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6/26/10 FCST: NE/SD/IA/MN/KS

From looks of 12z NAM, there appears to be a nice bullseye on the boundary from NE Nebraska into extreme SE South Dakota and NW Iowa. Timing looks to be mid-late afternoon with strong instability on both sides of the boundary. 40-50 kts. deep layer shear and 0-1km VGP should be favorable for tornadoes given the moist/warm (not hell capped) airmass in vicinity of the roughly e/w oriented boundary. Things may transition to more cold pool outflow dominated storms & supercells as the front begins to sag south and southeast further into NE/IA after 6-7pm time frame. Sure looks to me like a decent June setup. Will keep a watchful eye on tonight's data.... :cool:
 
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I was looking at the same area as well. Climatology favors tornadoes in this area in late June. Any storm that deviates due south could become tornadic.
 
Looks like the main threat for tornadic supercells will be near and east of the surface low, progged to be just N of Yankton, SD by 4 P.M. and the stationary front in place now. I'd say a good place to start off today would be Sioux Falls, as that has interstate and highway access.

At least the road network around here is pretty solid, but a word of warning to anyone who's chasing in this area - there are several washed out and still flooded roads in the area, for example US Rte 18 is closed. And with the 1-3 inches expected to come from these storms, more will be closed. Keep a sharp eye.
 
Chase Target for Saturday, June 26

Chase target:
Worthington, MN

Timing and storm mode:
Storms should develop by 5 PM CDT. All modes of severe weather is likely, including a tornado or two.

Discussion:
An outflow boundary from an early morning MCS extends from north-central IA into eastern IA. Further west, a synoptic cold front extends from Marshall, MN to Valentine, NE. Outflow from ongoing elevated convection in eastern SD is serving to reinforce the cold front. A warm front will sharpen along the IA/MN border by 00Z A WF/OFB triple point near Worthington, MN should be the focus for surface-based convection by late-afternoon. Capping should persist through 21Z with shortwave ridging in place. By 00Z, another in a series of H5 shortwaves will arrive to provide necessary forcing for convection. An axis of strong instability will develop, with MLCAPEs in excess of 3000 J/kg between I-90 in MN and US-30 in IA. Deep-layer shear will should increase to 40-50 kts as an H5 shortwave overspreads western MN and northwestern IA. Enhanced helicities exist along and north of the warm front and outflow boundaries.

Bill Schintler

11:23 AM CDT, 06/26/10
 
Tornado watch box is up,seems kinda early to me.Currently south of Vermillion,SD. grabbing lunch and headed north/northeast.Skies are all clear here.
 
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