textproduct: Gray - Portland

WHAT HAS CHANGED

Expanded PoP coverage into this afternoon as a cold front approaches. Building instability ahead of the front will create an environment favorable for isolated to scattered showers/storms as it pushes south through early evening. Morning showers have been short lived, but better fuel and shear will increase strength/longevity after noontime. In addition to lightning, stronger storms may contain heavy downpours and gusty winds.

KEY MESSAGES

1. Not quite as hot and humid today. There is a chance for a few storms, some strong, this afternoon south and east of the mountains.

2. Cooler and pleasant temperatures for much of next week, but likely warming up by the end of the week. Chances for rain Monday- Tuesday night.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Very warm to hot weather continues today but it won't be as stifling as the last couple of days as the warmest portion of the air mass has slid to the south of the forecast area bringing the very high dewpoint values along with it. Even still, southeastern NH should reach heat indices of around 95F. Therefore a heat advisory has been issued for that area. The rest of the forecast area should see heat inidices below 95F as gusty NW flow mixes dewpoints down into the lower to mid 60s.

A cold front moving across the forecast area during the afternoon may provide focus for a few thunderstorms. The best potential for a strong storm or two is across western and southern NH.

KEY MESSAGE 2 DESCRIPTION...

A wave of low pressure rides along today's sagging cold front (which will be situated over the Mid Atlantic by the start of the week). There remains a rather bimodel distribution with QPF. One grouping features a scenario where Canadian high pressure suppresses the wave south of our forecast area, with just clouds and light precipitation across southern New England. The other camp however brings rainfall further northeast, impacting the region more directly. However even in a more northern outcome, expecting precipitation to be light, with the heaviest totals south of our region. Late Monday through Tuesday evening is the potentially unsettled period to watch.

Depending on the outcome, temperatures may be on the mild side, with the warm sector squashed well to the south. The airmass aloft will be quite cooler as well. For reference, 850 mb temperatures were up around +20C during last week's heatwave, but will be dropping to around +12C by early next week.

High pressure is expected to return by mid week, signaling a warming and drying trend. This high may shift offshore by late week, potentially allowing for another return to hot/humid conditions as southwest flow becomes established. A trough also may be swinging southeast out of Canada by this time, indicating some sort of potential for thunderstorms towards the end of next week.

AVIATION /14Z SATURDAY THROUGH WEDNESDAY/

Through 12z Monday...Mostly VFR. Low probability of a couple of thunderstorms across western and southern NH this afternoon but coverage is expected to be limited. Mainly VFR tonight with light winds. Valley fog may develop at LEB and HIE tonight, but confidence is not high enough to put in the TAF.

Sunday and Sunday Night: VFR likely w/ no sig wx.

Outlook:

Monday: Increasing rain chances and clouds south to north in the afternoon. Patchy MVFR cigs across southern NH possible, otherwise VFR.

Monday Night: Continued rain chances across southern NH. MVFR possible.

Tuesday: Rain departs east, with improving cig in the late afternoon. VFR likely.

Wednesday: VFR likely under high pressure in the region.

MARINE

Conditions will continue to remain below SCA levels through Sunday. The waters will see primarily a west to southwest flow through Saturday before turning north to northwest behind a weak frontal boundary Saturday evening and night, then turning back south on Sunday.

Broad low pressure exiting the Great Lakes will move over New England Monday night into Tuesday. This exits east Tuesday night, with high pressure moving into New England Wednesday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...Heat Advisory until 9 PM EDT this evening for NHZ012>015. MARINE...None.