Convective Addiction

FCST: 07/19/10 – Western Corn Belt Region

Posted on 19. Jul, 2010 by Jesse in Forecasts, Uncategorized

An entrenched zone of westerly flow will contribute towards promulgating a series of mid level shortwave disturbances across the Midwest early this week, with an active convective day likely Monday.  Monday’s 00z suite of numerical model runs are fairly congruous in propelling a belt of H25 flow on the order of 100 kts across the Northern Plains and Upper Midwest, with the nose of this H25 jet maxima should impede on the far western cornbelt by 21z Monday.  Associated with this rather robust H25 flow will be H5 winds on the order of 40-50+ kts as the shortwave progresses east, with a fairly catawampus contour progged on the 500 mb height forecast (see below).  It should be noted that both the GFS and the NAM indicated a streak of H5 winds AOA 60kts over E IA and W IL, albeit in slightly incongruous locations, by 03z Tuesday.  H85 winds of 30-45kts will help to propel warm and humid air into the region, as a fairly stationary surface front may lift northward between US34 and I80 on Monday; an H85 jet streak AOA 50kts is evident on the GFS and the NAM juxtaposed with the aformentioned H5 corrdior of 50-60 kt winds between 03z and 06z Tuesday.  Surface winds INVO the frontal boundary will remain on the order of 10-20 kts.

H25 UA Profile – 21z 20100719

H5 Profile – 21z 20100719

H85 Profile – 00z 20100720

Progged Surface Map at 00z 20100720

South of the frontal boundary, SBCAPE values AOA 3000 J/KG, 0-3 km lapse rates AOA 7 (C)/km, SFC-500 mb bulk shear values of 40-60 kts and SB LI <-4 to -8 C will promote an environment ripe for deep convection by early afternoon.  While there is likely to be some rather insipid ongoing convection ahead of the surface warm front, current thinking is that the preeminent round of more robust convection will re-initiate in the unstable environment across the Western Corn Belt by 17z -19z Monday, perhaps in the form of a few discrete supercells in W IA before quickly congealing into a MCS with a significant risk for damaging winds >60 kts, large hail >1.00″ and possibly tornadoes, either with any discrete cells early in the evolution of this event or as transient spin ups associated with moving bow echoes.  This MCS should propagate ESE along the instability axis, perhaps reaching far N MN and W IL by far SE IA by 02z-03z TUE.

MUCAPE – 00z 20100720

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SB Lifted Index – 00z 20100720

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SFC-500 mb Bulk Shear – 00z 20100720

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SKEW-T near KBRL – 00z 20100720

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SPC SREF SIG TOR Ingredients - 00z 20100720

Forecast written by Convective Addiction’s Jesse L. Risley