RECORD HEAT, A FEW STORMS?

Several times this year my area has been highlighted for the possibility of severe weather. So far, it's largely gone around us or failed to materialize due to meager instability or warm temperatures aloft, what's known as a CAPPED environment. Tomorrow is another situation where some key ingredients such as shear and instability will be in place, but timing of a front may be too early to break another bout of significant capping. If by chance it does break, there is a short window in EC Iowa and northern Illinois between 3:00 and 6:00pm where severe storms could develop. The threat is very conditional and dependent on mesoscale details we won't know until late Thursday morning. For the moment, the Storm Prediction Center maintains the idea of the greatest risk over SC Wisconsin and NE Illinois and points east.

In advance of Thursday's threat, there is also a slight chance some storms could be ongoing around daybreak north of a warm front advancing through Iowa overnight. Strong warm advection combined with the low level jet could act as the catalyst for elevated development. There's plenty of instability, with water vapor increasing to over 1.6 inches. Some localized heavy rain, hail, and frequent lightning are possible in any updrafts that can get going. The area NW of the Quad Cities in EC and NE Iowa is most vulnerable to the potential. The 3k NAM simulated radar now shows more robust development in that area around 3:00-4:00 am.

The 3k indicates this for overnight rain, we'll see.

If there are any rogue storms early Thursday, the rapid movement of the warm front into Minnesota allows extremely warm air aloft to surge over my entire area. 850 temperatures mid-afternoon range from 19 to 24 degrees C. from north to south. That will create a healthy CAP that scours out any residual grunge from any morning convection, allowing rapid heating to take place. The EURO continues to indicate highs of 87 north to 98 in the south near Galesburg. 96 is showing in Moline.

Records for May 15th look like this. I will be surprised if at least Burlington and Moline do not break records.

Cedar Rapids.....94, 1941

Burlington..........93, 1944

Moline (QCA).....91, 1941

Dubuque............90, 1944

One additional note worth passing along are the dew points, which have a chance of reaching 70 before mixing out a bit later in the afternoon, especially west of the river. The muggy weather will be slightly offset by gusty south winds up to 35 mph.

Once the day's heating takes place and the storm thwarting CAP is established aloft, it comes down to timing a dry line to see if any part of my area can break the CAP and get storm development. The dry line is very evident over eastern Iowa around 5:00pm.

Once the dry line is through, that's it for any storm chances, as the convergence it creates departs and moisture is depleted behind it. So basically, it comes down to breaking the CAP when it comes to thunderstorm chances. It looks unlikely west of the Mississippi, but the 3K shows storms firing in far northern Illinois just east of Dubuque. The simulated satellite shows the storm towers going up over western Wisconsin and Illinois and then converging into a large storm complex off to the NE. Watch the orange colors blossom late in the day.

The actual storms are visible on the simulated radar, lined up north-south just east of the Quad Cities late afternoon.

Breaking it down, the 3k NAM says there is a chance the day could end up with some storms, especially in NW Illinois and Wisconsin. However, I need to caution this is just one model's interpretation. If the 3K ends up slower breaking the CAP, or zips the dry line through faster, that's the kiss of death for storms, and we end up with little to nothing anywhere, which is what most of my counties west of the river should see (and is possible further east as well). One thing we all will enjoy, is a sticky, windy, summery day with near record highs possible in the south.

Friday, brisk west winds will whip the area, initiating a cooling trend. It won't be that obvious in the south, where highs will still be in the low to mid 80s, but the air will be much drier with dew points down in the upper 30s to low 40s! Highs in the north should hold in the mid 70s.

The weekend looks breezy, pleasantly cool, and dry, with highs both Saturday and Sunday ranging from 65 north to 75 south. Say so long to summer for a while. The next rain chance holds or until Tuesday or Tuesday night. Stay cool and roll weather...TS