textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

The short term forecast for Southcentral begins with ridging in the Gulf of Alaska. This is allowing for lighter winds and clearer skies across the mainland. However, some areas of cloud cover remains, which may allow for overnight temperatures to remain above zero. A low arrives into the Gulf by Tuesday, which will bring gusty winds and precipitation to the coast. The low looks to take an eastern track, onshoring somewhere around Yakutat. Confidence in this scenario is increasing which is a change from yesterday's thinking which had the low track more to the west. With the east track, snowfall across the Kenai Peninsula, Anchorage, and the Mat-Su Valley is expected to be on the lesser side (2 to 3 inches). Most snowfall will fall in Eastern Prince William Sound including Valdez and Thompson Pass. Gusty winds are also possible in Thompson Pass, which could cause some blowing and drifting snow at times. After the low passes, a trailing trough will allow for more snow chances on Wednesday morning of a similar intensity as Tuesday's event. Wind speeds will also increase as the front from the trough lifts onshore.

After this point by Wednesday evening, some ridging builds into the Gulf, which will decrease winds and precipitation chances. This will be short lived as an atmospheric river rises into Southcentral. A low will coincide with this atmospheric river and will move somewhere west of Kodiak Island. There is much uncertainty with this event, but what is known is that much warmer air will rise into Southcentral, likely driving temperatures into the positive 30s and potentially even the 40s by the end of the week. Heavy precipitation is also likely with this event, but it is not clear exactly what type of precipitation that will be.

-JAR

..Active Advisories and Warnings

* A Winter Weather Advisory has been issued for the Central Aleutians until 9AM Thursday.

* An Extreme Cold Warning remains in effect for the western Kuskokwim Valley until 6PM AKST Thursday.

* An Extreme Cold Warning remains in effect for the central Alaska Peninsula including Port Heiden until 6PM AKST Thursday.

* A Cold Weather Advisory remains in effect from the southern Alaska Peninsula to mainland Southwest Alaska until 6PM AKST Thursday.

Discussion:

Aloft, the western domain continues to be comprised of a lifting arctic trough over mainland Alaska and a ridge anchored over the Western Bering Sea, with the mean zonal flow oriented almost north to south. Embedded in this flow is a weak shortwave dropping southward and nearing the Pribilof Islands this afternoon, with a wave of low pressure forming at the surface west of the Pribilof Islands and moving southward towards the Central Aleutians. This system makes its way to the Adak area Tuesday morning. On the heels of this low is a secondary 500 mb shortwave dropping southward from the Bering Strait to west of the Pribilofs, and then southward to the Central Aleutians. All model guidance suggests this system will be somewhat stronger than the first, and thus will be the more impactful of the two for blowing snow concerns. The bigger story here is that another arctic trough at around this time begins to dig southward, which will reinforce a bitterly cold airmass across the western domain. This airmass will be fairly short lived, however, as the trough takes a more positive tilt and becomes situated west of intense ridging building over the Gulf, which will set the stage for a potential atmospheric river event heading into Thursday. This would dramatically warm temperatures to near or above freezing across Southwest Alaska due to warm air advection that would accompany the low, which in turn would introduce precipitation type issues. A large amount of precipitation would also fall due to the large fetch of moisture being brought up from the tropics and subtropics. There is still much uncertainty with this scenario, but the signal is there for a signficiant pattern change heading into late week.

-AM/KC

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

The long term forecast begins with an amplified pattern over much of Alaska. A broad trough will be in place over the central Bering on Friday with strong southerly flow downstream of the trough, extending from the North Pacific up into Southcentral Alaska. Potential impacts from this atmospheric river will entail gusty winds into the northern Gulf coast and Prince William Sound, widespread rain showers into the coast, heavy snow at higher elevations, and a significant warm up in temperatures across all of Southcentral. The amplified pattern begins to break down on Saturday with a ridge of high pressure building over the eastern Bering and Southwest Alaska. A deepening trough west of the Aleutians will serve to reinforce downstream ridging through the end of the long term period early next week.

Models continue to exhibit small differences with the overall strength and track of the low Thursday into Friday, and there is still potential for changes to the forecast over the next 48 hours. However, overall confidence is increasing that the strongest winds will occur offshore of the Southcentral Coast from Kayak Island into Prince William Sound. Gales with gusts to 50+ knots are currently forecast. If the low on Thursday takes a track further north, the potential would increase for high winds through the Eastern Turnagain Arm lower elevations. Currently, the highest inland winds are forecast to remain over the mountains.

One last area of concern will be across the Central Aleutians early on Friday. A vigorous area of low pressure is progged to lift into the region with the potential for hurricane force gusts. This low is followed up with a large frontal system into the western Bering and Aleutians Sunday into Monday.

-BL

AVIATION

PANC...Drier air continues to work in aloft from the southwest this afternoon as surface winds remain light and out of the north to northeast. VFR ceilings will continue into the late this evening.

A shortwave lifts northward across the Gulf overnight bringing a return to MVFR conditions. Light snow begins near 15Z Tuesday and continues through 00Z Wednesday. After a break Wednesday evening, light snow returns 12Z Wednesday and continues into 00Z Thursday.