With the new calendar year, it is probably a good time to reflect back on 2011. The previous year will be remembered as an infamous year for deadly tornadoes in the US. The featured chart presents the yearly total of NWS issued severe thunderstorm and tornado warnings dating back to 1986 along with the total area covered by these warnings. The area value is expressed in normalized units of the size of the continental United States. For example, enough warnings were issued this past year to cover the CONUS seven times over. The total number of warnings came in slightly behind 2008. The large drop in areal coverage of warnings is due to the change to storm based warnings in 2008, which warns for only partial areas of counties.

Voting:
Good = 9
Bad = 2

Tags:   2011   nws   warnings  

The remnant of Tropical Storm Lee has been causing all kinds of grief over the southeastern US. A number of tornadoes were reported on Monday along with 99 tornado warnings issued. The featured map presents the number of county based tornado warnings issued so far this year. The largest total is 35 for Madison County, Alabama (Huntsville). More tornadoes are possible today over the Carolinas.

Voting:
Good = 14
Bad = 6

Tags:   nws   warnings  

Following up on yesterday's feature, today's looks at a comparison of tornado warned storm motion versus the severe thunderstorm warnings near in both space in time. Sometimes the sign of a storm that can produce a tornado is when the storm's path deviates from others around it. Typically, this deviation is a slight turn to the right (called right turners). Based on forecasted storm motions, just slightly more than half of the storms exhibit some bit of right turning. Another aspect to "right turners" is a decrease in speed as the storm's circulation strengthens. Again, just over half have forecasted speeds below those of warned severe thunderstorms around it. This is by no means an exhaustive look at this topic, but hopefully an interesting chart nonetheless. The bottom chart does contain an interesting dual maximum (25kts and 40kts) that may be a sign of a separation between isolated supercells (slower speeds) with linear convective complexes (typically faster moving).

Voting:
Good = 12
Bad = 5

Tags:   nws   warnings  

A severe thunderstorm developed over northcentral Iowa Tuesday afternoon and marched mostly south. This storm motion is not what we typically expect in Iowa of west to east moving storms. When the NWS issues severe thunderstorm warnings, they include a storm motion. The featured chart summarizes these storm motions issued by NWS offices with jurisdiction over Iowa. The upper chart presents a comparison between storm direction and date of year. It shows the favored direction of travel from the southwest in June to more west- northwesterly in July. The bottom chart compares storm speed with direction of travel. The fastest storms are clearly from the southwest with the largest concentration around 30 knots from the west. So our storms from the north-northwest on Tuesday are a bit rare, but not nearly unheard of like storms travelling from the east to west!

Voting:
Good = 16
Bad = 2

Tags:   nws   warnings  

The featured map presents the number of tornado warnings issued by each NWS forecast office so far this year. The largest value is 179 by the Memphis office. This year has seen more than its fair share of tornadoes. The largest numbers of warnings are shifted a bit east of the traditionally known tornado alley. Iowa has seen its share of severe weather recently, but most of it has been hail and wind.

Voting:
Good = 18
Bad = 7

Tags:   2011   warnings  

The featured chart displays the number of tornado warnings issued by the NWS for each day this year. There have been 9 days with over 100 warnings issued per day. In total, there have been 3,147 tornado warnings issued so far this year. This total is only about 300 warnings shy of the entire year's total for 2010.

Voting:
Good = 25
Bad = 16

Tags:   2011   warnings  

This past weekend saw yet another severe weather outbreak with numerous tornadoes reported over the deep south. The featured map (click for a better view) shows the difference in number of severe and tornado warnings this year versus last year. Only counties shown in dark blue have seen a decrease. The deep south certainly stands out with Alabama having all counties with higher totals than last year. The total count in this plot is 4,779 warnings for 2010 and 14,517 warnings for 2011. The total count for 2011 is the largest on record for the period prior to 18 April.

Voting:
Good = 23
Bad = 4

Tags:   2011   warnings  

The numbers on the featured plot show the yearly average March temperature for Iowa. The location of the number represents the spatial center of mass for all the severe thunderstorm and tornado warnings issued for March during that year. The map is attempting to show the relationship between average temperature in Iowa to the favoured are to where severe weather happens. The warmest temperatures mostly appear to the west and north in this map, which makes some logical sense as warmer weather would promote severe weather further north near Iowa. The coldest temperatures imply that severe weather is pushed to the south away from the state. The limited area of this plot also suggests that most of the severe weather happens in this area during March.

Voting:
Good = 9
Bad = 29

Tags:   march   warnings