textproduct: Fairbanks

SYNOPSIS

Well below normal temperatures for early March continue across all of Northern Alaska this week, with a brief reprieve coming this weekend. Despite daily lows in the -30s and -40s, the increasing sun angle is allowing for temperatures to quickly rise each afternoon to the single digits above and below zero. Expect this same diurnal pattern to continue at least until Thursday before the next weather system approaches from the southwest bringing light snow chances to the Interior and Alaska Range. Main focus for today's discussion will revolve around the interesting set up for Friday and Saturday's winter storm and the forecast uncertainties that still remain. Light snow accumulations are looking likely for portions of the Central and Eastern Interior, including Fairbanks, with highest totals in the Alaska range and White Mountains. Low confidence still exists in how much downsloping may occur which could greatly impact snowfall forecasts for those areas just to the north of the Alaska range. Higher confidence exists in the extended forecast going into next week as reinforcing shots of arctic air keep temperatures well below normal with additional chances for late season -40F lows.

KEY WEATHER MESSAGES

Central and Eastern Interior...

- Daytime highs moderate into the single digits below and above zero due to the increasing sun angles and sufficient daytime heating.

- A brief round of light snow today for the Upper Tanana Valley and Fortymile Country today, minor accumulations possible.

- Another chance for accumulating snowfall for most of the southeast Interior and Alaska Range Friday and Saturday. Winter Storm Watch for heavy snow has been issued for the Eastern Alaska Range south of Trims Camp early Friday morning through Saturday.

West Coast and Western Interior...

- Below normal temperatures continue with double digit sub zero lows continuing into early next week.

- Another round of strong northerly winds through the Bering Strait Thursday into the weekend, peaking on Saturday. Blowing snow concerns for coastal communities from Point Hope to the western Seward Peninsula and St Lawrence Island.

North Slope and Brooks Range...

- Below normal temperatures in the double digits below zero continue for the North Slope and Brooks Range.

- Northerly winds increase through the Brooks range this weekend.

- Another multi-day period of near blizzard conditions expected for the NE Arctic Coast Sunday through mid next week

FORECAST ANALYSIS AND DISCUSSION

Little day to day change this week in the overall weather for much of Alaska as surface high pressure and upper troughing overhead have kept a dry and cold airmass in place. Mainly clear skies and the increasing March sun angle have resulted in large diurnal temperature swings with lows each morning in the -20F to -45F range and highs reaching the single digits above and below zero. Coldest spots remain in interior valleys while those at elevation above the surface inversion have been noticeably warmer. Expect this pattern to persist into at least Friday morning before the core of the Arctic airmass shifts into the Northwest quadrant of the state as the next weather system moves in from the southwest.

Focus shifts to the next winter storm expected to impact portions of the Interior and Southern Alaska Friday through the weekend. This is a relatively complex set up leading to lower than normal confidence compared to the past several winter storms in February. The set up involves a persistent upper low over the YK Delta while strong southwesterly flow sets up on over the Gulf, directing numerous systems into the AK Peninsula and South Central Alaska. Ensemble guidance today has honed in on the track of the surface low, with stronger agreement in a track directly over Kodiak Island to the Kenai, then becoming quasi-stationary over South Central Alaska Saturday before quickly weakening and meandering into the Northeast Gulf over the weekend. The mid and upper level low appear to be offset just to the northwest, combining with the existing upper low in the YK Delta and becoming quasi-stationary over the Central Interior and weakening Saturday. Mid level vorticity maps show the frontal boundary on the leading edge of the system pushing north of the Alaska Range by Friday afternoon, then becoming elongated and stationary just south of the brooks range. This frontal boundary will likely be the focus for snow in the interior with heaviest snow expected near the front from Eagle to the White Mountains and toward the Dalton Highway Summits. Thinking Fairbanks and surrounding locations could see a brief period of heavier snow as this frontal boundary pushes through Friday afternoon into Friday evening, before the band shifts northward.

