7/11/08 FCST: NE/IA/SD/MN/WI

[Darren Addy]

I can't believe that I'm starting a forecast thread, but here goes nothing:

An "UNUSUALLY STRONG AND COLD TROUGH FOR THIS TIME OF YEAR" is currently working its way across NE/CNTRL Montana along with an associated cold front. It will move into Nebraska in the late afternoon and early evening and the forcing should have no problem overcoming the cap, particularly in the east central parts of the state where moisture looks good and there is a decently-sized bullseye of helicity. The majority of the eastern section of Nebraska will be sitting under 2000+ CAPE by 4 PM. Hail and wind are the main concerns, but storms in the area of the helicity could produce a tornado.

If anything, the models may be undershooting this one. There are already dewpoints over 70 in the eastern portions of the State and low level moisture is expected to continue to increase in the area.

I can think of worse places to be than sitting in Grand Island today. I think there will be some interesting storms within striking distance of there. I like the timing of this system and the fairly narrow corridor (at least in Nebraska) for the expected cap breakage well before sundown.

 

[Bill Schintler]

Chase Target for Today, July 11, 2008

Chase target:
20 miles west of St. Cloud, MN.

Timing and storm mode:
Elevated storms will develop from north to south across MN today, while becoming surface-based by late afternoon.

Synopsis:
SFC analysis indicates an OFB trailing from a departing MCS in the Lake of the Woods area SW to near Moorhead, MN. The synoptic WF extended from Cambridge, MN NW to Bemidji and then W along US 2 in NWRN MN. An axis of low-70’s dewpoints had worked into CNTRL MN. The WRF and GFS both have a poor handle on BL dewpoints, and generally have initialized with too much moisture over much of MN.

Discussion:
This afternoon, an unseasonably strong ULVL trough will surge SE into the upper Midwest. In response to strong forcing, ongoing elevated storms in NRN MN will develop S as the day progresses, while becoming SFC based. Strong instability will couple with modest shear parameters. MLCAPEs will increase in excess of 3000J/kg as mid-level lapse rates increase with the approaching trough. Deep layer shear of 30 kts early in SFC-based storm evolution will be sufficient for storm organization, and this will increase as the evening progresses.

- bill
11:20 AM, 07/11/08