textproduct: Gray - Portland

WHAT HAS CHANGED

Decreased rain chances after midnight tonight as main plume of moisture lifts northeast.

KEY MESSAGES

1. Rain with embedded thunder increases in coverage south to north this evening. Rain rates may be heavy at times, with localized amounts greater than 1 inch possible.

2. A passing cold front will initiate showers and thunderstorms Wednesday afternoon. A few of these storms may be strong to severe, with gusty winds the primary threat.

3. High pressure brings a period of mostly dry weather through the weekend before the pattern becomes more unsettled into early next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

CAMs have been sporadic with precipitation coverage into this evening. This leads to lower confidence in exact rain timing, but the general airmass still supports a period of synoptic rainfall tonight.

An area of rain that move through the morning hours has helped keep early afternoon temperatures a few degrees off previous forecast highs. This has also likely put a dent in possible destabilization ahead of a warm front lifting into southern New England. This region of showers did eventually succumb to dry air across central Maine, but expect a moistening airmass to arrive with PWATs near 2 inches.

Upstream convection should make its way towards southern NH this evening. Will need to monitor mesoanalysis for any upticks in surface CAPE. This would allow convection to continue to cycle into the southern portion of the forecast area. For now, this looks to stop around the NH/MA border, with elevated instability building up through the ME coast. This much should be useful for increasing rainfall rates through mid evening. The above average PWATs, saturated profiles, and deep warm cloud layers should compliment this with efficient rain processes. Any taller cores that develop could produce rain rates around 1 to 2 inches per hour. Any training may lead to isolated instances of flash flooding, mainly focused south and east of the foothills. However antecedent dry conditions is keeping flash flood guidance pretty high.

Forcing for the main period of rain is progressive, and diminishing coverage is expected around midnight SW to NE. There may be a few additional showers or rumbles of thunder after this, but PWATs will be diminishing amid less moisture.

KEY MESSAGE 2 DESCRIPTION...

A cold front will be approaching western NH come Wednesday morning. This will be bringing in much drier air behind it, but some mid levels will have already dried behind overnight rain.

This dry air is expected to hinder coverage of showers and thunderstorms initiated by the arriving cold front. While CAPE builds and shear is supportive, think the aspect of severe weather remains fairly isolated. It may not be until early afternoon that showers or storms develop along the front bisecting the CWA. These may contain gusty winds and lightning, but marginal winds in the low levels put a cap on intensity. These showers and storms look to make their way towards the ME/NH coasts by late afternoon, moving over the coastal waters into the evening.

A cooler night is then in store as dew point temps tumble and CAA brings overnight lows in the upper 40s to lower 50s across the area.

KEY MESSAGE 3 DESCRIPTION...

The rest of the week and into the weekend look to be more of a tranquil setting as high pressure builds into the region. A 500 mb broad trough brings in more westerly/northwesterly flow keeping temperatures around normal for this time of year. Thursday will be the coolest of the days, as the air mass behind the cold front settles into our CWA. The remainder of this week looks to have our area keeping to the low 80s as highs, with nighttime temperatures falling into the mid to upper 50s. With these conditions at night, it might be nice to open the windows!

Looking further ahead, the global models are all in decent agreement that at the start of next week, a wetter and more unsettled pattern will make a return to our area. This is due to high pressure, which had been dominating, exiting the area. The exact weather this far out cannot be set in stone for the time being, but I think it is fair to say that there looks to be a trend toward slightly cooler (and wetter) weather next week.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday...Intermittent restrictions expected this evening and overnight as periods of SHRA and TS push across the area. TS is most likely between 23z and 4z this evening at southern NH terminals and the ME coast, with +RA bringing periods of IFR vis. Cigs also decrease to IFR for most terminals after 00z. Varying rates of improvement tonight, but most SHRA/TS begins lifting north around midnight local. A trend to MVFR cigs is expected for remainder of the night, with VFR at most terminals by 12z Wed.

Wednesday see as cold front move across the area with a wind shift. SHRA/TS develop along this front in the early afternoon, nearing the ME/NH coasts by 00z Thurs.

Outlook... Thursday-Sunday: Generally VFR conditions are expected as high pressure settles over the region.

MARINE

Waves build into this evening with onshore flow ahead and behind a warm front. These winds continue much of Wednesday before a cold front crosses the coastal waters Wed evening. This will bring a wind shift and gradual decrease of wave heights overnight into early Thursday morning.

5 to 6 ft seas slowly decrease on Thursday, falling below SCA criteria Thursday night as high pressure builds into the region. Sub-SCA conditions are then expected to prevail through the weekend as high pressure slowly continues eastward over the waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ150-152- 154.