textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

A vigorous upper-level shortwave over the Susitna Valley this morning will continue to slide east over the Copper River Basin today before exiting the region tonight. Low-level southwesterly flow and weak isentropic lift ahead of this wave is resulting in widespread light snow from northern Cook Inlet into the Mat-Su Valleys. The snow is not expected to amount to much, on the order of up to an inch over most locations and up to two inches toward Sutton and Hatcher Pass, before tapering off by around noon.

An area of low pressure at the surface positioned over the eastern Kenai Peninsula this morning will move northeast into the Copper River Basin, embedded in the southwesterly flow out ahead of the eastward moving shortwave. This surface low is tapping into a deep moisture feed over the Gulf and advecting it through Prince William Sound into the coastal mountains and the Copper River Basin. Light snow over the basin this morning will be enhanced by this additional moisture, resulting in more widespread moderate to heavy snow mid-morning through mid-afternoon before slowly tapering off from west to east. Upslope area in the eastern half of the Copper River Basin will likely still see several more inches of snow before the event winds down. Gusty winds in Mentasta Pass and along portions of the Tok Cutoff may result in some localized blowing snow at times.

The focus then turns back to the west for Tuesday as this first system departs the region. A transient ridge moving over Southcentral Tuesday quickly exits as a strong front moves from the western Gulf to the northern Gulf with gales across western half of the Gulf and snow changing to rain for Kodiak Island. Snow will overspread the Kenai Peninsula, Cook Inlet, Anchorage Bowl, and parts of the Mat-Su Valleys by late Tuesday morning as the front moves to the northern Gulf. Strong southeasterly winds aloft out ahead of the front will likely allow any snow over the lee of the coastal mountains to diminish in intensity by Tuesday afternoon due to downsloping, but not before around an inch of snow or snow for places like Anchorage. Moreover, strengthening southeasterly surface winds will also allow for some warmer air near the surface to work into the eastern Kenai, likely resulting in any snow at the onset to change to a rain/snow mix, especially for Whittier and Portage. Seward may see all snow due to a lack of wind on Tuesday.

Forecast uncertainty builds by late Tuesday as a surface low develops along the triple point of the occluded front. The big question is where does this low spin up and track. Recent hi-res and NAM runs have shifted the low track to the west, with some guidance bringing the low up Cook Inlet. The GFS/EC/GEM all keep the low east of the Kenai Peninsula, albeit at different locations. The forecast favors the more eastward solution, weighted toward the GFS. This track would allow for the low to track into Prince William Sound before the low and its front move onshore early Wednesday as the associated upper-level wave moves across Southcentral. This track would result in a faster decrease in southeast winds, with winds becoming northerly in the wake of the low and snow filling back in across Cook Inlet north to the Mat Valley. In fact, this track would likely keep snow over the western Kenai through Tuesday, with snow amounts of 6" or more not out of the question. Similar amounts are also likely for the Susitna Valley and Turnagain Pass with lesser amounts for Anchorage and the Mat Valley. Several inches of snow are also likely from Valdez north into the Copper River Basin as the low lifts north. By Wednesday, the precipitation will become more showery as colder air aloft moves back in. A southerly flow near the surface may allow temperatures along the coast to push above freezing, resulting in a mix of rain and snow showers. Various shortwaves moving through the region may also allow for more organized snow showers across Cook Inlet and into the Mat-Su through Wednesday, resulting in the potential for additional snow accumulations.

-TM

AVIATION

PANC...Primarily MVFR conditions with periods of IFR conditions possible. Light snow may linger over the terminal until 21Z. Clearing skies through the evening may lead to favorable conditions for fog development overnight. Light northerly winds will persist.