textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

The forecast remains on track with only a few changes. The shortwave trough that brought light precipitation to the western half of Southcentral this morning has since lifted east- northeastward over the Copper River Basin, allowing for clear skies this afternoon for the northern Cook Inlet region. Panning out, this wave is embedded within a broad longwave trough that stretches from the western Bering to the eastern Gulf. Within this longwave, a more robust shortwave now over the Bering will round the base of the trough through tomorrow morning as a surface low continues to develop downstream across the far northern Gulf. Starting midday Wednesday, models have come into better agreement overnight and this morning in regards to the surface low placement, and the consensus now is that most precipitation with be mostly confined to the eastern Kenai Peninsula and Prince William Sound locations. The progression of the upper level wave has more clarity this afternoon as well in regards to timing as models have converged on the wave passing over the area Wednesday evening. The overall weak flow with this system will lead to the western fringes of precipitation propagating westward to encompass Anchorage and the Matanuska Valley as well Wednesday evening to early Thursday morning, and a sharp cutoff in rainfall extent will most likely line up just west of Anchorage.

Precipitation type from Wednesday afternoon through Thursday morning will be largely elevation dependent. For lower elevations areas such as the Anchorage Bowl northward to the Matanuska Valley, only a cold rain is expected as snow levels will remain too high and temperatures only drop to near 40 degrees F for overnight lows Thursday morning. With snow levels bottoming out anywhere from 1300 to 1800 feet during the bulk of the precipitation duration, higher elevation locations like Thompson Pass, South Fork Eagle River, Upper Hillside, and the Talkeetna Mountains are on track to see 1 to 3 inches of snowfall with isolated 4 inch amounts. Locations lower in elevation like the Anchorage Hillside, Rabbit Creek, Turnagain Pass, and Talkeetna will most likely see a rain/snow mix as temperatures and snow levels fall Wednesday night through Thursday morning. All said, there is a good amount of cold air advection aloft associated with the incoming trough, the coldest air of the season for most, however, it appears that the coldest air does not arrive until much of the precipitation is on its way out on Thursday.

The trough axis takes a negative tilt over Southcentral and begins to lift out of the region late Thursday morning to midday Thursday as the surface low skirts eastward. This will shift the precipitation eastward toward Valdez and Cordova; decreasing precipitation coverage to the west.

-AM

LONG TERM FORECAST (Days 4 through 7)

Looking ahead toward this weekend, models are synoptically in good agreement in the midrange forecast, featuring a low moving toward Kodiak Island from the North Pacific and another low into the Bering Sea from the west. Precipitation with east to southeast winds will be more than likely for Southcentral, especially closer to the Northern Gulf coast and Kodiak Island. By Sunday, the front extending from the Bering Sea low reaches Southwest Alaska and the Alaska Peninsula bringing rain, snow, and southerly flow across the area. As the low sinks southward Monday, models diverge on how far south the low will dip. Generally, the low appears to pass through the Alaska Peninsula and near Kodiak Island/Western Gulf. As this pattern sets up through the first half of next week, cold air advection and northerly winds will become enhanced through gaps along the Aleutians. If the low sinks south farther east, the Alaska Peninsula would see more cold air advection and those northerly winds. While temperatures overall for southern Mainland are trending cooler in the short term, some moderation of that trend is expected toward more seasonable norms, but will remain on the cooler side.

AVIATION

PANC...VFR with light northerly winds expected. Precipitation chances increase Wednesday morning between 12 and 18Z. Rain, and potentially lower ceilings (around 1000 feet), should be brief and showery, tapering off throughout the day.