textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

No significant changes to the forecast overnight. There is high confidence that a frontal system will bring a wintry mix of precipitation to Prince William Sound, the Kenai Peninsula, Southern Mat-Su Valleys, and the Anchorage Bowl late Saturday through early Monday. There is also high confidence that precipitation will fall as snow for all locations late Saturday or early Sunday through at least Sunday afternoon as the wind flow in the lower levels of the atmosphere remain northerly ahead of the front.

There are two or three aspects of this storm, however, that bring with it a higher level of uncertainty. The first is how far west the initial band of precipitation will move as it crosses the Kenai Peninsula. The GFS continues to progress this band quickly over Turnagain Arm and the Anchorage Bowl while the RRFS/REFS and GEM/RGEM try to stall out the band over Anchorage for a bit before moving over Cook Inlet. The NBM tries to split the difference with the band between Anchorage and Kenai. This brings lower confidence to snow amounts for areas from Palmer and Wasilla to Anchorage and Kenai. However, given the blend of models, the most likely (60-70%) scenario is 2 to 6 inches of snow for Anchorage and the Western Kenai Peninsula with 1 to 3 inches for the Mat-Su Valleys.

Similarly, the most likely (60-70%) scenario for the eastern Kenai Peninsula is 6 to 12 inches of snow for Whittier, Portage and the Seward Highway corridor to Primrose, with the highest amounts for Portage and Turnagain Pass. Lesser amounts, on the order of 1 to 3" of snow are likely for Seward given a strong northerly wind that will likely keep temperatures around or just above freezing, helping to limit snow accumulations.

The next issue will be the extent of warmer air aloft as the front moves west and an easterly flow develops at and near the surface. Model blends show snow levels rising to around 1200 ft, with high confidence that snow quickly changes to rain for Whittier, Portage, and eastern Turnagain Arm by Sunday night as temperatures rise into the upper 30s. The uncertainty lies in how much temperatures along the Seward Highway from Turnagain Pass to Primrose warm as the warmer air aloft moves in. As such, there is a low to medium chance (30-40%) that some areas along the road see freezing rain late Sunday night before a changeover to rain sometime Monday morning.

Snow will also fall across the southwest Kenai Peninsula with this event with 2 to 6 inches of snow likely (60-70%). For areas of the western Kenai and Anchorage Bowl, there remains a chance (30-40%) that snow may change to freezing rain Sunday night as the warmer air aloft reaches Cook Inlet. Again, there is some uncertainty with the extent of warm air. The GFS is the warmest solution with the GEM the coldest. The NBM and RRFS/REFS are a good middle ground pushing the warm nose to the Kenai area.

By Monday morning, uncertainty grows regarding whether this system lingers over the southern Kenai Peninsula or begins to lift back northward. Currently, the likely (60-70%) scenario is for precipitation to lift back to the north as light wintry mix, based on most guidance. The GFS is the one model stalling the front farther south.

Probabilistic snow totals from the previous forecast...

*Low/High end values are as follows: - Anchorage/Eagle River & western Kenai Peninsula: 2-4" (Low end) / 6-10" (High end). Higher elevations: up to a foot possible. - Seward: 1-3" (Low end) / 3-6" (High end). - Turnagain Pass to Moose Pass: 7 to 11" possible. - Portage: 9-11" with snowfall rates of up to 1" an hour.

KM/TM

AVIATION

PANC...Light northerly winds will persist through today and tonight. Morning satellite imagery reveals fog and low stratus with LIFR cigs and vis both over the terminal and just to the north of the terminal over Knik Arm. There is still some uncertainty as to how long this fog and low stratus will linger at or near the terminal. The expectation is for VFR conditions to return by the late morning hours.

Attention then turns to a weather system approaching from the east that will work into Prince William Sound by tonight. Precipitation looks to spill over the Chugach Range and into Anchorage by Sunday morning. Precipitation-type is expected to be in the form of snow Sunday morning. Expect low-end VFR conditions to MVFR conditions Sunday morning. IFR conditions are possible within bursts of heavier snow. There continues to be some uncertainty in regards to snow intensity and somewhat with the timing of the onset of snow. In lighter snow, expect more in the way of VRF conditions to be maintained. However, in heavier bursts of snow with high fall rates, expect more in the way of MVFR to possibly IFR conditions Sunday morning.