Past IEM Features tagged: stormmotion
Those of you that monitor RADAR reflectivity loops every day have likely noticed the weird storm motions this month. Typically storms travel from the southwest toward the northeast, but the past days have seen storms travel west, northwest, south, and about every other direction. The featured chart attempts to illustrate these odd storm motions by plotting a histogram of Des Moines NEXRAD storm motion tracks. The top panel shows the combined May and June climatology and the dominance of storms travelling from the southwest is obvious. The bottom panel shows the histogram for storms this month and it is about the antithesis of climatology. The reason for these weird storm motions is the very blocked up upper level flow pattern that currently has weak westerly moving flow over the state. The hope is that this pattern will break next week and we can start getting into more typical June storm patterns with stronger flow aloft.
When the National Weather Service issues Tornado and Severe Thunderstorm Warnings, they include how fast and the direction of travel that the warned storm is taking. The featured chart presents this combination for Tornado Warnings issued by NWS Des Moines. Values for the severe storms this past Saturday are highlighted in red. The lines on the plot represent a kernel density estimate with the centroid located near 30 MPH from the west-southwest. This dominate storm motion reflects the prevailing westerly motion of the middle part of the troposphere, which generally guide storms for west to east. The preference for a more southwesterly component reflects a flow pattern that is more favorable for warm air transport from the Gulf of Mexico north and cooler air transport of Canadian air south. Tornado producing storms feed off these contrasts.
Tags: stormmotion nws warnings