Saturday, June 14, 2014

Potentially Significant Severe Weather Discussion for Wednesday, June 18

This is a special severe weather discussion for Wednesday, June 18th, as new data suggests this may be a multi-day severe weather episode.

The projected surface analysis forecast for Wednesday by the Weather Prediction shows a storm system located in the Plains, with a warm front extended nearly due east through Minnesota and Wisconsin, making available a large swath of hot, humid air to the Central United States in the process. We see a cold front snaking down from the Dakotas into Nebraska and looping around the Rockies. A special point of interest is the dryline feature that is projected to extend from Kansas into Texas and New Mexico.

According to this graphic, we may be expecting two areas of severe weather on Wednesday. The first area would likely be near the dryline feature in the Southern Plains. As that cold front meanders east through the day on Wednesday, some thunderstorms should be able to initiate and sustain themselves in the very unstable environment, which we will discuss more about later. The second region of potentially active weather should be located in the Northern Plains, in the vicinity of the low pressure system. This upper level low feature looks to create favorable lower and mid-level wind fields that should be conducive for thunderstorm formation. The proximity of the warm front to the low pressure center means those in South Dakota, eastern Nebraska, and Minnesota may have to watch for some of the strongest storms, at least initially.

The forecast for convective available potential energy (CAPE) on Wednesday evening is shown above from the most recent GFS model forecast. In this image, we see that mass of warm and unstable air that has been pulled north by the aforementioned warm front in the North Plains. CAPE values look to exceed 6000 j/kg in eastern Minnesota, an incredible feat when one considers that 2000 j/kg of CAPE is typically sufficient for severe thunderstorm formation. This high instability combined with a favorable wind field makes the North Plains region more susceptible to the potential severe weather than the dryline feature in the South Plains.

We can also use analog dates to predict the future. This method of forecasting takes decades of weather observations and matches a handful of select dates up that are closest to the forecasted conditions. This image shows compiled severe weather reports from the top 15 analog dates, basically the 15 days that were the closest to projected conditions on Wednesday evening. When we look at the compiled severe weather reports, it is confirmed that the North Plains does look to be the hotspot for severe weather on Wednesday. We see numerous damaging wind and hail reports across the Dakotas, Michigan, Nebraska and Colorado, with multiple tornado reports intertwined. While this by no means confirms that this will be how the event transpires, it does give us a key glance into what this event has the potential to become.

Related: Potentially Significant Severe Weather Discussion for Thursday, June 19: CLICK HERE


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