textproduct: Gray - Portland

WHAT HAS CHANGED

A marginal chance for strong to severe thunderstorms has expanded across much of central and southern New Hampshire on Thursday.

KEY MESSAGES

1. Scattered showers move through the area this evening and overnight, with the chance for a few thunderstorms across southwest New Hampshire.

2. Warmer temps continue away from the coast, with another chance for a few strong to severe thunderstorms across central and southern parts of New Hampshire on Thursday.

3. Chances for showers continue on Friday with temperatures remaining above normal through Saturday.

4. A cold front brings higher rain chances Saturday night and Sunday and then cooler, drier, and breezy conditions to start out next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... A backdoor cold front has stalled just west of Maine/New Hampshire border today, with a sharp temperature gradient from west to east. While much of New Hampshire has warmed into the mid to upper 70s, much of Maine and eastern New Hampshire remains in the 50s to low 60s this afternoon. The front makes some further progress inland through the overnight hours, expanding the coverage of fog and low clouds inland overnight.

In addition to the front, remnant MCS systems continue to roll into Northern New England bringing showers and some scattered thunderstorms. A pop up thunderstorm remains possible across southwest New Hampshire this afternoon, and then there is another chance through the overnight hours as another remnant system from the Midwest passes through. Scattered showers are possible elsewhere overnight. Lows generally bottom out in the 40s to the east of the front, and 50s to the west of it.

KEY MESSAGE 2 DESCRIPTION... The front drifts a bit back toward the east tomorrow, yielding highs in the 70s to low 80s across central and southern New Hampshire. 60s are expected in most other areas, while highs in the 50s look most likely along the coast and through central Maine. Areas of fog, drizzle, and low clouds are likely along the coast for much of the day.

Another shortwave approaches from the west during the afternoon hours on Thursday. With the warm air mass across central and southern New Hampshire, this system will bring another round of potentially strong to severe storms during the afternoon and evening hours. Gusty winds and some hail will be the primary concern with these storms. The storms weaken as they move eastward into the marine layer, with showers expected across northern and eastern areas. The upper level low doesn't move offshore until Friday, which keeps the chance for some scattered showers ongoing through the overnight hours on Thursday.

KEY MESSAGE 3 DESCRIPTION... A frontal boundary remains nearly stationary on Friday, probably located somewhere across southern NH and into SW ME to start out while a 500mb shortwave approaches from the west. This will continue to support additional chances for showers through at least the morning and even a couple of thunderstorms with the NAM bringing more in the way of instability. A slight southward progression of the front is expected later in the day, which should lower precip chances and decrease clouds from north to south into Friday night. Highs are mostly in the 60s to lower 70s but could be cooler if the clouds or precip stay around longer. Also, some areas may see fog in the morning.

Moisture increases late Friday night and through the day Saturday as a cold front approaches from the west. This will be mainly in the low and upper levels with forecast soundings depicting a lot of dry air aloft. So, Saturday is expected to be dry during the day (except if the LL moisture is enough to support DZ near the coast), but the moist low levels could bring marine stratus and fog coastal areas, and this could linger near the coastline through Saturday. Fog and low stratus will also be possible farther inland early, but this should mix out fairly quickly. Otherwise, highs will be mainly in the upper 50s to mid 60s inland and cooler near the coast.

KEY MESSAGE 4 DESCRIPTION...

Wet weather then returns as rain overspreads the area from west to east Saturday evening and night and then continues for much of the day Sunday. Also, prior to the arrival of the rain, fog and stratus will probably come back along the coast and across portions of interior Maine and may be dense. As far as rainfall amounts, ensembles depict 0.25" to 0.50" of rain with higher totals closer to 0.75" possible.

Models are in pretty good agreement with the frontal passage being either late in the day Sunday or Sunday night, and rain coming to an end as drier air moves in behind the front. This will bring mostly dry conditions outside of the mountains for the day Monday, but it will also be cooler and breezy. Highs look to be slightly below normal and mostly in the 40s.

High pressure builds overhead Tuesday and then shifts south and east toward the middle of next week. This should bring a slight warming trend with dry conditions Tuesday and perhaps a chance of showers returning by next Wednesday.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR to MVFR give way to IFR overnight at most terminals with lowering ceilings and areas of fog, along with scattered showers. LIFR is more likely along the coast tonight into Thursday. Gradual improvement is likely during the day on Thursday inland, while only some improvement to possibly MVFR is likely along the coast. Ceilings lower again Thursday night, with showers and possibly a thunderstorm across southern terminals.

Outlook...

Friday: IFR to LIFR possible in the morning due to fog and low stratus. There is a chance for showers through the day, but conditions may improve to MVFR or VFR in the afternoon.

Friday night: Mainly VFR with coastal fog/stratus possible late.

Saturday: IFR to LIFR restrictions possible due to marine fog and stratus at the coastal sites, but fog may also occur inland during the morning. Otherwise VFR for inland terminals.

Saturday night-Sunday...Widespread restrictions and rain showers likely, and perhaps a storm or two, as a cold front crosses through.

Sunday night: Conditions return to VFR, except MVFR remains possible at HIE.

Monday: Mainly VFR with gusty northwest winds.

MARINE

Conditions remain below SCA levels through Thursday night as a frontal boundary remains stalled near the coast. Areas of fog remain likely through Thursday night. Conditions remain under SCA levels Friday, but fog is possible ahead of a weak boundary that will cross through switching winds to more NE later in the day. More fog and stratus are likely from early Saturday through Sunday as south to southeast winds and moisture increase ahead of a cold front that will also bring a round of showers through Saturday night on Sunday. SCA conditions are possible ahead of the front, but are more likely with the gusty west to northwest winds behind the front Sunday night and Monday. High pressure should then allow conditions to fall below SCA levels Tuesday into Tuesday night.

GYX WATCHES/WARNINGS/ADVISORIES

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