4/23/09 FCST: IA

[Scott Weberpal]

Not sure if this showed up on prevous run, but this mornings WRF shows an intersting scenario in SW IA tomorrow. An embedded shortwave splits off from the main flow and creates a strong veering kinematic profile. Accompanied by a weak attendant sfc trof (perhaps an indication of a weak sfc low in SW IA), adequate moisture, and strong vort max, it looks like an isolated supercell isn't out of the question. The current Day 2 (the early morning one) gives no indication of this possible event leading me to believe it has just showed up the on the models today - or I'm way out in right field!

 

[Jeff Duda]

Yes, that is very interesting. It did show up in the 12Z GFS run, also, but as a weaker shortwave. It's lighting up the QPF grids though, and the ARW simulated reflectivity field for Thursday in the afternoon and evening shows almost a single cell that bows out as it flies over E NE/IA. This feature did show up in the 06Z NAM run, so we'll have to see if it establishes run-run continuity to see if this will actually pan out. Most of the other models (SREF, NMM e.g.) do not show this feature.

 

[Jared Farrer]

I see this too, looks like good potential for an isolated severe event. Might even be one of those lone supercell events with the possibility of a tornado or two. I am giving it high potential at this point with such focused accent with that tight vort max. Good shear and good instability, I would think the red oak IA area is a good area.

 

[Jeff Duda]

The 18Z NAM still has it going strong, but a little farther south of where it was in the 12Z run. The 18Z GFS has all but eliminated it, but that is probably more due to the coarse resolution of the GFS against the very small scale of the feature. I'm excited to see what happens seeing as, if anything does, it will more or less go right over my head here in Ames. We haven't had any severe weather here yet this season.

 

[Andrew Pritchard]

This has actually been showing up on the models back to Monday, but this is the first time I've seen the cap breaking.

It has painted excellent hodographs and instability all across the boundary from western Iowa into western Illinois and eastern Missouri. However, a very strong cap had been in place on each run so I disregarded it. Seems now the WRF wants to break the cap in southern and central Iowa along the boundary, which if were to come to fruition would likely yield at least one, or more supercells depending on the extent of the cap breach. The GFS also weakens the cap a bit, but further south towards southern Iowa and NE Missouri around Kirksville. In either model run, hodographs with with excellent low level shear would yield high tornado probabilities if any portion of the cap is breached.

I've got some stuff going on tomorrow, but I'll keep an eye on the 0Z run and consider a run to southern Iowa. The cap could be scary, but the reward could be sweet with this one...

 

[afischer]

Haven't looked at tomorrow's set-up much at all (I hate saying that, but it's true in this case! ), but a quick glance at models vs. surface obs indicate the 12Z and 18Z runs of the NAM and GFS are currently running a good bit too high (around 5°F) on the surface dewpoints over much of southeast KS/eastern OK/AR. Unsurprisingly, the 18Z LMN RAOB shows skin-deep boundary layer moisture, though dewpoints locally in the 56-60F range are managing to "pool" (if you can call it that) just N of the the WNW-ENE oriented frontal boundary in eastern OK-AR. Assuming this is the primary source region for tomorrow aftn/eve over the lower MO river valley... I'll be surprised if we end up with a large reservoir of 60-64F sfc dewpoints that the NAM/GFS is advertising (and with constant mixing ratios forecast in the boundary layer by the NAM, no less!) Even the 12Z soundings along the coast showed a very shallow moist layer beneath a rather deep/ugly EML.

 

[Ryan Wichman]

SE Iowa soundings from the 12Z GFS seem to indicate that the cap may be vulnerable to being overtaken by the warm surface temperatures. Should this occur, the atmosphere is primed for supercellular development with large low-level hodographs and abundant instability on the order of AOA 2000J/Kg in the Keokuk, IA region. Not completely jumping on board that this will happen, but being so close to possible development would make this an easy target.

 

[John Farley]

The NAM, GFS, and RUC all agree on breaking out precip somewhere in northeast MO, southeast IA, and/or west-central IL during the 21Z-0Z period this afternoon/evening. Given that this is in an environment near the warm front with EHI better than 3, I think there is some potential for a supercell/tornado event if indeed any strong storms get going. The models vary quite a bit on where the convection might initialize, ranging from west of STL to southeast Iowa, but a good average might be somewhere in the area bounded by Kirksville, MO, Bowling Green, MO, and Quincy, IL. If we get some decent clearing in that area this afternoon, I will likely head that way for a look-see. I will be interested to see if SPC picks up on this area on the late morning convective outlook; so far they have not been impressed, but the model consistency on breaking out precip in this general area certainly has my attention.

 

[Andrew Pritchard]

One heck of an MCV currently traveling across northern Missouri. I'm still stuck in Champaign with stuff going on this evening, but should I get out I'd just head out in front of that thing. That's going to be your best shot at getting thunderstorms to redevelop in the heavily capped atmosphere.

Will have to watch and see how fast moisture does indeed return to the area in advance of the mcv as well. Be nice to see at least a 60F reading there in advance.

A line from Kirksville, MO to Quincy, IL looks like as good a bet as any this afternoon.

 

[Jesse Risley]

The 21Z forecast soundings in this area do appear favorable for a supercell or two if something can get going in the wake of these morning showers, followed by some afternoon heating.

Since I don't have far to go, I'll probably hang around and watch the northward progression of front and see if anything appreciable happens to fire. A big factor may be if and when those higher dews that are currently to the SSE of the area actually arrive, but I wouldn't rule out at least some isolated hailers.

 

[Ryan Wichman]

I have to say that I am not impressed by the surface moisture in the IA/IL/MO region right now. DP's are sitting at 50 at most stations with surface temperatures in the mid 70's. Just off to the south there are some mid to upper 80's associated with the warm front. Low hanging clouds are beginning to fill in, in front of the MV right now and this will really hurt our chances to warm up much further this afternoon. I think we will really need the moisture to ramp up here in the next few hours and see temperatures jump to near 80 for some nice cells to pop. Sitting and waiting in Macomb right now.