textproduct: Gray - Portland

WHAT HAS CHANGED

The forecast remains on track for this afternoon and evening as isolated showers are popping up on the seacoast. This activity should cease later this evening as the front continues to exit to the south.

KEY MESSAGES

1. Seasonably warm and mostly dry conditions are expected for the weekend.

2. The two main foci for next week will be the return of elevated heat and a threat for severe weather on Tuesday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... High pressure builds into the region tonight with a trough beginning to take shape at the 500 mb level. This trough axis swings through Saturday, but with dry air at the surface sensible weather likely is going to be limited to just an increase in afternoon clouds. Northwesterly flow keeps temperatures seasonable with highs in the low to mid-80s for areas south of the mountains, and 70s to the north. The trough axis then swings eastward which should make for a clearer day on Sunday allowing for temperatures a few degrees warmer in the north and interior. Sea breezes are going to keep temperatures similar on the coastal plain both days. Clear skies tonight (Friday night) through Sunday night are going to make for some cool nights as temperatures radiate down into the 50s and low 60s.

KEY MESSAGE 2 DESCRIPTION... Surface high pressure remains firm into early next week, keeping skies mostly cloud-free. On Monday, this will allow temperatures to rise into mid and upper 80s to maybe low 90s by mid-afternoon south of the mountains. A slight chance of a shower or storm will be possible over far northern NH and northwestern ME where forcing will be greatest.

Tuesday will see a continuation of the warming trend ahead of a southward-advancing cold front and according to latest NBM guidance looks to be the hottest day next week. High confidence exists in temperatures across the majority of our area reaching at least 90 degrees, with temperatures across southeastern NH and southwestern ME away from the immediate coast possibly reaching the mid to upper 90s. These air temperatures combined with ongoing low-level moisture advection resulting in dew points in the 60s, may create apparent temperatures around 100 degrees. Later on Tuesday, a low- level shortwave trough will approach the area. Downstream of this trough, scattered showers and storms are expected to fire, impacting mostly northern sections of our area through the evening and overnight hours. 1000-2000 J/kg of MUCAPE and stronger-than-average wind shear for this time of year will support clusters of storms capable of mainly strong to severe wind gusts and hail.

Further into the week, some uncertainty exists regarding the timing of the cold front's passage through our area on Wednesday, which would at least somewhat affect high temperatures that day. Model trends may be hinting at a slightly faster passage than previously expected, which would result in a somewhat cooler day Wednesday. Nonetheless, in the wake of the front air temperatures will only back down a little into the low 90s for the rest of the week. The humidity on the other hand will decrease, which will provide slight relief. There is also uncertainty over precipitation chances from Wednesday onward, although NBM PoP indicates at least a slight chance of showers for some Wednesday through next Friday as the Northeast transitions into troughing aloft with low pressure remaining the vicinity of the Canadian Maritimes through late week.

AVIATION /18Z FRIDAY THROUGH TUESDAY/

Through 18Z Saturday....VFR is expected to prevail through the day Saturday. The only exception would be valley fog or BR at LEB which could bring about MVFR/IFR conditions tonight.

Outlook:

Saturday night-Sunday night: VFR other than possible late night or early morning valley fog at HIE and LEB.

Monday: VFR expected.

Tuesday-Wednesday: A cold front brings increasing chances for showers and thunderstorms. Timing and extent of restrictions is uncertain, but MVFR or IFR will be possible over parts of the region.

MARINE

High pressure building over the waters will keep conditions below SCA criteria through the weekend. Winds remain generally northerly through Sunday, but afternoon sea breezes are anticipated as well.

Monday-Friday...High pressure centered moves out in the western Atlantic early next week as a cold front approaches. South to southwest flow increases Monday and Tuesday, potentially bringing SCA conditions. The front looks to cross the waters sometime in the late Tuesday to early Wednesday timeframe with winds turning west to northwest. Low pressure then looks to stay in the vicinity of the Canadian Maritimes, keeping winds mainly out of the west through late next week, although a couple of weak front could cross the waters during that time.

GYX WATCHES/WARNINGS/ADVISORIES

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