7/14/09 FCST: MN/NE/IA/MO/IL/WI

[Scott Weberpal]

Looks like decent potential for a good chase day somewhere along or east of the I-29 corridor. Strong deep layer shear, steep lapse rates yielding strong instability, and a cold front trailing a 997mb low which is situated along the US/Canada border at 00z. At this point, the NAM shows the best deep layer shear and best instability slightly out of sync in MN and N. IA, but they are better juxtaposed in NW MO/SW IA/SE NE.

Something very worth keeping an eye on.

 

[Bob Hartig]

This system certainly shows promise. Here are a couple shots from the 12Z NAM-WRF, showing SBCAPE and surface wind barbs, and 500 mb winds with wind barbs. I haven't checked the GFS, but according to the WRF at least, capping doesn't presently seem like it'll be an issue.

ADDENDUM: I just looked at the GFS, and it paints an ugly picture re capping, with 12-15 C 700mb temps through much of the region and formidable MLCINH. Sure hope the WRF is giving the more accurate read.

 

[Scott Weberpal]

Tuesday is continuing to look like a dream in NW MO for tornadic supercells with the NAM continuing to show CAPE exceeding 4000 j/kg and 0-1km SRH exceeding 200 m2/s2 locally. The NAM has also been fairly consistent with warm frontogenesis in the area and convection breaking out between 21z and 00z in every run so far. Last nights run showed early linear MCS making its way into NW MO during the afternoon, however, the 12z run this morning essentially eliminates that scenario. Still a few days out, but I haven't been this excited for a setup on day 3 since the days leading up to May 13.

 

[Michael O'Keeffe]

The NAM continues to show a potentially explosive setup over SE NE/NW MO/SW IA possibly into NE KS. Hopefully the morning convection it was showing doesn't ruin the setup. However if morning convection clears early enough and allows for destabilization I would expect significant supercells with some monster hail given the steep lapse rates and very high CAPE values as well as a few tornadoes given the classic long, looped hodographs and unusually strong wind fields for July.

Check out this ridiculous forecast sounding at 0z Tuesday for Falls City, NE.
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=FNB

 

[Scott Weberpal]

Just looked at H7 temps, something I didn't do earlier and it worries me. For some reason, the NAM shows a small pocket of 10-12c H7 temps surrounded by 12-15c temps on all sides - and that's exactly where the NAM continues to break out precip.

I'm really worried the precip the NAM breaks out at 00z is associated with a developing MCS as H85 winds increase in NW MO from 25kts at 21z to 40kts at 00z with a substantial cap still in place.

 

[Ryan Wichman]

I have to agree that the Falls City Skew-T looks juicy but after the year we have had I can see one of two, or both happening.

1) Convection early on ruins the chances to destabilize the atmosphere
2) That 700mb CAP remains stout

I agree that there will probably be severe weather on Tuesday, but it looks like it will happen after sunset and primarily be a wind event as it so often happens in the Midwest. Sitting right on the north edge of that 700mb CAP might be a smart play.

With all that being said, we are still 48+ hours out so a lot can evolve in that amount of time. That 700 mb CAP could really help to keep any precip from breaking out early on in the event and allow for maximum destabilization. With the nice directional shear, especially for July, and some good helicity values if something can go up it has a chance to be nasty. However, after all of the let downs this year, I'm almost ready to chalk up another 2009 fail before anything.

 

[Bob Hartig]

Being an optimist, with just enough forecasting knowledge to feel happy about this setup but also enough naivete to not get too concerned about the darker details right now, Tuesday looks to me to be the best thing I've seen in a long time. 700mb temps are of course an issue, but there are some great hodographs, and with a few days still left, it's hard for me to imagine that the cap won't break somewhere to the north of St. Joseph, MO, in southeast NE and/or southwest IA.

 

[Mike Hollingshead]

I'm not sure I'll be opting on that southern deal. Not sure I've seen anything good when it's at all close to the 100+ sfc temps. Just seeing the 100s in KS scares me. I think I'll settle on the fairly slow moving cold front with the lovely upper trough crossing the Dakotas. Crazy things seem to happen with little low level shear sometimes with a nice trough and great upper speed shear. And the thermo profile gets ridiculous.

Just check out nw IA, Orange City I believe on the GFS.

ORC

Almost 500 0-3km cape....! Can't recall seeing that much low level cape. LCLs just above the grass. 60 knot mid levels topped by almost 90 knots up stairs. Weakly sw sfc winds can be fine if the storm is scooting along to the east which it should with 60 knot mid-levels. Just seems possible to me somewhere south along that front could have some isolated fun for at least a little while.

 

[Brandon Sullivan]

Man.. I'm really tied on this one..

I want to believe the NAM which erodes CINH across NW MO by 00z, and shows increasing lift along and North of the WF and a well timed shortwave ahead of the cold front, which I hope could break the cap..

