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National Situation Update: Monday, March 20, 2006

Homeland Security Threat Level: YELLOW (ELEVATED).

Significant Weather Across the Nation

West: The storm moving off the Pacific will produce rain and mountain snow over western Oregon, northern and central California and western Nevada. The heaviest precipitation is forecast for southwest Oregon and northern California. Snow levels are expected to be as low as 3000 feet. A stationary front will produce significant snow from southeast Wyoming down through the Front Range of Colorado. Denver may see up to a foot of snow.

Midwest: A significant winter storm extends from Montana down to Nebraska. Snow will spread eastward into northwest Missouri late today. Parts of Nebraska may pick up 10 to 20 inches. Rain showers will extend from central and southern Missouri eastward through the Ohio Valley.

South: A low pressure system centered over Texas will produce significant amounts of rain in a broad swath from Texas into Tennessee. Scattered severe thunderstorms are forecast from eastern Texas through the Deep South as far east as Alabama.

Northeast: The Northeast will be dry except for isolated snow showers from Upstate New York to northern New England.

Hawaii: Flash flooding remains possible through today. The atmosphere over the Hawaiian Islands will remain unstable. A surface trough over the central islands along with weak upper air disturbances crossing the area will maintain the threat of heavy rainfall and possible flooding for all islands. (National Weather Service (NWS) media sources)

Flash Flooding in North Texas

News media report numerous road closures and water rescues due to flash flooding in North Texas, and one death when an automobile was swept into the water by the flooding. Parts of Dallas have recorded eight to 10 inches of rain since Friday. The NWS reports that flood watches and warnings are in effect throughout the area until 7:00 a.m. EST this morning, and that storm runoff and additional rain could result in further flooding. (NWS, news media sources)

Tornado Season

Tornadoes are one of nature's most violent storms. In an average year, about 1,000 tornadoes are reported across the United States, resulting in 80 deaths and over 1,500 injuries. A tornado is a violently rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more. Damage paths can be in excess of one mile wide and 50 miles long.

Tornado season usually means the peak period for historical tornado reports in an area, when averaged over the history of reports. There is a general northward shift in "tornado season" in the U.S. from late winter through mid summer. 

• In the southern states, peak tornado season is March through May,
• In the southern plains, peak tornado season is May into early June.
• In the northern plains and upper Midwest, peak tornado season is June or July.

However, tornadoes can happen any time of year if the conditions are right. (NOAA's National Weather Service, Storm Prediction Center)

Vernal Equinox Today

The first day of Spring marked by the vernal equinox occurs today at 1:26 pm (EST). At this time the center of the sun's disc crosses the earth's equator from the southern hemisphere to the north at a point just west of the Galapagos Islands. From now until the autumnal equinox daylight hours will outnumber those of the night. (U.S. Naval Observatory)

Tropical Weather Outlook

There are no tropical disturbances in the Atlantic or North Pacific Oceans.

In the South Pacific:

• On Monday (local time) Tropical Cyclone Larry smashed into Queensland, Australia about 62 miles south of Cairns, forcing thousands to evacuate their homes. Queensland State Premier Peter Beattie declared a state of emergency, saying it was the "worst cyclone in decades". Three people have been reported injured so far and up to 50,000 homes are without power. The storm was initially a category five (the strongest possible) but was downgraded to a category four shortly after it crossed the coastline. The system is currently dissipating over land.
• Yesterday's Tropical Cyclone Formation Alert (TCFA) has become Tropical Cyclone 18P (Wati) with winds of 63 to 81 miles per hour. The system is about 600 miles northeast of Queensland, Australia and moving southwest toward land but based on the current warning will begin turning to the southeast in 24 hours and not make landfall. 18P is not a threat to U.S. territories. (National Hurricane Center, Central Pacific Hurricane Center, and the Joint Typhoon Warning Center, Various Media)

Earthquake Activity

There have been eight minor earthquakes in Alaska during the last 24 hours ranging in magnitude from 2.5 to 4.3.  There were no reports of damage or injuries. (U.S. Geological Survey, National Earthquake Information Center)

Preliminary Damage Assessments

No new activity (FEMA HQ)

Disaster Declaration Activity

No new activity (FEMA HQ)