The past few days have seen a prolonged episode of hefty wind chill at Howard Pass: at or below -60°F since Friday evening, or nearly 120 hours.
Temperatures have hovered in the range -22°F to -32°F, with sustained winds of about 30-45 mph. Howard Pass has seen much worse in the past (search the blog archives), but this episode is actually the longest on record with wind chill remaining continuously at or below -60°F. The previous record was 105 hours in February 2013, the first winter we have data for. Also, late November 2021 saw 10 straight days with an average wind chill below -60°F, but with higher daily maximum values. [But note that the Howard Pass instrumentation was knocked out by severe conditions in a couple of winters, so there may have been more prolonged episodes that weren't recorded.]
[Update March 14: the wind chill finally rose above -60°F at 1pm today, so the new record is 136 hours.]
As in every other case of severe wind chill at Howard Pass, the wind has been continuously out of the north-northeast, i.e. perpendicular to the mountain range. The second graphic below shows the location:
Actual temperatures on the North Slope have been very cold: -40s for overnight minimum temperatures in many locations since Sunday, and even below -50°F at the Umiat HADS site (the Umiat RAWS isn't reporting). The Deadhorse ASOS reported -46°F on the 11th, which ties the coldest so late in the season since 2012 (when it was -49°F on March 16th).
The MSLP analysis from Sunday morning shows a very typical setup for North Slope cold and Howard Pass wind chill: high pressure draped across the Arctic coast, and a significant (but not extreme) north-south pressure gradient across state. The bunched isobars across the Brooks Range (to the north of Bettles, circled) highlight the potential for strong winds in the mountains. Click to enlarge:
Visiting Coeur d'alene Idaho right now to warm up. Mondo ridge brewing on the west coast. Should make its influence known in Eastern Alaska in a few days. I.E warmer weather! Mike
ReplyDeleteWhat's a mondo ridge?
DeleteHave a good trip!
My term for a relatively intense high pressure system. Mike
DeleteThanks for the post Richard! We're having a good run with the wind sensor - hope it continues. Pam NPS
ReplyDeleteHi Pam, you sure are - if I'm not mistaken this is 4 complete winters without lengthy downtime, well done!
DeleteSoon (in a couple days) we will have 12 hrs of daylight in Fairbanks. Despite the cold and winds noted here north, and as typically prior to September 20th, it'll soon warm into Spring. The Sun is regaining strength.
DeleteHoward Pass 3/17/24 ~-36F/wind gust ~75mph. Nothing alive and standing for miles.
DeleteIs low elevation alone what makes Howard Pass have so much lower windchill values than Atigun? Also that large, relatively flat spot in the Noatak Preserve has must have some very cold temperatures; any climate data from that Area?
ReplyDeleteYes, it's certainly very cold in the upland Noatak River valley, but being a broad valley location that would generally require clear and calm conditions with a strong inversion. High winds would normally mix out the inversion.
DeleteThe reason Howard Pass is so bad is that the surface-based cold air from the North Slope gets squeezed through the gap, with a very effective vertical cap from the surface-based inversion. It's a funnel effect in both the vertical and horizontal, unlike winds at a typical mountain location. Higher elevation locations are above the inversion and therefore warmer AND less windy in these "cold North Slope" events.
The valley through which the air blows is relatively free from the typical terrain-induced mechanical turbulence/mixing found elsewhere. "Relative" means compared with other passes in the Brooks Range that include frequent turns and steep sides that can narrow the passage. As Richard notes the flow of cold dense air can be capped by warmer air above. To the south lies the main Noatak valley that opens broadly in several directions, which can offer low resistance to the north->south flow.
DeleteAs a parallel example or analogy, look up "fish ladder" for an example of the potential effects of turbulence or mixing of flow for a fluid. Those ladders are similar to narrow non-linear mountain valleys from my observation of both.
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