textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with the incoming frontal system bringing widespread rain today with rain changing to snow in the mountains.

Chances for rain and snow showers have increased for Monday.

KEY MESSAGES

1. Frontal systems brings widespread rainfall through today with rain changing to snow from the mountains to the Canadian Border this afternoon.

2. Anomalously cold air aloft may lead to afternoon convective showers on Monday.

3. A cooler and unsettled pattern gradually moderates through the week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

No significant changes with the latest round of NWP guidance and NBM with regards to the incoming frontal system that crosses today. Occluding low pressure east of James Bay will send a cold front into northern New England this morning with widespread rain expected into the afternoon. A trough digging into the Ohio Valley will take on a slightly negative tilt with a wave of low pressure forming along the front. Temperatures at 925 mb will drop a few degrees below freezing across the mountains and points north this afternoon allowing for rain to change to snow with light accumulations to valley floors and couple inches across the higher terrain. Below freezing air at 925 mb will advect all the way to the coast and some snow cannot be ruled out south of the mountains although snow is not expected to accumulate. Highs temperatures will likely peak around mid day in the 40s with temperatures falling through the afternoon. Precipitation comes to an end this evening with breezy northwest winds advecting cooler and drier air into the region overnight. Storm total QPF will generally be 05 to 0.75 inches with higher amounts in the mountains. Low temperatures tonight will range from the mid 20s north to low 30s south.

KEY MESSAGE 2 DESCRIPTION...

Behind Sunday's cold front, the week will start on a chilly note. 700 mb temperatures will fall to -20C by Monday afternoon. Combined with upper-level temperature anomalies of -2.5 SD from climatology per the NAEFS situational awareness table, it will be unusually cold aloft. Regardless, the high April sun angle should still help daytime surface temperatures get into the 40s.

Monday's forecast had previously looked dry, but new guidance is suggesting a signal for some scattered afternoon convective showers. With such a cold airmass, it won't take a lot to get clouds to build vertically as the sun heats the surface. In fact, some guidance is suggesting modest instability of ~100 J/Kg SBCAPE with very steep low-level lapse rates near 9.0 K/Km. In addition, a shortwave and associated vort max will swing through, which will provide a source of lift. There is a chance for rain to mix with snow or possibly even graupel given these ingredients. Any showers that develop will be scattered and quick-hitting at any one location.

KEY MESSAGE 3 DESCRIPTION...

After a hard freeze on Tuesday morning, a moderating trend should commence as we head deeper into next week. Tuesday currently looks dry with some subsidence behind Monday's shortwave, but with anomalously cold air still upstairs, cannot rule out some cloud cover/showers in the mountains.

A difficult-to-time shortwave brings the next widespread chance for precipitation on Wednesday, but with POPs only hovering around 15- 30%, it does not look like a washout by any means. Regardless, light snow is once again possible for the northern zones given cold air lingering. Height rises late in the week suggest temperatures will rebound close to seasonal averages with 50s in the forecast for late week highs currently.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Ceilings will continue to lower over next couple of hours with drizzle at times at PWM. Fog and low cigs will bring IFR/LIFR across all sites by 03Z except LEB and HIE where MVFR may persist until 06Z and then lower to IFR. RA will begin from west to east on Sunday morning between 10-14Z (latest at KAUG and KRKD) with RA persisting through 21-00Z Monday along with FG. Light and variable winds during the morning will become NW with gusts up 20 kts by early afternoon. Conditions will gradually improve Sunday night but some restrictions will likely linger through 12Z Monday.

Outlook...

Monday: Scattered rain and snow showers may bring brief and localized restrictions Monday, especially at HIE. Otherwise mainly VFR conditions with NW winds at 10-15 kts during the daytime before becoming light and variable at night.

Tuesday: VFR conditions with light winds. Lowering ceilings possible at night.

Wednesday: Showers and MVFR are possible, otherwise VFR conditions continue.

Thursday - Friday: Mainly VFR expected.

MARINE

Southerly winds will prevail through the morning ahead of a cold front with gusts around 15 kts and seas less than 5 feet. The front crosses the waters tonight with NW winds gusting 20-25 kts and seas 4-5 feet. Brief SCA conditions will be possible this afternoon and evening outside of the bays.

Winds and seas diminish Monday into Tuesday as high pressure builds over the Northeast. High pressure shifts southeast of the waters Tuesday night into Wednesday as a weak system approaches from the west with winds turning southwesterly.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 4 PM this afternoon to midnight EDT tonight for ANZ150-152-154.