textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Satellite and radar imagery this afternoon shows lingering stratiform precipitation in the Gulf and along the coast from Cordova and eastward across the Copper River Valley as the low in the Gulf slowly exits to the east. Elsewhere, the northeasterly flow over Southcentral between the departing low and a ridge building to the north over the Interior has led to an increasingly warm and unstable airmass this afternoon. Robust convection aided by an easterly shortwave rotating around the north side of the low has initiated over the Talkeetna Mountains and moved over the Susitna Valley this afternoon. Enhanced easterly flow and up to 20 to 25 kts of deep layer wind shear could help support some more organized storm clusters forming over the Chugach and Talkeetna Mountains late this afternoon and evening. Steering flow will easily be strong enough to pull initial storm clusters west into the Mat-Su Valleys, with even Anchorage seeing a small chance (20% to 30%) of a thunderstorm moving off of the Hillside into lower elevations through the evening hours.

By Tuesday, Southcentral will shift back into a col (a gap in between larger weather systems) along with much weaker winds aloft. Showers and isolated thunderstorms will again be possible during the afternoon and evening, especially along and near the various mountain ranges as yet another shortwave moves into the Copper River Basin. This feature will move westward as the mid- level flow begins to shift southerly over western Southcentral ahead of a wave moving east from Bristol Bay. This should allow any showers and thunderstorms that do develop over the Kenai and Chugach Mountains to slowly lift northward across the western Kenai, around Anchorage, and into the southern Susitna Valley. In addition, the northern Susitna Valley and Talkeetnas will again have the best shot at seeing more widely scattered thunderstorms. Otherwise, expect another very warm day afternoon in the upper 60s to mid 70s across the interior valleys with an increase in southeasterly gap winds for typical locations beginning Tuesday afternoon and persisting through Tuesday night.

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

An upper-level ridge centered over the ALCAN will remain the dominant synoptic feature through much of the long-term period, supporting generally warmer conditions across mainland Alaska. While the ridge promotes periods of sunshine, several weak shortwaves rounding the ridge will keep the potential for scattered showers across portions of Southcentral through the weekend. The greatest chance for convective development will remain over the eastern Copper River Basin, where daytime heating combined with passing disturbances may support isolated to scattered afternoon and evening thunderstorms Friday through Sunday. Elsewhere across Southcentral, precipitation will be more limited.

Across the Bering Sea and Aleutians, an active pattern persists as a series of lows track eastward through the weekend, bringing periods of rain, low clouds, and locally gusty winds. Forecast confidence in the exact track and timing of these systems remains moderate, though the highest confidence for more persistent rainfall continues to be from Adak eastward to Unalaska.

Attention then turns to a stronger North Pacific low expected to move into the western and central Bering over the weekend before lifting toward Bristol Bay late Sunday into Monday. As the system approaches, widespread rain will overspread much of Southwest Alaska with increasing winds, especially along the Alaska Peninsula and Bristol Bay coast.

By Monday, the low is expected to continue tracking inland while gradually weakening, allowing rain to spread farther across the Kuskokwim Valley and portions of interior Southwest Alaska. Meanwhile, Southcentral Alaska will remain on the eastern periphery of the system beneath the upper-level ridge, supporting isolated showers over the higher terrain while lower elevation may experience a mix of clouds and sunshine. Although model spread increases by Monday regarding the exact evolution of the low, confidence is growing in a wetter pattern across Southwest Alaska.

AVIATION

PANC...VFR conditions and west-to-southwesterly winds will persist through late evening. A shower in the vicinity of the terminal is possible this afternoon and evening as an upper level wave moves through from the northeast. Southeasterly Turnagain Arm winds up to 30 kts are expected to develop Tuesday afternoon.