Sunday afternoon update

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Storm Reports:
3:55pm: Kingston (DeKalb Co.) report of 0.25 inch rain and strong wind
4:02pm: Belvidere (Boone Co.) report of pea sized hail
4:07pm: Paw Paw (Lee Co.) report of quarter sized hail
4:15pm: Woodstock (McHenry Co.) report of pea sized hail



Storm entering into western McHenry county between Harvard and Woodstock likely to produce large hail - watching this one closely.  Severe Thunderstorm Warning has been extended until 5pm for McHenry county

Severe Thunderstorm Warning has been canceled for Ogle county but continue until 4:45pm for Boone, McHenry and northern DeKalb counties





Severe Thunderstorm Warning for southern Boone, McHenry, Ogle and northern DeKalb counties until 4:45pm. 
Storms are currently moving northeast around 30 mph and will affect areas near Belvidere, Kirkland, Kingston and Genoa.  Frequent lightning, hail up to quarter size or greater as well as gusty winds all remain possible.

3:25 pm Update:  Storms continue their northeast movement through Ogle and Lee counties - now entering into the eastern sections of those counties.  Still no warnings, but hail, heavy rain as well as gusty winds remain possible.  Storms extend from Amboy northward to just west of Rochelle, Hillcrest and Stillman Valley.  There are also a couple cells in northern DeKalb county and southeast Boone county.



Thunderstorms have developed along and ahead of the main cold front this afternoon.  Earlier a severe thunderstorm warning had been issued for Whiteside county, but that has since expired.  Storms continue to move northeast around 30-40 mph and will likely affect Amboy, Ashton, Dixon and Franklin Grove.  The storm currently in western Lee county will likely produce frequent lightning, heavy rainfall, gusty winds and hail quarter size or larger.  As of right now, there are no current warnings for this storm.

There are a few more cells that have developed just south of Byron as well as in western McHenry county and just east of Janesville, WI.  All of these storms will be moving northeast.




A weather watch may be issued within the next couple hours across portions of southern Wisconsin as well as northern Illinois.  The heat that has built up so far this afternoon combined with an approaching cold front will allow for thunderstorm develop by mid-afternoon.  Despite the main forcing remaining north of the immediate area there appears to be enough instability that once storms get going they could produce locally strong winds and hail.


Here's the technical discussion from the Storm Prediction Center:

DISCUSSION...THIS AFTERNOON A COLD FRONT EXTENDS FROM WRN WI...ERN
   IA INTO NERN MO WITH WEAK PRE-FRONTAL CONVERGENCE BANDS INDICATED
   AHEAD OF THE FRONT. WARM SECTOR HAS BECOME MODERATELY UNSTABLE
   SUPPORTED BY A PLUME OF STEEPER /7-7.5 C/KM/ LAPSE RATES ABOVE UPPER
   50S BOUNDARY LAYER DEWPOINTS. PRE-FRONTAL NEAR SFC WINDS HAVE VEERED
   TO SSWLY TO THE SOUTH OF A NEWD EJECTING SHORTWAVE TROUGH LOCATED
   OVER THE UPPER MS VALLEY. THIS IS CONTRIBUTING TO WEAKER CONVERGENCE
   ALONG COLD FRONT. MOREOVER...DEEPER FORCING ASSOCIATED WITH EJECTING
   SHORTWAVE TROUGH WILL REMAIN NORTH OF THIS REGION. THESE FACTORS
   MAKE TIMING AND EXTENT OF THUNDERSTORM INITIATION IN THIS AREA
   SOMEWHAT UNCERTAIN. HOWEVER...AS TEMPERATURES WARM INTO THE UPPER
   80S...CONVECTIVE INHIBITION SHOULD WEAKEN ENOUGH FOR STORMS TO
   DEVELOP WHERE DEEPER BAROCLINIC ZONE INTERACTS WITH THE UNSTABLE
   WARM SECTOR. STRONGER FLOW ALOFT ATTENDING THE EJECTING IMPULSE WILL
   REMAIN NORTH OF THIS REGION WITH DEEP SHEAR GENERALLY AOB 30 KT
   SUPPORTIVE OF MULTICELLS. NEVERTHELESS...THE THERMODYNAMIC
   ENVIRONMENT WITH MODERATE INSTABILITY...STEEP MID LEVEL LAPSE RATES
   AND LARGE BOUNDARY LAYER TEMPERATURE-DEWPOINT SPREADS WILL PROMOTE A
   THREAT OF ISOLATED DAMAGING WIND AND HAIL.