April 12, 2014 Hail and Wind Event Across Northern Illinois

Overview

On the morning of April 12, 2014, a strong surface warm front lifted north across northern Illinois, but very warm and moist air several thousand feet above the surface had already rushed into the area. Thus the atmosphere was characterized by warm and unstable conditions aloft and relatively cool and dry conditions at the surface.

9 am surface observations
Rockford Airport at 9am had a temperature of 58 degrees and a low dewpoint (measure of moisture content in the atmosphere) of 34 degrees.

Modified aircraft sounding from RFD showing ~2000 J/kg of MUCAPE
MUCAPE is Most Unstable Convective Available Potential Energy- A measure used to quantify the total amount of instability in the atmosphere especially when the surface is more stable as it was at the time the storms formed. 2000 J/kg is high instability for northern Illinois in mid April and supportive of strong to severe storms if other factors are favorable.

The warm and unstable air 3 to 5 thousand feet above the surface was driven into the area by what meteorologists call a low level jet. Deep layer moisture convergence on the nose of this low level jet with 40 to 45 mph winds at the 850 mb level (4kft-5kt) along with additional lift provided by a midlevel disturbance caused a cluster of showers and thunderstorms to form over northeast Iowa and northwest Illinois.

850 mb analysis
South-southwest winds of 40-45 mph at 3 to 5 thousand feet above the surface into northwest Illinois indicates the strong low level jet pumping elevated warmth and moisture into the region.

Deep layer moisture convergence
The red contours over northern Illinois indicate moisture flowing together in a deep layer of the atmosphere, which helped provide the lift to form the initial cluster of thunderstorms.

13z Radar mosaic
Regional Radar at 8am CDT

Strong westerly winds of 50-60 mph were present at about 15,000 above the surface, with 40-45 mph southerly winds at 4 to 5,000 feet up in the atmosphere. This change in wind direction and speed is referred to as wind shear, and high values of it (like were present during the morning) are a key ingredient in the development of severe thunderstorms.

Crossover winds
500 mb (~15,000 ft AGL – dark blue) and 850 mb (~4-5kft AGL- red) wind arrows overlaid with radar data at 10am CDT. The red arrows pointing north (winds out of the south at 4-5kft) and blue arrows pointing east (winds out of the west at 15kft) show the large change in direction with height in the atmosphere and the presence of high levels of deep layer wind shear.

The combination of strong deep layer wind shear and high levels of atmospheric instability aloft allowed thunderstorms to acquire rotating updrafts, known as supercells. These storms often produce the most significant severe weather that can impact our area, including very large hail, damaging winds and tornadoes at times when lower level atmospheric conditions are supportive. A significant clockwise turning of the winds with height, also known as veering, is even more supportive of rotating storms, which is what we had today. Furthermore, while the original storm motion of the storm cluster west of our area was toward the northeast, supercells often take on a deviant motion. Typically, they become right movers, meaning they take on a path right of the overall storm motion. In the case of today’s storms, that meant towards the due east or even just south of east as shown in the image below.

The Event

A pair of supercells formed from the initial cluster over northeast Iowa and northwest Illinois and moved due east instead of northeast because they were right movers. These supercells went on to produce a swath of hail and wind damage in Winnebago, Boone and McHenry counties. Then the southern cell became more dominant, merging with the northern cell into one supercell that continued to produce very large hail over Lake and far northern Cook counties before exiting over Lake Michigan around noon CDT. Hail was as large as 2” in diameter portions of Boone, McHenry and Cook counties. The most significant wind damage occurred to a farmstead near the McHenry-Boone county border west-northwest of Marengo Illinois. Given that the near surface environment was still fairly dry when the storms moved across (shown by the Rockford 9am observation) this likely enhanced the wind potential from these storms.

Radar image at 1003 am on April 12, 2014
Radar image at 1003 am on April 12, 2014

Radar image at 1139 am on April 12, 2014
Radar image at 1139 am on April 12, 2014

The intense radar reflectivities of 65 to 75 dBZ (purple to blue colors) indicative of large hail at the lowest radar level.

Photos

Photo by Caleb Johnson, Rockford, IL
Photo by Caleb Johnson, Rockford, IL
Photo by Issac Reiter, Huntley, IL
Photo by Issac Reiter, Huntley, IL 
Photo by Nathan Monney, 1.5 miles north of Belvidere, IL
Photo by Nathan Monney, 1.5 miles north of Belvidere, IL 
Photo by Teri Jones Kolls, Harvard, IL
Photo by Teri Jones Kolls, Harvard, IL 
Photo by Tina Smith, west of Marengo, IL
Photo by Tina Smith, west of Marengo, IL 

Local Storm Report Summary

 

NWUS53 KLOT 121921
LSRLOT

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
221 PM CDT SAT APR 12 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1152 AM     HAIL             NORTHBROOK              42.13N 87.83W 
04/12/2014  E1.00 INCH       COOK               IL   TRAINED SPOTTER 

            UP TO QUARTER SIZED. 

