textproduct: Gray - Portland

WHAT HAS CHANGED

We are growing more and more confident that we will see measurable snowfall accumulations Thursday night/Friday morning across the region, especially elevations over 1000 feet across New Hampshire and portions of western Maine.

KEY MESSAGES

1. A late week coastal storm remains possible with rain and/or snow. Winter conditions remain possible for at least portions of the forecast area, with the highest confidence at elevations over 1000 feet.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

We will remain generally under zonal flow aloft through the rest of the day which will mean plenty of upslope clouds and isolated showers along and north of the mountains. South of the mountains will see mostly sunny conditions.

For tonight into Thursday morning, we transition into southwest flow aloft as a trough starts to dig and approach from the west. Models are in fairly good agreement that we should see an initial wave eject into the region by Thursday afternoon, leading to increasing precipitation chances. As a surface low develops and lifts into the Gulf of Maine Thursday night into Friday, we should see multiple rounds of precipitation wrapping around with the heaviest rates likely across southern New Hampshire, portions of central NH, and far southwest Maine. While models continue to come into better agreement, there are still multiple scenarios on the table. The GFS and ensemble continue to be the western outlier which would result in more significant snowfall accumulations with some potential even up to the coast. The ECMWF, CMC, and their respective ensembles keep most of the precipitation over New Hampshire and the southwest tip of Maine. The areas that we are most confident that could see a few inches of accumulation will be over the higher elevations (generally over 1000 feet) of New Hampshire and portions of western Maine. The two areas where we could see several inches of accumulation will be the Monadnock region and portions of the Whites. Here, NBM probabilities of at least 2 inches of snow are maximized around 60 to 70 percent. Increasing that threshold to 4 inches or more and the highest probabilities drop into the 20 to 40 percent range, maximized over the Monadnocks. Elsewhere across New Hampshire and western Maine, a few flakes could mix in at times with the rain or we could see a brief dusting.

Most of the guidance then has the bulk of steady precipitation moving out of the area by mid to late day Friday but the pattern will remain unsettled as the upper low is stubborn to push out. Thus, periodic rain and snow showers will remain possible through the weekend, especially across the mountains. We should dry out by the end of the weekend and into the next work week as high pressure settles in. Temperatures will generally remain average to slightly below average for this time of year through the rest of the week and into next week.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18z Thursday: VFR conditions expected at all terminals through the rest of today. An occasional shower cannot be ruled out either. There is a lower chance for a shower this evening at LEB and AUG. For tonight, ceilings will start to come down which will lead to potential MVFR categories at HIE first and then at MHT, CON, LEB, and possibly PSM by Thursday morning.

Outlook... Thursday: MVFR becoming more widespread through the day. Rain chances also start to increase during the day over New Hampshire sites. Precipitation chances then spread into portions of western Maine at night. Some snow may start to mix in. Scattered IFR visibilities are possible later in the afternoon and at night. Moderate confidence.

Friday-Saturday: Widespread MVFR/IFR ceiling and visibility restrictions are possible as a the system continues to bring rain and snow to the area. Low confidence in MVFR/IFR visibility. Moderate confidence in MVFR/IFR ceilings.

Sunday: Improving to VFR south of the mountains. HIE and LEB potentially stay MVFR. Moderate confidence.

Monday: VFR conditions expected. Moderate confidence.

MARINE

Sub-SCA conditions should prevail through the day on Thursday but conditions will start to deteriorate late in the afternoon and overnight into Friday. A period of Gale Force Winds during this time frame as low pressure moves into the Gulf of Maine and vicinity. A Gale Watch has been issued for all waters except for the bays. SCA conditions may hang around through much of High pressure then begins to build into the area by early next week which is going to return sub-SCA conditions to the waters.

GYX WATCHES/WARNINGS/ADVISORIES

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