Saturday, April 21, 2018

Cold Spring Day

Yesterday was a very chilly day for the time of year across interior Alaska, with breezy below-freezing conditions all day in most areas north of the Tanana and lower Yukon rivers.  Temperatures struggled to reach 20°F in the Yukon Flats despite plenty of sunshine, and Fairbanks only made it to 31°F.

The last time the daily high temperature was below freezing this late in the season in Fairbanks was during the record cold April of 2013 - you can read all about that in the blog archives here (Rick Thoman was the author then).  Prior to that it had been more than 10 years since a sub-freezing day in late April (2002).

The winds did not go calm last night, but temperatures dropped off sharply nonetheless, and on the North Slope this morning's temperatures were, well, Arctic.  Umiat made it to an impressive -27°F with still a light breeze this morning.  This is cold even by Umiat standards; in the combined history of data from Umiat sites, only 4 years were this cold so late in the season (but 1984 takes the cake, with -43°F on April 23).

Here are 24-hour low temperatures as of 5pm AKDT today:



To add insult to injury yesterday, a couple of inches of snow fell in parts of Fairbanks in the evening.  The airport's total of 1.8" was the most to fall this late in the spring since - you guessed it - 2013.  A 5-year return period is very consistent with the long term history for this kind of event, although there have been occasions with 6" or more at this late date or even into May.

The scene down on the Tanana River at Nenana was not encouraging for those with money on a very early breakup, and this morning looked less than spring-like at UAF:





The culprit for the renewed bout of winter was a sharp upper-level trough extending southwest from a cold low that dropped south to near Canada's northwest coast a couple of days earlier.


6 comments:

  1. One interesting and added bonus to the snowy weather last eve in Fairbanks was the dirt that got deposited during the event. All our vehicles (one had a fresh bath yesterday before) and most of the others seen today had a fine layer of loess on the hoods and windshields. There's road debris but this was an overall covering. Somewhere there was a source and it must have been breezy to lift that much airborne.

    Gary

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  2. Following on the observation above, are there any stations that routinely measure non-water precipitation (dust, volcanic ash, fire ash, etc.)? Besides road dust, I’d guess most of our “dust” comes off the Tanana sediments, but I wonder if some comes off rivers to the south. Do we have much dust fall in Fairbanks?

    Bill

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    1. Interesting observation, Gary - given that the wind was out of the northeast, suggesting the source was not from the Tanana valley.

      Bill - I'm not aware of any large-scale observing networks for dust etc but there may well be some. Historically the answer is certainly yes, there has been a lot of eolian deposition in the Fairbanks area over time; it is evident in the landforms at Creamers Field, for instance.

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  3. I recall watching the Pedro Dome Radar images for late afternoon into early evening 4/20/18 as the snow developed over the Fairbanks area. The precipitation returns showed flow from the south/southeast generally sourced in the direction of Healy or the Alaska Range east of that location, not northeast. The surface winds were northeast at the surface and the snow we experienced came with the winds. Somewhere there was a mixing of the two components.

    The loess that remained after the snow melted 4/21 may have been from vegetation that captured it over winter during various eolian events...or there was a source of exposed soils in the path of the wind. ???

    Gary

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  4. You're right, Gary. The Fairbanks sounding at 4pm revealed flow from north of east up to 3800' AGL, then veering to southerly by about 5500', then southwesterly above that. So a source region in or near the Alaska Range can't be ruled out.

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  5. Now we're due late this evening on for a warm Chinook and high winds in the Alaska Range. SW flow and shortwaves for the remainder of the week.

    We may lack the local precipitation to efficiently capture any further eolian loess so generated and carry it to the surface...but I'll note if it reappears. Just washed my black car, so we're probably going to see some again.

    My years living in Delta Junction ("where the wind never blows") made dust events a daily occurrence in the Spring. But for Fairbanks it's not all that common.

    Gary

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