1147 AM     HAIL             NORTHBROOK              42.13N 87.83W 
04/12/2014  M1.00 INCH       COOK               IL   TRAINED SPOTTER 

1144 AM     HAIL             DEERFIELD               42.17N 87.85W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1144 AM     HAIL             DEERFIELD               42.17N 87.85W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1144 AM     HAIL             DEERFIELD               42.17N 87.85W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1130 AM     HAIL             PALATINE                42.11N 88.04W 
04/12/2014  E1.75 INCH       COOK               IL   TRAINED SPOTTER 

            AT PALATINE HILLS GOLF COURSE

1130 AM     HAIL             BUFFALO GROVE           42.17N 87.96W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1130 AM     HAIL             PALATINE                42.11N 88.04W 
04/12/2014  M1.50 INCH       COOK               IL   TRAINED SPOTTER 

1130 AM     HAIL             ARLINGTON HEIGHTS       42.09N 87.98W 
04/12/2014  M1.00 INCH       COOK               IL   TRAINED SPOTTER 

            DUNDEE RD AND ROUTE 53. 

1130 AM     HAIL             WHEELING                42.13N 87.92W 
04/12/2014  E1.00 INCH       COOK               IL   TRAINED SPOTTER 

1130 AM     HAIL             LAKE ZURICH             42.19N 88.09W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1130 AM     HAIL             MCHENRY                 42.34N 88.29W 
04/12/2014  E0.75 INCH       MCHENRY            IL   TRAINED SPOTTER 

1130 AM     HAIL             LONG GROVE              42.20N 88.00W 
04/12/2014  E1.25 INCH       LAKE               IL   TRAINED SPOTTER 

            HAIL BEGAN AT 1125 AM. 

1130 AM     HAIL             N BUFFALO GROVE         42.17N 87.96W 
04/12/2014  E1.50 INCH       LAKE               IL   PUBLIC          

            LARGEST HAIL WAS JUST UNDER GOLF BALL SIZE. VIA FACEBOOK.


1130 AM     HAIL             N PALATINE              42.11N 88.04W 
04/12/2014  E1.50 INCH       COOK               IL   TRAINED SPOTTER 

            REPORT VIA FACEBOOK. TIME ESTIMATED BY RADAR. 

1130 AM     HAIL             HOFFMAN ESTATES         42.06N 88.14W 
04/12/2014  E1.00 INCH       COOK               IL   TRAINED SPOTTER 

1128 AM     HAIL             1 N BARRINGTON          42.17N 88.13W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

            VIA LAKE COUNTY EMA. 

1125 AM     HAIL             PALATINE                42.11N 88.04W 
04/12/2014  E1.75 INCH       COOK               IL   TRAINED SPOTTER 

1125 AM     HAIL             PALATINE                42.11N 88.04W 
04/12/2014  M1.50 INCH       COOK               IL   TRAINED SPOTTER 

1124 AM     HAIL             BARRINGTON              42.15N 88.13W 
04/12/2014  M2.00 INCH       COOK               IL   TRAINED SPOTTER 

1124 AM     HAIL             LAKE ZURICH             42.19N 88.09W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1122 AM     HAIL             HOFFMAN ESTATES         42.06N 88.14W 
04/12/2014  E0.75 INCH       COOK               IL   TRAINED SPOTTER 

1122 AM     HAIL             HAINESVILLE             42.34N 88.06W 
04/12/2014  E0.50 INCH       LAKE               IL   TRAINED SPOTTER 

1121 AM     HAIL             LAKE ZURICH             42.19N 88.09W 
04/12/2014  E1.75 INCH       LAKE               IL   TRAINED SPOTTER 

            UP TO GOLF BALL SIZED. 

1121 AM     HAIL             BARRINGTON              42.15N 88.13W 
04/12/2014  E1.75 INCH       COOK               IL   TRAINED SPOTTER 

1120 AM     HAIL             HOFFMAN ESTATES         42.06N 88.14W 
04/12/2014  E1.00 INCH       COOK               IL   TRAINED SPOTTER 

            VIA FACEBOOK. QUARTER SIZED AND SLIGHTLY LARGER. TIME 
            ESTIMATED BY RADAR. 

