textproduct: Gray - Portland

WHAT HAS CHANGED

Some uncertainty remains on cloud cover tonight which will affect overnight low temperatures given nearly calm winds. Less clouds would lead to lower temperatures overnight.

Continue to assess two weak systems that could bring light snow or snow showers to the region Saturday and again Sunday night into Monday.

KEY MESSAGES

1. Mild temperatures around or above seasonal averages are expected through this weekend with even warmer temperatures likely through midweek next week.

2. A cold front moves through on Sunday, bringing isolated, low impact chances of snow showers. The long term pattern supports active weather next week, with the potential for more widespread precipitation later in the week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Longwave troughing over New England will remain in place through Saturday. The trend has been to bring more zonal flow across the northern tier of the CONUS into next week, resulting in the displacement of cool continental airmass to the north.

Resulting surface temperatures remain within a few degrees of seasonal normals this weekend with highs from around 30 to the mid 30s and overnight lows in the teens and single digits above zero. Large factor for overnight temps this weekend will be cloud cover through the evening and overnight hours, especially tonight. Places where skies remain mostly clear overnight could fall an additional 10 degrees rather quickly in good radiational cooling conditions.

A more significant warmup remains possible Monday through Wednesday as low pressure passes through James Bay with mid/upper level jets to support deeper warm air advection across the central and eastern CONUS. This could lead to a couple days of coastal and interior locations reaching values around 40 degrees.

How mid and late week pattern shifts develop will determine if these values continue into the second half of the week or if most seasonable temperatures return.

KEY MESSAGE 2 DESCRIPTION... A chance for light snow or snow showers for the mountains Saturday as a look to next week could bring a few brushes with precip events.

Locked flow feeding from a continental airmass, moisture will be limited for disturbances entering New England this weekend. The best chance for flakes to fall will be in the mountains where the NW wind direction is favorable to make use of what moisture does arrive. Further downstream, downsloping will make the drier low levels hard to overcome. Kept the forecast of slight to chance PoPs Saturday into Saturday evening as a cold front looks to move through. A bit of instability may be available for heavier snow showers along the US/CAN border Sat evening, before departing overnight.

Guidance has begun to downplay another chance for precip Monday as drier northern stream looks to be winning out as low pressure remains well south exiting the Mid-Atlantic.

Gradual trend to zonal flow through mid week will bring a number of disturbances through the Ohio Valley and towards the Northeast Tuesday afternoon, Thursday, and later Friday into Saturday. While guidance has similar looking outcomes, there remain differences in intensity and slight shifts in track. While it has been hard to picture other precip types in the region while its been so cold, there will be the chance for some rain in one or more of these rounds given expected temperature trends. That said, being on the north side of these system could result in cooler temperatures during their passage.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18z Saturday: VFR. SKC conditions this evening will tend to fill in late tonight. Ceiling should remain VFR, but HIE could see lowering with SHSN into Saturday. SN could also bring IFR vis, tapering Sat evening. W winds increase through the day with gusts to 15 kts.

Outlook...

Sunday night-Mon Night: Some light snow showers may bring localized brief MVFR/IFR conditions Sunday night into Monday with MVFR ceilings common during this time as well. This is more likely at western TAF sites.

Tuesday: SHSN possible with MVFR/IFR in southern Maine.

Wednesday: A disturbance may bring SN to the region, but there is uncertainty if it will focus across most terminals in the region, or just across southern NH.

MARINE

High pressure noeses towards the region overnight tonight, with a cold front arriving Saturday evening. This will result in SCA conditions Saturday night through Sunday morning. Conditions may remain below SCA through early next week, but disturbances arriving mid to late week look to bring an uptick in winds and thus seas that may require additional headlines.

GYX WATCHES/WARNINGS/ADVISORIES

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