2014-06-30 FCST: MO IA IL WI

[chrisbray]

I'm seeing a decent chase opportunity coming up on Monday, especially given the time of the year. Lots of unpredictability remains but it look to be right in my backyard so I doubt I will be passing this one up.

GFS and NAM have some major differences per the 18z runs today, but overall I see enough qualities to get me excited. A very seasonably strong upper trough looks to make its way across the upper MS valley on Monday with a closed low hanging over Canada. I'm seeing 50-70 knot speedmax/shortwave crossing Iowa/Wisconsin/Illinois in the afternoon, and timing could be critical in regards to storm development

Both NAM/GFS at this point showing great instability (2500-4000 cape) and pretty good shear depending on the model (40-50 knots), forecast 3km EHIs in the 6-10 range around 21z Monday. Surface winds will be pretty much southerly or perhaps slightly veered or backed from there, depending on how it works out, with nice turning with height.

It will likely be an HP mess with PW forecast to be 1.75 to 2.25 inches!

But, I am hoping this pans out for one last local chase this year.

 

[Jim Parsons]

Central IA Monday....

 

[Jeff House]

Supercells are already in progress this morning. Morning rain is often considered bullish for tornadoes, to establish locally higher low level shear along outflow boundaries. It does not necessarily have to be light rain or drizzle; severe storms also count as morning rain, long as the ATMO can recover by afternoon. Today it should do so.

Upstairs turning will be excellent. Winds turn quickly from backed to veered at 700. From 500 up winds are nearly westerly. No veer-back issues are present today. Speed shear is more than enough, in fact quite robust for late June. At the surface high dewpoints are noted both sides of the boundary, at least the first county north. If the low to mid-60s dews stay a county or more north of the boundary, tornadoes would be favored with more time before cool pools undercut. Heating will be robust by afternoon with 70s dews south of the boundary keeping LCLs low.

Missouri River presents a logistics challenge out of eastern Nebraska. One might consider letting that stuff go this morning, and starting a chase from I-29 already east of the River. Position with the boundary, which should not move much. Then go east from there. That said, if already on top of an east Nebraska cell go for the morning catch first. They appear to be rooted at 13:30Z, subject to change with time. Good luck and chase safely!

 

[David Williams]

Question about Jim's skew-t example:

The atmosphere looks almost entirely saturated. Don't we need some dryer air above 800 hPa? Wouldn't a saturated skew-t like that indicate the current presence of a cell or immediately after the passage of a cell?... Oh wait, is that the point? The models are predicting a cell in that are during that time.