Juneau saw six hours of freezing rain yesterday morning, with the ASOS instrumentation suggesting that ice accretion may have reached 0.2", and then Haines suffered significant icing today. Hourly data from Haines shows freezing rain for about seven hours, and the ASOS algorithm indicated ice accretion of 0.3". The National Weather Service relayed reports of as much as 0.5" of ice, and they issued an Ice Storm Warning - apparently the first ever to be issued by the Juneau NWS office.
Freezing rain isn't particularly unusual for communities in the northern Southeast, of course, because the ingredients are quite easy to come by: cold low-level air drawn from the frigid interior, and warm air aloft from the Pacific. Haines ASOS data since 1996 indicates that freezing rain is reported at least once in just about every winter, and it's not uncommon to have a half-dozen days or more with freezing rain: for example, the winters of 2018-19, 2022-23, and 2023-24.
However, the data also suggests freezing rain isn't typically prolonged in Haines, as warm Pacific air usually wins out rather quickly. The hourly Haines data indicates that the record for consecutive hours with freezing rain is 9 hours - only a little more than today's event - and that occurred in December 2019. The NWS discussion highlighted the unusual nature of the current storm: "In fact, more freezing rain has been observed during this one event than some of the staff here at the office have seen over the past 18 years."
As is typically the case, the freezing rain eventually changed to plain rain for both Juneau and Haines, as temperatures rose above freezing. This is the normal course of events, as warm air typically erodes and displaces the surface-based cold air, at least in a coastal setting like Southeast Alaska. Here's the NWS graphic for how precipitation type depends on the vertical temperature profile:
Thanks for the write-up, Richard.
ReplyDeleteAs I was in Juneau when the heavy snow started (following some pretty serious cold [for Juneau] and Taku winds) and made my way north in time for some of the freezing rain in Haines, I can offer a boots on the ground assessment. My wife and I reported for Haines #2 coop 0.15 inches glaze Tuesday morning then 0.2 inches Wednesday. Roughly 8 hrs of freezing rain were reported at PAHN and it went on a little longer here (a little over a mile E of the ASOS).
It was definitely an unusual high amount of freezing rain, but it pales compared to just last December 30th. Then I reported 0.4 inches accretion and the ASOS reported about 14 hrs of freezing precip. It may not sound like a big difference (0.35 vs 0.4") but the effects were way more serious last year, with many trees down or bent way over around town. So my measurements/estimates are not to be taken as exact.
After last year's event I said at least to myself "that's the worst icing I've seen in my 17 years here." I'll have to dig back at some of the other years you mentioned to make sure my memory is not missing something also.
Thanks for the report, Jim. I was hoping you would chime in.
DeleteThanks for pointing out the event last December. My quick search missed it because the ASOS had one hour with plain rain in the middle, so that broke the "consecutive hours" algorithm. Apparently the ASOS temps were also slightly above freezing for most of the event (despite reporting FZRA), but no doubt it was colder at your place.
Here are some PAHN events that look like they may have been significant, based on duration:
Nov 17, 2018
Dec 8, 2019
Dec 6, 2020
Nov 20, 2022
Dec 7, 2022
Dec 26, 2022 (temps in the low 20s)
It sure seems like there has been an uptick in frequency of freezing rain there since 2022.