July 12, 2014: Look at the Severe Risk for Tomorrow

TODAY'S WEATHER: A few showers/storms late this morning and into the early afternoon today gave way to a pretty nice day, albeit humid. The high made it to 85F at EVV this afternoon, after 0.26" of rain was recorded with the convection earlier in the day. The low this morning was a muggy 72F.

SEVERE WEATHER OUTLINE: The real purpose of this post, though, is to outline the severe risk for tomorrow evening. The Storm Prediction Center has placed the entire Lower Ohio Valley under a slight risk for severe thunderstorms tomorrow afternoon and evening:

SPC Convective Outlook for Tomorrow, July 13

The threat is associated with a cold front that will dive across the Great Lakes into the Ohio Valley tomorrow. Forecasting the convection to fire well north of the Ohio River by 4 PM tomorrow, and gradually push southeast across the region heading into the evening hours. Here is the simulated radar reflectivity from the 12z NAM 4KM for tomorrow, valid at 7 PM CDT:

NAM 4KM shows convection south of the Ohio River by 7 PM.

With CAPE values expected to exceed 2,000 J/KG tomorrow afternoon, along with effective bulk shear values above 30kts, the storms should have no problem organizing into bowing line segments. Damaging wind is the main threat with these storms tomorrow, along with a chance of a tornado. The large hail risk is lower than previous events as the freezing level is well above the surface, in the 600mb range. Of course the hail potential is still there, but it will have to fall through a decent layer of above freezing air before reaching the surface.

Another threat for tomorrow is the heavy rainfall. The heavy rain threat is elevated for tomorrow greater than it normally would because of PWAT values approaching if not exceeding 2" just ahead of the boundary (basically, the atmosphere's ability to "ring" out the moisture available through all levels). Precipitable water values over 2" mean that the atmosphere is LOADED with moisture. Flash flooding is a big concern. Here is the projected PWAT values for tomorrow evening coming from the 18z run of the NAM:

Greatest precipitable water values (in excess of 2") across Southern IL into Southwest IN at 7 PM, according to the NAM.

REFRESHING air will be the story heading into midweek. I'll have details on that coming up after this severe weather. Follow @wxSam on Twitter for realtime updates tomorrow.