textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3 )

An area of low pressure currently over the western Sound and soon to overspread Whittier continues to be the focus for winter precipitation this afternoon and tonight. Current radar shows light returns from the Knik Arm down through Cook Inlet, Anchorage, and the Kenai Peninsula, with additional returns pushing into Prince William Sound and the coast. Snow has been persistent across Homer and Seldovia where a winter weather advisory remains in effect for 4 to 10 inches of total snowfall through Saturday morning. Snow has been much lighter elsewhere from Kenai into Anchorage, and only a dusting to possibly one half inch is forecast. Temperatures have warmed to above freezing along portions of the Seward Highway from the eastern Turnagain Arm down to Seward, and rain has been the primary form of precipitation. However, temperatures are expected to drop below freezing again later this evening/tonight with an additional 1 to 3 inches forecast from Girdwood to Turnagain Pass.

As the low continues to lift further inland light precipitation will remain possible through early Saturday morning while also expanding into the Susitna Valley. Model guidance has a second smaller trough dropping south from interior Alaska, converging upon the Southcentral low, with a brief chance for a second round of snow spreading into western portions of the Susitna Valley after midnight tonight. Accumulations here will also only amount to a dusting.

Precipitation across Southcentral clears out over the weekend with cooler temperatures to set in across the region. As soon as precipitation comes to an end on Saturday morning the potential for patchy fog will increase across the Mat-Valley, Anchorage Bowl, and Western Kenai Peninsula. Expect highs on Saturday to remain below freezing for all but coastal locations. Temperatures will trend cooler into Sunday with morning lows in the teens for the MatSu and Western Kenai Peninsula, to single digits across the Copper River Basin.

-BL

LONG TERM FORECAST (Days 4 through 7/Tuesday through Friday)

Starting on Tuesday, a vertically stacked low and large cyclonic circulation will be centered south of the Aleutians in a weakening phase. Short-waves embedded within the circulation will track from east to west from the western Gulf/Kodiak Island across the Alaska Peninsula and Bristol Bay and continuing westward across the southern bering Sea. None of the features look particularly strong, so would expect areas of precipitation and wind with typical winter- time impacts. Precipitation-type will be mainly rain, with Bristol Bay being the only location cold enough to see snow. The upper low will open up into a trough by Thursday (Thanksgiving), causing winds and precipitation to diminish.

Meanwhile, a strong ridge in the Arctic will build southward over the northern half of mainland Alaska. This looks far enough south to block any short-waves from the Aleutian trough from reaching interior SW AK or Southcentral AK. Thus, expect seasonably cool and dry conditions for these areas Tuesday through Wednesday. A short-wave will dig down the east side of the ridge on Wednesday, across the Yukon and into the Copper River Basin. This will bring marginally colder temperatures, though accompanying cloud cover will likely limit temperature drops. This trough will force the upper ridge to retreat back northward and allow a short-wave trough to approach Southcentral on Thursday. Model agreement with this feature is not great, but ensembles generally support this idea. With a cold air mass in place over Southcentral, the most likely outcome would be widespread light snow arriving sometime Thanksgiving Day.

As we continue to Friday, model guidance is in excellent agreement on amplification of the upper level flow and development of an Atmospheric River. However, as would be expected this far out in time, there is large spread in the location of the ridge/trough and track of a leading surface low from the Pacific. This evolving pattern does have good potential to bring higher impact weather to southern Alaska, with strong winds, mixed precipitation-types, and warming temperatures. Stay tuned as we monitor the location of key features and identify the areas where the greatest impacts are most likely.

-SEB

AVIATION

PANC...AN area of low pressure over western Prince William Sound will continue to pinwheel moisture and cloud cover over Anchorage and the terminal through early Saturday morning. MVFR ceilings are expected to persist through late this afternoon then lower to low MVFR or IFR ceilings and vis as steadier light snow develops. Light snow should taper off by 12z, early Saturday morning, as the low weakens and moves inland.

Lingering low-level moisture and a weakening wind flow in the lower half of the atmosphere will likely result in low stratus remaining over the terminal through Saturday morning. There is a chance that this cloud deck either continues to lower through early to mid morning, or erodes just enough to result the development of fog due to additional radiational cooling. Either way, clearing behind the low is not expected. Moreover, any drier air aloft coupled with lingering low stratus and/or fog, could result in some light flurries or freezing drizzle early to mid Saturday morning. Right now, this is a low confidence solution, but will be monitored.