Monthly Archives: September 2012

Welcome to Alaska, Baroclinic Style.

First, the weather in Alaska is different, very different. Everything you thought you had a decent grasp on is out the window; you are starting from scratch as a forecaster. Synoptic/marine storms take on a completely different structure than their land based relatives, and you are truly forecasting in a relatively data void region. Entire surface lows can form and exist in regions of the Bering Sea completely in-between all available marine observations (buoy, ship observations, C-MAN stations, etc.). Old school forecasting techniques such as advanced satellite analysis, advanced synoptic analysis, and pattern recognition are stressed to the maximum. The Bering Sea/North Pacific is the perfect breeding ground for spectacular synoptic scale cyclones amplifying on both extreme baroclinic energy (polar air mass proximity) and latent energy originating from the subtropics. 940 lows are common; 930 lows are not rare.

971 hpa low forming west of the Aleutian chain. The aftermath, for Anchorage, was the first substantial windstorm of the fall, resulting in substantial damage and widespread power outages across the area:



Second, Alaska terrain is incredibly complex. Glacier carved mountain terrain ranging from 4000 feet to 16,000 feet surround Anchorage and much of the other populated regions of Alaska.

Google Earth view looking into Valdez from Prince William Sound. In the background, on the left, is the 16,000 shield volcano, Mt. Sanford, which dominates the local terrain:


Complex terrain, defined:


Local pressure gradients, complex terrain flows, barrier jets, gap accelerations/winds, mountain wave dynamics, etc. dominate the local weather patterns, and they are innately intertwined with the track, position, intensity, and deepening/weakening rate of the synoptic scale cyclone. Small errors in the synoptic forecast can result in the difference between a major downslope windstorm or a minor wind event.

Instead of writing excessively about synoptic storm dynamics (or trying to, atleast), for once, I am going to sit back and enjoy the first (actually, second, see the above images) true rapid cyclone event since I arrived in Anchorage. Like all significant cyclones, it is a multi-faceted event ranging from 100+ MPH winds across the mountains and Turnagain Arm, storm force winds across the marine forecast zone in the Bering Sea and North Pacific, and heavy flooding rains across the coastal ranges..

NWS Anchorage weather headline for this weekend event:


15 Sep 00z NAM 4 km Hi Res 500 hpa:

15 Sep 00z ECMWF 39 hr simulation depicting a powerful 972 hpa bent-back occlusion.


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