textproduct: Gray - Portland

WHAT HAS CHANGED

Winter storm warnings and winter weather advisories have been issued in most areas for snowfall tonight through Sunday night.

KEY MESSAGES

1. Low pressure brings a round of wintry weather and accumulating snowfall to much of the area tonight through Sunday night.

2. Expect an active work week with multiple precipitation chances and temperatures around or a bit below normal for late March.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Low pressure tracks eastward from the Great Lakes through Southern New England tonight through Sunday. The low then deepens offshore Sunday night, but the main shield of snow from this deepening low is likely to stay offshore from our forecast area on Monday. With the parent low, snow spreads into western New Hampshire by late this evening, and expands eastward through the overnight hours across Maine.

With this set up, accumulating snowfall is expected across the forecast area. The Seacoast of New Hampshire is likely to see lesser amounts, with generally 1-2 inches expected before a transition to rain tomorrow morning. Greater accumulations are expected for central and northern areas, as well as into the MidCoast.

The highest amounts are expected through the higher terrain of Maine and New Hampshire. With an easterly flow, upslope snow likely enhances amounts across the southeastern facing terrain of the Whites Mountains, Ossipee Mountains, and through western Maine. For these areas, a winter storm warning has been issued for 6-10 inches of snow. Locally higher amounts are still possible across the higher peaks as well. East of here, a winter weather advisory has been issued for a general 3 to 6 inches of snow, but some locally higher totals will likely across locally higher terrain, even through the Camden Hills. And then across western New Hampshire and the Lakes region, a winter weather advisory has been issued for 3-6 inches of snow and some pockets of freezing rain. Downsloping conditions north of the Whites are likely to lead to totals more consistent with advisory levels, while more mixing limits totals around Concord and into the Lakes Region.

The bulk of the precip winds down Sunday evening, but light snow and spotty freezing drizzle likely still continues through the overnight hours. We've decided to treat this event as it's own entity ending Sunday night, but snow showers likely develop afterwards by late Sunday night into Monday morning as an upper level trough traverses through northern New England. So while, the main even winds down Sunday evening, some snow showers should still be expected overnight, especially across the north.

KEY MESSAGE 2 DESCRIPTION...

Monday starts will troughing overhead as the previous surface low moves out to sea. An inverted trough will extend back to the west of this low and keep snow showers in the forecast through the day. Some of the latest guidance continues to show some enhancement with this activity along and in the vicinity of the Maine/New Hampshire border so we decided to beef up precipitation chances here as some additional light accumulations seem possible. While surface winds/gusts do not seem overly impressive, the heaviest snow showers could exhibit some snow squall characteristics depending on how the environment sets up. One limiting factor could be mediocre mid-level lapse rates which will be steepening towards the evening. Snow showers will gradually diminish through the night.

Tuesday should mainly be dry as high pressure settles in through the day but the next weak wave and cold front approaches late Tuesday night/Wednesday morning. Precipitation chances will be maximized (30 to 50 percent) over the mountains through the evening on Wednesday as we are likely to see some scattered snow showers here. Once again, we could see at least a small chance for some snow squall activity given steep lapse rates and a saturated dendritic growth layer.

A stronger system is then forecast to cross the region sometime in the late Wednesday night through Friday morning time frame. Precipitation with this system looks to be a mixed bag, starting as snow late Wednesday night before transitioning to mainly rain or a mix by Thursday afternoon. Then, depending on how long precipitation lingers, we could change back to snow again late Thursday night or early Friday morning. Regarding temperatures, highs will mainly be in the 30s on Monday and then ranging from the 30s north to the 40s Tuesday through Thursday. A modest cool down is then possible Friday into the weekend.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

MVFR prevails at HIE through the overnight. VFR transitions lowers to MVFR and then IFR late tonight and Sunday morning as snow spreads from west to east. IFR prevails through the day Sunday, with snow mixing with or transitioning to rain at MHT, CON, and PSM, while snow continues elsewhere. Steady precip ends late Sunday and Sunday evening, while snow showers continue across northern terminals. Patchy freezing drizzle is also possible at all other terminals as IFR conditions prevail.

Outlook:

Monday-Monday night: VFR, though brief restrictions are possible with snow showers.

Tuesday: VFR expected.

Tuesday night-Wednesday: Brief periods of IFR possible under snow showers.

Wednesday night-Thursday night: IFR possible in rain and snow.

MARINE

SCA conditions in northwest winds ease this evening. Low pressure then tracks eastward through the Gulf of Maine tomorrow and Sunday night with SCA conditions in easterly flow possible by late Sunday morning, and continuing through Sunday night.

An active pattern is expected to continue through the coming work week, which will result in nearly continuous SCA conditions. There is a chance for gale force wind gusts Wednesday through Thursday depending on the location and strength of developing low pressure over or just east of the Gulf of Maine.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Storm Warning from 2 AM Sunday to 2 AM EDT Monday for MEZ007-008-012-013. Winter Weather Advisory from 5 AM Sunday to 5 AM EDT Monday for MEZ009-014-018>022-024>028-033. NH...Winter Storm Warning from 2 AM Sunday to 2 AM EDT Monday for NHZ004-006. Winter Weather Advisory from 11 PM this evening to midnight EDT Sunday night for NHZ001>003-005-007>010. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ150- 152-154.