With high pressure over the Arctic Ocean continuing to funnel very cold air into northern Alaska, surface conditions have become downright frigid across the interior and eastern North Slope, with widespread -40s and some -50s today. Umiat reached -55°F this morning according to the RAWS instrument, and saw a high of only -47°F this afternoon.
But at least there's no significant wind in Umiat. From Deadhorse all the way across to the Canadian coast, wind chill values are -70°F or lower, with stiff offshore breezes creating seriously nasty conditions.
The lowest temperatures occurred in the sheltered valleys of the interior North Slope to the south and southwest of Umiat; satellite measurements suggest some spots may have dropped below -65°F. Here's a satellite-observed temperature map courtesy of Twitter user wrighthydromet (click to enlarge).
Our favorite wind chill site, Howard Pass, also had a very extreme episode of wind chill yesterday, with sustained winds over 50mph in conjunction with temperatures below -40°F. This is the first time in 7 years that the Howard Pass thermometer has dropped below -40°F, although missing data is an issue.
Back in December I looked at the strong inverse relationship between wind and temperature at Howard Pass. Remarkably, -40°F or lower has only ever occurred with a wind speed of 37mph or higher, and the median wind is 48mph at such low temperatures. The chart below zooms in on the low-temperature portion of the hourly distribution of temperature and wind.
It's interesting to observe that while yesterday's cold blast was a typical wind chill episode at Howard Pass, the temperature didn't recover much last night as the winds quickly died down to almost nothing. Consequently, today's temperatures were easily the coldest on record for low wind speeds; this morning it was a full 10°F colder than previously observed at Howard Pass with a wind speed below 5mph. This illustrates the intensity of the cold air mass over northern Alaska.
Here's a surface analysis chart for 3am yesterday; notice the very strong pressure gradient over northwestern Alaska, an obvious prerequisite for these extreme wind chill episodes.
Brr... The inverse relationship with wind and temperature you mentioned is one we see here in northern and eastern SE such as Skagway and Juneau with the strong outflow and Taku winds at those places bringing in the frigid air. I often think when that air is in place then the wind drops the temp will drop rapidly, but it does not usually work like that at those 2 places. Partly because the wind rarely stops until another weather pattern is about to displace the cold air. Here in Haines the wind does sometimes calm down during these cold outflow periods but the temperature does not drop like I expect nor necessarily rise when the wind picks up. I guess we can't get much of a surface cold pool going. It's just cold period.
ReplyDeletePS check this for typo: This is the first time in 7 years that the Howard Pass thermometer has dropped below -40°F, although missing data is an issue.
That's interesting, Jim - thanks for pointing out the similar wind/temperature behavior in parts of SE.
DeletePerhaps the cold outflow itself involves/creates a strong inversion, so when winds die off it doesn't make much difference. But I agree, rather surprising.
If you're referring to "7 years", I think it's correct as far as the data goes: last -40F was in Feb 2014. (There was a -39.8F on Jan 10, 2019.)