The main area of concern is how much downsloping occurs on the north side of the Alaska range and into the interior. With the direction of the entire system coming from the southwest and likely tracking over and just east of the Alaska Range, downsloping into the interior may be relatively weak and directed more towards the Tanana Valley. There may be a brief period Friday afternoon into Friday evening where the orientation of the mid level low is good for southerly winds over the Alaska range and downsloping. Forecast soundings Friday show a strong easterly jet at and below 700mb associated with the approaching front, while southwest flow above that advects in deep moisture aloft. Both GFS and ECMWF forecast soundings show deep saturation through the column and DGZ to support snow as early as late Friday morning in Fairbanks and surrounding areas. There are signs of subtle mid level downsloping as evident by mid and low level dry air. While it should be snowing north of the Alaska Range and into the Central and Eastern Interior Friday, this drier layer from downsloping should keep snowfall rates and overall accumulations lower. Also watching a strong easterly low level jet on Friday, associated with the incoming front, which may lead to lower snow to liquid rations due to fracturing of snowflakes within the interior.

Overall, the timing of the best forcing for ascent appears to be offset from the time when the best conditions occur for snow in the interior without downsloping. Strongest forcing looks to be during the frontal passage during the day Friday, at the same time there will be some form of downsloping off the Alaska range. This combination leads to overall lighter snow as the strong forcing for ascent and heavier rates aloft battle with mid and low level dry air and subsidence.

By Friday night, the overall system begins to weaken and the low and mid level pressure gradient collapses. This is where downsloping shuts off and deeper saturation through the lower levels occurs, resulting in a brief period of heavier snow with better snow to liquid ratios. At this time, expect snow to be ongoing over the Eastern and Central Interior and also through the Alaska Range. This quasi-stationary system basically sits over top of the region while gradually weakening into Saturday night. The extended period of light to occasionally moderate snow should lead to widespread, yet light accumulations ranging from 4 to 7+ inches within the white mountains to a dusting to under 3 inches for much of the Interior. South and southwest facing slopes of the Alaska Range could see much higher amounts; therefore a Winter Storm Watch is still out for Isabell Pass and Eastern Alaska Range. A Winter Weather Advisory has been issued for the Dalton Highway Summits, Fortymile Country, White Mountains, and High Terrain South of the Yukon River where slightly higher snowfall amounts may occur under the stalled boundary.

Watching winds Friday and Saturday as this system moves in. A strong low level easterly jet develops as the frontal system moves northward into the state. This should lead to windy conditions with gusts of 35-45mph throughout the White Mountains and areas at elevation in the Eastern and Central Interior, leading to blowing snow and lower visibility at times. Expect northerly winds to increase through Brooks Range passes as the northerly pressure gradient tightens north of the front. Strong northerly winds develop through the Bering Strait Thursday and then peak on Saturday with gusts over 50 kts possible at times. Blowing snow and reduced visibility likely for areas right on the coast prone to strong northerly flow. Strong winds nearing Advisory levels are expected to occur within the Tanana Valley including Delta Junction on Friday. Downsloping around Delta Junction may result in the timing of the strongest winds occuring before the main round of snow arrives in the Tanana Valley. As the low level pressure gradient collapses Friday night and downsloping weakens, then Delta Junction and surrounding areas should begin receiving snow.

As mentioned above, there is lower confidence with this forecast as any deviations to the track of the system can significantly impact sensible weather impacts north of the Alaska range due to varying degrees of downsloping and where the best moisture transport and forcing are located. At the moment, expect light snowfall accumulations through the Central and Eastern Interior Friday into Saturday with heavier snow amounts north of Fairbanks in the White Mountains and also along south facing slopes of the Alaska Range.

EXTENDED FORECAST DAYS 4-7

By late Saturday into Sunday, an additional shortwave moves into the Gulf of Alaska and into Southeast Alaska shutting off moisture advection into the Interior and shifting the heaviest precipitation further southeast as well. As the entire system weakens while still overhead, expect snow to gradually become lighter and lighter before dissipating Saturday night.

Behind this system, yet another extended period of well below normal temperatures is expected for the majority of Alaska. Deep troughing sets up over NW Canada while ridging builds over the Bering and Siberia, placing Alaska within a strong northerly flow pattern aloft. This dry and cold pattern should support lows once again in the double digits below zero, possibly nearing -40F again in interior valleys. Will also have to watch for shortwaves riding over the ridge and into the West Coast bringing chances for light snow going into next week. Overall, the main focus will continue to be the cold going into mid March.

Coastal Hazard Potential Days 3 and 4...None

AFG WATCHES/WARNINGS/ADVISORIES

AK...Winter Storm Watch for AKZ850. PK...Brisk Wind Advisory for PKZ806-807-810-811-816-817-854-856-857. Brisk Wind Advisory for PKZ851.