textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

The pattern change is underway as the upper level ridge that has been the source of the warm and often sunny weather the past few days is moving eastward in response to a large upper level trough digging into the Bering Sea and merging with a low south of the Aleutians. Therefore expect cloud cover to increase today across Southcentral. There remains a chance for a thunderstorm this afternoon into early evening for the northern Susitna Valley and northern Copper Basin. However, thunderstorm activity is expected to be less than yesterday.

The big change gets going tonight as the front associated with the Bering Sea low will move across Kodiak and then up Cook Inlet. This front will bring more rainfall into Kodiak Island by this evening and then coastal Southcentral tonight with the rain spreading into more protected areas such as Anchorage and the Susitna Valley on Sunday. The Copper River Basin will remain drier due to downsloping from the strong southerly winds.

On Monday, the upper level flow will turn more southwesterly due to the main upper level low pushing into Southwest Alaska. This will bring more rainfall especially to the Susitna and Matanuska Valleys and probably Anchorage and the northern Kenai Peninsula as well. The gusty gap winds will likely persist through Monday as this pattern is favorable for them for Turnagain Arm, Knik River Valley an along the Copper River.

LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)

By Tuesday morning, there is general agreement of a vertically stacked low being over the Lower Yukon Valley. Troughing extends down through the Aleutians, with the most significant shortwave outside of the low being over the western Aleutian Chain. Models hint at shortwaves continuing to rotate around the low as it continues northward into the Interior. This will maintain chances for precipitation for much of the southern Mainland Tuesday. Specific timing of these waves is unknown, but the heaviest precipitation is expected to fall along coastal regions of the Northern Gulf Coast/Prince William Sound and along the Alaska Range in the western Susitna Valley. Out west, the Aleutians and Bering likely see showers Tuesday as the shortwave moves east. The shortwave over the western Aleutians becomes a closed low over the eastern Aleutians by Tuesday evening. This looks to pull additional moisture in and bring another round of rain for the eastern Aleutians, Southern AKPen, and Kodiak Island Tuesday night through Wednesday. This low crosses the southern AKPen into the Gulf Wednesday morning and moves into the Alaska Panhandle on Thursday. As the low moves through the Gulf on Wednesday, rainfall will likely shift to the northern Gulf Coast east of Prince William Sound with some spilling over into interior locations of Southcentral. Models diverge with resolving certain surface features (mainly whether or not a surface low develops in the Gulf on Wednesday). If a surface low develops in the Gulf Wednesday, rainfall may be enhanced along the northern Gulf coast. Some southeast gap winds (Turnagain, Knik, and Copper River winds) may be enhanced as well on Wednesday. These details will become more clear in the coming days.

To the west of the lows, models diverge on solutions between zonal flow and attempts at a ridge building in the Bering with additional shortwaves traversing into the southern Mainland. Either pattern would support cooler temperatures and mostly overcast skies across much of southern Alaska and the Bering with continued chances for precipitation across the southern Mainland.

-PA

AVIATION

PANC...VFR conditions will persist through the period, though ceilings may lower to under 5000 ft starting this afternoon with an approaching frontal system. This system will bring rain to the area overnight, though there is a question as to how much will make it to the terminal in the cross-barrier flow over the Chugach Mountains. The best chance for rain and a MVFR ceiling will be late tonight into early Sunday morning.

Winds should remain southerly to westerly today into tonight but remain at or under 10 kt through Sunday morning.