textproduct: Gray - Portland

SYNOPSIS

Weak low pressure looks to pass to our south looks to mostly miss our area to the south, but light snow is likely over southern New Hampshire tonight into Saturday morning. Next potential storm arrives for Sunday night and Monday and will likely be more of a mixed bag to rain. Windy and cold early to mid week.

NEAR TERM /THROUGH TODAY/

High pressure will build across northern New England today and as a result it will be quite cold. However, the good part is that the winds will be much lighter than they were this past evening. Expect increasing clouds this afternoon as low pressure moves eastward from Ohio.

SHORT TERM /TONIGHT THROUGH SATURDAY/

Still some uncertainty in tonight's forecast as low pressure passes to our south but overspreads southern zones with a some light snow. Still not the absolute best agreement amongst the various guidance sources, but confidence is high enough to go with categorical PoPs across southern NH. Took a blend of PoPs for the northern extent of the the light snow and that ends up being roughly from just north of KLEB southeastward to York County ME. However, there could be an hour or two period where it advances a little farther north. Highest totals should be across southwestern NH where 1 to 3 inches is possible, perhaps up to 4 in some spots.

Low pressure is lone gone Saturday, leaving high pressure in it's wake.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Overview: Near to below normal temps continue thru the extended. Messy winter storm possible Sun night into Mon with travel impacts anticipated.

Key Messages:

-A storm is likely Sun night into Mon. At the end of the holiday weekend that could bring significant travel impacts, especially if surface cold air hangs tough.

Forecast Details: Surface ridging in place early Sun. NBM guidance seems rather warm considering favorable radiational cooling conditions and fresh snowcover. I feel more comfortable blending in some 25th percentile NBM guidance along with MOS to capture those cooler temps.

Attention then turns towards a messy winter storm arriving late Sun into Mon. Over the last several days the upper air pattern has evolved slightly. Trending towards more upper level confluence in the vicinity of the mouth of the St. Lawrence. This would tend to promote or reinforce high pressure and makes active cold air damming more likely in my opinion than the passive/in-situ variety. NBM guidance is doing a passable job by keeping interior portions of the forecast area at or below freezing thru Mon afternoon. However it is a known issue for the NBM, and I feel that temps could be even colder than what the mean shows. A blend of the 25th and 50th percentiles of the NBM may be a fair place to start, given that there is still plenty of uncertainty when it comes to this system.

DESI cluster analysis shows that ensemble guidance is trying to resolve two main features. One being the shortwave trof itself, and the other the upper low/trof over Newfoundland into the north Atlantic. A stronger shortwave trof combined with a weaker upper low downstream ends up favoring more QPF locally, and more wintry QPF. That also happens to be where 40 percent of the members reside in the range of scenarios. Seeing as the NBM is already categorical PoP I see no reason to change that, but considering the above discussion about temps I will make sure that there is remains wintry mix in the forecast. It is way too early to get into details regarding ptype, so the plan will be to include both sleet and freezing rain where any changeover is anticipated.

Beyond that portion of the forecast the forecast area will get into a westerly flow, cold advection pattern. Will have to watch for any stronger shortwave trof to sneak into the flow, but otherwise precip will generally be tied to orographic lift over the mtns.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Short Term...VFR conditions continue most everywhere through most of the day today. Restrictions are likely at KEEN and KLEB and MHT tonight as light snow moves into the area. These restrictions may potentially reach out to KCON and KPSM as well for a brief period. VFR remains in the north and across Maine locations through Saturday.

Long Term...VFR conditions to start the period on Sun. Conditions will quickly deteriorate Sun night however as the next storm arrives. Widespread IFR or lower conditions are expected in the warm advection pattern over the top of colder surface air. In addition to the low CIGs, ptype may be an issue especially for inland TAF sites. However I cannot rule out some frozen or freezing precip even at the coast for a time. Mixed precip events are always a rather low confidence affair and this one is no different. That precip threat continues thru Mon before westerly winds clear out both precip and low CIGs. Tue could be a bit gusty and I could see surface gusts around 25 kt. MVFR CIGs may linger in the mtns in upslope flow, especially around HIE.

MARINE

Short Term...Any gales diminish to SCA levels early this morning. Northerly winds persist but weaken considerably by this afternoon, as high pressure moves overhead. Seas also gradually lower through the day, becoming 2-4ft by Saturday morning.

Long Term...High pressure will continue drifting east thru Sun. Southerly winds increase Sun night into Mon, with SCA conditions likely outside the bays. Once winds shift to westerly behind the cold front late Mon, gale force wind gusts become possible. This may include all waters. Gale force wind gusts may linger thru Tue before gradually diminishing. However gusty winds and SCAs may continue for much of the week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Warning until 10 AM EST this morning for ANZ150>154. Freezing Spray Advisory until 10 AM EST this morning for ANZ150>153.