textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

A complex low is moving through the Gulf of Alaska and is currently near Kodiak Island. Rain is being pushed into Kodiak and along the coast of Southcentral from shortwaves moving around the low. These shortwaves near the low are also creating a coastal ridge over the Chugach Range, allowing for elevated southeasterly winds (10 to 15 mph, with gusts around 25 mph) in Palmer, South Anchorage, and the Copper River Basin through Tuesday. Isolated thunderstorms will have a 10 to 20% chance of forming, mostly over the foothills of the the Talkeetna Mountains and Alaska Range. Southeasterly flow along the coast will allow for downslope drying on the lee of the mountain ranges, but light rain showers will still have a 20 to 30% chance of occurring.

By Tuesday, a more robust trough from the low will move across Southcentral from east to west and reaching well into the Copper River Basin and Susitna Valley. This wave will produce steadier rainfall, which will cause moderate to heavy rain over the northern and western Susitna Valley. Upslope enhancement will promote higher rainfall amounts farther inland, near the Talkeetna Mountains and the Alaska Range. Lower elevations (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. The band of moderate to heavy rainfall will linger over the Susitna Valley through Wednesday. Between Tuesday and Wednesday, 1 to 2 inches of rain will fall between Cantwell, through Talkeetna and Skwentna toward the west Alaska Range. Confidence is higher today, but there is still some uncertainty regarding how long the band of rain lasts over the Susitna Valley. 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 rainfall associated with them will be lighter. Thursday will see moisture move into the Copper River Basin. This, combined with continued easterly waves will allow chances (50 to 60%) for showers.

-JAR/Rux

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

The long-term pattern continues to feature an unsettled pattern across the Southern Mainland. A low pressure system in the Bering Sea will continue to bring showery conditions across the Central Aleutians, Eastern Aleutians, and Pribilof Islands Friday and Saturday before the rain moves to the Southern Alaska Peninsula (AKPEN) for Sunday. A ridge builds in behind this system with likely low stratus and misty conditions filling in across the central Bering Sea and Central Aleutians Saturday evening into Sunday. This ridge and the associated low stratus will move eastward through Monday across the rest of the Aleutians and Southern AKPEN while the Western Aleutians and western Bering will contend with North Pacific fronts.

Southcentral and Southwest Alaska will also remain unsettled as a series of easterly waves moves across the Southern Mainland from Yukon, Canada and shortwaves lift from the North Pacific, the the Gulf of Alaska, and over Southcentral Alaska. Most steady precipitation with these disturbances between Friday and Monday will look to fall across interior portions of the Southwest Alaska with scattered rain showers across Southcentral Alaska. The one challenge with the long-term forecast, with regards to the interior locations, will be assessing how much instability will be available. This will determine how much of a threat lightning strikes could become. Right now, Friday afternoon looks to be the most unstable day across Southwest Alaska with Sunday afternoon across the Copper River Basin of Southcentral Alaska.

AVIATION

PANC...VFR conditions are expected to persist. A southeasterly Turnagain Arm wind will strengthen this afternoon/evening and has a chance of producing gusts up to 25 kts before diminishing by around 09Z Tuesday morning.

FIRE WEATHER

Key Message:

Wetting rain chances increase for Tuesday and Wednesday across interior Southcentral Alaska and interior Southwest Alaska.

Discussion:

A strong easterly to southeasterly shortwave will lift across the Gulf of Alaska through Monday night and spread wetting rains beginning Tuesday morning across the Copper River Basin. The airmass this upper-level disturbance is moving over will be stable, so lightning should be little threat. Steady wetting rains will move to the Susitna Valley by late Tuesday morning. Wetting rains then shift to interior of Southwest Alaska by Tuesday afternoon to Tuesday evening with areas along the Western Alaska Range as well as Port Alsworth and northward seeing steady rain. This steady rain will last across interior Southwest Alaska will last through Wednesday morning before tapering off. Southeast flow behind the upper-level disturbance, now over Southwest Alaska by Wednesday afternoon, will allow for more moisture to wring out across the Western Susitna Valley along the Alaska Range through Wednesday evening which will result in more wetting rain for that area.