4/6/10 FCST: NE, IA, IL, MO, KS, OK,

[Mike Smith]

OK, I'll start off Tuesday's thread.

Models indicating the 12Z position of the upper trough be in the vicinity of the Four Corners. Over the years, I have found that is a near ideal position for thunderstorms to develop along the I-35 corridor in OK and U.S. 81 corridor in KS and NE.

18Z Saturday NAM shows 1,500 to 2,200 j of CAPE just ahead of the dry line and spreading out along the warm front near I-80 in IA-IL. This is more than enough instability given the strong dynamics that will be in place.

By 00Z, the NAM indicates a strong vort max near HLC which should cause the SFC low to move to between DSM and OMA with severe thunderstorms possible from northern Illinois into OK.

 

[Jeff Duda]

Thing I have liked about Tuesday's setup: upper level support is finally there

Things I have not liked about Tuesday's setup: winds at all levels veer out, and timing isn't the best in my neck of the woods (IA).

 

[Mike Hollingshead]

Tuesday seems to have been going down hill fairly steadily as of recent runs and multiple models. Negative tilt idea pretty much gone and not coming back. Neutral tilt idea seems like it is already going bye bye too. More and more it looks like it wants to come out positive tilt with a big ol cold front. I only hope it is at least real close to here for initiation. Maybe the southern extent/western OK part of the day can work out....given of course the GFS is completely wrong and NAM is completely right.

 

[Scott Weberpal]

One constant concerning Tuesday has been the enhanced SRH immediately northeast of the sfc low where sfc winds remain backed. If I had to choose a day to chase the next few days, it would be Tuesday. Moisture in amply in place, the cap shouldn't be an issue, and the upper support finally arrives.

The cooler H5 temps should make their way into NW Iowa before 00z and help kick off a line of storms from just NE of the low southwestward through Iowa and into Nebraska. Unfortunately a big caveat is the orientation of anvil level flow parallel to the front making seeding a significant problem to the hopefully lone supercell northeast of the low. Best bet is to hope something goes up just ahead of the line, or a sup can remain discreet northeast of the low for an hour or two before everything lines out.

At this point I've essentially given up on Monday and I'll likely give NW IA a shot on Tuesday.

 

[Brendon Lindsey]

Well looks like a chase day for me. NAM 12z Data looks as if its painting a target around Chickasha,OK basing this off of the EHI, Instability, Lift, and Moisture. The dryline looks great. Low lovel winds will be roaring in Eastern OK. the 12z GFS paints a target a bit more to the NE, probably in between Tulsa and OKC. I want to be just east of the dryline tomorrow afternoon where the most lift and instability are, NAM is returning DP into the 65+ range right ahead of the DL in C. OK right before dark. Lets hope the cap will break, and let a few isolated sups form. I would call this my first legit chase this year. I will be chasing C. OK - NNE OK - maybe SE KS. Someone can come along if they help with gas.(PM me) I wouldnt mind hoppin in with someone else if you are in the region. Lets hope the forecast shows some positive stuff the next two main runs.

 

[rdale]

I'd be okay popping MI into the mix... Warm front setting up near I-96, great looking directional shear. Question is leftover debris from today's midwest stuff, but if we can keep enough breaks into warm us up I can see some chaseability around here.

 

[Bill Schintler]

Chase targets Tuesday

Chase target, south:
Cox City, OK (40 miles south of OKC).

Storms will backbuild from northeast to southwest along an advancing cold front, with supercells possible early in storm evolution, and quickly transitioning into a linear mode with minimal severe weather potential. A “tail-end Chalieâ€￾ may be the preferred target location, with storm initiation after 7 PM CDT. Individual cells will track towards the northeast at 30 kts.

Chase target, north:
Lawn Hill, IA (50 miles north-northeast of Des Moines).

Storm initiation will be 5 PM CDT, with supercells likely. Storm motion will be towards the northeast at 40 kts. All modes of severe weather are likely, including a tornado or two.

Discussion - OK:

An advancing DL should provide the focus for convection by early evening. A narrow axis of instability will develop along and E of the DL, coincident LCL’s around 1000 m AGL. Instability is modest, but sufficient for storm organization given the available shear. Strong capping will inhibit convection until after 00Z when 700mb temperatures cool 2-3 degrees with the approach of a mid-level impulse. Initially weak LLVL shear will increase after 01Z as the veering LLJ increases to 30 kts, with SFC-3km SRH’s increasing to 200m2/s2. Deep-layer shear of 60kts will be sufficient for storm organization. A CF will surge to the southeast, overtaking the DL from N to S across OK between 00Z and 06Z.