1120 AM     HAIL             LAKE ZURICH             42.19N 88.09W 
04/12/2014  M1.25 INCH       LAKE               IL   TRAINED SPOTTER 

1116 AM     HAIL             ROUND LAKE PARK         42.32N 88.06W 
04/12/2014  E1.00 INCH       LAKE               IL   TRAINED SPOTTER 

1115 AM     HAIL             CARPENTERSVILLE         42.12N 88.27W 
04/12/2014  M1.50 INCH       KANE               IL   TRAINED SPOTTER 

1115 AM     HAIL             ALGONQUIN               42.16N 88.30W 
04/12/2014  M2.00 INCH       MCHENRY            IL   PUBLIC          

            HAIL AS LARGE AS 2 INCH DIAMETER BEGAN JUST AFTER 11 AM 
            AND ENDED AT ABOUT 1115 AM. REPORT AND PHOTO VIA TWITTER.


1115 AM     HAIL             ISLAND LAKE             42.28N 88.20W 
04/12/2014  E0.75 INCH       MCHENRY            IL   TRAINED SPOTTER 

1113 AM     HAIL             CARY                    42.21N 88.25W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

1112 AM     HAIL             ALGONQUIN               42.16N 88.30W 
04/12/2014  M1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

1112 AM     HAIL             HAINESVILLE             42.34N 88.06W 
04/12/2014  E1.00 INCH       LAKE               IL   EMERGENCY MNGR  

1110 AM     HAIL             1 SW PISTAKEE HIGHLANDS 42.39N 88.23W 
04/12/2014  E0.88 INCH       MCHENRY            IL   TRAINED SPOTTER 

            IN JOHNSBURG

1108 AM     HAIL             CRYSTAL LAKE            42.23N 88.33W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

1107 AM     HAIL             LAKE IN THE HILLS       42.19N 88.32W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

1105 AM     HAIL             ANTIOCH                 42.47N 88.08W 
04/12/2014  M0.75 INCH       LAKE               IL   TRAINED SPOTTER 

1105 AM     HAIL             N ALGONQUIN             42.16N 88.30W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

            MAINLY QUARTER SIZED HAIL WITH A FEW PIECES OF GOLF BALL 
            SIZED. 

1105 AM     HAIL             CRYSTAL LAKE            42.23N 88.33W 
04/12/2014  E1.75 INCH       MCHENRY            IL   TRAINED SPOTTER 

1104 AM     HAIL             HUNTLEY                 42.17N 88.42W 
04/12/2014  E1.25 INCH       MCHENRY            IL   PUBLIC          

1100 AM     HAIL             LAKE IN THE HILLS       42.19N 88.32W 
04/12/2014  E1.25 INCH       MCHENRY            IL   TRAINED SPOTTER 

1100 AM     HAIL             LAKE IN THE HILLS       42.19N 88.32W 
04/12/2014  E1.50 INCH       MCHENRY            IL   TRAINED SPOTTER 

            QUARTER TO PING PONG BALL SIZED HAIL. 

1100 AM     HAIL             SPRING GROVE            42.44N 88.24W 
04/12/2014  E0.50 INCH       MCHENRY            IL   CO-OP OBSERVER  

            COVERING THE GROUND. 

1059 AM     HAIL             4 N HUNTLEY             42.23N 88.42W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

            PEA TO QUARTER SIZED HAIL COVERING THE GROUND LASTED 5 
            MINUTES. 

1058 AM     HAIL             HUNTLEY                 42.17N 88.42W 
04/12/2014  E1.25 INCH       MCHENRY            IL   TRAINED SPOTTER 

1054 AM     HAIL             MCHENRY                 42.34N 88.29W 
04/12/2014  E1.50 INCH       MCHENRY            IL   TRAINED SPOTTER 

            ROUTE 120 AND RIDGE ROAD. HAIL LASTED 5 MINUTES. 

1054 AM     HAIL             CRYSTAL LAKE            42.23N 88.33W 
04/12/2014  E0.75 INCH       MCHENRY            IL   CO-OP OBSERVER  

            COVERING THE GROUND. 

1047 AM     HAIL             UNION                   42.23N 88.54W 
04/12/2014  M1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

            HAIL COVERING GROUND. 1 INCH LARGEST STONES. AT ILLINOIS 
            RAILWAY MUSEUM.

1045 AM     HAIL             WOODSTOCK               42.31N 88.44W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

            DIME TO QUARTER SIZED HAIL QUEEN ANNE STREET AND TODD 
            ROAD COVERING THE GROUND. 

1042 AM     HAIL             MARENGO                 42.25N 88.60W 
04/12/2014  E1.00 INCH       MCHENRY            IL   TRAINED SPOTTER 

            QUARTER SIZED HAIL COVERING THE GROUND BEGAN AT REPORT 
            TIME AND LASTED 2 TO 3 MINUTES. 

