textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this forecast package.

KEY MESSAGES

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

2. Thunderstorms expected Tuesday night-Wednesday afternoon; locally heavy rainfall possible.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

An upper level ridge axis will start it's approach today as it begins to deamplify. After some valley fog this morning, we should see plenty of sunshine the rest of today and a little bit of a breeze in the afternoon. Temperatures will be a touch warmer today than yesterday but still right around (or just slightly above) normal for this time of the year, ranging from the upper 60s and lower 70s north, to the upper 70s and lower 80s south. Lows tonight will mainly be in the 50s as the ridge axis crosses the forecast area from west to east. By Tuesday morning, we transition back into southwest flow aloft as the next longwave trough approaches.

KEY MESSAGE 2 DESCRIPTION...

A slow moving deep trough digs into the region as a 990 mb surface low swings through Quebec. The low-level response across the Northeast will be southerly flow increasing, which should really advect in a juicy airmass as PWATs surge to 1.5-2.0" by Tuesday night; 90th percentile of climatology. There is a signal for some IVT transport with a tropical connection to the Gulf Coast. Combined with freezing levels up around 13-14 kft, it looks to be an environment primed for efficient and locally heavy rainfall.

Can begin to parse out potential convective evolution as hi-res guidance is just coming into range this evening. Currently strong model consensus we will remain north of the warm sector on Tuesday, with a late arrival of storms during the evening hours, past peak heating. Respectable MUCAPE suggests thunderstorms may persist into the night locally, but with high freezing levels and low-level stability, not concerned about severe weather. SPC Day 3 outlook clips SW NH with a marginal risk, where a slightly earlier storm arrival is possible.

After the initial lead shortwave pushes offshore early Wednesday, current indications are the region sees some modest destabilization. Also some signals for a bit of a "cold pool aloft" type of setup as the upper-level trough swings in, with cooling temperatures aloft. An inspection of regional soundings shows weak low-level shear, but strong deep-layer shear. Most likely concern would be for gusty winds and small hail, in addition to a second straight day of locally heavy rainfall.

Should generally have near seasonable temperatures this upcoming week. Strong cold front Wednesday night should really dry things out with dew points in the 40s-50s for the remainder of the week.

AVIATION /10Z MONDAY THROUGH FRIDAY/

Through tonight...Expect mainly VFR conditions thru tonight with only a VFR cu field developing by late morning. Winds will not be gusty today, but rather a steady breeze in the late morning/afternoon when mixing begins, turning southerly in the afternoon as the sea breeze takes over.

Outlook...

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-Saturday: VFR, no sig wx.

MARINE

Expect sub SCA conditions through 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.