textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Aside from areas of wintry precipitation across Southcentral, there are quite a few marine lightning strikes to speak of across the far northern Gulf near Cordova due to some instability associated with colder air moving in aloft and a surface low located over the north-central Gulf. This activity is located downstream of relatively broad troughing over much of Alaska, allowing for additional lift and steeper/steepening lapse rates. These isolated thunderstorms will move eastward towards Yakutat through tonight, and has been reflected in marine products with this afternoon forecast package.

The big story is lower elevation rainfall with a few flakes mixed in and higher elevation snow continuing this afternoon across the northern Cook Inlet region northward into the Matanuska Valley. Precipitation type has not only been elevation driven, but also intensity driven as well. Even in places where the predominant precipitation type has been rain today, there have been flakes mixing in with heavier precipitation rates just a few hundred feet up in elevation. The forecast largely remains on track as we continue to watch the progression of two trough axises; one negatively tilted trough stretching from the Cook Inlet region into the Gulf and lifting northward and another digging southeastward over Southwest Alaska to the west. The main forecast challenge over the course of the short term will be honing in on how quickly these two features phase as the first trough continues to lift towards the southern Copper River Basin as the second trough moves south and eastward through this evening and overnight. The GFS has consistently been the slower solution, and lingers the secondary trough over Southcentral for longer, which in turn would keep precipitation chances around through Friday morning or so. Although the GFS is starting to look more like an outlier compared to other deterministic models that bring precipitation out of the region faster, its consistency increases forecaster confidence that precipitation will linger for longer than what the EC and some of the other models currently depict. If the GFS is "more correct" than the other models, and should showers train over the higher elevation areas like Glen Alps or South Fork tonight, up to 5 inches of snowfall will be possible.

By Thursday morning, the southern most trough axis will move into the southern Copper River Basin, the Panhandle, and Yukon Territory, while an arm of the notably colder upper low/trough moves southward over the western Alaska Range and greater Bristol Bay area. This will continue to provide lift for showers along the Chugach and Kenai Mountains, with some precipitation possible for Anchorage and the Matanuska Valley. By this time, the airmass aloft will be quite cold, dropping snow levels as low as 800 ft or so. It is not out of the realm of possibility for some near sea level areas from Anchorage north to Palmer to see some snowflakes Thursday morning if a heavier shower moves overhead and mixes colder air down closer to the surface. Areas along the upper Hillside and South Fork Eagle River are likely (60 to 70 percent chance) to get a dusting up to 3 inches depending on the elevation and intensity of the showers. By Friday morning, precipitation should be out of the area, and with clearing skies, the first hard freeze with temperatures less than 30 degrees is likely for many of the population centers.

AM/CJ

LONG TERM FORECAST (Days 4 through 7)

No change from previous discussion... Looking ahead toward this weekend, models are synoptically in good agreement in the mid- range 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...Periods of low clouds and occasional rainfall will linger into this evening and into at least the first half of tomorrow as a trough gradually crosses the area. CIGs may oscillate between IFR and MVFR through the duration. Winds will generally remain out of the north, though may become light/variable at times. Precipitation will taper off Thursday evening (after 00z) in wake of the trough, though lingering low-level moisture may trap low clouds for a little while thereafter.