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PKZ129 Passage Canal- 401 Am Akst Wed Mar 8 2023
.small craft advisory Thursday...
Today..W wind 15 kt diminishing to 10 kt in the afternoon. Seas 2 ft.
Tonight..W wind 10 kt. Seas 2 ft.
Thu..W wind 25 kt. Gusts to 35 kt near whittier in the afternoon. Seas 2 ft.
Thu night..W wind 25 kt. Seas 3 ft.
Fri..W wind 25 kt. Seas 3 ft.
Sat..W wind 15 kt. Seas 2 ft.
Sun..W wind 10 kt. Seas 2 ft.

PKZ100
No data

FXAK68 PAFC 080208 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 508 PM AKST Thu Dec 7 2023

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

Main changes from previous package:

- Winter Weather Advisories issued for the Kenai Peninsula, Anchorage and Matanuska Valley due mainly expectation for briefly moderate to snowfall rates briefly approaching 1-2 inches per hour later this evening into tonight with the lifting trough and surface cold front.

- Snowfall amounts increased from roughly 1-3" to 3-5" across the Anchorage Bowl and Matanuska Valley with locally up to 9 inches on the upper Anchorage Hillside.

- Pushed back end time for snowfall to ~10 am AKST Friday across the Mat- Su Valleys and Anchorage to late Friday morning due to lingering snow showers persisting behind the frontal passage and a slightly slower progression of the trough.

A potent upper trough is now beginning to work it's way up from Kodiak Island towards the southern Cook Inlet and Kenai Peninsula as it acquires an increasingly negative tilt. At the surface, a cold/occluded front is rushing northeast just ahead of the upper trough, now just starting to make it to Homer, Anchor Point and Seldovia. Bands of moderate to locally heavy snow are moving quickly northeast along and ahead of both the upper trough, while much more showery snowfall (fueled by steep low/mid level lapse rates with cold air moving in aloft) is now pushing onshore along the coast between Seward and much of Prince William Sound. There are hints of a low spinning up along the front on radar just southeast of Soldotna, however it's likely a new low will soon consolidate farther south and move northeast into Prince William Sound at the front and blast of cold air continues in the same direction.

The cold front may take on properties of a snow squall at times with snow rates exceeding an inch per hour as it sweeps through, as well as the potential for gusty winds. Low-density ("fluffy")
snow combined with gusty winds will result in the potential for significantly reduced visibility. The front is expected to push through rather quickly, so the heaviest snow should only last an hour or two at most in most areas. As the front sweeps through, models indicate deep pressure falls at the surface and surface cyclogenesis at what becomes the effective triple point off the Kenai Peninsula. As this moves up towards the western Prince William Sound, higher snow rates and for a bit longer period of time are looking likely for the Whittier/Portage area.

Models (including ensemble systems) continue to be in remarkable agreement with liquid equivalent with this system, indicating a general range of approximately 0.2 to 0.5 inches over much of southcentral, with some higher amounts over higher terrain. With the strong lift and very cold temperatures aloft snow to liquid ratios are expected to be around 15-20:1, resulting in snow accumulations ranging from 2 to 9 inches throughout many areas, including Anchorage and the Mat-Su Valley. Model consensus favors a bullseye over the Whittier- Portage area, with mean ensemble values near 0.6", suggesting snow totals of 8-12 inches in short order today.

For Friday and Saturday Southcentral will move into a showery regime as the cold trough moves over Southwest Alaska. A few weak shortwaves and steeper lapse rates will likely generate bands of showers, though the location and intensity will be hard to dial in.
Favored areas will be Valdez and Cordova, where the cold air streaming over a long fetch of warm water may generate bands of intense, low density snow.

Another much stronger system - with potential for widespread and potentially moderate to heavy precipitation - will begin to take shape on Sunday as a flat ridge begins to build into the Gulf while a large, deep North Pacific low organizes south of the Alaska Peninsula and begins to interact with the Arctic air in place over portions of the Mainland. Model agreement by this point is rather poor regarding details at this juncture, but expect an active pattern with potential for additional rounds of widespread precipitation across much of Southcentral starting as early as Sunday/Monday. Stay tuned as we monitor for the potential for more impactful winter weather by the start of next week.

