Polar lows are small, somewhat elusive, and usually quite potent…cool stuff for weather watchers. They are small compared to their more common, mid-latitude big brother lows, up to a few hundred miles across, compared to a thousand or more miles across for the later. They are more like the size of hurricanes. For that reason, and because they sometimes look a lot like hurricanes on satellite imagery, and because they do share some structural similarities, they are sometimes called arctic hurricanes. The Bering Sea is a hot spot (sorry for all the puns) for polar lows but certainly not the only area…the North Atlantic is a good place too. A interesting polar low recently tracked across the southern Bering, strongly affecting the Pribilof Islands: St. Paul and St. George, but each of the two in curiously differing ways, as we’ll see. Here’s the Infrared satellite image from 15 UTC (6 am AST) on Jan 3rd. The polar low was still about 200 miles west of the Pribilofs. With most typical low pressure systems, they’d be in the thick of it, but this average-sized polar lows is not yet affecting their weather:
Polar lows often are most impressive on satellite images (many show a more “closed” look than this one) and less so on surface maps due to their size compared to the scale of the typical maps. Here’s the surface maps for 9 hours later ( as usual click for larger version):
You can see the small polar low in the center of the map, between Dutch Harbor and the Pribilof Islands. Note how much larger the lows to its west and east are. Even though this low is almost a far south as the other two, it is within the polar air mass, north of the polar front (the fronts associated with the mid-latitude lows). That’s where polar lows are found and get their name (for a while they were called arctic lows). The lows that form along the polar front (you would think these might be called polar lows but they’re not) depend on the temperature contrast between the cold polar air to the north and a warmer air mass to the south. Polar lows depend on the temperature contrast between the cold polar air coming off continents (Siberia in the case of Bering Sea lows) and the warmth of the water itself. Look at this initialization of the NAM model.
You can see the cold polar air mass as the green (and blue) which has been drawn south by the big low in the North Pacific. Note that this low is well drawn by the model. Five or ten years ago the models would have had a hard time even seeing this low and harder yet forecasting its movement and development. That’s why polar lows have been, over the years, first unknown, then mysterious, then elusive: Their size allows them to slip between surface weather stations in the synoptic network…especially the sparse network over the polar oceans. In recent years better satellite coverage, more ocean buoys, and higher resolution computer models have about erased the “elusive” label…but they are still cool. And we still don’t often get the full ground report from a first-order manned weather station, including upper air balloon soundings, as we did in this case. Here are the surface observation from the St. Paul Island NWS office (the times are in AST):
Site M/A Day Time Sky Conditions VIS Weather Temp DP Wind(kt) Alt RH Chill Peak
PASN AP 03 0702 FEW018 BKN042 OVC070 10 19 16 13010 969 88% 7 PASN AP 03 0731 OVC028 9 S- 21 12 11011 967 68% 9 PASN AA 03 0753 SCT025 BKN030 OVC080 10 P 21 14 13017 966 74% 6 PASN AA 03 0853 FEW018 OVC032 7 S- 21 16 10018 963 81% 5 PASN AP 03 0905 SCT018 OVC027 3 S-BS- 21 18 11018G25 963 88% 5 PASN AP 03 0942 OVC017 2 S-BS- 19 18 11021 962 96% 2 26 PASN AA 03 0953 OVC019 2 1/2 S-BS- 20 17 10023G29 962 88% 2 29 PASN AA 03 1053 FEW015 OVC021 2 S-BS- 20 17 10023 960 88% 2 29 PASN AP 03 1112 SCT016 OVC020 3 S-BS- 19 18 10020 960 96% 2 28 PASN AP 03 1134 FEW014 OVC024 1 1/2 S-BS- 19 18 09024G28 958 96% 1 28 PASN AP 03 1143 FEW014 OVC024 2 1/2 S-BS- 19 18 09022G27 958 96% 1 28 PASN AA 03 1153 FEW020 OVC026 2 1/2 S-BS- 21 17 09022 957 84% 4 28 PASN AP 03 1209 FEW015 OVC022 1 1/2 S-BS- 21 18 09022G29 956 88% 4 29 PASN AA 03 1253 FEW012 OVC019 1 1/2 S-BS- 21 19 09024 954 92% 3 32 PASN AP 03 1304 VV014 3/4 S-BS- 21 18 09023G30 953 88% 4 30 PASN AP 03 1311 VV011 1/4 S-BS 19 19 09025G31 953 100% 0 31 PASN AP 03 1320 