Discussion - IA:

The western CONUS synoptic-scale trough will work slowly towards the E while amplifying over the next 36 hours, forming a closed circulation over NEB between 00z and 06z, 04/07. SFC low pressure will track track slowly along an NE/SW-oriented boundary. Ongoing convection along and N of I-80 will lift to the NE during the morning hours, however limited clearing and subsequent destabilization will take place. ST will blanket much of the state except for CNTRL through SCNTRL IA where clearing will take place after 17Z. Locally backed SFC flow, enhanced by an outflow boundary from morning convection, may exist along the WF immediately NE of the low over CNTRL IA; along the NWRN periphery of a 50 kt southwesterly LLJ. A 80-90kt H5 streak currently over currently over AZ will enhance deep layer shear in IA between 18Z and 00Z. Warm-sector dewpoints will increase to AOA 65F. A significant tornado parameter of 3-4 is indicated the SPC SREF.

- Bill
10:22 PM CDT, 04/05/10

 

[Darrin Rasberry]

At this point, I have no choice but to target central Iowa, as that is where I work. I get off at two, so I hope that the NAM's pushing of the trough verifies, and not the GFS's prediction of its loitering over Nebraska all day.

I don't really enjoy the positive tilt with all its attendant parallel-to-the-boundary southwesterlies, so count me a critic of the 10% area outlined just now - at least in Iowa's neck of the woods, and especially if the GFS verifies. But as it's virtually over my head, I don't really have anything to lose. Target: Newton, IA

 

[Brendon Lindsey]

hmmm

Well I dont really know what to think, I dont have too much faith in storms forming around OKC until well after dark. I could use some help forecasting the cap, WOW the (12z NAM +12 ) and the (12zRuc +12) are completely different by about 150 mi.. Ruc showing crazy ehi abd instability over NE OK. RUC is speeding up, NAM is slowing down. If I had to throw out a target for possible before dark action, closest to me, How about Bartlesville, towards Ponca city maybe. Cap is a problem. Lets get some input on this thread or by PM. I am willing to learn. Gfs 12z still to come.

 

[John Vandehei]

I think I'd second the recommendation of adding MI to the list, although it appears the threat will only be for a couple more hours. Already a tornado warning out as I type this.

 

[Kevin Walters]

I feel there is potential for tornadoes along or just on the cool side of the warm front currently lifting slowly to the North in Iowa. There is heating taking place across the Southern part of the state with surface winds gusting over 20 mph. Here in Central Iowa we have East winds with low clouds and light rain. Directional wind shear looks very good at low levels. Any storms that form and remain discrete will rotate.

 

[Jeff Duda]

I feel there is potential for tornadoes along or just on the cool side of the warm front currently lifting slowly to the North in Iowa. There is heating taking place across the Southern part of the state with surface winds gusting over 20 mph. Here in Central Iowa we have East winds with low clouds and light rain. Directional wind shear looks very good at low levels. Any storms that form and remain discrete will rotate.

I think you're forgetting that in Iowa in April, there will be NO instability north of the warm front. Also, current SPC mesoanalyses show that 850 mb winds are due west everywhere in S IA, and the 7C isotherm at 700 mb (which was more than sufficient for capping yesterday) is already north of an Osceola to Ottumwa line). I think the only chance for tornadoes in IA today are within 20 or so mi south of the warm front. That's the only place where there will be enough shear and instability to get a tornado to form.

 

[Kevin Walters]

There have been several times we have seen tornadoes form in April, in Iowa, with surprisingly meager amounts of CAPE on the cool side of warm fronts. We shall see.

 

[Brendon Lindsey]

CHECK this out, It shows us hope for the southern target. If I dont bag a storm before dark, overnight towards TQH will be sweet.

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/

 

[Chris Hovanic]

Heading to near or just east of Yates Center, KS...targeting this area due to model forecasts of persistent backing surface winds this evening. Also hoping greater mid-level westerly wind component will keep convection more discrete as compared to areas further northeast along frontal zone.