textproduct: Gray - Portland

WHAT HAS CHANGED

Increasing confidence in a plowable snow for at least northern/ central portions of the forecast area Sunday and Sunday night.

KEY MESSAGES

1. Quick hitting system still on track to bring a period of snow from the White Mountains northward in NH and much of western Maine with some slick travel likely through this evening. Rain will be the dominant precipitation type across south-central NH and far southwestern Maine.

2. Widespread snow and rain event expected Sunday-Sunday night with a plowable snow likely for much of the area...especially away from far southern NH and the immediate coast. There is some potential for lighter snow to linger into Monday.

3. Active weather week continues For Tuesday and beyond with multiple precipitation chances and temperatures at or a bit below normal for late March.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A wave of low pressure over the eastern Great Lakes will trek east this evening continuing to spread precipitation across the forecast area. Latest radar presentation and surface obs show snow has already broken out along and north of the mountains. There will be several hours of decent H8 Fgen forcing through roughly 7 PM this evening that will bring potential for snowfall rates around 1 inch per hour in the mountains. Surface temperatures near freezing across the north will likely lower through the afternoon with the aid of wet bulbing. These falling temperatures combined with snowfall rates will likely bring slick travel through this evening. There have not been any significant changes to the snowfall forecast since the last package with 2-5 inches forecast along and north of the mountains with the high end of the range confined to the higher terrain.

South of the mountains precipitation will be mainly rain. The exception will be portions of interior Maine from KLEW to KWVL where dynamic cooling will allow for rain to mix with snow along with potential for a brief period snow between 5-8 PM that could slicken up roads for the evening commute.

Precipitation will taper off from NW to SE after 8 PM this evening. Dry air aloft may allow for snow to end across the mountains and north as freezing drizzle. Winds will shift northwesterly towards day break allowing for clearing skies Saturday morning. The NW gradient will tighten around mid day Saturday that may allow for winds to gust around 25-30 mph downstream from the mountains with high gusts in the terrain.

KEY MESSAGE 2 DESCRIPTION...

Weak wave riding along polar front will allow for precipitation to develop associated with isentropic ascent spreading across the area Sunday. Then...a stronger...upstream shortwave dives into the northeast Sunday night and Monday with stronger low pressure developing along the front and then lifting north and east. This system will have more moisture to work with then the one tonight with PWATs south of the frontal boundary reaching 1". The initial frontal wave/isentropic ascent supports up to 0.5" of liquid. The wildcard is then the second wave of low pressure that develops and whether it can throw more precipitation into the mix for Monday. The EC/EC-EPS is more bullish in this regard resulting in high probabilities of >0.5" liquid through daybreak Monday with a low probability /10-20%/ of 1" of liquid.

As for PTYPE...expect all snow at onset late Saturday night/early Sunday morning with llevel warming supporting a transition to rain over southern NH and SW Maine with some difference in just how far north and east the rain/snow line will reach. For areas that remain all snow...a plowable snow is likely with snowfall in the 3-6+" range possible by Sunday evening with slick travel likely through the day Sunday. Further south more mix and warmer temperatures will result in a coating to a slushy inch or two before the changeover. Overall...this event may necessitate winter weather advisories with travel impacts Sunday into at least Monday morning.

In the more robust solutions...the precipitation looks to come in two waves...one daytime Sunday and the next early Monday. The Monday batch would be all snow throughout the region with colder temperatures arriving as low pressure takes shape to our east. Thus...while initial snow will be wet...see only a very limited power outage threat as temperatures cool Sunday night and additional snow is not as sticky.

We/ll continue to watch the evolution of the second half of this event to determine overall magnitude of impacts.

KEY MESSAGE 3 DESCRIPTION...

A parade of shortwaves embedded within the west northwest flow aloft along the polar jet axis are poised to move through the region for the middle and latter portions of next week. Given the fast flow...there is a fair amount of spread amongst the global ensembles with the EC/EC-EPS more bullish on a signal for precipitation on Wednesday while there is a clearer signal for another event by Friday. Given their source region...pattern recognition suggest that these will not be heavy precipitation producers...but temps aloft are cool enough that snow will be the favored PTYPE in the mountains and foothills with rain to the south and along the coast. Best weather day looks to be Tuesday with some sun and a brief respite between systems. Temperatures aloft are a bit below normal for late March... favoring highs in the 30s across the mountains to the lower 40s over southern areas and along the coast...3-5F below normal for this time of year.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through Saturday night: Conditions will deteriorate to IFR/LIFR through this evening in lowering cigs and rain along and south of a line from KLEB to KRKD. KHIE will likely see LIFR in snow through 00Z this evening and KAUG will see a rain and snow mix briefly changing to snow within a couple hours either side 00Z. IFR likely lingers overnight in low cigs and drizzle while steady precipitation ends by midnight. NW winds bring drier air by Saturday morning that will bring conditions to VFR through the day Saturday.

Outlook (Sunday through Next Week): An active weather week is expected with numerous chances for precipitation and therefore restrictions. Widespread LIFR/IFR conditions appear likely in Snow and Rain/Snow for Sunday-Sunday night with some potential for precipitation & restrictions to linger into Monday. Improving conditions are expected Tuesday before additional chances for precipitation/restrictions arrive Wednesday and again Friday. There is some potential for gusty northwest winds on Wednesday and again late Friday behind a series of fast-moving weather systems.

MARINE

A wave of low pressure crossing the waters will bring increasing southerly flow through this evening with winds shifting northwesterly Saturday morning as the low departs. Winds and seas will bring SCA conditions into Saturday morning with elevated seas allowing SCAs to continue through Saturday afternoon.

Outlook (Sunday through Next Week): An active pattern is expected for Sunday through the coming week...which will result in nearly continuous SCA conditions through the week. There is a low probability for gale force wind gusts in the Wednesday- Thursday timeframe depending on the location and strength of developing low pressure over or just east of the Gulf of Maine.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 5 PM this afternoon to 8 PM EDT Saturday for ANZ150-152-154.