textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes since the previous forecast cycle. An isolated to widely scattered strong to severe thunderstorm remains possible across southwestern NH this afternoon and early evening.

KEY MESSAGES

1. Warm with a chance for showers and thunderstorms this afternoon and evening. A few strong to severe thunderstorms are possible across southwest New Hampshire.

2. Generally above normal temperatures persist into the weekend, along with chances for showers most days.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

New England will sit within the warm sector of low pressure to our west today as an advancing frontal boundary approaches from the west. Ahead of this frontal boundary, southerly winds combined with partly cloudy skies will help to warm temperatures into the 60s across much of western ME with middle to upper 70s in southern NH. Temperatures will fall during the afternoon across much of southwestern ME as a sea breeze boundary advances inland while southern NH stays well into the 70s. The SPC REFS shows mean SBCAPE approaching 500-1000 J/KG for a few hours this afternoon across southwestern NH with up to 500 J/KG towards the Nashua-Concord Corridor. Latest CAMS indicate there will be up to around 40 kts of deep layer shear in place as well. Despite steep low-lvl lapse rates, mid-lvl lapse rates currently appear rather weak and this should help mitigate storm intensity some. The latest SPC outlook places portions of southern NH into a MRGL Risk (Level 1 out of 5) with the primary threat being locally strong to damaging winds. Further to the east and north towards ME, instability will drop off quickly due to the marine layer and therefore severe storms are not anticipated in those locations.

Any lingering storms in southern NH this evening will end with the loss of daytime heating but scattered showers will remain possible through the first half of the night areawide. Low temperatures will range from the 40s across much of western ME with 50s in NH. Patchy fog is possible through Wednesday morning.

KEY MESSAGE 2 DESCRIPTION...

Mid-level ridging is anticipated to continue through the second half of the week, though conditions looked to be more unsettled than not. The unsettled weather, in addition to a backdoor cold front and a seabreeze, will complicate the temperature forecast on Thursday + Friday.

A complex frontal boundary looks to pivot across New England Wednesday evening, allowing for a damp afternoon. Upwind from our showers, a region of modest instability, 60kts of mean shear and 800J of MUCAPE allows for convective initiation over central New York. These storms will move eastward with storms that develop likely maintaining strength as they move across southern New Hampshire Wednesday night. This is due to an increase in MUCAPE, despite the development of a strong night-time diurnal cap. These storms look to move progressively but they also could be solid rainmakers as well, with PWATs above the 99th percentile Wednesday night.

A low pressure system follows right behind the aforementioned frontal boundary, allowing for more showers and thunderstorms Thursday afternoon and into Friday morning. Conditions may dry a little, but generally overcast and showery weather could continue through the weekend.

AVIATION /02Z TUESDAY THROUGH SATURDAY/

Through 06Z Wednesday: Mainly VFR conditions are expected through 18Z Tuesday, outside of any patchy FG. Winds will be light and variable. S-SE winds will then increase to 10-15 kts, gusts to 20 kts after 18Z Tuesday with an increasing chance for scattered showers across all TAF sites along with lowering ceilings to MVFR-IFR. There is the potential for TSRA at KLEB, KCON, and KMHT between roughly 21Z-00Z with locally gusty winds possible to around 40 kts. Elsewhere, the marine layer will limit the storm threat. Scattered SHRA will remain possible through 06Z Wednesday along with patchy FG.

Outlook:

Wednesday-Thursday: MVFR due to showers and thunderstorms.

Friday-Saturday: MVFR due to showers and thunderstorms, though brief windows of VFR are possible.

Sunday: MVFR due to showers and thunderstorms.

MARINE

Southerly winds and seas generally stay below SCA threshold through tonight, although an occasional gust up to around 25 kts is possible. Sub-SCA conditions continue through the rest of the week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Tuesday for ANZ150-152-154.