textproduct: Gray - Portland

WHAT HAS CHANGED

Greater confidence in showers and thunderstorms this afternoon has resulted in greater forecast rainfall across northern New Hampshire and western Maine. The flash flooding risk has increased given the potential for two rounds of heavy rain from slow moving showers and thunderstorms through early evening.

KEY MESSAGES

1. Widespread showers and storms overspread the forecast area today. Locally heavy rainfall is likely and isolated instances of flash flooding are possible.

2. Heat and humidity continue through Monday, followed by a gradual cool down through the end of the week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

An upper level ridge axis will continue to move east of the forecast area this morning as a leading shortwave approaches in southwest flow aloft. Height falls and elevated instability will bring scattered showers early this morning along with a few rumbles of thunder. CAMs depict deeper and more widespread development towards the Kennebec Valley and western ME mountains through the morning hours with an initial round of moderate to heavy rain.

A better chance for widespread showers and thunderstorms will be possible in the afternoon hours as better upper level forcing interacts with weak surface low and trough/front. RAP soundings suggest we could see widespread MUCAPE values in the 1000 to 1500 J/kg across New Hampshire and portions of western Maine and generally lower moving east. Shear will be lacking so the severe threat is low, but slow storm motions and high dewpoints/PWATs may lead to some torrential downpours with localized rainfall rates in the 1+ inch per hour range.

As of now, CAMs are suggesting that areas that see the greatest coverage of showers and storms will be over northern New Hampshire, the western Maine mountains/foothills, and over into the Kennebec River Valley and Midcoast areas. Areas under the heaviest cores could see localized flash flooding through the evening hours, especially if overlapping the morning round in western/central ME. Rain will gradually diminish through the evening with mostly dry conditions overnight.

KEY MESSAGE 2 DESCRIPTION...

Hot and humid conditions will persist on Sunday as we remain under the influence of the Bermuda High. Partly cloudy skies will prevail with high temperatures into the lower 80s across the north with upper 80s to near 90 degrees further to the south. Dew points will remain elevated into the 60s near 70, although they may begin lowering some late day from north to south behind a cold front. This front may also bring scattered showers and thunderstorms, especially across the north and over western ME. Sunday night will feature low temperatures into the lower 60s in most places with most shower activity coming to an end.

It will remain warm on Monday with high temperatures into the middle to upper 80s south of the mountains but dew points will only be into the lower 60s, and therefore heat indices will not be much of a factor. A series of additional cold fronts will cross through mid to late week, bringing rounds of scattered showers and possible thunderstorms... although no day currently looks like a washout. Temperatures will also cool towards seasonable averages with highs into the upper 70s to lower 80s. Dew points will lower as well with overnight low temperatures into the 50s.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Through 06z Sunday...Variable conditions are likely through Saturday night as multiple rounds of SHRA/TSRA overspread the area along with patchy fog and marine influences. Fog may develop through early morning as skies thin behind showers overnight. Marine stratus or fog will bring potential for MVFR to IFR at PSM, PWM, and RKD. MVFR cigs may linger near the coast Saturday otherwise mainly VFR outside of TSRA this afternoon and evening. Low level moisture lingers Saturday night bringing the potential for patchy fog.

Outlook:

Sunday/Sunday Night: Mainly VFR conditions outside of any possible SHRA/TSRA late day.

Monday/Monday Night: Mainly VFR conditions during the daytime before SHRA/TSRA arrives overnight, likely bringing MVFR or lower restrictions.

Tuesday/Tuesday Night: Mainly VFR conditions outside of any possible SHRA/TSRA.

Wednesday/Wednesday Night: Mainly VFR conditions.

MARINE

Disturbances crossing the waters early this morning and later this afternoon will bring the potential for thunderstorms over the waters. Humid conditions remain in place continuing the potential for fog over the waters through tonight. Otherwise, winds and seas remain below SCA thresholds.

Winds and seas will largely remain below SCA criteria through the period as a series of cold fronts cross over the waters.

GYX WATCHES/WARNINGS/ADVISORIES

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