textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Messages:

- Frost Advisory is in effect overnight tonight from 2 AM to 9 AM AKDT for the Anchorage and Lower Matanuska Valley. Coldest prone locations (Butte, Muldoon, Campbell Tract, and the Eagle River Valley) could see temperatures near or below freezing. Main concern is for frost sensitive outdoor plants and vegetation.

- Termination dust and snow is possible for the higher elevations and passes. Snow levels this morning across the Alaska Range near Cantwell/Broad Pass, Talkeetnas, Western Chugach, and Kenai Mountains bottom out to roughly 2500 to 3000 feet. To the Central Chugach and eastern Alaska Range, near 4000 feet. - Gusty offshore winds continue over the next few days with the strongest winds along the coast and through gaps and passes this afternoon and evening.

Discussion:

Gusty offshore winds will continue along the coast and through gaps and passes for the next few days. Strongest winds are expected this afternoon and evening. Precipitation associated with an upper-level low will continue south through Southcentral moving from northwest to southeast throughout the day. Generally, precipitation will end by this afternoon for most locations. The only place that could see precipitation linger is for the Richardson Highway south of Glennallen. There is also a slight chance (30 percent) for a brief shower early in the afternoon across Anchorage and the Mat Valley, enhanced by orographic lift associated as a shortwave behind the low circulation passes through. Temperatures are expected to trend cooler as an arctic airmass moves through and skies clear across the region.

With colder air moving in aloft, lapse rates are becoming more unstable. Lower elevations will see primarily rain though. Several lightning strikes were observed however with showers near Cordova and east this morning. Strong showers moving across the MatSu and Anchorage produced a couple lightning strikes near Big Lake and the vicinity of Anchorage. At higher elevations, snow is possible at higher elevations this morning with termination dust on the mountain peaks and through Broad, Tahneta, Isabel, and Hatcher Passes. Snow levels this morning across the Alaska Range near Cantwell/Broad Pass, Talkeetnas, Western Chugach, and Kenai Mountains bottom out to roughly 2500 to 3000 feet. To the Central Chugach and eastern Alaska Range, near 4000 feet. Road temperatures will be warm enough to limit accumulation.

Temperatures will cool considerably behind this low. Clearing skies and a cold airmass will allow temperatures to fall sharply tonight into Tuesday morning. A Frost Advisory is in effect from 2 AM to 9 AM AKDT Tuesday for Anchorage and the Lower Matanuska Valley. Temperatures could fall as low as the upper 20s in typically colder locations, with frost capable of occurring. Other portions of Southcentral, including the lower Susitna Valley and western Kenai Peninsula, will also have the potential for near- freezing temperatures and patchy frost Tuesday morning. Wednesday morning will remain chilly, though frost potential currently looks less widespread as temperatures begin to moderate.

Tuesday into Wednesday, broad northwesterly flow remains over Southcentral as the main upper low shifts southeast. Additional weak shortwaves embedded within the flow may produce periods of increases cloud cover and isolated to scattered showers, particularly over the higher terrain and Copper River Basin. By Wednesday, model guidance show heights beginning to rise as an upper-level ridge builds eastward toward Southcentral, allowing for a gradual moderating and drying trend.

LM/Rux

LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)

The long-term period looks to remain active, especially across Southwest Alaska, The Bering Sea, and the Aleutian Chain. Thursday features a strong upper-level low in the western Bering with a ridge moving into the western Gulf of Alaska. A strong shortwave will move north along a stalled frontal boundary which will lead to the development of a surface low between Saint Matthew Island and Saint Lawrence Island late Thursday morning into Thursday afternoon. This low and its front will aid in another round of heavy rain for the and gusty southwesterly winds along the coast for Thursday.

Across Southcentral Alaska, the ridge will be overhead for much of Thursday with relatively quiet weather anticipated. The ridge moves east to the eastern Gulf of Alaska and into Yukon, Canada for Friday which will open the door to southwest flow aloft. Steady rain from Southwest will move into Southcentral through Friday as a plethora of shortwaves lift up and over the area from North Pacific and Gulf. Showers continue over Southwest, the Aleutian Chain, and Southcentral for Saturday as a broad upper- level trough remains in the Bering and southwest flow aloft remains across Southcentral.

Guidance diverges for Saturday evening and into Sunday and forecast confidence begins to wane. The point of disagreement comes with how guidance handles the strength and track of a shortwave rounding the base of the broad Bering trough as well as the placement of the upper- level ridge to the east. The GFS and Canadian guidance have the ridge farther to the southeast with its axis mostly over British Columbia while the European guidance has the ridge axis more to the west with its axis over Southeast Alaska. The GFS also closes the shortwave off into an upper-level over the Gulf the Canadian and European guidance depicts more of an open wave(s). Regardless, Saturday night through Sunday looks wet across the Southern Mainland, its a matter of pinpointing who receives higher magnitudes of rain and who sees just showers. As timing gets closer, details should become more clearer on these points of disagreement.

AVIATION

PANC...Rainfall may lower ceilings to MVFR conditions this morning. A few lightning strikes have been observed this morning in the vicinity and the threat for isolated thunderstorms will last until 16Z. Generally expect a drying trend with clearing skies throughout the day. However, there is a small chance (30 percent) that a brief shower may occur early this afternoon, but all precipitation should be out of the area by 00Z. Gusty northerly winds are expected to increase throughout the day.