textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

A negatively-tilted upper trough that moved quickly past much of Southcentral this morning has shifted steadily east since this morning, now extending from near Cordova up into the Copper Basin. Steady snow and rain near the coast has also given way to widespread bands of showers behind the trough passage as cool air moving in aloft supports very steep deep layer lapse rates and an overall unstable atmospheric profile. These clusters of showers are riding up through disorganized southwesterly flow setting up across the region. A particularly vigorous area of rain and snow showers is now moving up into the Kenai Peninsula and Cook Inlet along and ahead of a weak shortwave impulse driving northeast from the western Gulf. This could bring another quick round of snow to parts of Anchorage and the Mat-Su Valleys as it continues north later this evening into tonight. While briefly heavy snowfall rates will be possible with the convective nature of these showers, most of the western Kenai Peninsula up through the Mat-Su is not expected to see more than an inch or so of new accumulation overnight. Bands of showers in the form of rain along the immediate coast and mountain snow will also continue to stream into Prince William Sound and much of the Chugach Range this evening into tonight.

Forecast details from Tuesday onward remain rather murky. Overall, the pattern for Tuesday will be fairly similar to today, with continued southwest flow and areas of rain and snow showers moving past at times, especially along the Gulf Coast. From Tuesday night into Wednesday, an inverted trough extending from a low entering the far eastern Gulf will begin to bend northwest into the vicinity of Middleton Island. A swath of moisture coupled with weak lift north of the surface trough could make it into eastern fringes of the outlook area near Valdez and Cordova by Wednesday afternoon, but this remains highly uncertain given the model spread for where this feature sets up and for the track of the low moving up into the eastern Gulf.

Forecast confidence deteriorates even further by Wednesday night into Thursday. A complex trough moving south of the Aleutians is expected to bend northeast towards the Alaska Peninsula between Wednesday and Thursday, likely inducing the development of a strong surface low somewhere between Bristol Bay and the western Gulf. This discrepancy in where the low forms has significant implications regarding any potential for strong winds and precipitation type/amounts near and to the east of this system across Southcentral. The signal through the noise is that much of the Gulf could experience gale force winds, possibly stronger, from Wednesday night into Thursday, with potential for heavy rain and snow for coastal parts of Southcentral along and ahead of the low's front. The air mass moving in with this system also looks fairly mild, and this could cause some issues with mixed precipitation types for anything that makes it over the coastal mountains into the Mat Valley, Anchorage and Cook Inlet region. However, this will hinge on details for the progression of this low that are still far from fully resolved. Stay tuned for updates as we follow this next upcoming storm system and as confidence for the track and intensity of this feature improves.

-AS

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

Forecast confidence is generally low from late this week through early next week. Generally expect stormy weather as a low impacts Southern Alaska on Friday, followed by a brief break before the next storm moves into the Bering Sea from the west.

Broad upper level troughing will be present over the Bering Sea by the start of the long term forecast period. A robust shortwave curving up from the North Pacific will spur the development of a surface low near the Alaska Peninsula. However, model solutions remain very divergent, which makes forecast details and potential impacts difficult to pinpoint. Among the deterministic solutions, low tracks range from the low curving up the Southwest Alaska coastline, to the low moving onshore in Bristol Bay, to the low curving up the Gulf coast towards Prince William Sound. Given the strength of this low (minimum MSLP as low as 950-960 mb), gales are likely, with sustained storm force winds possible. All told, this will be a potentially impactful storm, and one to watch as forecast confidence gradually improves.

As the aforementioned low gradually weakens and exits out of the Southern Mainland, a ridge will move in, followed by the front from a strong low that moves in by Saturday. Winds to storm force are possible with this front, impacting the Western and Central Bering/Aleutians. As the front approaches the Mainland by Monday, secondary lows developing along the front will lead to stormy weather along the Bering Sea, though uncertainty with low tracks will once again lead to difficulty pinpointing exact details. Overall, a low-confidence long-term forecast.