2011-05-28 FCST: KS/MO/IL/CO

[Matt Hunt]

Tomorrow there will be a somewhat stationary front from near the low in KS and draped across central/northern MO into central IL. A weak impulse is expected to move ENE through the Ozark region tomorrow afternoon/evening. In addition, AM convection should lay down some outflow boundaries which could serve as sources of lift for surface based storms. Parameters look amazing for supercells and tornadoes if storms can fire. Bulk shear 0-500mb is at 40-50 kts in the warm sector, and hodographs are large clockwise curves. Instability should be around 1000-2000 J/kg, depending on clearing out of the early convection. If that convection hangs around too late, it could kill any chances for storms. However, if storms initiate, all of the ingredients are there, plus storm motions will be extremely manageable at 10-15 kts.

I'm planning to head toward St. Louis late morning/early afternoon, depending on how things look in the morning. There may actually be a better chance in MO, but terrain is not very good, and I'd rather not go that far. Just depends where that impulse is come late afternoon.

Anyone else planning on chasing this one?

 

[Joel Wright]

....Anyone else planning on chasing this one?

Yeah I'm liking the potential of this event. It's sort of a sleeper setup at this point due to the conditional nature of it. The deep layer shear over far eastern Missouri into the southern half of Illinois is very nice to say the least. Issues with lingering elevated morning convection, and the building mid-level cap are the only things keeping this from being a great setup. If morning convection gets out of the way in time, and if the cap can be broken it could be quite nice from the St. Louis area through the southern half of Illinois. I tentatively plan on heading somewhere south of Springfield Illinois.

 

[Scott Weberpal]

The moist adiabatic lapse rates between 850 and about 650mb will put a damper on updraft acceleration. Not good to have >500 j/kg of CAPE in the 850-650 mb range...

http://www.twisterdata.com/data/tmp.../RUC_255_2011052812_F12_38.5000N_89.0000W.png

If for some reason those lapse rates steepen, the potential for tornadoes will be much greater - however, at this point I think the potential is very minimal; even given storm initiation.

I think it will be hard enough to get a storm going today as-is. However, if the low-level lapse-rates were better, I'd be down there in a heartbeat.

 

[Mark Blue]

Latest indications in the 12Z model runs (NAM and RUC) show a Denver Cyclone setting up today with surface winds out of the SE and turning with height to WSW at 500 mb. The surface winds should help to bring dewpoints into the lower 50s in Eastern CO this afternoon with the richer moisture being located south and east of the area. The one stickler here is how much boundary layer warming we will have with daytime heating this afternoon. With forecast highs in the lower 70s, CAPE won't be much more than 1000 j/kg at best during the late afternoon, but that is enough in the high plains. There are pockets of decent helicity and EHI that are co-located up against the front range (nice bullseye over Denver) showing up on the model runs and with low pressure setting up along a surface boundary that will be draped over the region we have a decent chance of a few isolated supercells developing that will mostly be a hail threat, but tornadoes and landspouts are always a possibility in these scenarios. Here's a forecast sounding and hodograph for today at 0Z for the Denver area: Denver Hodo. Interestingly enough, the hodographs look even better out east by Limon and along I-70 and east central Colorado for late this afternoon. For the time being our target is right here at home, but we may drift out east on E-470 this afternoon as that provides a good vantage point to observe the storms that are forming along the front range.

 

[Matthew E. Engelbrecht]

...adding CO to this thread.

Increasing moisture along the front range of CO underneath a moderately strong upper-air flow may contribute to organized thunderstorm activity in this area today. At 16Z, a DCVZ was located from about Platteville-Denver International Airport-Parker-Castle Rock. Morning water vapor imagery indicated a weak upper-air disturbance in the flow just east of SLC. As this disturbance approaches N CO, surface winds along the plains should increase and back to the SE, contributing to helicity values exceeding 300 m2/s2 over a large area of eastern CO by 03Z. Forecast surface temperatures in the low 70s in areas with full insolation along with dew points increasing to around 50 degrees may locally increase CAPE to 1000 J/Kg. This disturbance should be able to erode CIN enough from the Denver metro area and points north to allow for scattered thunderstorm development around mid-afternoon. Southward extent of activity may be limited by increasing 700 mb temperatures, but severe potential may be greatest in areas between Denver and Limon. My plan is to head east of Denver to the Watkins/Bennett area by mid-afternoon to see what develops, paying particular attention to any storms south of I-70.

Edit: You beat me to it, Mark.