Dry cold, wet cold? no.
Winter cold and summer cold? no. Bitterly cold vs extremely cold? no. Calm vs windy cold? close.
All these would make good blog subjects, but what I’m thinking about today is domestic cold vs imported cold. Seriously.
I have a good recent example.
Although several coastal areas were in on this latest dramatic weather scene, let’s pick on Skagway again, since the scene was most dramatic there. Continuing a few days of warm weather, with winds mostly southerly and light to moderate in strength, Saturday, Jan 26th turned up the volume a bit: south winds around 25 kts (45 km/hr) and temperature reaching 42F (5.6C). Up until noon anyway. That is when the cold air train arrived from the interior. Winds switched to the north, blew almost immediately around 25 kts again, but with gusts up to 48 kts (89 km/hr), and the temperature started a steep decline, losing 10 degrees in the first hour and 30 Fahrenheit degrees in less than 12. Here’s a graphic:
Here’s some more detail from the ASOS observations. The time column is in AST (the time in the remarks however is in UTC.) Only selected columns and remarks are shown.
day time clouds vis wx tm dp wnd pres 26 0953 FEW032 BKN055 OVC070 10 40 32 21030G35 935 26 1053 FEW037 BKN050 OVC070 10 40 32 21029G36 934 26 1153 BKN055 OVC070 10 40 32 21026G36 935 26 1253 FEW042 OVC055 10 S- 30 20 05020G37 938 26 1308 FEW042 OVC055 6 S- 28 18 04032G48 934 WSHFT 2148 26 1353 OVC060 8 S- 25 14 05020G35 942 PRESRR 26 1453 FEW029 OVC050 9 S- 23 8 04021G36 947 26 1548 BKN027 BKN034 OVC048 6 S- 19 9 04022G36 950
That is imported cold. Quick and unmerciful. Much worse than locally made cold due to the sudden onset and the wind. By the time the Yukon Express had run its course, Skagwegians were dealing with temperatures down to -5F (-21C) and wind chills around -30F (-34C). Sure, the actual temperature was somewhat colder than that in the interior, but most people would probably take it over the days of relentless wind. And there is no daytime warming at this time of year like folks down south are used to.
Why can imported cold come on so quickly?
Because “making cold” takes time. But replacing the air on hand with colder air can happen very quickly.
Local cold involves cooling the air that is already in place. Although this happens everywhere at certain times, the polar regions lose heat to space for a living. It’s a good analogy since the heat loss of the polar regions plays a big part in the earth’s heat economy, the transactions of which creates what we experience as the weather.
Cold cannot be created, but you can consider these polar regions as where cold air masses are created. These areas are called air mass source regions. The term polar is not used here in a strict sense (i.e., poleward of the arctic and antarctic circles), but includes areas that fit the description of world-class heat wasters. Polar oceans lose heat pretty much year round, while large land masses such as Siberia, Canada and Alaska lose it in the winter but gain in the summer (Antarctica is a different case since it is almost completely glaciated, and right over the pole, whereas arctic land masses are a little closer to the equator).
The interior of Alaska is one such cold air mass source region, and cold is considered a natural resource there. Auto manufacturers bring their cars up to see how (if) they function at 40 below or colder. There are several research labs with the word “cold” in their titles. There are ice and snow sculpture competitions and festivals. But Southeast Alaska and other coastal locations are not source regions for cold or warmth. We are receiving regions (I just made that term up). When the severe cold of the interior is pushed (or pulled) down over the panhandle we get a blast of imported cold.
Here’s the surface map (from early Monday morning, the cold air still flowing through the passes) showing the high pushing from the interior, the low pulling from the Pacific and the tight gradient over the northern panhandle.
Skagway, for all its charms and beauties, is right in the raceway between the interior with its cold, dry air, and the ocean with its warm, moist air. There is precious little in-between weather. This SE cold receiving region is most harsh at Skagway, a bit less so for Haines, and less and less so as you move south and west (away from the continent). Sitka and Ketchikan really are in the banana belt. The northern fjords and some more southerly but inner channels (e.g. Hyder) hardly fit the mild stereotype of the rest. They are colder and snowier in winter and warmer and sunnier in summer, and dryer year-round. And they are first in line when the cold air freight train comes down the mountains with no brakes.
