Sunday, January 8, 2017

Severe Cold Spell Possible

For those hardy residents of Alaska's interior who enjoy the occasional spell of intensely cold winter weather, and who have felt that the warmth of recent years has been over the top, the latest forecast indications may be welcome.  Others will feel less enthusiastic.  Recent forecasts have been coming into agreement with expectations for a period of very cold weather later this month, and there's a chance the cold may be extreme and prolonged.  Here are the 500mb height anomaly forecasts from 3 leading models for 7-10 days from now (click to enlarge): notice the extremely pronounced trough over Alaska and the good agreement between the models.


Here are the CPC's latest 6-10 and 8-14 day forecasts, emphasizing the likelihood of unusual cold over southwestern portions of the interior in particular:



And here are a few words from Rick Thoman (note this is personal opinion, not official NWS guidance):

"Models having been pointing this way for some days, and now we have increasing agreement on the potential for a period of prolonged deep cold Jan 15-21 or so. The basic forecast pattern has similarities to portions of the 1989 and 1999 cold events. The devil is in the details (of course), especially east of 150W, where there is potential for clouds and snow to wrap around from the GoA, and so keep surface temps higher (just as we saw in the 1999 event).

North of the Alaska Range there is a plausible potential for multiple days with 850mb temps lower than -35C and surface temps lower than -60F, which in the past has resulted in some of the commuter airlines (and Everett's) shutting down service to rural communities."

For reference, here's a chart of the mean 500mb height anomaly during January 20-30, 1989, when extraordinarily cold conditions affected the interior.  It's hard to imagine, but the temperature in Bettles dropped below -60°F on 9 out of the 11 days in this period, including -69°F on January 26.  Fairbanks reached "only" -51°F but had many days that stayed at or below -40°.


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9 comments:

  1. NL7YJanuary 8, 2017 at 10:57 PM

    Thanks for the warning, and yes I've seen this forecast from other sources. The only enthusiasm I can suggest is from those that live in the hills above the potential inversion. The rest of us will adapt and endure.

    Gary

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  2. Eric LundellJanuary 9, 2017 at 5:18 PM

    Richard, you are famous again.

    http://www.newsminer.com/news/alaska_news/interior-alaska-forecast-calls-for-severe-cold--below-zero/article_d2f0b4e8-d6c6-11e6-afa7-33042cb0cf6e.html

    ReplyDelete
  3. NL7YJanuary 9, 2017 at 5:33 PM

    There was a time when you could tell how cold it was by the number of road snakes...rubber fan belts that decided to quit their day job onboard vehicles and head for warmer climates. That and how far ahead the street lights could be seen are good indicators in the ice fog.

    Gary

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  4. RickJanuary 10, 2017 at 5:44 AM

    An critical factor will be the presence or absence of clouds (not just power plant effluent) and flurries. Fairbanksians may recall in the 1999 event we were spared several days of extreme cold but were treated to light snow & 30 to 40 below.

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  5. NL7YJanuary 10, 2017 at 10:54 AM

    With 850 mb temps forecast to be -30 or below there's not a lot of room for variance in cold at the surface. Sure low spots not exposed to wind can collect cold especially along river drainages or in pockets in terrain. And the inversion layer might be thicker than usual adding to cold depth and air pollution.

    I wonder how much cloud cover can affect surface temps versus clear under the forecast conditions? How many degrees of cold might some be spared?

    Gary

    ReplyDelete
    Replies
    1. Richard JamesJanuary 10, 2017 at 1:42 PM

      Gary, interesting question - I see no fundamental reason why cloud cover would affect surface temperatures less when it's cold aloft - but deep cold is associated with upper-level troughs that tend to produce more cloud cover and thus less inversion. High pressure is clear and calm, thus favorable for strong inversions, but also tends to be warm aloft.

      Some careful historical analysis might be able to illustrate these differences.

      Delete
    2. RickJanuary 10, 2017 at 8:10 PM

      Here's a quick example of the diff between clouds and clear from the 1999 event with little change in airmass:

      Feb 02, 1999 3am, light snow, sfc temp -34.5C, temp at ~285m AGL -37.5C

      Feb 05, 1999, 3am clear, ice fog, sfc temp -46.7C, temp at ~285m AGL -37.5C

      Delete
    3. NL7YJanuary 10, 2017 at 8:35 PM

      Thanks Rick for the reference...looks like potentially ~22F colder under clear skies during those conditions. So yes -50's F is a potential but perhaps the forecast I linked below will prove correct and upper air moisture will offer some clouds in some areas.

      Another good NWS comment source I forgot to mention:

      https://twitter.com/NWSFairbanks

      Gary

      Delete
  6. NL7YJanuary 10, 2017 at 7:43 PM

    The NWS is again doing an excellent job of providing forecast analyses for the near future's predicted cold event. Gives affected folks time to prepare if they choose:

    http://forecast.weather.gov/product.php?site=CRH&product=PMD&issuedby=AK

    http://forecast.weather.gov/product.php?site=CRH&product=AFD&issuedby=AFG

    Gary

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