Monday, October 19, 2015

Freezing Rain

Rain has been reported on each of the last 4 days in Fairbanks, with an occasional bit of snow mixed in.  Temperatures were hovering near freezing this morning, leading to icy conditions and provoking a winter storm warning from the National Weather Service.

As one might expect, freezing rain or rain at temperatures close to freezing is rather common at this time of year in Fairbanks, although it requires an unusually warm airmass aloft.  This morning's sounding from Fairbanks (shown below) revealed above-freezing temperatures from about 2000-4500 feet elevation, but sub-freezing conditions existed closer to the ground.  This means that rain falling out of the warm cloud layer aloft was chilled to or below freezing before reaching the ground, and so ice formed readily on ground-level surfaces in locations where the air was at or below freezing.

The history of hourly observations since 1950 (see chart below) shows that October has the highest frequency of freezing or near-freezing rain, with the phenomenon occurring in nearly 40% of all years.  The frequency peaks in mid-October, so today's event is right on schedule for this kind of thing.

The chart below shows that the distribution of October cold rain events has been fairly even through the years, although today's event is the first since 2006.  It seems freezing rain has taken a preference for deep winter in recent years.


  1. All this precip led to a rolling fog event last evening. The sky cleared some and I suspect radiation fog developed and moved northward over the Tanana Valley and eventually Fairbanks.

    It could be seen developing and moving from the Borough camera north of town. We went from a reported 10 miles visibility to 0.25 from 15:53 to 16:53 AKDT. The relative humidity went from the 70's to mid-90's at the same time.


    1. I wonder how frequently fog condx are experienced in October for Interior Alaska? We're socked in again tonight in Fairbanks.


    2. Gary,

      Looking at the hourly data, it appears that fog is reported with visibility at or below 0.5 miles on about 7% of October days. This frequency is somewhat higher than in August and September, but not as high as in January, when ice fog develops. It used to be that fog was much more common throughout the winter (Dec-Feb) than in October, but since 2000 only January has topped October.

      Here's an earlier discussion of visibility and temperature trends.

  2. Rain is always a beautiful and fantastic to enjoy but it can be a curse when such freezing weather comes. Application designing