textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Currently, a North Pacific low is moving into the Gulf of Alaska. This low is pushing moisture up into Southcentral, leading to scattered showers along the coast and into the Kenai Peninsula. Meanwhile, isolated showers and thunderstorms are forming in the Talkeetna Mountains and the Copper River Basin as instability remains elevated. Shortwaves from the low are creating a coastal ridge over the Chugach Range. This will allow for elevated southeasterly winds (10 to 15 mph) in Palmer, South Anchorage, and the Copper River Basin today through Monday. Monday will be similar to today except with increased shower activity as the low moves further into the Gulf and additional shortwaves push into Southcentral. The Anchorage area will be downsloped due to easterly flow, but light rain showers will still have a 20 to 30% chance of occurring.

By Tuesday, a strong shortwave from the low will move across Southcentral from the east. This wave will produce a deformation band, which will cause moderate to heavy rain first in higher elevations of the Alaska Range and the Talkeetna Mountains. Lower elevation areas including Anchorage will see less rainfall due to downsloping, but the sheer amount of moisture making it in will allow at least 0.05 to 0.10 inches of rain to fall. By Tuesday afternoon, the band of moderate to heavy rainfall will move over the northern and western Susitna Valley including Talkeetna and Skwentna, where it will linger through Wednesday. Between Tuesday and Wednesday, between 1 and 3 inches of rainfall will fall depending on where the band of rain sets up. There is uncertainty with this event and if the rain band sets up further west, the lower amounts of rainfall will be seen. Conversely, if the rain band sets up further east, the higher end of the range will be more likely. By Wednesday evening, rainfall will decrease in intensity as the low moves more to the east and the strong shortwave inland dissipates. Additional shortwaves will move through, but these will not be nearly as strong and rainfall associated with them will be lighter.

-JAR

AVIATION

PANC...VFR conditions are expected to persist through the period. A Turnagain Arm wind will develop this afternoon/evening and has a chance of producing gusts up to 20 kts before diminishing by around 14Z Monday morning.

FIRE WEATHER

For Southcentral Alaska:

A Red Flag Warning remains in effect for Southern, Central, Western and Northern Susitna Valley and the Lower Matanuska Valley due to LIGHTNING until 1 AM AKDT Saturday.

Discussion: Scattered showers and wet thunderstorms have developed this afternoon across the Susitna Valley, mainly along the eastern slopes of the Talkeetnas and west of the Talkeetnas where temperatures have warmed well into the 70s today. Storm motion is slow today and to the northwest with time. Although these storms are producing locally heavy downpours and could drop some small hail, the primary concern is frequent lightning strikes outside of areas that see rainfall for potential fire starts. Storm coverage will likely increase as the afternoon wears on and begin to decrease late this evening as we lose daytime heating and associated upper level energy exits the region. A few remnant showers could linger early Saturday morning. There is medium to high (70-80%) confidence that the focus for thunderstorm activity Saturday afternoon will likely shift eastward to the Copper River Basin, meaning less storm coverage across the Susitna Valley and lower Matanuska Valley.

For Southwest Alaska:

A Red Flag Warning remains in effect for Lime Village due to lightning until 1 AM AKDT Saturday.

Discussion: The forecast looks on track regarding the Red Flag Warning in effect through tonight. Scattered wet thunderstorms are currently developing off the foothills of the Western Alaska Range in Lime Village, with the expectation that 10 to 15 kt of steering flow will lead to northwest propagation of thunderstorms through the evening. Given modeled CAPE ranging from 300-700 J/kg, these thunderstorms may produce hail and gusty winds in addition to frequent lightning. For tomorrow, have increased the footprint of thunderstorms across the Kuskokwim River corridor from the coast to Lime Village, but confidence is lower regarding where there may be widely scattered or perhaps even scattered thunderstorms. While max surface-based CAPE looks lower for tomorrow, there looks to be a larger footprint of 200-400 J/kg, which would likely be sufficient to produce widely scattered thunderstorms. However, there is poor model agreement regarding where the highest CAPE will be; as such, have put in a preliminary area of widely-scattered thunderstorms in Kuskokwim Valley East and Lime Village where temperatures will likely be warmest and skies clearest.

-AM/KC