Short Term Forecast Southcentral Alaska
The upper-level ridge that was in place yesterday is now moving off the east in response to an upper-level shortwave associated with a strong frontal system moving into Southwest Alaska this morning. Clouds have now moved across most of Southcentral this morning, but not before overnight low temperatures fell into the mid 20s to lower 30s for most locations and into the teens and single digits in the Copper River Basin.
As of 4 AM, precipitation is already beginning to fill in from Kodiak Island north to Seldovia and northwestern Susitna Valley. Another area of showers south of Prince William Sound is also being pulled northward in the developing southerly flow in the wake of the ridge. Along the coast, gap winds are keeping temperatures above freezing, allowing for the incoming showers to fall as rain. Farther inland, any precipitation that does develop this morning across the Susitna Valley will likely fall as snow due to the colder temperatures. One caveat to all this is increasing warm air advection in the lower levels of the atmosphere this morning with a forecasted warm nose of air between 1,500 ft and 3,000 ft pushing above freezing all the way into the southern and central Susitna Valley. Given this, there is a 15-25% chance that a few areas that typically do not see winds and warming temperatures right away with these systems (e.g. Willow to Talkeetna) could see a brief period of very light freezing rain later this morning as the steadier precipitation moves in before temperatures warm up and change any snow or mixed precipitation to all rain.
As the front moves into Southcentral, southeasterly gap winds will kick in, warming temperatures across Turnagain Arm and parts of the Mat Valley. Precipitation here will likely be all rain with this system. Farther north across the northern Susitna and Copper River Valleys temperatures will likely (70-80%) remain between 29 and 34 degrees, allowing for a mostly snow event with several inches of accumulation. Winter Weather Advisories are out for these areas for 4" to 12" of snow through Sunday.
A surface low will then develop along the stalling front somewhere near the southern tip of the Kenai Peninsula as another potent shortwave moves across the AKPen and induces the surface low development. The upper-level wave then becomes negatively tilted by Sunday afternoon as the surface low strengthens. This will help to shut off the gap winds allow for steadier precipitation to fill in across Cook Inlet and the southern Mat- Su valleys before these features quickly move east and the precipitation shuts off from west to east through Sunday night into Monday morning.
A transient ridge moves quickly through the region on Monday before the next wave approaches from the west with another round of snow for the northern half of both the Susitna and Copper River Valleys for Monday.
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3).