textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes to the forecast at this time.

KEY MESSAGES

1. Fair weather expected to start the week as temperatures remain within a couple degrees of normal for mid-July.

2. Rounds of showers and thunderstorms are possible Tuesday evening through Wednesday evening.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure moves out to the Great Lakes this evening, bringing a cool night with lighter winds. This afternoon's gusts were supported by a tight pressure gradient around low pressure exiting to the northeast. The Ohio Valley high and cooler airmass will allow decoupling to occur and begin a decent radiational cooling night. Amid the calm winds, overnight lows enter the mid 40s across the mountains with low to mid 50s across the interior and coast.

High pressure passes to the south of New England Monday, and low level winds lack the magnitude they had on Sunday. Thus expect just diurnal breeze for most of the day with light cumulus developing amid weak moisture. Decent sun should bump highs a couple degrees higher than Sunday.

Clouds then thicken and begin to lower overnight into Tuesday. This will likely keep the temp range a little tighter through Tuesday. Come Tuesday evening, a push of moisture arrives from the south and west to bring our next chance of precipitation.

KEY MESSAGE 2 DESCRIPTION...

Upper trough continues to dig into the Great Lakes Tuesday evening, with moisture advection into the Northeast and New England. IVT is fairly broad through this time period, with a northerly stream advecting what westerlies bring across the TN Valley. Greater IVT enhancement is noted into Tuesday night with values likely to exceed 750 kg/m/s across both EPS and GEFS ensembles. This lies just off the New England coast, so will need to monitor should any further southerly advection takes this more inland. This should bring PWATs 1.5 to 2.0 inches into the region as low pressure pivots through James Bay.

Other heavy precip parameters are elevated, and while the system should be progressive, will want to monitor any training of moderate to heavy rain rates.

Guidance currently brings the best forcing through Tuesday night into Wednesday morning, not idea for additional convection/severe chances. However if moisture lingers into the afternoon, some additional development will be possible for thunderstorms.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Through 18z Monday...NW gusts continue this afternoon, beginning to truly subside after 00z. These become light a variable, remaining VFR tonight. Could see some valley fog towards HIE prior to sunrise Mon. Not as gusty Monday, but could see a sharp increase in winds once mixing begins. VFR continues with a cu field developing late morning.

Outlook...

Monday Night: VFR. No sig wx.

Tuesday: VFR with increasing and lowering clouds. SHRA south to north in the evening.

Tuesday night-Wednesday: SHRA/RA overspreads the area south to north. Widespread MVFR likely, IFR cigs/vis possible in periods of rainfall. This may linger for southern ME terminals into Wednesday afternoon.

Wednesday Night-Thursday: Improving to VFR Wed night with rain exiting northeast. No sig wx.

Friday: VFR, no sig wx.

MARINE

SCA conditions have subsided behind an exiting cold front. Expect below SCA condition through Monday and Tuesday as high pressure moves south of New England. An advancing low pressure system through Ontario and Quebec will bring a cold front towards the coastal waters Wednesday. Expect increasing SE to S winds and waves Tues night through Wednesday afternoon, with an SCA likely needed.

High pressure returns late week, leading to lighter winds and seas.

GYX WATCHES/WARNINGS/ADVISORIES

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