We are starting off to a foggy start this morning, but that will gradually burn off to make way for a partly sunny afternoon. Later this afternoon there is a chance for severe storms to form in northern Iowa and these storms will drift off to the southeast. The dynamics are sufficient enough for storms to turn severe.
When determining if a storm will form, a few things we look for is: CAPE, low level shear, bulk shear and if there is a cap or not. CAPE stands for Convective Available Potential Energy. It is a measurement of the amount of energy available for convection or the upward development of a cloud. A good CAPE value would be between 2000-25000 J/kg or greater, but is sufficient enough at 1500 J/kg. Today’s CAPE value will be between 2000-25000 J/kg. Shear is another thing we look for which is a variation in wind speed and/or direction over a short distance with height. Today’s low level shear is weak, however bulk shear is decent enough for supercell thunderstorms to exist. The last thing we look at is if there is a cap or not. This cap is a layer of relatively warm air aloft, which suppresses the development of thunderstorms. Since there will be no cap this afternoon, thunderstorms should be allowed to form.
With these conditions, storms should become severe later this afternoon with large hail and damaging winds the main threats. There is a slight chance that there could be an isolated tornado or two in far northwest and northern Iowa early this evening. Rainfall totals is another thing of interest. The heaviest rainfall totals will be in northwest and northern Iowa where amounts will be around a half inch with locally higher amounts possible. The further south and east you go, rainfall totals will start to taper off. Totals in the southern half of the state will be between a a tenth to a quarter of an inch. We will continue to track this risk for severe weather and will bring the latest updates on our facebook page and right here at Iowachase.com.