textproduct: Gray - Portland

WHAT HAS CHANGED

Tuesday night through Wednesday has continued to trend colder, increasing the chances for sleet and/or freezing rain across northern areas, especially the western ME mountains. A brief period of wintry mix also can't be ruled out farther south toward the foothills and Augusta region of western ME.

KEY MESSAGES

1. One more day of very warm temperatures will continue to eat away at the snowpack, with melt staying controlled. Ice movement has been observed with at least one jam reported on the Upper Ammonoosuc. Flood risk remains low at this time, but these areas will have to be monitored closely as we get back to active weather for the second part of the week.

2. Low pressure brings widespread precipitation chances for the middle of this week. Rain is expected south of the mountains, while low-level temperatures are trending cold enough to support freezing rain and sleet across northern areas, particularly the western ME mountains, and possibly as far south as the foothills.

3.Cooler temperatures return to finish up the workweek and into the weekend with an active pattern supporting additional rounds of precipitation.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Today has shaped up nicely with many locations making it into the upper 50s and low 60s early this afternoon. There are plenty of clouds out there as low pressure well to our northwest continues to move easterly, but they have not been a factor. The seabreeze hasn't really been a factor either as even the Midcoast is seeing temperatures into the low 50s. With this in mind, and more anomalous warmth with clear skies on the way, I have continued trending temperatures up slightly for tomorrow. It should be noted that there is still a 5-10 degree spread in the 25th-75th NBM percentiles, but I think that just speaks to how much location is going to determine how high you see temperatures climb tomorrow. Based on today it seems like it should be pretty easy for interior locations to climb into the mid- to upper 60s, with locations in the Merrimack Valley maybe even seeing 70. I am still a little hesitant about going too warm in coastal locations, particularly the Midcoast, but with most of the coastline parallel to the winds I don't think low to mid-60s is out of the question. Another potentially cooler spot is going to be the Western Maine Mountains as a front begins to encroach on that area, but it shouldn't be by much as the front has been trending later. Snowpack will continue to be reduced, but with controlled melt keeping rivers from seeing significant rises. With that beings said river ice is also seeing decay and shifting as a result. This has caused at least one jam that we know of, and while streamflows have been low due to ongoing drought conditions rivers will have to be watched closely as we move back into a more active weather pattern for the second half of the week.

KEY MESSAGE 2 DESCRIPTION...

Low pressure crosses the Great Lakes Tuesday and then across northern New England Wednesday night into Thursday, sending a strong cold front through the region. The column begins to saturate Tuesday night with most of northern New England north of/on the cold side of a backdoor cold front and NE winds supporting CAD setting up. Based on forecast soundings, expected fog to develop with weak lift also supportive of drizzle in some areas. Temperatures are also trending cold enough to support freezing drizzle or light freezing rain/sleet across portions of the western ME mountains and possibly toward the ME foothills/Augusta regions.

Have blended in the NAM temperatures as it tends to do the better of the models in CAD scenarios, and this keeps temps in the mid-upper 20s across the western ME mountains and northern NH for much of the day Wednesday and temperatures around the freezing mark southward toward the ME foothills and Augusta region into at least Wednesday morning. These areas have increasing potential to see a longer period of sleet and/or freezing rain especially the western ME mountains where temperatures stay colder longer. I have not favored one over the other as the warm nose with forecast soundings warm enough aloft to support freezing rain, but the cold layer at the lowest levels may also be cold enough and deep enough to refreeze it.

For rest of the area, cool and cloudy/dreary conditions with fog will likely continue through Wednesday, but temperatures are expected to stay "warm" enough for precip to rain or drizzle. Depending on where the front sets up, parts of southern NH may get into the 40s or 50s.

Low pressure approaches Wednesday evening/night with temperatures warming as the warm front lifts north. It's uncertain how far north or how quickly this occurs, but northern areas still below freezing should eventually get above with ptype switching to rain. The cold front moves through Thursday morning, with temperatures falling through the afternoon. As the cold air pushes in, there may be a brief period of light snow as precipitation comes to an end. Breezy conditions also kick in behind the front with forecast soundings suggesting 30-40 mph possible.

KEY MESSAGE 3 DESCRIPTION...

Temperatures return to near normals for highs Friday into the weekend, ranging from the mid 30s to lower 40s. The pattern remains active with ensembles in surprisingly good agreement this far out with timing of two distinct systems to keep an eye on. The first is late Friday into Friday night and the second is late Sunday into Monday. Precipitation types are more uncertain, but both could feature rain and some wintry variety depending on track. Between these system, there will likely be a dry period between Saturday afternoon through Sunday afternoon.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Through 18Z Tuesday...Gusty winds taper off this evening with VFR conditions prevailing through Tuesday morning. Models continue to hint as some low level wind shear overnight, but observations last night showed mostly unidirectional flow so have left it out of the TAFs for tonight.

Outlook...

Tuesday afternoon: Mostly VFR, but conditions will be trending downward through the evening as moisture increases ahead of an incoming system.

Tuesday Night - Thursday: IFR or lower possible with fog, low ceilings, drizzle, and rain, but can't rule out a period of wintry mix as far south as AUG on Wednesday. Rain could end as snow on Thursday as a cold front moves through, and westerly winds are expected to become breezy behind the front on Thursday. Conditions likely start to improve from west to east later in the day on Thursday.

Thursday night: Mostly VFR.

Friday: VFR, but chances for restrictions/precipitation increase late in the day.

Friday night: IFR possible with light snow.

Saturday: Most sites return to VFR in the afternoon.

MARINE

Southerly winds increase this evening and gusts 25-30 kts should last through the first part of tonight before tapering off. Waves will be a little slower to settle off the central coast of Maine so SCAs remain in effect there until Tuesday morning, but the bays and southern waters drop out overnight. Conditions are expected to be fair through the day Tuesday.

Tuesday night-Monday...Easterly winds may approach SCA levels Wednesday, but are more likely Wednesday night as southerly flow increases ahead of a cold front that will cross during the first half of Thursday. Wind gusts may approach gale force ahead of the front, but gales appear more likely with the west winds behind the front late Thursday into Thursday night. Additional periods of at least SCA conditions, possible gales too, over the weekend into early next week as two additional system move across the region. The first is late Friday into early Saturday with the second late Sunday into Monday.

CLIMATE

Temperatures on Tuesday will approach daily record highs at long term climate sites.

Site Location Forecast Temperate Record Temperature Record Year Augusta 65F 64F 2016 Concord 70F 72F 1878 Portland 65F 66F 2016

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 7 AM EDT Tuesday for ANZ150-152. Small Craft Advisory until 2 AM EDT Tuesday for ANZ151-153. Small Craft Advisory until 2 AM EDT Tuesday for ANZ154.