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National Situation Update: Monday, March 9, 2009

Homeland Security Threat Level: YELLOW (ELEVATED).

Significant National Weather

West:
Several frontal systems and an upper-level storm will spread snow across the northern half of the region.
Rain will fall in coastal areas of Washington and Oregon. Snow is forecast for Idaho, Montana, Wyoming, Utah and Colorado. Accumulations of more than 12 inches will be common with higher amounts in Utah's Wasatch mountains.  High temperatures will range from 15 to more than 30 degrees below average across the Northwest.
Midwest:
A cold front dropping into the region will bring snow to portions of the Dakotas and northern Minnesota. Snowfall accumulations of a foot or more are expected in some locations.  A ridge of high pressure building in behind the front will result in a tight pressure gradient and gusty winds across the Plains and Upper Midwest. Blizzard conditions will be possible with wind gusts of 40 to 50 mph.  Along the stalled front, showers and thunderstorms are forecast across portions of southeast Kansas, Missouri, Iowa, western Illinois and western Kentucky; some of these thunderstorms may become severe.  This area of precipitation will spread east across Illinois into the southern Great Lakes by tomorrow exacerbating existing river flooding and increasing the potential for localized flash flooding.

South:
A stalled front will produce rain showers and isolated to widely scattered thunderstorms from Oklahoma and Texas eastward to northern Alabama and Georgia.  An upper-level disturbance may cause thunderstorms over Oklahoma and Texas to become severe with gusty winds, hail and possible isolated tornadoes.  Fire danger will remain high in Texas and Oklahoma due to gusty winds.  High temperatures will remain well above average across much of the region by 10-20 degrees with high temperatures in the 70s and 80s.
Northeast:
A low pressure system moving into the region will produce rain from the Mid-Atlantic to northern portions of New York and southern New England.  Upstate New York to central New England will receive a wintery mix and some locations could see up to eight inches.  High temperatures will range from the 30s in Maine to the 70s and low 80s across southern Virginia. (NOAA, National Weather Service, Various Media Sources)

Tornado Climatology
Because a tornado is part of a severe thunderstorm, and thunderstorms occur all over the Earth, tornadoes are not limited to any specific geographic location. In fact, tornadoes have been documented in every one of the United States, and on every continent, with the exception of Antarctica (even there, a tornado occurrence is not impossible). In terms of absolute tornado counts, the United States leads the list, with an average of over 1,000 tornadoes recorded each year. A distant second is Canada, with around 100 per year.

Tornado Alley
In the United States, there are two regions that get proportionately more tornadoes than anywhere else. Florida is one and Tornado Alley is the other. Florida has a lot of tornadoes simply because it is home to almost daily thunderstorms. In addition, the Florida peninsula is also impacted by tropical cyclones and when these cyclones move ashore, the embedded thunderstorms will often produce tornadoes. However, despite the violent nature of a tropical cyclone, most of the tornadoes they spawn (some being water spouts) are normally relatively weak.
Strong to violent tornadoes (those of F3 or stronger on the Enhanced Fujita Tornado Damage Intensity Scale), are relatively rare, and are not usually experienced outside of the central United States. Although its boundaries are debatable (depending on which criteria you use - frequency, intensity, per unit area), the area from central Texas, northward to northern Iowa, and from central Kansas and Nebraska east to western Ohio is collectively known as Tornado Alley. Climatologically, Tornado Alley is ideally positioned for the formation of super-cell thunderstorms, and therefore is also home to many violent tornadoes.  Overall, for the U.S., most tornadoes (around 83%) are considered weak (F0), and around 98% of all U.S. tornadoes are below F3 intensity. That leaves just about 2% of all U.S. tornadoes to be categorized as violent (F3 and above). Of these violent twisters, thankfully just around 0.4% achieve F5 status, with winds over 261 mph and nearly complete destruction. However, given that on average over 1000 tornadoes hit the U.S. each year, that means that 20 can be expected to be violent and around 4 might be incredible. Fortunately, recent years have not seen as many F4 and F5 tornadoes as those probabilities would indicate.

