textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Messages:

- Special Weather Statement has been issued for strong winds tomorrow, Tuesday for Anchorage, Anchorage Hillside, Palmer and Butte.

- Several rounds of widespread rainfall across the Susitna Valley this week will allow for rises on many small streams and rivers, and localized ponding in low-lying or poor drainage areas.

Discussion:

Several features of note this morning. A shortwave ridge over the Gulf will continue to flatten today as several systems move in from the west. The first of these systems is a small shortwave trough that is riding over the ridge. The system brought some rain to the southern Kenai Peninsula overnight and has since moved out into the Gulf as it weakens and gets absorbed into the flow.

The next system of note is the more substantial trough positioned near the Bering Strait this morning with front sweeping across Southwest AK. Broad isentropic ascent ahead of this front combined with modest moisture transport on southwesterly flow has resulted in a broad region of scattered rain showers over inland Bristol Bay and into the central Interior. Another area of rain was also noted near the surface low near the Y-K Delta region. The surface low will lift to the NE today with rain becoming more focused along and near the front as the trough becomes more negatively tilted and forcing increases along the front. Lee troughing will also become more pronounced just off the eastern Kenai Peninsula, helping to increase rain chances for Prince William Sound and the northern Gulf coastal zones. Greatest rain amounts still look to be focused over the Susitna Valley, where a half inch to around an inch of rainfall is possible for areas from Petersville east to Talkeetna and along the Talkeetna Mountains to Hatcher Pass. Given recent rainfall events over the past few months, rises along areas creeks and rivers can be anticipated, along with ponding in low-lying and poor drainage areas. This system will depart fairly quickly with rainfall generally ending from west to east by late tonight into Wednesday morning.

In addition to widespread rainfall, winds will begin to increase this morning along the Turnagain Arm and Anchorage Hillside and the pressure gradient tightens along the Chugach Mountains. Gusts around 40 mph are possible for portions of south and west Anchorage, including the airport, particularly this afternoon and early evening. Strong winds are also expected through the Knik Valley and Copper River Basin gaps as the front moves through. Winds will begin to subside tonight as the gradient starts to relax with the passage of the front.

Looking towards later in the week... Wednesday afternoon and Thursday bring a brief respite from wind and rain before another Bering low brings another round of widespread rainfall to Southwest and Southcentral.

- PP

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

An active, progressive pattern continues through the end of the week and into early next week as multiple systems quickly track from west to east. This will generally bring periods of active weather, with brief lulls in between for most locations.

By Friday morning, a 990 mb low will have tracked just east of St. Laurence Island and begins to move inland near the Norton Sound, bringing moderate to heavy precipitation across much of southwestern Alaska. Concurrently, southwesterly small-craft to gale- force winds will continue to push into Bristol Bay and the Kuskokwim Delta coast. Widespread precipitation will also filter into Southcentral, and will be particularly heavy for the northern Gulf coast and Talkeetna Mountains. Turnagain/Knik gaps winds will likely return Friday, bringing potential for gusty conditions around Anchorage and Palmer. River levels across the Susitna Valley, such as the Yentna River at Lake Creek will have to be monitored closely with this system for potential flooding concerns.

By Saturday morning, the trough ejects a surface low into the Gulf, causing rainfall to taper off from west to east across the mainland as this low continues toward the Alaskan Panhandle. Some showers may linger in spots, particularly for Prince William Sound and the western/central Chugach, though conditions will gradually improve as ridging rebuilds over the region. A separate North Pacific low moves into the western bering by Saturday which will likely bring another wave of precipitation to the western/central Aleutians.

Deterministic solutions begin to differ substantially by Monday. However, ensemble means show a broad ridge amplifying just south of the Aleutians, which could set up a period of moist flow. Another shortwave appears to work down the mainland by Monday. If this feature can tap into this moisture, another round of widespread precipitation could be on track for much of the southern Alaska early next week.

-CW

AVIATION

PANC...Southerly winds pick up this morning with gusts to 25 kts and increase with gusts to 30 kts later this morning (after 18Z). Light rain expected over the terminal through today. Cloud ceilings will drop below 5000 ft after 18Z.