textproduct: Gray - Portland

WHAT HAS CHANGED

Have increased rain chances for parts of southern NH and into interior Maine for the afternoon based on trends. No big changes to the forecast for tonight into Sunday with most precipitation still expected to be in western ME from the distant coastal low.

KEY MESSAGES

1. Mostly cloudy and showery weather continue into early this evening, and then a distant coastal low will likely bring more rain to portions of western ME overnight tonight and into Sunday. Winter-like conditions continue in the higher elevations with subfreezing winds chills and a couple more inches of snow on the highest peaks.

2. Temperatures warm Monday into Tuesday along with breezy southwest winds. Highs on Tuesday will around 10 degrees above normal.

3. An active pattern is likely from late Tuesday through Friday as waves of low pressure track along a slow moving front. Precipitation likely averages above normal for the period.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Mostly cloudy skies with scattered showers will be the ongoing theme the rest of this afternoon into early this evening as broad lift remains across the area with the approach of an upper trough. Some partial clearing may bring enough instability for a thunderstorm or two across southern NH that produce graupel or even small hail. Latest trends and short-range guidance favor southern NH and into the interior and foothills of western ME, PoPs are roughly 50-70% into early this evening.

Going into tonight and Sunday morning, moisture streaming northward from a deepening low pressure lifting NNE offshore of the Eastern Seaboard, along with the approaching 500mb trough, will result in additional rainfall for portions of the the area. Highest rain chances continue to be across the Kennebec Valley and Midcoast with a sharp cutoff likely somewhere to the west where little to no precip may fall (with the exception of upslope rain or snow showers in the mountains). Model consensus is generally in the Portsmouth- Portland-Lewiston/Auburn vicinity with this cutoff but could be slightly to the west or farther east toward Augusta.

At any rate, rainfall amounts in the Kennebec Valley/Midcoast are expected to be around 0.25" to 0.50" and possibly more in the 0.50" to 0.75" range closer to Penobscot Bay. The highest mountain peaks in the Whites may pick up another couple inches of snow.

The strong low pressure will pull farther to the east Sunday morning and afternoon, and the drier air will work farther east into western ME. There's still some uncertainty how quickly this occurs, but the trend will be for rain to taper off from west to east in the late morning and afternoon hours. That said, forecast soundings continue to show steep lapse rates and a moist layer with a bit of instability aloft. So periods of mostly cloudy skies along with a couple of additional showers remain possible through the afternoon before clouds fade toward sunset.

Aside from the clouds and shower chances, it will be breezy as stronger winds aloft mix down with gusts mostly in the 20-25 mph range but may be up to 30 mph at times in some areas per forecast soundings. Temperatures will be mostly in the 50s for highs, possibly around 60 in parts of southern NH.

500mb ridge builds overhead Sunday night keeping conditions dry for the vast majority of northern New England. The one exception is a shortwave quickly moving across or just north of the Great Lakes that could bring some showers to northern NH and the western ME mountains overnight and toward daybreak Monday. This will also bring more clouds, but the amount of cloud cover and how quickly clouds move in will determine how cool or not cool it gets, but it does look like there will be a period of mostly clear skies for some of the night south of the mountains. So patchy frost is again possible with lows in the 30s , especially if winds are able to drop off enough.

KEY MESSAGE 2 DESCRIPTION...

Modest height rises and a warm front lifting north of the area will bring about a warming trend Monday. The warm front will bring chances for showers in the mountains with potential for light accumulating snow on the summit of Mt Washington Monday morning. Skies will turn mostly sunny Monday afternoon as southwest winds ramp up with gusts 25 to 30 mph. Southwest winds will allow much of the area to warm into the mid to upper 60s as these winds will inhibit any sea breezes.

Southwest flow deepens Tuesday as a trough and cold front approach from the west. This flow regime will advect +15C to +19C air at 925 mb into the area Tuesday afternoon and with favorable mixing this will yield temperatures into 70s across much of the area with portions of southern NH making a run at 80 degrees. Southwest winds will also limit sea breezes from Casco Bay southwards. Peak wind gusts will be around 25 to 30 mph. Cloud cover and chances for showers and thunderstorm will increase from a slow moving front that approaches late in the day that could limit temperatures in the mountains and point northward.

KEY MESSAGE 3 DESCRIPTION...

A slow moving and then stalling cold front and a consolidating split flow regime will bring multiple chances for beneficial rainfall late Tuesday through Friday. Chances for showers and storms increase NW to SE Tuesday afternoon and evening while areas along the coastal plain likely stay dry into Tuesday night. Latest available NWP guidance suggest that upwards of 1000 J/kg of MU CAPE and deep layer shear around 35 kts will be possible Tuesday afternoon from the CT Valley through central NH and into western Maine mountains. This would support some organized updrafts while the limiting potential for strong to severe storms will be forcing remaining to the west. Machine Learning Guidance out of CSU does show a modest signal for severe storms Tuesday so will have to watch trends as we get into the window of CAM guidance in the next 24 to 36 hours.

Chances for showers will push towards the coast Tuesday night into Wednesday as the front stalls near western New England. The presence of the stalled front will keep likely chances for showers going through the day Wednesday. On Thursday, southern stream energy will merge with persistent troughing over Hudson Bay that could result in an organized area of low pressure tracking over New England. Ensembles suggest that a good soaking rain is likely Thursday into Friday with mean QPF around 0.75 inches. This system combined with rainfall Tuesday into Wednesday continue to bring high probabilities that much of the area will see at least 1 inch of rain by Friday.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through 18Z Sunday...A mix of MVFR to VFR cigs and scattered showers are expected into early this evening. For tonight into Sunday morning, IFR to MVFR ceilings are most likely for the western ME terminals and maybe PSM along with increasing chances for rain. MVFR ceilings are possible for the other NH terminals. NH terminals will likely be VFR Sunday morning with ongoing restrictions in western ME, but some improvement for the western ME terminals is possible late morning and toward the end of the TAF period. Northwest gusts 20-25 kt possible in NH in the morning.

Outlook:

Rest of Sunday: The western Maine terminals return to VFR. Otherwise, breezy conditions continue with 20-25 kt gusts possible out of the north to northwest.

Sunday night: Mainly VFR expected, but there is a chance of showers at HIE late.

Monday-Monday Night: Mainly VFR expected, with gusty southwest winds. Rain showers could bring restrictions at HIE.

Tuesday-Tuesday Night: Mainly VFR with gusty southwest winds during the day Tuesday. Chances for showers and thunderstorms increase NW to SE Tuesday afternoon, although storms are unlikely from CON to AUG and points south. Chances for showers Tuesday night bring some potential for MVFR.

Wednesday through Friday: MVFR likely with low CIGs and rain showers. IFR possible Wednesday night through Thursday night in low CIGs and widespread rain. Drying trend Friday will bring improving conditions.

MARINE

Through Sunday night...Winds will turn northerly tonight into early Sunday in response to low pressure passing to the south and east of the Gulf of Maine. Can't rule out a few gusts to around 25 kt and a brief period of 5 ft seas across the coastal waters during this time frame, but in general, conditions look to remain just shy of SCA levels. Winds back to more westerly late Sunday and Sunday night as the low lifts northward into the Canadian Maritimes, but again conditions are currently expected to stay just under SCA levels.

Slow moving front will bring increasing SW flow Monday into Tuesday with SCAs likely and possible Gales late Tuesday into Wednesday. South to southwest winds relax some Wednesday night into Thursday while SCAs will likely still be needed into Friday morning.

GYX WATCHES/WARNINGS/ADVISORIES

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