North American cold wave winds down; Atlantic storm stronger than Sandy winding up

The January 2013 North American cold wave is winding down, after bringing five days of bitter cold to Canada and the Midwest and Northeast U.S. In the U.S., below-zero temperatures were recorded Friday morning in just six states east of the Rockies--half as many as on Thursday morning. The coldest spot was Saranac Lake in New York's Adirondack Mountains, which bottomed out at -18°F (-28°). In nearby Malone, NY, flooding is occurring, thanks to an ice jam on the Salmon River caused by this week's cold weather. The weather was a bit warmer on Mt. Washington, New Hampshire today, where the temperature of -17°F (-27°C) combined with a wind of 81 mph to create a wind chill of -61°F (-52°C). The most dangerous winter weather today will be due to the Wrath of Khan--a low pressure system traversing Tennessee and Kentucky has been named Winter Storm Kahn by TWC, and will bring as much as 0.5" of ice accumulation from eastern Tennessee and Kentucky through North Carolina and northern South Carolina, potentially causing major power outages. Snow will impact areas from the Ohio Valley through western Pennsylvania, West Virginia and Virginia, with 1" expected in D.C. and 1 - 3" in Baltimore.


Figure 1. A powerful extratropical storm with a central pressure of 984 mb begins to wind up about 500 miles east of Newfoundland, Canada, at 10 am EST January 25, 2013.

How low will it go? Massive Atlantic storm winding up
In the Northern Atlantic, an extratropical storm that brought up to 6" of snow to Maryland on Thursday is rapidly intensifying about 500 miles east of Newfoundland, Canada, and figures to become one of the most intense storms ever observed in the North Atlantic. This meteorological "bomb" was analyzed with a central pressure of 984 mb at 12Z (7 am EST) Friday morning by NOAA's Ocean Prediction Center; the GFS and ECMWF models both predict that the storm will deepen by 60 mb in 24 hours, reaching a central pressure of 924 - 928 mb by 7 am EST Saturday morning. This is the central pressure one commonly sees in Category 4 hurricanes, and is a very rare intensity for an extratropical storm to attain. Since extratropical storms do not form eyewalls, the winds of the massive Atlantic low are predicted to peak at 90 mph (Category 1 hurricane strength), with significant wave heights reaching 52 feet (16 meters.) Fortunately, the storm is expected to weaken dramatically before reaching any land areas, and will only be a concern to shipping. The intensification process will be aided by the strong contrast between the frigid Arctic air flowing off the coast of Canada from this week's cold blast, and the warm air lying over the warm waters of the Gulf Stream current. The ultimate strength of the storm will depend upon where the center tracks in relation to several warm eddies of the Gulf Stream along its path. According to wunderground's weather historian Christopher C. Burt's post on Super Extratropical Storms, the all-time record lowest pressure for a North Atlantic extratropical storm is 913 mb, set on January 11, 1993, near Scotland's Shetland Islands. The mighty 1993 storm broke apart the super oil tanker Braer on a rocky shoal in the Shetland Islands, causing a massive oil spill.

Other notable Atlantic extratropical storms, as catalogued by British weather historian, Stephen Burt:

920.2 mb (27.17”) measured by the ship Uyir while she sailed southeast of Greenland on December 15, 1986. The British Met. Office calculated that the central pressure of the storm, which was centered some distance southeast of the ship, was 916 mb (27.05”).

921.1 mb (27.20”) on Feb. 5, 1870 measured by the ship Neier at 49°N 26°W (another ship in the area measured 925.5 mb)

924 mb (27.28”) on Feb. 4, 1824 at Reykjavik, Iceland (the lowest on land measured pressure in the North Atlantic)

925.5 mb (27.33”) on Dec. 4, 1929 by the SS Westpool somewhere in the Atlantic (exact location unknown)

925.6 mb (27.33”) on Jan. 26, 1884 at Ochtertyre, Perthshire, U.K. (the lowest pressure recorded on land in the U.K.)

For comparison’s sake, the lowest pressure measured on land during an extra-tropical storm in the United States (aside from Alaska) was 952 mb 28.10” at Bridgehampton, New York (Long Island) on March 1 during, the Great Billy Sunday Snowstorm.


Figure 2. Infrared satellite image of the North Atlantic Storm of January 11, 1993 at 0600Z when it deepened into the strongest extra-tropical cyclone ever observed on earth, with a central pressure of 913 mb (26.96”). Satellite image from EUMETSAT Meteosat-4.

Intense winter storms are expected to increase in number due to climate change
In my 2010 blog post, The future of intense winter storms, I discuss how evidence for an observed increase in intense wintertime cyclones in the North Atlantic is uncertain. In particular, intense Nor'easters affecting the Northeast U.S. showed no increase in number over the latter part of the 20th century. This analysis is supported by the fact that wintertime wave heights recorded since the mid-1970s by the three buoys along the central U.S. Atlantic coast have shown little change (Komar and Allan, 2007a,b, 2008). However, even though Nor'easters have not been getting stronger, they have been dropping more precipitation, in the form of both rain and snow. Several studies (Geng and Sugi, 2001, and Paciorek et al., 2002) found an increase in intense winter storms over both the North Atlantic, but Benestad and Chen (2006) found no trend in the western parts of the North Atlantic, and Gulev et al. (2001) found a small small decrease in intense winter storms in the Atlantic.

The U.S. Global Change Research Program (USGCRP), a scientific advisory board created by the President and Congress, concluded this in their 2009 U.S. Climate Impacts Report: "Cold-season storm tracks are shifting northward and the strongest storms are likely to become stronger and more frequent". The USGRP concluded that an increase of between four and twelve intense wintertime extratropical storms per year could be expected over the Northern Hemisphere by 2100, depending upon the amount of greenhouse gases put into the air (Figure 3). If we assume that the current climate is producing the same number of intense winter storms as it did over the period 1961-2000--about 53--this represents an increase of between 8% and 23% in intense wintertime extratropical storms. Two studies--Pinto et al. (2007) and Bengtsson et al. 2006--suggest that the more intense winter cyclones will affect only certain preferred regions, namely northwestern Europe and Alaska's Aleutian Islands. At least three other studies also find that northwestern Europe--including the British Isles, the Netherlands, northern France, northern Germany, Denmark and Norway--can expect a significant increase in intense wintertime cyclones in a future warmer world (Lionello et al., 2008; Leckebusch and Ulbrich 2004; and Leckebusch et al., 2006). None of these studies showed a significant increase in the number of intense Nor'easters affecting the Northeast U.S.


Figure 3. The projected change in intense wintertime extratropical storms with central pressures < 970 mb for the Northern Hemisphere under various emission scenarios. Storms counted occur poleward of 30°N during the 120-day season beginning November 15. A future with relatively low emissions of greenhouse gases (B1 scenario, blue line) is expected to result in an additional four intense extratropical storms per year, while up to twelve additional intense storms per year can be expected in a future with high emissions (red and black lines). Humanity is currently on a high emissions track. Figure was adapted from Lambert and Fyfe (2006), and was taken from Weather and Climate Extremes in a Changing Climate, a 2009 report from the the U.S. Global Change Research Program (USGCRP). The USGRP began as a presidential initiative in 1989 and was mandated by Congress in the Global Change Research Act of 1990, which called for "a comprehensive and integrated United States research program which will assist the Nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change".

Links
Wunderground's weather historian Christopher C. Burt's posts on Super Extratropical Storms and World and U.S. Lowest Barometric Pressure Records

Claudio Cassardo's January 23, 2013 post, Very low minima of extratropical cyclones in North Atlantic

Jeff Masters