textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Messages:

* A Wind Advisory remains in effect for Anchorage and the Hillside until 10AM Tuesday. 40 to 50 mph gusts are expected for west/south Anchorage, while the Seward Highway near the Turnagain Arm and the Hillside will see gusts up to 60 mph.

* Flood Watch remains in effect for Central/Western Susitna Valley through Friday morning, due to heavy rainfall. Flood watches have been CANCELED for the rest of the Susitna Valley and the Matanuska Valley.

* Flood Watch for Seward and the eastern Kenai Peninsula has been CANCELED.

Discussion:

Current radar returns and observations suggest the system that has been advertised has/will way underperform in terms of rainfall for some areas, and to a lesser extent, wind. It has been quite a dramatic shift just looking real time satellite imagery and observations versus what model guidance has been suggesting over the last 24 to 48 hours. For rainfall, these discrepancies have been significant enough to cancel the Flood Watch that was in effect for Seward, and the Flood Watch for the Susitna Valley has been trimmed back to only include the Central and Western portions of the Valley. The locations still under a Flood Watch are Petersville, Cache Creek, Talkeetna, and communities along the Yentna and Skwentna Rivers through Friday morning.

The drastic changes in the near term forecast mostly stem from the ridge situated across the eastern Gulf being stubborn to gain momentum. This has stalled the incoming front much more to the west than the overall thinking and model consensus yesterday. This is actually great news, particularly for Seward/Resurrection Bay, and the Flood Watch for this area has been canceled. Seward's wind direction has also shifted since the front/atmospheric river stalled prematurely. Rather than a due south wind, a south- southwest wind they are observing instead is much less conducive for heavy rainfall amounts. Looking at the radar, the axis of rainfall is situated along a corridor from the central part of the Cook Inlet to Talkeetna. The Anchorage Bowl has been mostly dry for the better part of the day due to southeasterly downsloping, though the current radar suggest rain showers will continue fill in over the course of the afternoon as moisture overspreads the area from west to east. The best chance of seeing periods of moderate rainfall for Anchorage will be this evening and overnight as the ridge attempts to erode and the axis of moisture shifts eastward. That said, many areas around Anchorage will be lucky to see much more than 0.3 inches of rainfall.

Wind wise, things remain mostly on track, though the Anchorage Hillside has seen winds marginally underperform today. Nevertheless, the overall message for wind potential remains the same, and the Wind Advisory remains in effect through 10AM Tuesday for Anchorage and the Hillside, with an emphasis on west/south Anchorage, along the Seward Highway near the Turnagain Arm, and for the Hillside. Coastal ridging is still in place, which is continuing the Turnagain Arm wind, Knik Wind, and Copper River winds. The main difference today is that due to the front stalling much farther west than expected, the east to west gradient is not quite as strong as expected. Looking ahead to Tuesday afternoon, the latest model guidance has also been to bring rainfall out of much of the area more quickly, with the exception for coastal areas such as the southern/eastern Kenai Peninsula. The front, as of now, is expected to venture eastward into the Gulf, but will likely weaken/shear apart as it further approaches the ridge, which will gradually diminish any remaining rain chances through mid week.

-AM

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

To start out the longer term period, an upper-level low will remain in place across interior Alaska on Friday. This low moves off to the east across Yukon, Canada by Saturday. Aside from some scattered showers at times across the Southern Mainland, expect mostly quiet weather for Friday and Saturday.

The long-term forecast becomes more uncertain for Saturday and Sunday, especially for the Bering and Aleutians. The point of uncertainty arises with how guidance wants to handle upper-level energy coming out of Kamchatka. The Canadian and European suites want to develop this energy more than the GFS. Hence the GFS has a drier solution across the Aleutian Chain while the European and Canadian suites are wetter. Also of note, while the Canadian and European guidance does develop the Kamchatka energy, the resulting surface low is not expected to be strong at this time.

Across the Southern Mainland for Sunday, like the Bering, there is some uncertainty in the forecast. The Canadian and European suites take a shortwave moving out of the Arctic and keep it confined more to Northern Alaska which would be a drier solution for the Southern Alaska. The GFS, on the other hand, wants to dig this shortwave more to south and over Southern Alaska which would be a wetter solution for both Southwest and Southcentral Alaska for Sunday. For Monday, an upper-level low over interior Alaska moves south towards Southern Alaska. There does not look to be a lot of moisture with this system at this time and the likely outcome for Monday will be that this upper-level system helps to kick off some diurnally-forced showers across Southcentral and Southwest Alaska.

AVIATION

PANC...Strong southeasterly Turnagain Arm winds will persist through the TAF period, but should begin to drop off steadily late tonight through early Tuesday afternoon. Periods of steady to briefly moderate rain will continue to move over the terminal through Tuesday morning, but The drying effects from southeast winds will likely keep ceilings mostly in VFR range, but dips into MVFR range will be possible overnight tonight into early Tuesday morning with periods of heavier rainfall.