textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Messages:

- Strong winds through Cook Inlet today, with localized gusty southeasterly gap winds through Turnagain Arm, Anchorage, Knik Valley, and Copper River Valley.

- For Susitna Valley, rain totals around 0.5 to 1.5 inches through Saturday will allow for rises on many small streams and rivers, and localized ponding in low-lying or poor drainage areas.

- From Saturday through Sunday, showers taper off by Saturday morning and gusty northerly to westerly winds pick up, strongest along the coast.

Discussion:

The first push of widespread rain is moving across Southcentral this morning, and will soon move into the Copper Basin. This current round of rain is associated with a frontal system lifting across interior Alaska and generally extending out east from the parent low just NE of the Seward Peninsula and down towards Prince William Sound. Widespread rain will taper off to showers pretty quickly behind this front, but a secondary front will complicate the forecast later today as showers reinvigorate with the passage of the front and associated trough. Right now it appears that the bulk of the lower to mid-level forcing will be somewhat split between the Gulf and further north closer to the low. This would place the best chances for precipitation over the northern Susitna Valley and the higher terrain of the Alaska Range and Talkeetna and Chugach Mountains, and another round of showers for the northern and central Gulf. Despite the showers, there will likely be some breaks in cloudcover.

This system will also bring another round of gusty gap flow winds for the Turnagain Arm, Knik, and Copper Valley. Similar to the Tuesday event, winds with gusts up to 35-45 mph (with isolated gusts to 50) are possible for west Anchorage and Turnagain Arm, and 40-55 mph for the Hillside. Eagle River will also see gusty winds with gusts of 25 to 30 mph possible. The western Gulf will see small craft to gales move in behind the front and the development of a barrier jet will allow for some high end small craft to even gale force winds along the northern Gulf coast and into Prince William Sound. These strong winds will likely push inland some bringing gusty winds to Cordova Friday night.

- PP/KC

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

The progressive pattern looks to continue through late Tuesday or early Wednesday as multiple multiple upper-level wave southeast from the Chukchi Sea to the Alaska Panhandle. This will generally bring periods of active weather, with some lulls between systems.

The combination of cold air advection, a northwesterly low-level jet, and a shortwave trough through the northwesterly flow, will lead to and increase in northwesterly winds through the Barren Islands and around Kodiak Island/the AKPen, as well as northerly and westerly gap winds for Seward and Whittier by late Monday. Clouds and scattered showers will linger across portions of Southcentral Alaska as these waves move through, especially for the higher terrain and through the Copper River Basin.

Farther west, an upper-level ridge will build over the North Pacific, extending across the Aleutians, by late Monday. A warm front attached to a Kamchatka Low will move overtop the ridge and into the southern Bering for Tuesday morning. This feature looks to transition into an elongated surface low as it phases with a shortwave trough moving southeast through the Y-K Delta, brining more rain and gusty winds from Bristol Bay to Kodiak Island.

Model agreement then falls apart late Tuesday through Thursday. The biggest question will be how amplified the longwave pattern gets as the aforementioned ridge begins extend north and east ahead of a deepening trough over the far western Aleutians. Most guidance is beginning to advertise a ridge axis moving over Southcentral with multiple upper-level waves and resultant surface lows moving into the western half of the Bering from the North Pacific. The surface fronts associated with these surface features look to move as far east as western Alaska Wednesday and Thursday with additional rounds of heavy rain and gusty south to southwest winds.

- TM

AVIATION

PANC...MVFR conditions may briefly dip to IFR this morning before improving back to VFR by 18-21Z. Rain will taper off to showers for much of the afternoon before ending late tonight. Southeasterly Turnagain Arm winds will remain gusty through about 06-09Z with gusts of 35 to 45 kt possible before diminishing overnight.