SPC WATCH
"SEL1
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 61...CORRECTED
NWS STORM PREDICTION CENTER NORMAN OK
405 PM CDT WED MAR 30 2016
CORRECTED FOR EXPIRATION TIME
THE NWS STORM PREDICTION CENTER HAS ISSUED A
* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
NORTHEAST KANSAS
EXTREME NORTHWEST MISSOURI
* EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 405 PM
UNTIL 900 PM CDT.
* PRIMARY THREATS INCLUDE...
ISOLATED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE
SUMMARY...STORMS FORMING IN NORTHEAST KANSAS WILL SPREAD
NORTHEASTWARD THIS EVENING AND CONTINUE TO POSE A RISK FOR AT LEAST
ISOLATED LARGE HAIL FOR THE NEXT FEW HOURS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 30
STATUTE MILES EAST AND WEST OF A LINE FROM 20 MILES NORTHWEST OF
SAINT JOSEPH MISSOURI TO 10 MILES SOUTH SOUTHWEST OF EMPORIA
KANSAS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED
WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 58...WW 59...WW 60...
AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM
MOTION VECTOR 22030."
The above watch is a severe thunderstorm warning for Northeast Kansas and the Northwesternmost part of Missouri. The watch began at 4:05 PM. Thunderstorms tend to occur in the afternoon when conditions are most ideal. In the case of a severe thunderstorm, which relies on favorable conditions over a large geographic region, the conditions here would have included changes in atmospheric wind shear, updrafts, moisture in the lower troposphere, and most importantly, vertical wind shear which creates the horizontal rolling motion in the air. Warm afternoon conditions would have contributed as well, with the cold front quickly pushing beneath the warm, dry afternoon air.
This warning includes a threat of isolated large hail events, up to 1.5 inches in diameter. Hail is major hazard of thunderstorms and costs about a billion dollars a year in damage just in the U.S. Hail forms when an ice pellet begins to fall to the ground and receives a liquid water coating in the warmer low portion of the cloud. Updrafts send the coated pellet back up to the colder part and the water freezes. This process will repeat until the hail grows too large for updrafts to carry it back up, and then it falls to the ground. We had a nice, brief hailstorm here in Salt Lake just today.
The watch warns that severe thunderstorms can and do produce tornadoes. This one did not, but if it had, it would have been the result of large pressure variances over short distances producing horizontal wind shear around an a large updraft at the rear of the storm, which itself would be the cause of the large pressure difference.
I included two Doppler images here. The first is the local Doppler. Since NEXRAD stations only have a range of about 217 miles, if the image is circular, you can determine that it was taken from just one station. The second Doppler image shows the whole nation and came from some combination of the United States' 158 NEXRAD sites.
Pings from radar bounce off of objects like rain and hail in the atmosphere and return energy back to the site. It works like regular radar. As an aside, I took trigonometry last semester and I think it's really neat to see polar coordinates in use. I suppose it makes sense that trig would be used in radar, but I'd never thought about it.
In both Doppler images you can see some bright banding in the center. The higher reflectivity of liquid coated frozen material means that these are likely the areas that are receiving hail. The surrounding areas that have smoother gradients should be receiving large amounts of rain.
As for the infrared and visible images, I can't tell if this is an MCS or a squall line. It doesn't have the characteristic isolation from other storms and it doesn't have the rotation, although there may be one sitting just north of western Tennessee. They do sometimes embed themselves in squall lines. From the visible image, it looks like it may be too low-lying, however. There is a large area with no clouds at all just over Kansas and southeastern Nebraska that may be an area of low pressure which the storm is rotating around. This leads me to believe that it may be an MCS.
The infrared and visible images are similar, except for one key difference. The infrared doesn't show the high cloud tops over Arkansas and Missouri that you can see in the visible image.
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