23 June 2010 Severe Thunderstorms

June 23rd Severe Thunderstorms
Another batch of severe weather affected Northern Illinois and Northwest Indiana on the evening of June 23rd.  Severe winds and flooding were the main threats from these storms; however, several reports of funnel clouds were received throughout the event.
Meteorological Setup
An area of low pressure was centered over Iowa earlier in the day with a trailing cold front stretching southwest through Central Kansas. High pressure was centered over the Southeastern US allowing additional Gulf of Mexico moisture to stream north into the Midwest.  An upper level trough was located over Minnesota and Iowa with an anomalously strong 200hPa jet core of 100 knots to the north of the forecast area. A storm system from the previous night had dropped heavy rainfall with clouds lingering over much of Northern Illinois during the late morning and early afternoon. Ahead of the front, unseasonably strong southwest flow (Fig. 3 & 4) was pushing warm, moist air (Fig. 2 & 7) into Northern Illinois and Northwest Indiana. As skies cleared out in the afternoon, temperatures soared into the mid to upper 80s with dew points in the mid to upper 70s (Fig. 1).  Mid level winds were quite strong, on the order of 50 knots as evident by a special 18Z upper air sounding from Quad Cities (KDVN) (Fig. 8).  These stronger mid level winds an important factor in creating the strong shear to support the severe weather, and these strong mid level winds were also able to mix down to the surface with the severe thunderstorms.

Figure 1: 3PM CDT Temperatures (lines) and dew points (shaded).
As temperatures and dew points increased through the day, the atmosphere became explosively unstable. Thunderstorms initiated along the cold front in Southern Iowa by 4 PM CDT and by 5 PM (Fig. 5) storms quickly congealed into a line as they began to enter the northwestern counties of the Chicago forecast area.

Figure 2: 3PM CDT Precipitable water (In) lowest 400hPa
In addition to the rapidly developing line of thunderstorms, precipitable water values (Fig. 2) were approximately 2”  inches, which was nearly 4 standard deviations above normal (Fig. 7) at 7 PM CDT. The very moist atmosphere allowed for an enhanced flooding threat over already saturated soils of North Central Illinois and Northwest Indiana.

Figure 3: 1PM CDT 0-6KM Bulk Shear Isotachs and Values (shaded)

Figure 4: 10 AM CDT 850hPa Isotachs and Values (shaded)

Figure 5: WSR-88D KLOT 5PM CDT Reflectivity.

Figure 6: WSR-88D KLOT 6PM CDT Reflectivity.

Figure 7: 21Z Jun. 23 2010 - SREF PWAT Anoms.


Figure 8: 18Z Sounding from KDVN


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