textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Message:

Winter Weather Advisories remain in effect through 6 PM today for 4 to 7 inches for the Lower Matanuska Valley, from Palmer northward toward Hatcher Pass and 6 to 9 inches for the Upper Matanuska Valley, including Sutton and Chickaloon.

Discussion:

Light radar echoes are beginning to spread across the Susitna Valley and northern Cook Inlet this morning, and with ceilings dropping below 2500-3000 ft expect light snow to start making it to the surface across a good portion of the Susitna Valley within the next hour or two. Snow will quickly spread over western Southcentral this morning, but favored locations for the higher snowfall amounts will be the western slopes of the Chugach and Talkeetna Mountains, and the Alaska Range in the Copper River Basin. Overall, the forecast remains on track with just some minor tweaks for timing. This system will move through rather quickly with the heaviest snowfall expected by late morning to early afternoon then quickly winding down by this evening as the system pushes west. Given this, areas outside the advisories will see lighter snowfall amounts of about 1 to 4 inches for the Anchorage Bowl, Turnagain Arm, and northern Susitna Valley. The western Kenai Peninsula will see a light dusting up to an inch with the possibility of a period of rain and snow mix.

Today's snowfall is driven by a shortwave trough lifting north across the Bering towards the Bering Strait this morning. Satellite imagery indicates that the associated front has moved inland over Southwest Alaska with the front looking to push through Bethel by about 6 AM. This front is clearing the Southwest Alaska coast several hours earlier than models are indicating. This front will continue to translate eastwards as a secondary shortwave quickly moves in behind to reinforce the front.

Cold air advection behind the cold front will lead to rapidly strengthening gap winds, first across the western Gulf, southern Cook Inlet, and Kodiak Island this afternoon and spreading to the northern Gulf Coast and Prince William Sound by this evening. There could be some localized areas of blowing snow, most notably through Thompson Pass - though generally expect very light accumulation for coastal areas prior to onset of winds which will limit the amount of transportable snow.

There will be partial clearing of skies overnight tonight, but a strong westerly flow aloft will bring additional short-waves into Southcentral tonight through Sunday. These will low amplitude short- waves with very little moisture to work with, so at most there might be some upslope snow along the west sides of mountain ranges with little to no snow accumulation. More than anything, it will bring another round of clouds into the region. While colder air settles over the region tonight, the presence of clouds (and winds in some locations) will initially limit the amount of cooling. Decreasing clouds Sunday through Sunday night along with a reinforcing shot of cold air advection from Interior AK will cool surface temperatures more significantly Sunday night and into the early part of next week. With a high amplitude ridge building upstream, a strong northerly jet and cold air advecting from north to south will favor persistent gap winds along the coast and high probability of strong winds in The Valdez/Thompson Pass area. The exact placement of the ridge and axis of strongest cold air advection will determine how strong those winds will be, with a High Wind warning (75 mph) not out of the question for Thompson Pass.

- PP/SEB

AVIATION

PANC...VFR conditions expected early this morning transitioning to a light snow as early as 15Z, dropping cigs and vis to MVFR and eventually IFR later in the morning. Patchy fog near the terminal this morning. 1.5 to 3 inches of snow is expected. Precipitation will come to an end by 03Z, with skies clearing out by the early evening. Cooler and drier period coming late this weekend into early next week.