-Brown/AS

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

An upper level low with a series of embedded shortwaves sets up over the Kuskokwim River delta and Bristol Bay through Saturday.
Winds across much of the Bering will remain largely small craft advisory strength, with some gales along the northeastern portions. Light snow continues across much of Southwest Alaska as well as the Eastern Aleutians and southern Alaska Peninsula overnight into Friday. The southern AKPen will continue to see periods of snow showers behind the front, accompanied by a colder air mass covering almost all of the Bering and Southwest Alaska.
Temperature across the Southwest Mainland are expected to drop into the teens and single digits by Friday and approach near zero by Saturday. Overnight temperatures for inland areas will reach at or below zero Friday night and Saturday night, while areas along the coast will drop into the single digits. Windy conditions may cause reduced visibility from blowing snow and freezing spray near ice free water and across large portions of the Bering Sea and Bristol Bay.

.LONG TERM FORECAST (Days 4 through 7)
Monday through Thursday

The longwave trough extending over Western Alaska undergoes some moderate broadening as some energetic shortwaves rotate through the pattern. The main axis drifts Eastward, and the mid-trough low center dips into into the Gulf of Alaska by the end of the period. Ridging on both sides maintains their amplitude. Ensemble forecast keeps a good forecast basis for all features, with the exception of the shortwave traffic along the Western Alaska coast.
Gusty Northerly winds over the Eastern Bering increase to gale force for late Tuesday through Thursday. An approaching North Pacific low and front expand the areas of gales across the Central and Eastern Aleutians Wednesday and Thursday. A moderate front approaches the Western Aleutians and Bering, bringing Southerly gales from midweek on. Locally moderate snow showers over the Bering give way to mixed rain and snow or rain along the Aleutians and Alaska Peninsula by the end of the forecast period.

As the trough slides to the East, increasing moisture pushes inland across Southcentral to the Alaska Range ahead of the North Pacific low moving into the Gulf through Thursday. This low brings an extended fetch of moisture which will add to expected multi- day precipitation events. Coastal zones into the Prince William Sound area will see locally heavier mixed rain and snow changing to rain Tuesday. Interior areas should remain snow, with a transition zone around the Anchorage area. Gusty winds around Kodiak Island will be close to gale force on Monday, diminishing Tuesday.

Kutz

AVIATION

PANC...IFR/LIFR ceilings and visibility will improve to MVFR/IFR as low- level northeasterly winds begin to increase ahead of a strong cold front that will move through Anchorage later this evening. However, light to moderate snow, with some periods of heavy snow, is likely this afternoon/evening, particularly in the 02-06z timeframe. Snow rates at or in excess of 1 inch per hour may occur for an hour or two in that window, with visibility briefly to a half mile or less. Total snow accumulation of 1 to 4 inches is most likely. The snow will be of low-density ("fluffy"), likely contributing to some visibility issues that will be enhanced by gusty winds. Conditions will greatly improve by later tonight in the post-front regime. Some lingering flurries are possible, but additional accumulation is unlikely.

Continued with LLWS for a brief period this afternoon as SE winds pick up above a lighter northeast wind. This should be brief as winds will increase out of the SW as the front pushes through.

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Anchorage (Knik Arm)
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Thu -- 02:17 AM AKST     22.11 feet High Tide
Thu -- 02:53 AM AKST     Moonrise
Thu -- 08:49 AM AKST     8.55 feet Low Tide
Thu -- 09:57 AM AKST     Sunrise
Thu -- 02:11 PM AKST     Moonset
Thu -- 02:43 PM AKST     26.04 feet High Tide
Thu -- 03:44 PM AKST     Sunset
Thu -- 09:36 PM AKST     6.61 feet Low Tide
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Anchorage (Knik Arm), Alaska, Tide feet

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