1030 AM     TSTM WND GST     HARVARD                 42.42N 88.62W 
04/12/2014  M55.00 MPH       MCHENRY            IL   TRAINED SPOTTER 

            ALSO HALF INCH DIAMETER/DIME SIZED HAIL. 

1025 AM     TSTM WND DMG     5 WNW MARENGO           42.28N 88.69W 
04/12/2014                   MCHENRY            IL   PUBLIC          

            LARGE GRAIN AUGERS RIPPED FROM TOP OF GRAIN 
            BINS...SHINGLES PEELED OFF ROOFS...IRRIGATION SYSTEMS 
            BLOWN OVER...BARNS BLOWN DOWN AND A BRANCH STUCK INTO THE
            SIDE OF A HOUSE. REPORT VIA FACEBOOK. 

1015 AM     TSTM WND DMG     CHERRY VALLEY           42.24N 88.96W 
04/12/2014                   WINNEBAGO          IL   LAW ENFORCEMENT 

            LARGE TREE BRANCHES DOWN NEAR CHERRY VALLEY. 

1015 AM     HAIL             POPLAR GROVE            42.37N 88.82W 
04/12/2014  M2.00 INCH       BOONE              IL   PUBLIC          

            ROUTE 76 NEAR POPLAR GROVE AIRPORT. TIME ESTIMATED BY 
            RADAR. REPORT VIA FACEBOOK. 

1014 AM     HAIL             ROCKFORD                42.27N 89.06W 
04/12/2014  E1.75 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            UP TO PING PONG BALL TO GOLF BALL SIZED.

1013 AM     HAIL             SE ROCKFORD             42.27N 89.06W 
04/12/2014  E1.25 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

1012 AM     HAIL             ROCKFORD                42.27N 89.06W 
04/12/2014  E1.50 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            UPDATED REPORT FROM 1 MILE NORTHWEST OF I-39 AND US 20 
            BYPASS. 

1011 AM     TSTM WND DMG     S ROCKFORD              42.27N 89.06W 
04/12/2014                   WINNEBAGO          IL   LAW ENFORCEMENT 

            JUST SOUTH OF THE CITY IN UNINCORPORATED ROCKFORD...TREES
            DOWN ACROSS ROADWAYS. 

1010 AM     HAIL             LOVES PARK              42.34N 89.01W 
04/12/2014  E1.00 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

1010 AM     HAIL             ROCKFORD                42.27N 89.06W 
04/12/2014  M1.75 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            GOLF BALL HAIL ON WYOMING STREET IN ROCKFORD.

1008 AM     HAIL             N BELVIDERE             42.25N 88.85W 
04/12/2014  E1.00 INCH       BOONE              IL   TRAINED SPOTTER 

            NORTH OF BELVIDERE.

1007 AM     HAIL             ROCKFORD                42.27N 89.06W 
04/12/2014  E1.00 INCH       WINNEBAGO          IL   LAW ENFORCEMENT 

1001 AM     HAIL             ROCKFORD                42.27N 89.06W 
04/12/2014  M1.00 INCH       WINNEBAGO          IL   BROADCAST MEDIA 

            SOUTHEAST SIDE OF ROCKFORD. 

0958 AM     HAIL             ROCKFORD                42.27N 89.06W 
04/12/2014  M1.25 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            1 INCH TO 1 AND A QUARTER SIZED HAIL. HAIL BROKE GLASS IN
            AN OUTSIDE LIGHT FIXTURE. LOCATION 1 MILE NORTHWEST OF 
            I-39 AND US 20 BYPASS.

0958 AM     HAIL             SE ROCKFORD             42.27N 89.06W 
04/12/2014  E1.00 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            LASTED ABOUT 2 MINUTES. SOUTHEAST PORTION OF ROCKFORD 
            NEAR PERRYVILLE ROAD. 

0954 AM     HAIL             ROCKFORD AIRPORT        42.20N 89.10W 
04/12/2014  M1.00 INCH       WINNEBAGO          IL   OFFICIAL NWS OBS

            REPORTED ON 954 AM OBSERVATION. 

0945 AM     HAIL             4 SSE ROCKFORD          42.22N 89.03W 
04/12/2014  E1.00 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            QUARTER SIZED HAIL ON THE SOUTHEAST SIDE OF ROCKFORD. 

0944 AM     HAIL             1 E ROCKFORD AIRPORT    42.20N 89.08W 
04/12/2014  M1.00 INCH       WINNEBAGO          IL   TRAINED SPOTTER 

            HAIL LASTED ABOUT 3 MINUTES.


&&

$$

RC

 



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