While the peak occurrences for severe weather events in the United States happen between March and October, severe weather can occur at any time. In order to save lives, branches of the National Oceanic and Atmospheric Administration (NOAA) will issue public watches and warnings.
Knowing the difference between the two can prepare individuals for the necessary steps to take when considering the threat of severe weather. Watches and warnings issued to the public are based on different criteria.
"A watch is issued when conditions are favorable, for example, either for a severe thunderstorm or tornadoes," AccuWeather.com Senior Meteorologist Dan Kottlowski said. "It doesn't mean severe weather is imminent."
"Typical watches cover about 25,000 square miles, or about half the size of Iowa," according to the SPC.
Kottlowski said there are no set criteria for issuing watches, but if the conditions seem consistent with a developing severe weather pattern, watches can be changed and altered by monitoring ongoing developments.
"It can vary," he said. "There is not just one set of ingredients; every watch may have a different set of perimeters from one day to the next since it is based on a synoptic situation that may change within several hours."
Warnings mean that severe weather is imminent and is based on specific criteria and existing reports received by the NWS.
(Photo/NOAA Photo Library)
The criteria include hail that totals more than 1 inch in diameter and wind speeds of 55 mph.
"Lightning is not a criteria for a severe thunderstorm warning," Kottlowski said. "Heavy rain is not either."
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Warnings must follow the two main criteria, he said, adding urban flood and stream advisories, flash flood watches and warnings, and flood watches and warnings, may accompany a storm with heavy rain.
Warnings are issued through the efforts of individuals working for the NWS.
"The way a warning is issued is that a meteorologist will monitor the weather by radar and look for particular areas where there could be high impact damage," Kottlowski said. "They will issue a warning and there will be a signature for an existing storm or developing tornado."
Trained NWS spotters will verify reports of rotation or storm damage.
"This gives the meteorologists confidence in what they are seeing on radar," he said.
The Seattle area is facing drenching rain and abundant clouds through the early part of the week.
Sun and warm temperatures will be disrupted by weekend rain and possible thunderstorms.
Cold air sweeping in this weekend will help pave the way for a storm with snow, sleet and rain Sunday afternoon into Monday morning around Harrisburg, Pennsylvania.
Cold air sweeping in this weekend will help pave the way for a winter storm Sunday into Monday morning around Pittsburgh.
A snowstorm reaching into Detroit on Sunday will drop enough snow to shovel and plow with more snow possible by midweek.
A storm will bring a heavy snowfall to the Cleveland area into early Monday morning with major travel disruptions.
Pacific Northwest (1987)
A storm produced wind gusts to 100 mph at Cape Blanco, OR and up to six inches of rain in the northern coastal mountain ranges.
St. Louis, MO (1893)
Snow and sleet with thunder and lighting at 13 degrees. (Thunder on and off for 3 hours).
Texas to New England (1951)
one of the greatest ice storms in U.S. history. Storm ran from Texas to New England. (Jan 28-Feb 4). 1/2 to 4 inches of ice collapsed buildings downed wires, trees, etc. At least 36 killed. Over a $100 million damage.