VV007 1/4 SBS 19 19 09026G32 952 100% 0 32 PASN AP 03 1338 VV004 1/4 SBS 21 21 08029G35 950 100% 2 35 PASN AA 03 1353 VV004 1/4 SBS 22 21 07028G34 949 96% 3 35 PASN AP 03 1419 VV006 1/4 SBS 21 21 08030G35 947 100% 2 37 PASN AA 03 1453 VV005 1/4 SBS 21 21 07032G41 944 100% 1 44 PASN AP 03 1512 VV004 1/4 SBS 21 21 07031G41 943 100% 1 41 PASN AA 03 1553 VV003 1/4 SBS 20 20 08035G44 942 100% -1 44 PASN AA 03 1653 VV004 1/4 S+BS 20 19 07036G44 941 96% -1 45 PASN AP 03 1700 1/4 S+BS 19 19 07034G45 942 100% -2 45 PASN AA 03 1753 1/4 S+BS 18 18 06034G43 941 100% -4 47 PASN AA 03 1853 1/2 SBS 18 18 05032G42 941 100% -3 44 PASN AA 03 1953 1/4 S+BS 17 17 04032G43 941 100% -4 PASN AA 03 2053 1/4 S+BS 15 14 03035G43 941 96% -8 PASN AA 03 2153 1/2 BS 14 13 941 96% PASN AA 03 2253 1/2 BS 13 12 04031G88 942 96% -10 PASN AP 03 2311 3/4 BS- 12 12 942 100% PASN AP 03 2341 1 BS- 12 12 942 100% PASN AP 03 2351 3/4 BS- 12 10 03033G38 942 91% -12 PASN AA 03 2353 3/4 BS- 13 11 03033G38 943 91% -10 PASN AP 04 0033 VV020 3/4 S-BS- 12 12 03027G38 943 100% -10 47 PASN AP 04 0040 VV005 3/4 S-BS- 12 12 03026G36 943 100% -10 47 PASN AA 04 0053 VV005 1 S-BS- 13 12 03025G34 943 96% -8 47 PASN AP 04 0111 OVC010 3/4 S-BS- 12 12 03026G34 943 100% -10 36 PASN AP 04 0130 VV005 3/4 S-BS- 12 12 03029G33 943 100% -10 36 PASN AP 04 0142 VV005 1 1/4 S-BS- 12 12 03027G31 943 100% -10 36 PASN AA 04 0153 VV005 3/4 S-BS- 13 12 03025G32 943 96% -8 36 PASN AP 04 0204 VV005 1 S-BS- 14 12 03025G32 943 92% -7 32 PASN AP 04 0240 OVC010 1 1/2 BS- 12 10 03025 943 91% -9 32 PASN AA 04 0253 OVC010 1 1/2 BS- 13 11 03025G31 943 91% -8 32 PASN AP 04 0258 OVC005 1 1/4 BS- 12 10 03026G31 943 91% -10 30 PASN AP 04 0314 OVC010 2 S-BS- 12 10 03023 943 91% -9 30 PASN AP 04 0328 OVC010 3 S-BS- 12 10 03023G27 943 91% -9 30 PASN AP 04 0337 OVC010 2 S-BS- 12 10 03020G29 943 91% -7 30 PASN AA 04 0353 OVC010 3 S-BS- 13 10 02023 944 87% -7 PASN AP 04 0402 OVC010 2 1/2 S-BS- 12 9 03020G28 944 87% -7 28 PASN AP 04 0448 OVC010 1 1/2 S-BS- 12 9 01022 945 87% -8 29 PASN AA 04 0453 OVC010 1 1/4 BS- 12 9 01020 945 87% -7 PASN AP 04 0504 OVC012 3 BS- 10 9 01020 945 96% -10
This low brought near blizzard conditions (although the wind met the strict NWS criteria the visibility did not) to St. Paul including sustained winds of 40 mph with gusts as high as 54 mph, snow, blowing snow and wind chills around 10 below F…and quite few hours of the worst of it. The interesting thing is while the winds at St. Paul came up steadily throughout the day on the 3rd, at 50-mile-away-neighbor St. George, the wind initially came up, then from around 2 pm to 11 pm winds were light — even calm much of the time — before returning with similar ferocity as at St Paul. This is because it appears the low center went right over St. George. They were in the eye, if you will…a hurricane sized one. Here are observations for a few hours during that time with St. Paul’s obs (PASN), copied from above, paired with St. George’s (PAPB). Again, times are in standard time:
Site M/A Day Time Sky Conditions VIS Weather Temp DP Wind(kt) Alt RH Chill Peak PASN AA 03 1653 VV004 1/4 S+BS 20 19 07036G44 941 96% -1 45 PAPB AA 03 1653 SCT022 SCT120 10 22 19 00000 938 88% 22 PASN AA 03 1753 1/4 S+BS 18 18 06034G43 941 100% -4 47 PAPB AA 03 1753 BKN055 BKN100 BKN110 10 23 15 00000 937 71% 23 PASN AA 03 1853 1/2 SBS 18 18 05032G42 941 100% -3 44 PAPB AA 03 1853 CLR 10 19 15 08004 935 84% 12 PASN AA 03 1953 1/4 S+BS 17 17 04032G43 941 100% -4 PAPB AA 03 1953 FEW013 SCT019 BKN039 10 21 15 00003 933 77% 21
Imagine a St. George resident calling, at around 7 pm, a friend or relative on St. Paul, where the weather is usually pretty much the same, saying, “What a nice evening. My wife and I just went for a walk. It’s calm, mild and what a beautiful moon out! I thought you might want to do the same.” The friend replies, “What! Did you go to Hawaii? I’m not sure I’d be able to force the door open with this blizzard raging.” This is a great example of how tightly wound these polar lows can be. I think they are way cool. What do you think? Click the comments link and let me know.
Here are some good polar low links:
Polar low blog by Erik W. Kolstad — http://polarlows.wordpress.com/
National Snow and Ice Data Center page — http://nsidc.org/arcticmet/patterns/polar_low.html
