Sunday, August 26, 2018

Wet and Westerly August

As more rain moves across the interior today, adding to the moisture tally in this very wet August, it's interesting to note that it has been nearly a decade since Fairbanks saw an August that was both wet and notably wetter than July.  As we noted last year, July has become considerably wetter than August in recent years, mostly because of an increase in frequency of the heaviest rain events in July.

Here's another look at the big picture based on 20-year running means of the July and August precipitation totals; in the past 20 years, July has become as wet as August used to be in the 1930s and 1940s.  (Click to enlarge the image.)


But this year is bucking the trend, as July produced only 1.01" of rain in Fairbanks, but August is above 3.5" and climbing; this will be one of the wetter Augusts on record in Fairbanks.  Also of note is that Fairbanks saw a daily total of 1" earlier this month, and this hasn't happened in August since 1990; whereas July has produced 8 such days since 2003.

A couple of weeks ago I discussed the connection between August rains and strengthening westerly flow aloft at this time of year, and as if to reinforce that message, the speed of the westerly flow above Fairbanks this month has been close to a record.


Moreover, it turns out that the very heavy rains of August 5-6 were associated with the strongest westerly flow on record for so early in the autumn, as measured by Fairbanks balloon soundings.  The sounding below had a mean westerly wind component of 65 knots, or hurricane force, based on the values at 850, 700, 500, and 300 mb.


The view of the sky from the UAF webcam back on August 5th looked - to me - decidedly maritime, which might reflect the fact that the air aloft was making the trip from the Bering Sea to Fairbanks in a matter of 6 hours or less.



The previous record for strongest westerly flow before August 15 was on August 12, 1967, and Fairbanksans will know that date: it was the single wettest day in Fairbanks history, and the flooding was catastrophic.  Here's Rick Thoman's 50th anniversary blog post about it last year: https://ak-wx.blogspot.com/2017/08/the-fairbanks-flood-of-1967-rainfall.html

6 comments:

  1. The underground water table around Fairbanks is high and nearby rivers as well. They even closed one of the paved runways at Fairbanks International due to surface damage - but not the main one used by big rigs.

    The smaller more easterly runway began to show cracks and fissures at its southerly end. It's built over what were previous side river channels now constrained by the nearby flood control project.

    Zoom in for a look at the tar filled runway cracks from an earlier time at lower water levels:

    https://www.google.com/maps/@64.7824845,-147.8648569,2500a,35y,38.82t/data=!3m1!1e3

    Gary

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    1. Interesting, Gary. The north end certainly looks to be in better shape in the Google view. Sounds like a challenging project for the hydrological engineers.

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    2. Note the nearby access roads surrounding the airport show comparatively few signs of weathering or sub-surface disturbance. The closed runway has always had a surface discontinuity or dip over the old river channel that was filled to create the airstrip. Nature never sleeps.

      Gary

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  2. The city of Anchorage has also experienced a wetter then normal August this year. Given the forecast, Fairbanks could end up with more total precipitation in August then Anchorage. One good outcome to all of this moisture has been the ample wild raspberries in Southcentral this year.

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    1. Looks like it's the third year in a row to have a wet August in Anchorage.

      I'm surprised to see that Fairbanks is wetter than Anchorage about a third of the time in August; but of course Anchorage is nearly always wetter in September.

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