|Fig 1 -- SPC Day 1 convective outlook for April 19, 2011.|
|Fig 2 -- SPC Mesoanalysis of surface mean sea-level pressure (black contours), temperature (solid red and brown contours), dewpoint (colored shadings) and winds barbs) for 18Z (1PM CDT), April 19, 2011.|
|Fig 3 -- Visible Satellite image from GOES-E at 1815Z (115 PM CDT), April 19, 2011. From the College of DuPage.|
|Fig 4 -- 12Z Sounding from KSGF on April 19, 2011. From the SPC.|
In contrast to Springfield, MO's sounding, Lincoln, Illinois's 12Z sounding shows a slightly different picture:
|Fig 5 -- 12Z sounding from KILX on April 19, 2011. From the SPC.|
Lincoln, Illinois was north of the warm front this morning, underneath that area of thick low-level clouds we saw on the visible satellite image. You can see this thick cloudiness on the sounding above--the air is saturated all the way up to around 700mb--the dewpoint and temperature are the same through that entire layer. There is also a rather strong inversion present from around 850-950mb. Because that cloud deck has been around all day, there hasn't been much sunlight getting through and, consequently, very little warming. In fact, at 2PM CDT, Lincoln's reported surface temperature was only 50 degrees--not the best for strong convection. Furthermore, that inversion layer is NOT potential unstable--lifting will not quickly erode through that layer. Granted the warm front will move north--and that will bring much warmer air behind it. However, because Lincoln has already spent much of the day under clouds and is still very chilly, the odds of maintaining strong thunderstorms here and further north will be somewhat lower. This is part of the reason why the risk drops off north of the warm front.
That was just a quick look at some of the setup for today. The SPC is calling for large hail and strong winds with a few isolated strong torandoes in today's event. Much of Missouri and southern Illinois is under a tornado watch as those cumulus clouds keep building under the cap, waiting for the cap to erode or for the cold front to come marching on through. If you live in a threatened area, please stay alert this afternoon. The past few weeks have shown us just how fast and destructive these storms can be.