textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Messages:

- Another round of rainfall Thursday night through Friday over the Susitna Valley will allow for rises on many small streams and rivers, and localized ponding in low-lying or poor drainage areas.

Discussion:

The system that brought widespread rainfall across Southcentral yesterday has mostly departed the area as of this morning. The low has lifted into the NE corner of Alaska with front now pushing across the Canadian Yukon. There are some lingering showers still ongoing this morning over the SE corner of the Copper Basin, but these will continue to weaken and dissipate through the morning. While a drier airmass has moved in behind the aforementioned system, some areas have hung on to a mid-level cloud deck overnight. Temperatures have also fallen as the drier airmass pushes in with morning temperatures dropping into the 40s for most areas. Fog has tried to form in some of these areas that have cleared out, but have had to compete with falling dewpoints. The most widespread area of fog has developed along portions of the Glenn Highway north of Anchorage and into Palmer-Wasilla and on up towards Willow. Most of the fog has been relatively light with visibilities of 1 to 3 miles, but there have been some pockets of dense fog where visibility has dropped below 1 mile at times. As such, have issued an SPS for fog in this area until 9 AM this morning. Could see a few more areas of fog pop up near sunrise before diurnal heating starts to mix out the boundary layer.

More seasonable temperatures today with drier conditions as we remain under westerly to northwesterly flow aloft. A weak shortwave moving through the flow later today could spark some showers along the Alaska Range and Talkeetna Mountains. An upper ridge will build into western Alaska tonight then translate east with time. Thursday will be the driest day for Southcentral with high pressure over the region; however, another strong system will bring another round of widespread rainfall beginning late Thursday and Friday.

Cloud cover increases Thursday afternoon and evening from west to east as the next system approaches from the Bering. Widespread precipitation will spill over the Alaska Range into Kodiak Island and western Southcentral late Thursday night and spread across all of Southcentral on Friday. Precipitation will be heaviest along the northern Gulf Coast into the Chugach Mountains. Southwest winds will strengthen in the western Gulf and Shelikof Strait to small-craft by Friday morning. Additionally, a surface low looks to develop in the northern Gulf Friday morning. Depending on the strength of the pressure gradient with the coastal ridge, this will enhance easterly and southeasterly winds Friday, especially in properly aligned gaps (Turnagain Arm, Knik River, and Barrier Jet).

- PP/PA

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

The active, progressive pattern continues into early next week as multiple systems track from west to east. This will generally bring periods of active weather, with lulls in between for Southwest and Southcentral Alaska.

By Saturday, a trough will be over much of Alaska. This will likely bring widespread rainfall and elevated winds to coastal and mainland Southcentral and Southwest Alaska. This trough will quickly push eastward and weak ridging/zonal flow will set in, allowing for wind speeds and rainfall to dwindle. The Bering will see a trough with an associated front move in from the west. Sunday will see this front progress eastward, leading to a swath of rainfall and gusty winds across the Aleutians. However, the exact intensity and path of this weather is uncertain as of now. For Southcentral, ridging will continue, with lighter winds and clearer skies.

Uncertainty increases on Monday as a low moves into the Bering. The exact track of it cannot be determined at this point, but gusty winds and rainfall will likely arise somewhere along the Aleutians. A plume of moisture riding up and around a ridge in the North Pacific will lead to heavier rainfall with this low. Again, the exact rainfall amounts will depend on the track of the low moving into the Bering. Southcentral will have a low move into the Gulf of Alaska. Once again, there is much uncertainty with wind speeds and rainfall intensity with them being highly dependent on how strong the low is.

-JAR

AVIATION

PANC...Light winds and VFR conditions are anticipated through the prevailing period. However, light winds and high pressure building over the region may allow for pockets of fog to develop near the terminal around sunrise both this morning and Thursday morning.