Severe evening ahead? Watching late PM/evening severe storm chances; some metro tornado risk?

Watched Weather Pot

If everyday is a weather puzzle, today's puzzle has some missing pieces.

Many ingredients are coming together for thunderstorms today in Minnesota, but a few key missing ingredients may delay the onset of storms -- and possibly push the highest severe threat south into Iowa. There is a history of recent "severe risk days" in Minnesota panning out to a big fat nothing. There's a small chance could happen again today.

Maybe.

A cold front will trigger storms today across Minnesota and Iowa, it's just a question of where, when & how strong.

Behind the front, cooler fresher breezes blow again as "northwest flow" returns through the upcoming weekend. No complaints mind you with plenty of sun and spectacular mild days and cool nights. But it's hard to call our Aug-tember weather pattern "summer."

Mid 80s as we move into State Fair week may have to do this year. That would feel pretty good in this "summer" of 2013.

Tracking today's severe risk

It's a cool and quiet morning in most of Minnesota. Debris clouds and cool temps combined to create a stable layer of air in much of central and southern Minnesota early today. One of the weather geeky parameters we look at for severe storms development is called "Theta-e" which is a measure of instability. High Theta-e means good T-Storm chances, and "low Theta-e" sounds like a potentially treatable medical condition for older men. I'll let your imagination do the rest.

The bottom line? A bull's eye of stable air sits over central Minnesota centered on Willmar, St. Cloud and the Twin Cities this morning. That should limit  T-Storm development through midday and possibly into early afternoon.

Storm chances increase later this afternoon and evening

As debris clouds thin this afternoon, sunshine will heat the lower levels of the atmosphere. A southbound cold front will trigger scattered showers and T-Storms this afternoon and evening. The onset of storms may be delayed until late afternoon and evening. Here's the High resolution radar (HRR) product which suggests a line of storms in northern Minnesota, and strong individual storms (discrete supercells) developing around 4 to 5 p.m. near St. Cloud & Willmar.

If that happens, there is a risk that one or two of these "discrete supercells" could go briefly tornadic between about 5 and 7 p.m. this evening just west of the metro. NOAA's Storm Prediction Center puts that chance at about 5 percent for the Twin Cities and southern Minnesota.

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There is a 5 percent risk of a tornado late today according to NOAA's SPC.

The trend favors the individual storms congealing into a line of storms sagging slowly south into the metro by around 7-8pm tonight.

This seems like a reasonable solution to me given today's trends. We'll have to watch for possible severe storms with locally heavy rain, wind and hail in the metro and southern Minnesota this evening.

The highest overall risk for high winds and damaging hail favors southeast Minnesota and Iowa this evening.

Keep an eye out for possible (likely) watches and warnings, especially late this afternoon and evening.