some potentially strong.

3. Expect cooler and dry conditions to end the work week with temperatures around or slightly below normal for this time of year through the weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure will slide offshore early this morning allowing SFC winds to have an easterly component going through the day today. With ocean temperatures still in the 40s, most Maine zones outside of the mountains should be a good deal cooler today. Temperatures will continue to be quite warm in much of NH as the ocean will obviously have lesser of a cooling influence.

A modest burst of WAA aloft will aid in a chance for showers across central and northern NH this morning, with perhaps even a rumble of thunder will relatively steep lapse rates aloft. This activity should lift northeastward into the western ME mountains and foothills by late morning then dry out. The rest of the forecast area should remain dry.

Showers and perhaps a few rumbles of thunder may affect northernmost NH and the western ME mountains tonight but the bulk of the activity should remain in Canada as warm front returns northward there.

KEY MESSAGE 2 DESCRIPTION...

A progressive low amplitude shortwave trough will pass north of the forecast area on Tuesday, flattening the ridge a bit and leading to some modest height falls. A band of mid-level westerlys in the 40 to 50 knot range will spread across the region through early afternoon, which could lead to some early day storms in the vicinity of the southern Kennebec Valley and portions of the Midcoast. A second wave will approach New Hampshire late afternoon or early evening. Storms may be ongoing over Vermont before moving into New Hampshire and we could also have some additional development over the mountains. In both potential storm regimes, storm coverage remains uncertain given nebulous forcing mechanisms and less than ideal diurnal timing (early in the day for the eastern storms and closer to evening for the western/northern storms). All in all, both environments could see CAPE values in the 500 to 1000 J/kg range and deep layer shear up to 35 knots or so. Thus, any storms that do form could become strong or marginally severe with the primary threats of small hail, gusty winds, and frequent lightning. Showers and storms should diminish mid to late evening.

A cold front will move across the area of Wednesday and guidance has continued the trend of speeding that passage up. In fact, the NAM almost has the front around the Midcoast by 18z. So, we do have a risk for some stronger storms earlier in the day on Wednesday along and ahead of the front but the window will be short before the boundary moves out over the waters.

Tuesday and Wednesday will also be the warmest days of the year thus far with widespread highs in the 80s and potentially even in the lower 90s. Tuesday's highs will range from the upper 70s and lower 80s north, to the upper 80s and lower 90s south. Coastal areas may be a little bit cooler given an onshore wind component. Wednesday will be a touch cooler for most with the passage of the cold front. We will still see widespread highs in the low to mid 80s along and south of the Foothills. Temperatures over the higher terrain will max out in the lower 60s to low/mid 70s.

KEY MESSAGE 3 DESCRIPTION...

We will cool down behind the front through the rest of the work week and into the weekend. The coolest day will be on Thursday when highs will mainly range from the low to mid 50s north, to the low to mid 60s south. We warm just slightly on Friday and temperatures generally stay around or slightly below normal through the weekend. The weather pattern also favors dry conditions during this time frame.

AVIATION /06Z MONDAY THROUGH FRIDAY/

Through 12z Tuesday...VFR today with lighter winds. Winds will have an easterly component. VFR tonight for most locations. However, with low level easterlies we may see some MVFR restrictions in mist, especially on the coastal plain.

Outlook:

Tuesday: Afternoon SHRA/TS chances near the US/CAN border. There is uncertainty how far east and south SHRA/TS develop in the afternoon.

Tuesday night: Coverage of SHRA decreases. VFR forecast.

Wednesday: A cold front passes through the region with SHRA/TS west to east through the day. MVFR possible w/ frontal passage and in showers/storms.

Wednesday night: Winds shift NW with VFR behind exiting cold front.

Thursday and Thursday night: VFR expected with no sig wx.

Friday and Friday night: VFR expected with no sig wx.

MARINE

High pressure moves over the waters today with relatively light easterly to southeasterly winds.

Winds may approach SCA criteria on the coastal waters Tuesday and Wednesday as southerly fetch builds. Winds then become offshore behind a stronger cold front Wed evening. High pressure builds in from the west mid to late week.

GYX WATCHES/WARNINGS/ADVISORIES

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