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 Archive | January

US Extreme Weather Events 2011

Jan 31, 2012

Tags:Dr. Grey,Dr. Klotzbach,Earthquake,East Pacific,El Nino,Hurricane Irene,Hurricane Outlook,Hurricane Prediction,Hurricane Season 2011,Hurricane Season 2012,HUrricane Season Update,La Nina,Meteorology,Polar Vortex,Tropical,Tropics,Weather,Winter

U.S Extreme Weather Events in 2011

No matter what stands out to each of us about 2011, a common thread shared by many was the severity of nation’s weather. Varied, atypical, and at times both devastating and tragic, 2011 was an exceptionally active year for major-impact weather events in the US.

The National Oceanic & Atmospheric Administration identified no fewer than a dozen events with economical damage exceeding a billion dollars. The events are listed in chronological order below. How many of these “billion-dollar disasters do you recall?

1.Groundhog Day Blizzard, Jan 29-Feb 3, 2011, 1-2+ feet of snowfall, OK to MI to New England

2.Midwest-Southeast Tornadoes, Apr 4-5, 2011, 46 tornadoes, LA-AR-KY-OH eastward to interior east coast states

3.Midwest-Southeast Tornadoes, Apr 14-16, 2011, 177 tornadoes (EF0-EF3), TX-OK-KS eastward to east coast

4.Southeast-Ohio Valley-Midwest Tornadoes, April 25-28, 2011, 343 tornadoes, 321 fatalities, TX-AR-MO-MI eastward to east coast

5.Midwest-Southeast Tornadoes, May 22-27, 2011, 180 tornadoes, 177 fatalities, (including EF5 Joplin, MO ,158 dead), Gt. Plains to Appalachians

6.Midwest-Southeast Tornadoes, Severe Wind and Hail, June 18-22, 2011, 81 tornadoes, widespread severe wind and hail, high plains to east coast

7.Exceptional/Extreme Drought and Heat Wave, Spring-Fall 2011, Southwest-Southern Plains-Gulf Coast

8.Mississippi River Flooding, Spring-Summer 2011

9.Upper Midwest-Plains Flooding, Summer 2011

10.Hurricane Irene, Aug 20-29, 2011, NC to NY & New England

11.Southwest Wildfires, Spring-Fall, 2011, TX-NM-AZ

12.Pre-Halloween Nor’easter Heavy Snowfall, October 29-30, 2011, 1-2+ feet of snowfall, northeastern PA to southern ME

2011 – Record Breaking Year for Tornadoes

Arguably, the most notorious weather events from 2011 were tornadoes. In fact, 2011 was a record breaking year for confirmed tornadoes in the US. Five spring-time severe storms events, totaling 827 tornadoes, resulted in nearly 500 fatalities with at least a billion dollars in losses caused by each event. Some of these tornadoes were long-track storms that were on the ground for prolonged periods. 84 tornadoes were rated as strong and violent, and was the second largest number of these potentially most destructive tornadoes that have occurred since 1950 (Fig.1).

Fig. 1. Tornadoes are rated on a scale (Enhanced Fujita scale) from 0-5. The potentially most destructive tornadoes (strong to voilent; EF3-EF5) from March-August in the US since 1950-2010 are shown above (countrsey NOAA). The 84 strong-voilent tornadoes in 2011 were the second highest total since 1950 and the most since 1974.

Fig. 2. Deadly tornado (EF-5) strikes Joplin, MO on 22 May 2011 (NOAA).

Tornadoes 2012 ?

So, what were the factors that drove the exceptional 2011 tornado season? Are those factors discernable in the climatological data, and to what extent might they again occur in 2012? These are topics for our next discussion, coming in February 2012.

Rod Gonski, Author

Kermit Keeter, Editor

Jeremy Gilchrist, Reviewer


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A Mild Start To Winter In The Eastern US

Jan 04, 2012

Tags:Dr. Grey,Dr. Klotzbach,Earthquake,East Pacific,El Nino,Hurricane Irene,Hurricane Outlook,Hurricane Prediction,Hurricane Season 2011,Hurricane Season 2012,HUrricane Season Update,La Nina,Meteorology,Polar Vortex,Tropical,Tropics,Weather,Winter

With the arrival of the New Year, many people east of the Mississippi River have been wondering what has happened to winter. Most areas of the Eastern US have seen well below normal snowfall and unseasonably warm weather. This is especially attention grabbing following the previous two winters, when much of the East saw well above normal snowfall and below normal temperatures. The reasons accounting for winter’s mildness thus far is the continuation of La Nina along with positive North Atlantic (NAO) and Arctic Oscillations (AO). These features drastically influence longer term global weather patterns and their state.

Most have heard of La Nina (cooler than normal equatorial waters in the Pacific), or it’s opposite El Nino (warmer than normal) and their influences on winter weather patterns (Fig.1); but unless you are in the field of meteorology, you are likely not aware of the NAO and AO, two principal mechanisms driving winter weather in the East.

The NAO is an oscillation of the pressure difference between an area of low pressure near Iceland and high pressure near the Azores in the subtropical Atlantic. When the NAO is positive, there is a significant difference in pressure between the two with a strong Azores High. When the NAO is negative, the difference in pressure weakens and the aforementioned Azores High is not as strong (Fig. 2). The AO is similar to the NAO, except it represents oscillations in atmospheric pressure in the polar region and the central Atlantic. The AO takes into account the difference between low pressure near the North Pole and high pressure over the central Atlantic. When the AO is positive, the pressure difference is greater with the central Atlantic High being strong. When the AO is negative, the opposite is true with a small difference and weaker area of high pressure in the mid latitudes (Fig. 3).

So, just how have the North Atlantic and the Arctic Oscillation led to a mild winter and a lack of snow in the Eastern US thus far? As previously stated, the positive phase of both oscillations results in strong high pressure in the mid and subtropical latitudes of the Atlantic. This is exactly what has been happening this winter with the western periphery of strong high pressure dominating the Eastern US. As a result, the higher pressures have kept the Arctic air from progressing southward. This has also resulted in a very unfavorable storm track for snowfall in the East with winter storms tracking well west and north of the Eastern US

It is lower pressures in the central Atlantic associated with a negative North Atlantic Oscillation and negative Arctic Oscillation that are more favorable for setting up weather patterns conducive for cold and snow in the Eastern US. So far the winter of 2011-2012 has yet to see this occur. With that in mind, the oscillation patterns could change as the current state of the science does not allow for an accurate prediction of the oscillation patterns more than a just few weeks in advance. Stay tuned.

Figure 1 - A typical La Nina Pattern

Figure 2 - The NAO

Figure 3 - The AO

Images courtesy:  NOAA, State Climate Office of North Carolina.

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