This is an overview of the severe weather due to happen over the course of today.
We will start with how unstable the atmosphere will be, since that plays a big role in severe storms.
BEST LIFTED INDEX
The Best Lifted Index was very surprising this morning. Values of this sort are usually found around in Mexico. Below is the latest image of right now from the RUC.
First off, notice the value of -12 out in Iowa. That is an extremely delicate situation. Should severe storms enter that area with the value of -12, I would definitely expect very large hail and strong tornadoes. Luckily, that will not happen. It may happen this evening, but not right now.
Let's fast forward 12 hours to when the severe weather is projected to actually happen.
First off, we do see a weak definition of a squall line. However, the SPC actually cut off the tail end of the outlook, leading me to less and less believe the idea of a squall line throughout the Plains and south central US. It looks more like a small squall line as well as clusters of disorganized storms.
Anyhow, it appears values of -6 and -4 will be in the severe area. Main concern will still be in Iowa, where maximum values appear to be -8. Overall, this is definitely a situation to watch for Iowa.
LAPSE RATES
Another indicator of instability is lapse rates. Remember, values at 9.5 are 'absolutely unstable'. Below is the RUC image form right now at the time of publishing.
Lapse rates are temperature drops with height. We see an extremely unstable situation in Nebraska at this time, with values from 8.5 to 9 degrees.
Next, let's fast forward 12 hours to the severe weather time frame.
These values aren't very impressive where the storms are forecast to occur. However, still back in Iowa and Nebraska, the lapse rates will remain very high and unstable.
FORECAST RADAR REFLECTIVITY
This is basically what the radar is forecast to look like in the near future. Let's take a look 10 or 12 hours in the future using the RUC to see what the storms will look like.
That line extending south was actually a weak squall line in hour 10. However in this image, hour 12, we see the storms only beginning to affect the area. This RUC method has been right in some situations while wrong in others. However, this looks like a good bet, but I would add in areas of yellow if I could to this image. Below is an animation of a WRF run from Wright Weather.
This animation is an overall good tool to use as a predicted radar lookout 48 hours in the future.
STORM PREDICTION CENTER'S OUTLOOK
So these are the SPC's outlooks for today's severe weather. The images, in order, are the overall risk, hail risk, tornado risk, and damaging wind risk.
It appears to be no coincidence that the tornado risk and damaging wind risks are in the same areas, as atmospheric turbulence can create damaging surface winds as well as violent tornadoes. The Hail risk is also most concentrated in the wind/tornado threat, leading me to believe any storms that develop in that area will have strong lifting, meaning it will be able to throw water droplets high enough into the air to freeze into hail. That hail risk also extends into Illinois and the Southern Great Lakes. It appears that, although that lifting mechanism will weaken as the complex moves off, that lift will remain able to generate small hail.
This has been an overview of a Happening Now situation. These are issued when a weather event is due to happen today.
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