:: T-Storm on a Stick
The MN State Fair is in full swing this week. Invariably, fairgoers at some point will encounter a thunderstorm at the fair, and tomorrow looks like it could ripen for the chance. Warm southerly flow today and tomorrow is ushering in moisture and instability. Tonights late 00Z NAM run paints a very volatile picture with CAPE values surging to 4500J/kg and PWATs to the 2" range by 00Z tomorrow. This is all kept in check by CIN values in the mid-layers of the atmosphere well into the -1000's. That type of inhibition is borne of the H70 temp progs, which show that layer warming to over 15° C by late afternoon. The capping will only be broken by airmass forcing along the frontal boundary or by a shortwave ripple across the still very zonal upper jet. NAM seems to favor former scenario, as it now paints best precip bulleyes along the frontal zone through the forecast. This is contrasted to the 18Z run where it figured an early afternoon initiation timeframe.
Speaking of shortwave ripples, this is the only other variable that needs watching and waiting. Currently one of these energy ripples is spreading from the Sioux Empire into SWern MN. Just before sundown, mid-layer cumulus clouds were developing across this area. Present infra-red imagery indicated the clouds continue to build in this area. Should lifting continue overnight, we could see an early-AM round of thunder shaking us from bed near dawn.
At current time, will advise that 50/50 chance of thunderstorms in NWS grid for lakeville looks reasonable, but remainder of forecast will depend on just what happens with overnight convection chance, and affect (if any) on convective chances Monday. Will update in the AM.