Area Forecast Discussion

SYNOPSIS

Unsettled and in some cases messy weather is ongoing across Northern Alaska and will continue for the next several days. A system over the Bering Sea is pushing a front northeastward across the West Coast and Interior, with strong easterly winds occurring in marine areas moving north with the front. The front is also bringing widespread snowfall to the YK Delta and southwestern Interior which will spread into the Interior all through the day today. With afternoon highs above freezing for much of the Interior, we could see a rain/snow mix at times particularly farther south. Any wet/slushy spots will likely refreeze overnight, leading to potentially icy surfaces. Poor drainage areas could see localized pooling/ponding of water. After some cooler conditions in Western Alaska on Tuesday, another system brings more wind and precipitation, some potentially mixed, to Northern Alaska Wednesday into Thursday, and the potential for much warmer conditions across the area.

KEY WEATHER MESSAGES

Central and Eastern Interior...

- Scattered light snow showers continue across the Interior this morning, with a front moving in by this afternoon into Monday bringing in more moderate, widespread snowfall through early next week.

- Snowfall totals will range from around 1-4" in the valleys and 3-8" in the mountains. Locally higher totals are expected in the Alaska Range, where around 8-16" of snow is expected for higher elevations of the Parks and Richardson Highways with locally higher totals above pass level.

- High temperatures will continue to be above freezing for most, leading to the potential for a rain/snow mix at times particularly farther south. Any wet/slushy spots will likely refreeze overnight, leading to potentially icy surfaces. Poor drainage areas could see continued pooling/ponding of water.

West Coast and Western Interior...

- A front is bringing strong easterly winds to most of the West Coast, with the strongest winds at St. Lawrence Island and through the Bering Strait, where northeast winds could gust around 50-65 mph. Areas of blowing snow could significantly reduce visibilities at times in these areas.

- This same front is producing snowfall in an area extending from Norton Sound to the Western Alaska Range which will gradually shift northeastward through the day today.

- Rain will likely mix with the snow in the Lower Yukon and Upper Kuskokwim Valleys from Mountain Village to McGrath with the best chances being this afternoon.

- Prior to the rain, snow amounts will be around 4 to 7 inches. North of the mixing line, snow amounts will range between 5 to 10 inches from Ruby to Kaltag and 3 to 6 inches in the Kobuk Valley.

- Any rain across the area will change back to light snow and snow showers Monday afternoon which will linger into Tuesday.

- Winds will also gradually weaken on Monday and Tuesday. Another system looks to move into the area on Wednesday.

North Slope and Brooks Range...

- Generally quiet weather on the North Slope with below normal, cold temperatures continuing into next week.

- Another area of snow arrives on today, particularly late in the day and gradually traverses north to the coast Sunday night and Monday.

- This second round of snow will bring another 1 to 3 inches in the North-Central Brooks Range with around 1 inch on the North Slope.

FORECAST ANALYSIS AND DISCUSSION

Active weather continues in Northern Alaska. An trough extends across the North Slope and into the north-central Interior, with ridging over the Gulf extending northward to meet it. A strong, vertically-stacked low in the Bering Sea (surface pressure ~965 mb) is pushing a warm front across southwestern Alaska, which is bringing a broad area of easterly winds and precipitation to the area. This low is at the center of a mature extratropical cyclone; an occluded front wrapped around the low center extends eastward to a triple point where a warm and cold front converge over the YK Delta. Over the water, peak winds of gale to storm force are expected to continue across the area through the day as the front pushes inland. Along the front, an extensive band of precipitation is currently affecting the YK Delta and Lower Yukon Valley region and will move northeastward today.

