Polar low blasts the Pribilof Islands

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:

4abf03-1453

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):

sfcmap04-00

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.

NAM12_Pacific_t85slp_20120104_0000_F000

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

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