Monday, March 14, 2016

First Severe Threat of the Season Arriving Tuesday

Signs of spring: Warmer temperatures, flowers beginning to bloom, buds growing on trees and the possibility of severe weather.

Tuesday's threat for strong to severe thunderstorms will be the first of the season and for Northern Illinois, so it's important to start thinking about severe weather preparedness and how to remain 'Weather Aware' tomorrow afternoon.

Showers have already begun developing in the western Plains late Tuesday evening, with the area highlighted in red from Missouri, Nebraska and SW Iowa more likely to see thunderstorms intensify during the late evening and overnight.

That cluster of storms will move east through Central Iowa and into Eastern Iowa and West-Central Illinois by daybreak Tuesday.  More than likely these will be in a weakening stage and will not pose any threat for severe weather.  However, small hail can't be ruled out west of a line from Freeport to Dixon.

Low pressure will strengthen over the Plains and Midwest Tuesday with southeast winds increasing at the surface by Tuesday afternoon.  Southeast winds at the surface, but southwest west just a few thousand feet above the surface of the earth will increase the spin, or shear, in the atmosphere.  By late afternoon Tuesday, low pressure will move into Northeast Iowa and Northwest Illinois with a warm front near I-80 and I-88.  The point where the warm front, cold front and low pressure system come together is called the 'triple point'.  And this often times can be an area of enhanced rotation in the atmosphere.  One concern heading into Tuesday afternoon will be the possibility of the warm front staying south of Stateline and having more of a stable air mass in place over Northern Illinois with strong east winds.  If this were to occur our threat for severe weather, or thunderstorms in general, would be reduced slightly. 

Because of these features, the Storm Prediction Center has placed Northern Illinois and far Southern Wisconsin under a slight risk for severe weather.

Here's how I believe the weather Tuesday will play out:  Weakening showers/storms will occur west of Rockford and move slightly to the southeast during the mid-morning.  Additional showers will hold together over Southern Wisconsin and far Northern Illinois into early afternoon.

As the cold front moves closer to the Mississippi River Tuesday afternoon, an increase in instability above the surface will occur.  We might not completely realize instability at the surface due to cloud cover, though.  A line of thunderstorms will then quickly develop east of the Mississippi River around 4pm and 5pm.  This line will then quickly race east towards Rockford between 6pm and 8pm.  After 8pm/9pm, the front will have passed with the storm threat moving towards Chicago.

Late winter/early spring storm systems might not have all ingredients come together to sustain severe weather, but it's important to remain 'Weather Aware' Tuesday.  Have a way to receive watches and warnings and know make sure you know what to do or where to go if severe weather were to occur. 

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