Friday afternoon update - Watching the storms this weekend/early next week

A stationary front lies just to the south of the Stateline and while a slight shift back north is possible as a weak upper level low moves out of Iowa and into northern Illinois, the front will likely remain just  to the south through the afternoon.  South of the front instability has been building across central and southern Illinois and back through central Iowa.  Showers and thunderstorms will develop in central Iowa and central Illinois later this afternoon with a few scattered storms likely in Northern Illinois and Southern Wisconsin.  Severe weather isn't anticipated, however, storms could produce heavy rain - especially storms that build to the immediate south and west.  Once the sun sets tonight the storm activity will begin to decrease. 

The stationary front will remain to the south of us Saturday with the focus for severe weather across parts of Kansas, Nebraska, South Dakota and Minnesota.  The threat for severe weather will then shift further east on Sunday from the Plains to the Midwest (including N. IL and S. WI) late in the afternoon.  Low pressure will move slowly through the Plains pulling the warm front northward back into N. IL and S. WI.  Instability will begin to build along with the humidity as moisture from the Gulf lifts north.  Right now, it looks like the greatest threat for severe weather will be across southern Iowa, Missouri, eastern Kansas and Oklahoma.  However, Illinois and Wisconsin are highlighted within the slight risk for Sunday.  The severe threat shifts slightly further southwest Monday and Tuesday.  If we can continue to experience enough instability early next week then the possibility of strong storms will exist as well.   

Rockford Marathon Forecast

Headed out to the Rockford Marathon this weekend?  The marathon and half marathon begin at 7am on Sunday, May 19th with the 10K run beginning at 7:15am. 

Whether you're running or watching, you'll start to notice the humidity levels creeping up a bit through the morning and early afternoon.  Typically, runners perform their best when the temperature is between 45° and 50°.  Temperatures at the start of the race will likely be in the low to middle 60s with a relative humidity value over 70%.

Deadly Tornadoes Across North Texas

10:28pm Update: NWS has now confirmed 16 tornadoes from Wednesday. These are still preliminary numbers. More detailed information on each of the tornadoes can be found here.

5:51pm Update: The National Weather Service has now confirmed 13 tornadoes from Wednesday night. These are still preliminary numbers.

Original Post: A series of tornadoes struck the Dallas-Fort Worth area Wednesday night, and the preliminary reports are not good.

According to the National Weather Service, ten tornadoes were reported Wednesday night, resulting in at least six deaths. Seven people are still missing with a few dozen injuries. The hardest hit town was Granbury. That tornado was an EF-4, which produced winds in excess of 200mph.

Here's video (Courtesy of George Kourounis) of one of the tornadoes that struck Wednesday night in Millsap, Texas.

We'll keep you updated as the National Weather Service learns more about these deadly tornadoes. Until then, thoughts and prayers go out to everyone affected by these storms.

Increasing storm threat this weekend/early next week

There is growing concern for potentially strong to severe thunderstorms this weekend and early next week across the Plains and Midwest.  The SPC (Storm Prediction Center) has had the Plains highlighted for a risk of severe storms nearly all week with the threat extending further east Sunday and Monday.  A strong and deepening low pressure system will lift north through the central and northern Plains.  Unlike with the weather this past week moisture from the Gulf will be wide open streaming in to the mid-Mississippi River Valley.  A strong cold front combined with a deepening upper level trough will move out of the Rockies early this weekend.  Areas from central Nebraska through South Dakota hold the greatest threat for severe weather Saturday afternoon.  The weather locally may end up mostly dry during the day.  As the system slowly progresses east so will the storm threat putting places from Oklahoma, Kansas, Missouri, Iowa and western Illinois in line for potentially severe storms Sunday and Monday.

The devil is in the details, though.  Storms west of here will likely influence the weather here locally.  However, it's important not to let your guard down despite a very slow start to the severe weather season.  Updates will continue right here as we get closer to the weekend.

Along with the storm threat will also come the threat for heavy rain Sunday night through Wednesday.  This system will be slow to leave through the week with numerous rounds of storms possible.

Click here for the technical discussion from the Storm Prediction Center regarding the weather this weekend and early next week.  

Viewer Photos



Michael Chunko
Sinnissippi Park

Matt Rodewald

Linda Chunko

Pat Hochstein

Michael Chunko
Sinnissippi Park Lagoon

LIVE streaming video from CBS DFW - Tornado damage from Wednesday evening

CBS Dallas Live Stream

Damage from storms in Wisconsin...Possible heat burst

A narrow line of thunderstorms developed west of Madison Tuesday evening causing widespread wind damage between Madison and Milwaukee.  The thunderstorms were weakening, however, as they moved into south-central Wisconsin so one would think that the damage shouldn't have been that great.  If you were out yesterday afternoon you knew it was hot, but it was a dry heat.  A dry air mass was in place near the surface and as the rain from the weakening thunderstorms fell into the dry layer it evaporated and caused the strong wind gusts observed.  These features show similar characteristics of a heat burst.

What is a heat burst, you ask?

A heat burst usually begins as a thunderstorm is decaying, or weakening.  Typically the air will cool as it evaporates before reaching the ground.  In a thunderstorm that produces a heat burst, the air sinks but it rapidly warms before reaching the surface often times causing strong winds but also a quick rise in temperatures.  If a very dry air mass is present around the thunderstorm, rapid evaporation occurs which causes a significant amount of cooling of the surrounding air in a short amount of time forcing the air inside the weakening thunderstorm to sink very quickly.  This is similar to a downburst (strong winds at the surface), but a downburst contains strong winds and cool, moist air and evaporation is still occurring keeping the surrounding air cool.  In a heat burst, all the water in the sinking air is evaporated before it reaches the ground.  The air then begins to warm due to compression.  This warming sometimes slows the descent of the downdraft but if the air has sufficient momentum (or speed) built up, the hot and very dry air will still make it to the surface and will be felt as a hot, gusty wind. 

Observations recorded during a heat burst show a spike in the temperature but a drop in the dew point.  Heat bursts are actually pretty common, especially ones that produce a 10° temperature increase.  Typically this type of phenomena occurs either late at night or early in the morning as a decaying thunderstorm moves through.  The weather station near at the Sullivan/Milwaukee NWS office reported almost a 10° temperature rise coincident with sustained winds of 20 mph and gusts near 40 mph.