textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Despite snow beginning to trend down across portions of Southcentral, active weather continues with several weather products ongoing. Winter storm warnings and advisories from the MatSu down into Anchorage, as well as the southwest and northwest Kenai Peninsula, the Eastern Turnagain Arm, Kachemak Bay and Whittier, remain in effect through early Wednesday. Some of these may need to be expired sooner than later, depending on radar trends and observations. As flow becomes more westerly into tonight, upslope flow against the Chugach may allow for snow to linger for a longer period of time on the Eagle River and Anchorage Hillsides. The extremely cold air aloft will also continue to support very high snow ratios, resulting in continued snow despite very little moisture.

Temperatures will continue to cool over the next couple of days, beginning tonight, as low pressure departs the region to the southeast. Overnight lows across Southcentral will dip below zero tonight, and back into the minus teens and 20s Wednesday night. Cold weather advisories will likely be needed by Wednesday night and Thursday morning as wind chills will are expected to approach -30 degrees for many Southcentral locations, including the Western Kenai Peninsula, Turnagain Pass, Whittier, the Susitna Valley and much for the Copper River Basin.

As mentioned in the morning discussion, this cold and clear period will be short lived as a front and inverted trough from a strong north Pacific low moves into the coast Thursday afternoon. Kodiak and the Sound will be the first to get another round of snow and wind, with light snow likely spilling over into the greater Cook Inlet region and Mat-Su Valleys. Moving into the weekend the forecast begins to muddy based upon if and where lows develop along the front, but the pattern remains very active. Stay tuned.

BL

LONG TERM FORECAST (Days 4 through 7: Friday through Monday)

No major changes to the previous discussion:

An Arctic air mass will be in place across much of the southern Mainland at the start of the period on Friday, with a deep upper level low initially centered over Southcentral. A narrow ridge will likely be in place across parts of the Bering Sea, extending from the North Pacific into parts of Northeast Russia and Kamchatka. A frontal system associated with a low moving south of Atka will bring strong easterly winds and rain/snow south of the Bering ridge along much of the Aleutian Chain on Thursday, changing back to snow from west to east along the Chain through Friday as the front slides back to south and colder air drives south across the Bering. Strong northeast surface winds will likely be ongoing along the Southwest Coast and out across much of the Bering Sea as a strong north-south pressure gradient combines with strong westerly cold advection of Arctic air from Southwest. This will likely support areas of heavy freezing spray across the eastern Bering Sea, especially within close proximity to the sea ice edge until winds begin to weaken and turn more northerly on Friday.

A very active pattern is likely to continue through the weekend as the upper level pattern amplifies with time. The upper low/trough over Southcentral will retrograde west through the weekend, becoming part of a deepening longwave trough setting up across the Bering and Aleutians. At the same time, a longwave ridge will develop downstream of the main upper trough, building steadily into the eastern Gulf and Southeast through Sunday. This will put Southcentral squarely within the prevailing storm track between the very cold Arctic air building over northern/western Alaska and the much warmer Pacific air and high pressure building into the Gulf and Southeast. This could extend a period of major volatility in temperatures and precipitation already getting started this week for part of Southcentral and along the western Alaska Range in Southwest Alaska into the weekend. Multiple large swings between periods of cold temperatures and drier conditions and warmer temperatures with light to moderate snow will be possible as a series of lows move north into the region within a corridor of southerly flow setting up between the ridge to the southeast and trough to the northwest.

Meanwhile, most of Southwest will stay colder and drier through the weekend as the Arctic air mass remains entrenched in place. Much of the Aleutian Chain could see periods of ocean-effect snow showers through Monday as cold air streaming south modifies and picks up moisture from the warmer ocean surface.

-AS/TM

AVIATION

PANC...IFR to LIFR conditions in moderate snow this afternoon should steadily improve this evening into tonight as snow ends and as ceilings rise to MVFR levels. There is some uncertainty regarding how quickly ceilings will continue to rise through Wednesday morning, but cold, dry air filtering back in should favor a return to VFR conditions. Gusty north winds still look possible for this evening, and these winds could lead to areas of blowing and drifting snow this evening into tonight.