For the winter of 2012-2013, it was the 4th calendar day where the Anchorage International Airport reported freezing rain. The seasonal average is 6 days. The chart immediately below shows the count by season for the last 18 winters.
In looking at the events over the previous 18 winters (that's how far back the easily obtainable hourly observation go back via the NCDC website), the coldest that freezing rain (actually freezing drizzle) was observed was 15°F on 3/5/2012 (at 3 p.m.). Conveniently, this is the exact time of an upper air sounding. The chart below shows the sounding at the time of that observation as well as last Friday's event sounding. Interestingly, the 2012 sounding it is very similar to the Fairbanks sounding from their freezing rain event last week. The chart below shows the sounding from Friday's freezing rain event in Anchorage and the one on 3/5/12. The 2012 profile looks eerily similar to the Fairbanks sounding from 11/13/13. Fortunately the 2012 event in Anchorage produced very little in the way of accumulations and the associated travel difficulties.
How difficult would it be to fish out other freezing rain soundings and compare them? And then compare to non-freezing rain profiles?ReplyDelete
Eric, I updated the chart at the end of the post to include the Anchorage RAOBs from 3/5/12 and 11/22/13. The temperature profile from last week has the classic appearance of a freezing rain (or sleet) event. That is, the temperature at the surface is below freezing and a wedge of above freezing air exists fairly close to the surface. Last Friday's profile showed above freezing temperatures between 1,000' and 5,000' (approximately). Usually when the entire atmospheric profile is below freezing, all you get is snow. However, in unusual circumstances, you can still have liquid precipitation.Delete