textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes since the previous forecast cycle.

KEY MESSAGES

1. Scattered showers will persist today with a few gusty thunderstorms possible.

2. Fair weather this weekend will give way to more unsettled weather for the first part of next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A frontal boundary and weak H5 trof will cross the area today, providing a forcing mechanism for ascent. Scattered showers this morning will likely become more widespread this afternoon with partly sunny skies mixed in between. Forecast soundings from latest CAMs show some modest daytime instability with MUCAPE and MLCAPE up to around 500 J/KG and up to 35 kts of 0-6km bulk shear. This may allow for a few gusty thunderstorms to develop with a few potentially becoming close to severe thresholds. High temperatures will be into the upper 70s to lower 80s south of the mountains with lower to middle 70s towards the Canadian Border.

Showers and storms will wane tonight with low temperatures falling to around 50 across the interior valleys with middle to upper 50s elsewhere. Valley fog is possible.

High pressure will return for Friday into Friday night, allowing for dry conditions with mainly sunny skies and clear conditions at night. High temperatures will be into the 70s to lower 80s from north to south with low temperatures into the 40s across interior valleys with 50s elsewhere. Valley fog is once again possible.

KEY MESSAGE 2 DESCRIPTION... A sharp trough axis moves east of the area Saturday with the increased northwesterly flow dropping 850 mb temps down to +9 to 10C. Normally this would only be good for temperatures in the low to mid 70s (which is likely north of the mountains), but northwesterly surface flow tends to give us boost from downsloping winds south of the mountains so we could see closer to the upper 70s and low 80s. Ridging aloft and surface high pressure will keep it mostly dry. This persists through the first half of Sunday with dry weather and similar temperatures. Sunday night is when the weather looks to take a turn with low pressure approaching the region. Global models continue to agree on this, so confidence is increasing that we see some rain Sunday night into Monday. However, the point of contention is the track and therefore the spread in how much rainfall we may see is high with the 25th-75th percentiles ranging from nada to 0.75". The ECMWF Ensemble is currently on the high end with the track of the low going overhead and then deepening as it moves off the coast. The GEFS and GEPS take the track more south of the area with the GEFS having the weaker low and the the GEPS ending up in the middle with some strengthening over the gulf of Maine. Current NBM probabilities of around a half inch of rain are low (30-40%). The pattern remains unsettled into midweek as broad troughing develops at 500 mb once again. Southwesterly flow will likely begin a warming trend with the track of surface high pressure determining how warm we get, and ultimately the chances for precipitation as well.

AVIATION /06Z THURSDAY THROUGH MONDAY/

Through 06Z Friday...Scattered SHRA will remain possible tonight along with valley FG at LEB and HIE, bringing IFR-LIFR restrictions. SHRA and TSRA will result in TEMPO restrictions today with light S flow at 5-15 kts. Mainly VFR conditions are expected tonight but LEB and HIE may once again have IFR-LIFR restrictions late at night due to FG. Light and variable winds will prevail.

Outlook: Friday: Patchy LIFR in the morning due to valley fog. VFR through the rest of the day

Saturday-Sunday: VFR expected.

Sunday night-Monday: MVFR due to showers and thunderstorms.

MARINE

Winds and seas will remain below SCA criteria through the end of the week as a weak front crosses today, followed by high pressure on Friday.

High pressure builds over the waters bringing fair conditions through the weekend. Conditions early next week are going to depend on the track of low pressure, but as of now it looks like the coastal waters may stay below SCA conditions.

GYX WATCHES/WARNINGS/ADVISORIES

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