Ahead of the front in the Interior, snow showers are occurring with a wave/trough moving through the area. Upslope flow is occuring on the south side of the Alaska Range, especially the on the eastern side south of Trims Camp, supporting high snowfall rates at times. There could still be some messiness, with potential icy/slick conditions again possible. As the front itself shifts into the area (while occluding as the cold front rapidly overtakes it), the general showery activity will increase in coverage and intensity significantly. Several tenths of an inch of liquid-equivalent precipitation will be possible in the Western and Central Interior, where high snow ratios of around 15:1 be possible. This could yield over six inches of snow across much of the area from today through Tuesday. The highest snowfall amounts will be likely in the Middle Yukon Valley area, where final storm totals as high as 7 to 10 inches will be possible. Similar totals will be possible in remote parts of the Lower Yukon Valley as well as in the Upper Koyukuk Valley, although in the latter case, this snowfall will be dispersed over the course of multiple days. Today, when high winds in marine areas (including St. Lawrence Island) can combine with falling or fresh snow, blowing snow or blizzard conditions will be possible. By this evening, as the low becomes offset from its baroclinic source, it will rapidly weaken, with winds decreasing in the northern Bering Sea. They could nonetheless remain brisk and northerly through the Bering Strait and on St. Lawrence Island even as they taper off elsewhere, with continuing blowing snow potential for these areas. A strong surface pressure gradient of about 4 to 6 mb across the Alaska Range will develop today. This will permit breezy/gusty winds through the passes (but especially Isabel Pass) from later this morning into Monday.

This evening, frontal moisture will overspread the warmer Central and Eastern Interior; while some periods of melting precipitation could occur, extended periods of precip or just heavy/showery precip could allow for low-level temperatures to cool enough to permit snow instead of just rain or rain/snow mix. Even with snow, there will still likely be some melting on ground surfaces, especially in the lower valleys. Up to a few inches of snow total, especially in the hills, will be possible from then through Monday morning. Better accumulations will be possible in the White Mountains and Upper Chena Valley, where upsloping or convectively driven showers will be more likely. Easterly winds will pick up on the eastern Arctic Coast from this evening into Monday night as high pressure develops over the Beaufort Sea, with sustained winds of 15 to 20 mph with gusts of 25 to 30 mph.

A newly-developed cold front on the south side of the Arctic trough, by this point centered over the western North Slope, will swing southward and eastward on Tuesday, briefly dropping temperatures across Western Alaska into the 20s and teens (single digits in inland parts of the Seward Peninsula). Temperatures will also fall to a lesser extent in the Central and Eastern Interior. A low moving into the southeastern Bering Sea will begin pushing another warm front into the area around this same time frame, with an additional round of easterly to southeasterly winds and precipitation beginning to affect the area.

EXTENDED FORECAST DAYS 4-7

The low in the Bering Sea Wednesday morning will have a warmer airmass to work with than the one affecting the area today; as the leading warm front moves in, it will quickly push out the cold air that just moved in, and with it, high temperatures across the area will rise back above freezing by Wednesday into Thursday. It will also bring another round of precipitation, with better chances for rain or rain/snow mix in the Western Interior than with the first system given the warmer airmass. The precipitation band moves in a more south-to-north direction, which will also limit the precipitation in the Central/Eastern Interior to a greater extent while allowing for much more to fall over the western North Slope. Some showers will nonetheless be possible in some of these areas, although precipitation does not appear very significant at the current time. In some areas in the Interior, warming could be notable once the warm front moves through, especially where postfrontal warming can combine with downsloping off the Alaska Range. Some areas could thus see highs in the 40s or even low 50s.

Coastal Hazard Potential Days 3 and 4...None

AFG WATCHES / WARNINGS / ADVISORIES

AK...Wind Advisory for AKZ849. Winter Storm Warning for AKZ829-830-850-852. Winter Weather Advisory for AKZ820-821-832-834-838-842-843-846- 848. Winter Storm Warning for AKZ824>826. Blizzard Warning for AKZ827. PK...Brisk Wind Advisory for PKZ803. Brisk Wind Advisory for PKZ804. Brisk Wind Advisory for PKZ805. Brisk Wind Advisory for PKZ806-807-810-811-856-857. Brisk Wind Advisory for PKZ812. Gale Warning for PKZ816. Heavy Freezing Spray Warning for PKZ816. Gale Warning for PKZ817. Gale Warning for PKZ850-853. Brisk Wind Advisory for PKZ852.