Forecast 8/8/09

Target Area:

Lake Wilson, MN

Timing:

20Z

Storm Mode:

All modes of convection are possible with super cell / multi cell favored late afternoon to early evening.

Synopsis:

An upper level ridge is centered over the target area per the 12Z soundings. Winds at 200mb are WSW at ~80kts. There is a surface low centered on KSFD as of 18Z with a warm front extending to the ENE on a line from KSFD to, Redwood falls MN, Glenwood City WI, then to the ESE. There is a trough of low pressure extending from the surface low to the N and extending from the surface low to the SSW according to a 17Z hand analysis.

12Z 200mb

Discussion:

Convection is ongoing to the W of the target area as of 18Z with one cell already warned to the W of KSFD. The RUC shows very little movement in the surface low over the next 12 hours. The low should continue to slide ENE along the nearly stationary warm front over the target area. The latest RUC runs show a trend to keep surface winds backed through 22Z in SW MN. With CAPE values in excess of 3000Jkg and 0-3km helicity values over 100 the atmosphere is certainly primed for potentially serious convection through the late afternoon and evening hours.

The activity should continue into the evening moving through an environment with sustained shear and an excellent inflow of 70+Td's from the SE. Deep moisture is available with 850mbTd's approaching 70 over southern MN according to the 12Z RUC run. 700mb temps are progged to be in the 12 degree range at 20Z, however given the convection to the west, the trough of low pressure and the warm front, there should be plenty of forcing available to break the cap with CinH values falling to -50 by 21Z.

The only down side I see to this setup is the probability that it will line out into an MCS/MVC later in the evening. However, if cells can remain discrete during the late afternoon and early evening hours this is very chaseable.

18Z Surface (Don't have a scanner at the house for my hand surface analysis so here is one from DA)