Now is the time to get prepared for a very dangerous and widespread severe weather outbreak over the next several days. Saturday-Tuesday, a very dynamic storm system will develop over the Plains and will slowly move east. All ingredients needed for severe weather will be available and in place the next several days. These ingredients are: lift, shear, moisture, and instability. LIFT: Upper-level dynamics and a negatively tilted trough will cause divergence aloft. When there is divergence aloft, the air at the surface is forced to fill the void aloft by producing convergence and uplift at the surface. We will also see faster winds aloft, which produces uplift. Finally, a cold front, a warm front, and the dry line will produce even more uplift in the affected areas over the next several days. SHEAR: There are two main types of wind shear we look for, speed and directional shear. We will have both of these in the risk areas. Speed shear is the wind at different levels moving at different speeds and this causes rotation throughout the atmosphere. Directional shear is wind moving in different directions as we head up in the atmosphere. We will have veering winds with this event. Veering winds are the clockwise change of winds heading up through the atmosphere. At the surface, winds will be from the southeast, but as we go up, these winds will be veering towards the south, southwest, west, and northwest up through the atmosphere. Shear helps produce and maintain strong updrafts,
which allows storms to become severe. Shear also increases the amount of spin in the air and helps in tornadogenesis. MOISTURE: The low pressure over the Plains and the counter-clockwise flow around the system will be bringing moisture north from the Gulf. To the east, an area of high pressure over the Southeast and Mid-Atlantic will produce clockwise flow and it will also help moisture stream north from the Gulf. These two features working together will usher in ample moisture into the areas. INSTABILITY: With the moist air mass in place, instability will build across the risk area as daytime heating heats up the atmosphere. The air near the surface warms faster and with cooler air above, the warm air wants to rise. This moist rising air helps clouds form and from clouds we get precip and then thunderstorm development. Each day, it will be very warm and instability values will be quiet high over the weekend. With these ingredients coming together, this is why the SPC and model output data are showing a very stormy forecast. Once again, this will be a multi-day severe weather outbreak, and each day the risk area and severe weather threat shift east. All modes of severe weather will be possible during this event, and that includes large hail, damaging winds, tornadoes, some of which will be large and violent, and a serious threat from flash flooding. Pay very close attention if you live in the areas that have been highlighted by the SPC in a threat for severe weather. With such a dynamic and dangerous situation developing, as well as the likelihood of storms impacting areas during the overnight hours, it is extremely important to have multiple sources for severe weather notifications. Like is done everyday, we will be updating each day’s Severe Weather Outlook and monitoring every risk, watch, and warning that is issued. Stay safe. Follow us on Twitter. Like us on Facebook. Add us to your Google+ circles. MyWARN is available in the Google Play Store and as always our very popular iOS version is available for download in the iTunes Store. Get MyWARN now from the iTunes Store and the Google Play Store.