Daily and Seasonal Peak Occurrences
Because most tornadoes are related to the strength of a thunderstorm, and thunderstorms normally gain most of their energy from solar heating and latent heat released by the condensation of water vapor, it is not surprising that most tornadoes occur in the afternoon and evening hours, with a minimum frequency around dawn (when temperatures are lowest and radiation deficits are highest).  Since tornadoes occur throughout the year and at any time somewhere in the U.S., there really is no national tornado season (as there is with Atlantic hurricanes).  Regionally, however, the frequency of tornadoes in the United States is closely tied with the progression of the warm season. Most of the early spring tornadoes in the U.S. tend to occur in the lower latitudes of the Southeast and south Central regions. Gulf States, such as Mississippi and Louisiana, are the frequent recipients of tornadoes from February to April. Late spring tornadoes migrate a bit farther north, often into Kansas, Nebraska and the Tennessee Valley region. By mid-summer, Tornado Alley is active and tornadoes may occur throughout the U.S. Late summer tends to bring some of the stronger tornadoes into the upper Midwest and Ohio Valleys, and the pattern shifts back southward into late autumn. The fewest tornadoes are documented during the winter months. (Excerpt from www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html )

Midwest Severe Storms
A low pressure system moved across the Midwest yesterday bringing severe thunderstorms, tornadoes, hail and damaging winds.  The heaviest amount of rain occurred in northern Illinois where 4 to 6 inches were reported.  Heavy rainfall caused widespread minor flooding throughout the region with isolated areas of moderate flooding.  Additional rainfall is forecast for Monday evening and Tuesday for the upper Midwest.  The National Weather Service (NWS) issued flood warnings for numerous rivers due to heavy rainfall in Iowa, Missouri, Illinois, Indiana, Ohio and Michigan.

Region V:
Illinois

  • 10 preliminary reports of tornadoes.  (NOAA Storm Prediction Center)
  • 2 injuries as a result of a tornado and hail.
  • Sporadic power outages and damage reported.
  • Illinois River at LaSalle is currently at 23.68 ft and is expected to crest at 30.9 ft, moderate flood stage on Tuesday, March 10.  At 27.5 ft, the Hennepin Levee is expected to overtop and some flooding of low lying residences in Ottawa.
  • No shelters are open.
  • No requests for Federal assistance.

Indiana

  • 6 preliminary reports of tornadoes.   (NOAA Storm Prediction Center) 
  • 2 non-life threatening injuries.
  • 2 local shelters open with no occupants at this time.
  • Several homes destroyed.
  • Sporadic power outages due to downed transmission lines.
  • No requests for Federal assistance.

Ohio

  • 4 preliminary reports of tornadoes. (NOAA Storm Prediction Center)
  • Minor damage reported.
  • No requests for Federal assistance.

Texas Wildfires

Loma del Norte (Brewster County): 800 acres; 75% contained (no updated containment information available),  no structures destroyed. FMAG #2797 approved March 3.
Linn San Manuel: 1,650 acres; percentage 80% contained; 2 structures destroyed.
West Fork Fire: 2,400 acres; 80% contained; no structures destroyed. (Southern Area Coordination Center Morning Report Mar 8)

Volcano Activity

Redoubt Volcano, Alaska
Unrest at Redoubt Volcano continues. Seismicity is at low levels compared to the past month and is dominated by small discrete earthquakes. Seismic activity has declined over the week.  Aviation Color Code is ORANGE and the Volcano Alert Level is WATCH.

Fire Management Assistance Grant (FMAG)

No activity. (FEMA HQ)

Disaster Declaration Activity

No activity. (FEMA HQ)

Tropical Weather Outlook

Eastern Pacific:
There are no current tropical cyclone warnings.  (NOAA, HPC, National Hurricane Center, Central Pacific Hurricane Center and the Joint Typhoon Warning Center)

Earthquake Activity

No significant activity. (USGS, Earthquake Hazards Program)

Last Modified: Thursday, 04-Jun-2009 16:27:01 EDT