Time to Prepare, Not Panic

So far this severe weather season has been pretty quiet locally, but that may be changing in 24 hours.  Before we get into the forecast discussion, I want to stress the importance of planning!  With the proper planning you will be prepared for any weather event.  And that's important! 

Tonight, Tuesday night, I want you to sit down with your family and discuss where you would go if severe weather were to occur.  Do you have a basement?  If not, where on the lowest level of your home would you need to be.  Best place would be an interior room, such as a bathroom or closet, and away from windows.  Think about putting as many walls between you the outside as possible.  How about a safety kit.  Do you have one that is either located in or near your safe place?  If not, can you easily take that with you should you need to take shelter?  These are the questions and discussions you need to have with your family so everyone knows what actions to take when severe weather occurs.

Don't be afraid to ask your place of employment where you would need to go if severe weather were to occur while you were working.  If you're out at the store, take time to ask a store manager where the safest place in the store would be.  If you're going to be outside, look for where you would need to take shelter.  And make sure you have multiple ways to receive watches and warnings. 

Now, let's get into the forecast for Wednesday because even 24 hours out there are still a few 'what if's'.  Showers and isolated thunderstorms have already started to develop over central Iowa near Cedar Rapids.  This was expected as the low level jet begins to increase and runs into the warm front well south of the Stateline.  The general motion of those storms are to the southeast.  So it's going to be a while before we see anything move into Northern Illinois.

A Flash Flood Watch has been issued for all of Northern Illinois beginning late tonight for our NW counties and early Wednesday morning for North-Central Illinois.

As the low level jet increases tonight it will help push the warm front northeast closer to west-central Illinois late tonight and early Wednesday morning.  The expectation is that the storms out west in Iowa will continue to grow along the warm front, with storms that are now over the Northern Plains moving southeast along the front closer to Northwest Illinois by Wednesday morning.  It's possible that the heaviest rain axis may stay just west of the immediate area closer to the Mississippi River and Eastern Iowa.  Either way, the severe threat for Wednesday morning will be relatively low.  Biggest weather threats for the morning will be heavy rainfall and isolated large hail.  The hail would occur as storms become elevated, meaning they are north of the warm front and displaced a little from the more unstable air.

Most of our models have a lot of the morning activity moving out of here a little before Noon.  Then our attention will turn towards Wednesday afternoon and evening.

I want to stress that it is not set in stone that we will see severe weather Wednesday afternoon.  Limiting factors to anything developing during the afternoon would be if the morning activity keeps the warm front south of the Stateline.  If that's the case, storms would be more likely to develop closer to west-central Illinois.  If storms from the morning do clear out early then the warm front could quickly pull north and actually move into Southern Wisconsin.  If that were to happen then our temperatures would warm quickly, but the extreme warmth aloft could place a 'cap' on our atmosphere not allowing thunderstorms to break through that cap and grow in height.

The scenario that would bring us the highest severe weather threat Wednesday would be if the warm front were to lie near the Wisconsin/Illinois border or just slightly to the south.  Where the low pressure, warm front and cold front meet is referred to as the 'triple point'.  If clearing does take place during the afternoon, storms would quickly develop near the triple point.  Initially these storms would be supercells posing a wind and even tornado risk.  The reason for the tornado threat is because of the great amount of wind shear in the atmosphere.  Winds at the surface will be coming in from the south/southeast while winds in the upper level of the atmosphere are coming in from the west/northwest.  This creates a great amount of spin in the atmosphere which is what is needed to get rotating thunderstorms.

Individual storms will then quickly grow into a damaging wind MCS and move east along the warm front near Chicago and Indiana. If storms develop right over North-Central Illinois, there will be a higher threat for tornadoes.  If storms initially develop to the west of us, our threat could turn into a damaging wind threat.

Time frame for the morning and afternoon:
Morning storms will move in west of Rockford between 4am and 7am.  General motion of these will be to the southeast along the warm front.

Should afternoon storms develop the time frame for those would be between 4pm and 11pm.

Again, it's important to plan and pay attention to the forecasts for Wednesday.  A lot can change between now and Wednesday afternoon.  And a little bit of a shift in the warm front, low pressure or morning storms could have a BIG impact on what happens in the afternoon.