textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Message: A Red Flag Warning has been issued for LIGHTNING for the Southern, Central, Western, and Northern Susitna Valley, and the Lower Matanuska Valley from 1PM AKDT Friday to 1AM AKDT Saturday.

Discussion:

Aloft, an exiting Gulf low moving inland over the Alaska Panhandle combined with a ridge axis situated along the Al-Can border and over Southcentral is pushing subtle easterly waves over the Copper River Basin to the Susitna Valley. Weak troughing stretches westward over the Gulf from the upper low and contains a shortwave trough located just east of Kodiak Island. Out west, a polar trough continues to dig southward from the Seward Peninsula to the Kuskokwim Delta Coast.

Although temperatures have warmed well into the 70s today, the limited upper level lift has only initiated a couple of showers across the Susitna Valley and the Copper River Basin. The chance of isolated thunderstorms remain for the Susitna Valley for this afternoon/evening. The warming trend is also on track to continue through the end of the short term.

As the upper level trough to the west continues to dig over Southwest Alaska, it will begin to interact with the upper level ridge centered over Southcentral. By Friday morning, the reinforced southerly flow between the two features will lift the aforementioned shortwave northward and over the Susitna Valley by the early afternoon. With temperatures again warming to near 80 degrees for this area, stronger upper level forcing with this shortwave will kick off an active afternoon and evening of widely scattered to scattered thunderstorms. Although the storms will be "wet" in nature with brief, heavy downpours, ample cloud to ground lightning strikes in the vicinity of the storms pose the threat of new fire starts. As we lose daytime heating late Friday evening and very early Saturday morning, any remaining storm activity will weaken into just areas of showers.

Upper level energy rotating around the ridge axis will continue through Saturday afternoon. However, the primary forecast challenge for Saturday will be fine tuning the track of another stronger shortwave lifting out of the Gulf and over Southcentral. There is still quite a spread in the models regarding timing and placement of this wave, so storm coverage for Saturday as of now is of lower confidence. This shortwave will be the main driver of storm potential for Saturday afternoon/evening.

By Sunday morning, there is fair agreement among the global models of a relatively weak area of low pressure entering the western Gulf, which has the potential to bring rainfall to Kodiak Island.

-AM

AVIATION

PANC...VFR conditions and light winds will persist. There is a chance of showers, and potentially a thunderstorm, in the vicinity of the airport for late Friday afternoon into Friday evening.

FIRE WEATHER

Key Message... - A Red Flag Warning has been issued for Southern, Central, Western and Northern Susitna Valley and the Lower Matanuska Valley due to lightning, which is in effect from 1 PM Friday to 1 AM AKDT Saturday.

An increasingly unstable pattern will persist across Southcentral through the weekend as upper-level energy rotates around high pressure over the region. Temperatures will warm into the upper 60s and lower 70s with some interior locations reaching the mid to upper 70s. Minimum relative humidities will fall into the mid-30s, while winds remain generally light, with west to southwest winds around 5 to 10 mph and localized afternoon sea breezes.

Isolated showers and wet thunderstorms are possible this afternoon and evening across the western Copper River Basin, Susitna Valley and higher terrain.

As the approaching shortwave moves into the area Friday, shower and thunderstorm coverage is expected to increase, particularly across the Susitna Valley and Copper River Basin, with isolated thunderstorms also possible across the western Kenai Peninsula and higher elevations surrounding Anchorage. A Red Flag Warning has been issued for due to lightning.

Thunderstorm chances are expected to continue into Saturday, though activity will become increasingly focused over inland and mountainous areas.

LM