.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Key Points:

* A River Flood Advisory for the Lower Kuskokwim River communities has been allowed to expire. Water levels have peaked and should continue to trend down. A Coastal Flood Advisory for the Kuskokwim Delta coastal communities continues through 1AM AKDT tonight.

* A stronger storm system remains forecast to track across the Aleutians into the Southern Bering Sea Monday afternoon then track toward Southwest AK through Tuesday. There remains high uncertainty in the exact track of this storm and locations most at risk of coastal storm surge flooding.

Discussion:

An upper low sits over Norton Sound this afternoon with a broad area of small craft winds spread across the eastern Bering. This low is also maintaining showers across the Kuskokwim Delta into the Kuskokwim Mountains. Precipitation is expected to trend down through the overnight hours tonight, though light rain will still be possible in some areas through Monday morning. High pressure behind the departing upper low and the next incoming system to the west will see most precipitation come to an end across Southwest Alaska by midday on Monday.

The main focus for the next few days will encompass a deepening low pressure system over the western Bering on Monday. A deep low over Kamchatka is expected to dig into the Bering while interacting with a vigorous, lead-shortwave trough emerging from the North Pacific into the southern Bering. The end result will be the development of a stronger upper low over the southern Bering through Tuesday, which then tracks into Southwest Alaska.
Forecast models continue to trend toward a stronger low solution with widespread gales across much of the Bering and a swath of storm force winds on the south of the low. This swath of stronger winds ultimately gets directed into Bristol Bay on Tuesday with building seas of 15 to 20 feet possible.

There remains continued uncertainty with the exact track of the low as models have various discrepancies. Have leaned the forecast toward the EC and Canadian, which are reasonably aligned. The GFS, however, continues to be the southern outlier, though consistently south. The NAM is more of a middle ground solution but does ultimately trend the lower further south. The one area of higher confidence remains in the winds. Regardless of the northern or southern track, model continue to bring the strongest winds into Bristol Bay. Questions that need to be resolved, however, are the placement of the low and duration of winds. A further north and deeper solution of the low would extend the duration of winds into Bristol Bay and possibly necessitate some flood products. A more southerly track, such as the GFS solution, would still bring very strong winds into Bristol Bay, but for a shorter duration as the GFS solution is more progressive with the low.

Finally, based on the orientation of the low as it occludes in a bent-back fashion, the potential increases for the development of a sting jet as cold air is drawn into the backside of the low.
This sting jet could bring storm force winds into the Pribilof Islands late Monday, but uncertainty is too high in where the sting jet will ultimately develop. Keep an eye on the forecast as forecast details become more clear over the next 24 hours.



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

By the start of Thursday morning a building ridge over the eastern Bering Sea appears to settle in. The resiliency of ridges is usually a point of contention in the model solutions, however agreement is currently strong regarding a fairly strong ridge remaining over the area, warding several low pressure systems off south of the Chain into the early portions of the weekend. Model uncertainty is much higher to the east in Southcentral and the Gulf of Alaska. By Friday morning, the GFS solution pulls a fairly strong low pressure system up from the northern Pacific into the Central Gulf, spreading wind and rain across the coast, whereas the Euro and Canadian models keep a mild trough in the northern Pacific, with Southcentral staying clear. By Sunday morning, solutions comes back into better agreement with the ridging over the eastern Bering weakening as a strong low pressure system fills over the western Aleutians and a new low over the the Gulf of Alaska. A broad troughing pattern looks to resume thereafter, which will keep shower chances in play for both Southwest and Southcentral Alaska through the remainder of the long term period.

-CL

AVIATION

PANC...Overall, conditions will be quite persistent at the terminal, with gusty southerly winds due to low level instability and flow into a low tracking across Interior Alaska. There will be some fluctuations in strength of wind gusts, but generally remaining between 25 and 35 kts through at least 18Z Monday.
Winds will finally slacken after 18Z as the low over the Interior dissipates and a short-wave ridge approaches from the west.

Meanwhile, a series of weak short-waves will track overhead through Monday, leading to occasional showers in the area. The mean atmospheric flow will be out of the southwest, favoring the front range Chugach for showers, though can't rule out a shower or two at the terminal. Ceilings should remain VFR, though expect lowering of the ceilings with one particular short-wave coming through Monday morning. For now, have indicated low end VFR ceilings, but expect there will be some MVFR ceilings in the vicinity and perhaps even very briefly at the terminal.