textproduct: Gray - Portland

WHAT HAS CHANGED

A wind advisory has expanded inland through Southern New Hampshire and York County. Rainfall amounts have trended upward. High elevation snowfall coverage has expanded down to around 2000ft.

KEY MESSAGES

1. A potent storm brings rain and wind tonight into Saturday.

2. This storm also brings accumulating snowfall to the higher terrain, with heavy snowfall accumulations likely across the highest peaks. This brings dangerous winter hiking conditions tonight and Saturday.

3. Frost is possible across the north Saturday night as a cool airmass settles in.

4. Cool and showery weather will give way to a warming and drying trend by the end of the week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A compact low pressure system diving southward strengthens across New England tonight into Saturday. The storm brings a soaking rainfall to much of the area, along with some strong and gusty winds along the coast and through the Seacoast region of New Hampshire.

Rain is pushing southeastward this afternoon as the low tracks toward New England. Rain spreads to the coastline through the afternoon and evening hours. After a period of rain, a few hours of dry conditions are likely across southern New Hampshire late this evening and into the overnight hours as the axis of moisture pivots around the low pressure system. Rain then presses southward again later tonight. Elsewhere, rain continues through the overnight hours. The rain gradually shuts off from north to south starting in the predawn hours, and eventually moving offshore by the mid afternoon hours on Saturday.

The axis of the heaviest rainfall looks to extend from the White Mountain region through the southern coasts. Along this axis, areas of 2-3 in of rain are likely. Most other areas likely see 1-2 in of rain. However, lighter amounts are expected along an axis from Somerset County southward through Knox County. Also, southwest New Hampshire is likely to see lighter amounts less than an inch as well.

Another component of this system will be the wind. A period of strong ENE gusts is likely as the storm pivots through late tonight and Saturday morning. The strongest gusts are expected along the southern coasts and through the Seacoast Region. Gusts of 45-55 mph are likely, with the strongest gusts along the immediate coastline. With leaves on the trees and a steady rainfall accompanying the wind, scattered power outages are possible through the advisory area. With the leaves on the trees, impacts will be higher than similar wind speeds would bring during the wintertime. The wind advisory has been expanded inland into interior York County and southern New Hampshire to account for this.

KEY MESSAGE 2 DESCRIPTION...

Another aspect of this system will be high elevation snow. High res models have consistently been depicting a heavy thump of snow outside of the mountains as well. While this is not impossible, it would be unprecedented for this late in the season. Flakes may mix into the lower elevations near the foothills and Lakes Region of New Hampshire, but accumulations will likely remain confined to elevations above 2000ft, where snow is not unprecedented at this time of year. Above 3000ft, snowfall accumulations are likely, with the highest peaks possibly picking up around a foot of snow. Hikers and high elevations campers should prepare for winter conditions if venturing out tonight or tomorrow, with wind chills in the teens and single digits accompanying the snow.

KEY MESSAGE 3 DESCRIPTION...

Behind the storm system, cool air settles in Saturday night, with frost possible across northern areas as temps cool into the low to mid 30s. Widespread upper 30s to near 40 degrees are expected elsewhere.

KEY MESSAGE 4 DESCRIPTION... The next shortwave is expected to arrive Sunday afternoon into Sunday night. This system will take a similar track to Saturday's event, and will overall be a less amplified version of it. 850 mb temperatures will still be anomalously cold for this time of year (4-6C). After a dry start to Sunday, can expect showers to develop during the afternoon, fueled by cold temperatures aloft as well as a lobe of vorticity swinging in from Quebec. Looking at the possible morning sunshine and model soundings, a few stronger cells will contain lightning and even some small pea size hail canned be ruled due to the cold pool aloft and strong late May sun.

Into next week, an omega block pattern will keep a firm grip over the CONUS through the first half of next week, with upstream ridging over the Canadian Prairies and troughing over the Northeast U.S. For our sensible weather, we will maintain well below normal 500 mb heights as well as below average 850mb and 500 mb temperatures, albeit not as anomalous as this upcoming weekend. With a persistent cold pool aloft, combined with the strong June sun, it will not take much surface heating for diurnally-driven showers to develop each day. These will be scattered in nature, so while most of next week has daily precipitation chances, it will not be raining the entire time, with the best chances for clearing skies to be at night and during the early morning hours. Guidance is coming into to better agreement for a pattern shift by Thursday/Friday next week as amplifying ridging across the Ohio River Valley pushes into the Northeast by the end of the workweek. This will bring at least a short period of warm and dry conditions.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR gradually descends to IFR through the overnight hours as rain moves into all terminals. Northeasterly wind gusts of 30-40kt are likely at southern and coastal terminals late tonight into tomorrow morning. Conditions gradually improve to VFR from north to south through the day tomorrow, arriving last at PSM and MHT in the mid afternoon. VFR then likely prevails Saturday night.

Outlook:

Sunday: VFR conditions expected in the morning before MVFR and IFR conditions return under afternoon showers that will last into the night. An isolated thunderstorm or two can't be ruled out, but coverage will remain low.

Monday: Patchy morning fog and a few lingering showers will give away to improving conditions as cloud decks scatter out and rise above 5K.

Tuesday - Wednesday: A few afternoon showers can't be ruled out bringing tempo MVFR ceilings, but overall improving aviation conditions.

Thursday - Friday: High pressure is favored with VFR conditions and no aviation impacts expected.

MARINE

East-Northeast winds steadily increase to gale force tonight, with storm force winds likely across the southern waters as a compact low pressure system strengthens overnight. The storm then exits the Gulf of Maine tomorrow afternoon, with winds and seas subsiding through the afternoon and evening. Seas remain at SCA levels through tomorrow night.

Seas will subside below SCA candidness during the day on Sunday as Northeast winds slacken. Another weak area of low pressure will track across the Gulf of Maine on Monday bringing an increase in easterly winds with gusts back up to 20kts but waves will remain around 3 feet.

General NE wind pattern will remain through Wednesday next week with the potential for SCA conditions again the middle of next week. There is a potential coastal low pressure system in this period, how strong and close does it track to the Gulf of Maine is still uncertain, but enough confidence there could be a close approach system. High pressure looks to briefly return at the end of the work week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Wind Advisory from 5 AM to 11 AM EDT Saturday for MEZ018-023- 024. High Surf Advisory from 8 AM to 8 PM EDT Saturday for MEZ023- 024. NH...Wind Advisory from 5 AM to 11 AM EDT Saturday for NHZ010- 012>014. High Surf Advisory from 8 AM to 8 PM EDT Saturday for NHZ014. MARINE...Gale Warning from 2 AM to 2 PM EDT Saturday for ANZ150-152-153. Small Craft Advisory from 2 AM to 11 AM EDT Saturday for ANZ151. Storm Warning from 2 AM to 11 AM EDT Saturday for ANZ154-182- 184. Gale Warning from 2 AM to 8 PM EDT Saturday for ANZ180.