But, as Scott so cleverly said, I am worried about the precip evolution progged by the NAM..

Regardless, will have overnight MCS the night before to worry about, so wont really have a good picture until that morning..

As far as what mike said, definitely the best upper level support near his link, but I dont recall much luck/experience with a lack of substantial low level turning..

I still would like a WF play in NW MO.. we shall see.. The parameters are there, but it wont matter if the cap dont break or decaying mcs kills it in the morning..

 

[Mike Kovalchick]

The HPC Model Diagnostic Discussion throws out the NAM/GFS and perfers the 9z SERF. (among other models.)

http://www.hpc.ncep.noaa.gov/discussions/pmdhmd.html

The 9z SERF would pinpoint East-Central Iowa area as favored:

http://www.spc.noaa.gov/exper/sref/frames.php?run=2009071209

 

[Mike Hollingshead]

Strange, 9z SREF compared to 12z GFS look similar in sfc and mid-level trough placements to me.

http://www.spc.noaa.gov/exper/sref/gifs/2009071209/SREF_H5__f063.gif

http://www.rap.ucar.edu/weather/model/gfs060hr_500_wnd.gif

http://www.spc.noaa.gov/exper/sref/gifs/2009071209/SREF_wind_vector_10m_f063.gif

http://www.rap.ucar.edu/weather/model/gfs060hr_sfc_mslp.gif

http://www.spc.noaa.gov/exper/sref/gifs/2009071209/SREF_SFC_LI_f063.gif

http://www.rap.ucar.edu/weather/model/gfs060hr_sfc_pwat.gif

Of course those will be changing.

CAPE shows the cf well.

http://w1.spc.woc.noaa.gov/exper/sref/gifs/2009071209/SREF_SFCCAPE_MEDIAN_MXMN__f063.gif

twister data cape

West edge Sioux Falls to sc NE on both, hard to line up much similar.

 

[Dustin Wilcox]

Despite what it wants to do with QPF, this here just scares me, at least for the Southern Area: http://grib2.com/nam/cplains/C-PLAINS_NAM218_700_GPHTMPRH_57HR.gif
I'm not throwing in the towell (still haven't learned how to) but the more and more times I bake under a hot summer sun and watch amazing parameters go to waste, the easier and easier it becomes to at least trick myself into thinking I'm throwing in the towell. Despite the off Hour being a touch cooler with UA temps cooling between 21Z and 0Z and the model breaking out precip, this currently looks to me like one of those days where the composite indicies will trick you into heading out, then the meso-analyisis page will trick you into staying and overlooking the Basic UA section, with the result being nothing but wasted time.

 

[Jeff Duda]

I've been watching this day's setup, too, and even with looking at the latest SREF forecast (15Z) I continue to see the same theme playing out: the best shear and helicity are to the east across central and eastern Iowa/northeast MO, whereas the instability axis is off to the west near the Missouri River. Thus there is a displacement between the best instability and best shear. However, there may be sufficient instability to the east in SC/SE IA where shear is better. Also, 700mb temps (and the cap) appear to be a little weaker to the east, and the temps cool southward between 21Z and 03Z as the front and trough move in.

 

[Brandon Sullivan]

I've been watching this day's setup, too, and even with looking at the latest SREF forecast (15Z) I continue to see the same theme playing out: the best shear and helicity are to the east across central and eastern Iowa/northeast MO, whereas the instability axis is off to the west near the Missouri River. Thus there is a displacement between the best instability and best shear. However, there may be sufficient instability to the east in SC/SE IA where shear is better. Also, 700mb temps (and the cap) appear to be a little weaker to the east, and the temps cool southward between 21Z and 03Z as the front and trough move in.

The SREF IMO has a poor handle on this setup.. The NAM and EC seem to be more reasonable on the system. Even if the CAPE/Shear were real on the SREF, the frontal boundaries or any significant forcing wouldnt be present..

Along the Warm Front especially, the best low level shear and instability should be juxtaposed the best, but this area is somewhat separated from the best UA support, but deep layer shear of 45-55 Kts will still provide favorable support for supercells, should storms form..

As for what Dustin said, I know exactly how he feels.. I have the same feelings.. The low level shear will certainly be enhanced along the warm front, which will be enhanced likely by the morning convection and differential heating. But none of that matters if the cap doesnt go..

 

[Matthew Piechota]

Ya nothing will matter if the CAP holds, it looks to be pretty strong. there is less forcing the further east with less instability.

we need better helicity further west. as brandon said, best LL shear will be enhanced along the WF where that sets up. if the CAP does go, things could get interesting. the shear is there, as is moisture. models do show temps cooling after 21z

need the CAP to go and get the helicity and instability to line up alittle better then progs are showing now.

will also be interesting to see if the NAM/GFS line up with the SREF or vice versa.