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PKZ141 Kachemak Bay- 401 Am Akst Wed Mar 8 2023
Today..Variable wind less than 10 kt. Seas 2 ft.
Tonight..SW wind 15 kt becoming S 10 kt after midnight. Seas 2 ft.
Thu..Variable wind less than 10 kt becoming N 10 kt in the afternoon. Seas 2 ft.
Thu night..NE wind 15 kt. Seas 3 ft.
Fri through Sat..N wind 25 kt. Seas 3 ft.
Sun..N wind 20 kt. Seas 2 ft.

PKZ100
No data

FXAK68 PAFC 071359 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 459 AM AKST Thu Dec 7 2023

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

Radar and satellite imagery continue to show snow and rain for portions of the Prince William Sound and northern Gulf of Alaska associated with a weakening area of low pressure. With a weakening low comes a weakening pressure gradient, and therefore subsiding winds across Thompson Pass. The Blizzard Warning has been allowed to expire, though some non-trivial winds with some light additional snowfall may continue to bring occasional reduced visibility to that area of the Richardson Highway through the remainder of the morning.

Attention turns towards a strong upper-level trough and associated cold front that'll move through southcentral Alaska today. As of 430am, satellite imagery currently shows the trough / cold front pushing through the AK Peninsula and encroaching on Kodiak Island.
Steep low/mid-level lapse rates owing to the cold air (~-15C at 850mb) will produce rather vigorous snow shower activity along the frontal interface as this front sweeps through. Snow all the way down to sea level will begin in Kodiak (mainly the western side) and then spread quickly into the Kenai Peninsula before sunrise, and north into Anchorage and the Mat-Su in the afternoon to evening hours.

This 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 0.1 to 0.3 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 6 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.

-Brown

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

Longwave troughing with a series of embedded shortwaves moves across the Bering Sea and Southwest Alaska over the next few days.
As a whole, the system that is now near the Seward Peninsula is weakening. Winds across much of the Bering have diminished to small craft, with some gales along the northeastern portions. Snow continues across much of Southwest Alaska as well as the Eastern Aleutians and southern Alaska Peninsula today. Chances across Southwest diminish into the afternoon as the initial front moves across the Kilbuck Mountains. 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.



.LONG TERM FORECAST (Days 4 through 7)
Sunday through Wednesday

High pressure over the Russian Far East and The Western Canadian Provinces bracket the long wave trough over Central Alaska through Wednesday. Trough axis shifts Eastward, moving a pocket low towards the Gulf by the end of the forecast period. Forecast confidence starts mixed, due to transient shortwaves over the Eastern Bering and low centers moving along the South coasts.
However, model confidence improves by midweek. With the trough through the Central Mainland as a well developed North Pacific low moves along South of the Alaska Peninsula into the Gulf of Alaska for Monday and Tuesday. Considerable moisture will be pumped into most of Southcentral Alaska, with heavier rain or mixed rain/snow from the Kenai Peninsula along the coastal zones to the Canadian border. Inland areas into the foothills of the Alaska Range remain cold enough for snow.

For the Alaska Peninsula and the Aleutians, snow changes over to mixed rain and snow as a North Pacific low presses closer to the Chain. Near gale force winds increase to areas of gales over the Eastern Bering through Wednesday. The Central Aleutians open with areas of gales associated with the North Pacific low for Sunday.
As the low moves Eastward, gale force winds straddle the Alaska Peninsula, and spread into the Gulf Monday through Wednesday. A gale force barrier jet forms over the Northern Gulf late Monday, diminishing through Wednesday.

Kutz

AVIATION
VFR conditions this morning will quickly degrade this afternoon and evening as a rather strong cold front moves through Anchorage. Ceilings will gradually lower to MVFR heights, with some brief sub-1kft IFR CIGs also possible today. Heavy, though brief, snow is likely this afternoon, particularly in the 02-06z timeframe. Snow rates at or in excess of 1/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. Conditions will greatly improve by later this evening in the post-front regime. Some lingering flurries are possible, but additional accumulation is unlikely.

Included 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.

-Brown

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