Saturday, January 20, 2018

Freezing Rain

Freezing rain created a fair bit of disruption in the Fairbanks area this week, with an initial round of light rain for a couple of hours on Monday morning followed by much more persistent and significant rainfall on Tuesday evening and overnight into Wednesday.  A very substantial snowfall also occurred, and the liquid-equivalent precipitation total was well over half an inch; this was the wettest January storm in 18 years.  There was also enough wind to produce Fairbanks' first ASOS report of "blowing snow" this winter - not a common occurrence in the sheltered Fairbanks bowl.

Here's the surface analysis from early Wednesday morning, courtesy of Environment Canada; a trough axis and low pressure center are indicated very close to Fairbanks.  The Fairbanks sounding from the same time is also shown below - note the strong southwest flow throughout the troposphere and the high precipitable water (total moisture content) of 1.22 cm.



In view of this rather significant freezing rain event, it's interesting to look back at the long-term history of similar conditions in Fairbanks winters.  The chart below shows the percentage of hourly observations in Fairbanks with either drizzle or rain reported at the top of the hour, for winters back to 1950-51  (thanks to Rick Thoman for the idea for this chart).


There has certainly been an uptick of winter rain and drizzle events in recent years, but the 1960s saw a couple of remarkable winters with a lot of freezing precipitation.  In particular, January 1963 stands out as highly anomalous; here's how it unfolded:

- freezing drizzle for 19 hours beginning at 9am on the 14th
- 6 hours of freezing rain on the evening of the 15th
- 4 more hours of freezing rain on the evening of the 16th
- freezing rain throughout the first half of the 19th, ending as plain rain in the afternoon when temperatures rose above freezing
- the afternoon sounding on the 19th recorded the highest precipitable water on record for the month of January in Fairbanks (1.66 cm)
- more plain rain on the morning of the 20th
- intermittent freezing drizzle and a bit of freezing rain on the 25th and 26th
- a few more hours of freezing drizzle late on the 29th and overnight Jan 30-31

Road conditions must have been somewhere between treacherous and impossible by the end of that month.  A quick look at the 500mb height map for January 1963 (below) shows an interesting dipole pattern, with much above-normal heights near and south of Alaska and also near Iceland.  The Arctic Oscillation was strongly negative, indicating a weak circumpolar flow that allowed cold air to spill south and, conversely, warm air to surge north.  Consequently it was a very cold month in the lower 48, and Europe was extremely cold; England had its coldest calendar month of the entire 20th century.  In some ways the topsy turvy pattern resembles recent conditions: both winters (1963 and 2018) produced headline-making cold at lower latitudes but exceptional warmth in Alaska and the Arctic.



2 comments:

  1. I usually avoid believing these tabloids but here's some info on current cold affecting Britain:

    https://www.thesun.co.uk/news/5386542/britain-braced-arctic-12c-winter-snow-uk/

    Meanwhile it was close to -30F again in Fairbanks under clearing skies.

    Gary

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  2. I forgot to mention that Rick T deserves credit for the idea behind the chart (percentage of hourly observations)... I've corrected this in the text.

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