UPDATE: Today's 12Z NMM-WRF continues to show the maximum Storm-Relative Helicity this morning and no significant areas this afternoon where storms are expected to break out. The model does show several areas of EHI over 2.0 ("Supercells more likely, Mesocyclone-Induced Tornadoes Possible") in Missouri late this afternoon (see below), but all in all, neither one points to a major tornado outbreak. The SPC's risk areas were exactly the same at the noon update as they were this morning. We'll see what happens.

ORIGINAL POST:

Today's severe weather outbreak in the Plains and Midwest may get pretty exciting (and dangerous). The SPC [JessePedia] has been hyping the risk with a "Moderate Risk" for the last 3 days - something they rarely do. Of course, they have been known to overstate the risk a couple times this year (not sure why, this is unusual for them) when they issued a High Risk (which they still could do later this morning). So it remains to be seen how big of a tornado outbreak this one will be.

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As such, I'd like to "test" the output from the government's hi-res 4KM WRF model via our Pro Site (30-DAY FREE TRIAL) to see how accurate it's predictions will be. These maps are from the 00Z run last night; I'll replace them with the 12Z run when it comes in this afternoon, but by then it will be too late to use it for planning purposes. In the maps below I'm showing the maximum numbers and coverage area this afternoon for several different Severe Weather Indices [JessePedia] from the Forecast Models [JessePedia]. The chart below shows the number at which the indices predict widespread severe weather, and the maximum number where things would go "off the charts."

First, we'll look at the maximum predicted CAPE today, one of the oldest among the indices (and hence better at predicting general thunderstorm strength, as opposed to tornadoes).

If this prediction is right, the biggest clusters of Spotter Reports that we'll see this afternoon and evening will be from Central Oklahoma to Kansas City. We're off the charts at 4000+ so a widespread severe weather outbreak seems likely, according to this index.

Now we'll move on to Lifted Index, probably the oldest indicator of thunderstorms. It says approximately the same thing (off the charts at <-10), though the axis is tilted to be southeast of Kansas City.

And finally, the SWEAT index, which is fairly consistent, though the numbers (450-500) say "Severe Thunderstorms, Tornadoes Possible" but don't predict a massive tornado outbreak.

As a final note, I will show the two indices specifically designed to look at tornado severity, but from the lower-resolution WRF-NMM model. These show that the strongest tornadoes may be on the northward fringe of the severe weather area, which is probably why the Moderate Risk is positioned further north than the CAPE or LI seem to say it should be (and it's probably further east because the violent storms will move eastward).

The Storm Relative Helicity Index above shows values of 550 near Kansas City (and showed a wide area of 500+ in most of Kansas on the image 3 hours before). This is off the charts, beyond the level of "Violent Tornadoes (F4/F5) Possible" so this speaks to the severity of the tornadoes that may form.

And the Energy Helicity Index shows 6.0, again off the charts above "Violent Mesocyclone-Induced Tornadoes (F4/F5) Possible." Note however that both maps above show their best numbers this morning, *before* the storms will form. It will be interesting to see whether or not that has a bearing.

Of course, that's only 5 indexes, out of a dozen, and there are a dozen more models predicting one or more index, or the factors that make up the index. The indices disagree with each other on timing and placement. I don't have time to examine them all today, but I trust that the SPC and AccuWeather are, and I hope you understand how difficult severe weather forecasting can be.

How will the storms form and move? Well, the 4-KM WRF is taking a guess at that too, saying cells will break out in Kansas, Oklahoma and Missouri, then merge into a line moving southeast overnight.

Tune in tomorrow, and we'll see how the models did.

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