6/11/06 FCST: CO / WY / NE / KS

[Tony Laubach]

Post frontal action shaping up well for Colorado on Sunday. Upslope flow behind the front will set the table for our beloved "Day 2" action. Saturday will give the day to allow the front to advance south of the area giving the return flow behind it to pump in the moisture. Shear looks overall pretty good and would expect severe storms to initiate mid-afternoon from the mountains and move onto the plains into the better moisture and low level shear. Sunday has the potential to be a good tornado day for areas in Northeast Colorado with good SFC moisture and shear present. CAPES oughta be more than enough to keep storms healthy and promote large hail as well.

Past setups this year have shown dews mixing out as the day goes on. This pattern seems better as winds more from the southwest at higher levels will bring some moisture in and hopefully keep it from mixing out. Temps will be high once again along the front range which is biggest concern for me as it'll promote the dreaded high LCLs making a hail situation the primary threat.

Am eagerly looking forward to the first real Colorado event in our climatological favored time!

 

[Bill Schintler]

Chase target:
Akron, CO (18 miles E. of Brush on US 34).

Timing:
Storms will reach the target by 8 PM CDT (7 PM MDT, sunset in Akron is 8:21 MDT).

Comments:
An upslope event, with storms initiating in the Rockies to the west of Fort Collins and Boulder by 4 PM CDT, and moving to the east and southeast into deeper moisture and shear through 8 PM CDT. A few discrete storms are likely before sunset, after which time an evolution into a multicell complex will take place. there will also be a small possibility of a tornado or two, especially where the storms interact with a pre-existing boundary resulting from tonights convection.

Discussion:
03Z analysis clearly shows an OFB just S of and parallel to US-40 in ERN CO, and this boundary was slowing as it pushed to the S at 10 mph. This feature should enhance convergence and backing of SFC flow tomorrow as it lifts back to the N. To the S of the boundary, SFC moisture was very limited with SFC dewpoints in the low-40's F, while dewpoints in the mid- to upper-50's were more prevalent to the N. DNR and DDC soundings were quite dry in the lower levels, while LBF indicated a 50mb deep moist layer with a mean dewpoint of 12C in upslope flow. The environment in WRN NE has no doubt been modified since then by evening convective activity, however it is felt that sufficient airmass recovery should take place tomorrow afternoon as strong insolation and upslope flow resumes. The 00Z NAM has initialized by as much as 5F too high with regard to SFC dewpoints and also does not have a handle on the mesoscale features of the current convection such as the aforementioned OFB. The 30hr NAM also forecasts a QPF bomb in NERN CO, but this is due in part to its overly optimistic moisture forecast. All in all, feel that SFC dewpoints should reach 50F with SERLY SFC flow, and this will lead to moderate instability at a SFC elevation of nearly 5000ft.

All guidance depicts the evolution and translation of one or more lead mid-level waves through the target area by 00Z (GFS weaker and further S in comparison the NAM) - the WV loop currently shows this feature lifting into WRN CA ahead of the main trough in the Pacific. H7 temps should cool to the +8 to +10C range as a result, and this should contribute towards convective temperatures in the low-80s F at an elevation of 4700ft. This temperature should be reached by 23Z. Increased directional and speed shear will result from the presence of this wave, with deep layer shear increasing to 40kts along with (SFC-3km) helicities increasing to as much 300m2/s2 as a SWRLY 35kt H7 max lifts over 15kt SERLY SFC flow to the N of the OFB.

- bill