textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Generally speaking, the pattern this afternoon remains similar to what we saw yesterday. Southcentral continues to sit within a zone of southwesterly flow between a weakening low moving up the western Alaska coast and an upper ridge focused over British Columbia and Southeast. Relatively mild conditions in the 20s and 30s near the surface contrasting with much colder temperatures in the mid to upper levels is continuing to support an unstable air mass along with several areas of convective showers drifting north from the Gulf into much of the Gulf Coast. A low-amplitude shortwave trough progressing northeast from near Kodiak Island into the Kenai Peninsula is helping to support more aggravated shower activity near the Barren Islands and along the southern coast of the Kenai Peninsula. Some of this activity will likely shift north towards the eastern Chugach Mountains, Anchorage and the Mat-Su Valleys this evening as the trough progresses towards the Talkeetnas overnight.

While the exact track of individual shower clusters over the next several hours is uncertain, no single location across the Mat-Su, Anchorage and western Kenai Peninsula is expected to see much accumulation tonight. The observed Anchorage sounding from this morning also showed a dry layer from about 1000 to 5000 ft, and this dry air prevented much of the snow that moved past the Anchorage Bowl last evening from reaching the ground. It would not be surprising to see this dry layer act as a spoiler for heavier snow showers that try to move inland up towards Anchorage and Palmer again tonight.

Looking to Wednesday and beyond, clarity is still rather lacking for the evolution of a complex and much more active pattern taking shape across the region. A shortwave trough with numerous smaller embedded waves is expected to round the base of the longwave trough sitting out over the Bering Sea between Wednesday and Thursday, with the bulk of the energy expected to lift northeast towards the AKPen. Several differing scenarios remain on the table for how this system ultimately evolves, though the bigger picture impacts to Southcentral will not differ too much overall in spite of the poor model agreement. Guidance continues to struggle with the location and track of a surface low expected to spin up ahead of the incoming shortwave. The general consensus is now that the surface low will initially form close to the southern end of the AKPen on Wednesday evening, but solutions quickly diverge from there, bringing the center somewhere between Bristol Bay and the northern Gulf on Thursday.

In terms of the impacts from this system to Southcentral, there are really still two but similar scenarios for how this plays out. If the low takes the more northerly track into Bristol Bay and the southern Cook Inlet, this would generally favor more warm air making it into interior valleys, with more of a Chinook pattern that could result in temperatures across much of the Kenai Peninsula, Anchorage and Mat Valley warming a few degrees above freezing on Thursday. This would also be more favorable for more intense southeast winds to develop along the Turnagain Arm and much of the Kenai Mountains. If the low skirts more south into Kodiak Island and the Barrens, this would keep inland temperatures cooler and snow levels lower across the Kenai and Chugach Mountains. Either way, heavy precipitation enhanced by upslope flow with increasing southeasterlies ahead of the low and its front is expected along the coast from the southern Kenai Peninsula out to Prince William Sound late Wednesday into Thursday. There will also be a threat for periods of light freezing rain/sprinkles to make it into parts of the western Kenai Peninsula, Anchorage and the Mat Valley as a warm nose aloft develops overtop a layer sitting at/below freezing close to the surface on Thursday. Fortunately, it looks like anything that does "spill over" from the mountains will stay fairly light, albeit it does not take much freezing rain to create treacherously slick surfaces.

From late Thursday into Friday, there is a loose consensus that the low and supporting trough will continue to shift northeast to somewhere in the vicinity of Prince William Sound. This could entail a band of rain switching over to snow moving up into western parts of the outlook area as a cooler air mass begins to work in from the west. However, this will depend on how the system evolves on Thursday and how quickly it shifts northeast, so the details are still very difficult to pin down at this point.

-AS

AVIATION

PANC...Generally, VFR conditions are expected. However, skies will clear tonight, which may lead to MVFR to IFR conditions with fog and stratus possibly developing in the Inlet.