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.