Wet April 2011 for Central & Southeast Illinois

An active weather pattern persisted across the area for the entire month of April.  This resulted in well above normal rainfall amounts, ranging from around 125% of normal in the northwest part of the state, to over 300% of normal in southern Illinois.  Maps below from NOAA MRCC show percent of normal rainfall, and actual rainfall amounts across the Midwest for April.  

In addition to the heavy rain, several intense storm systems brought severe weather to the region.  Severe weather events on April 15 and April 19 produced the first tornadoes of the severe weather season for central IL.   A frontal boundary wavered across the Ohio Valley April 22-27, causing an extended period of heavy rain over the southern half of the state which led to flash flooding during the event, and river flooding through the end of the month for much of central and southeast Illinois.

April 15 Review
Severe thunderstorms impacted parts of central and southeast Illinois on Friday, April 15th.  A deepening area of low pressure across northern Missouri helped pull a warm front northward into the region.  To the north of the front, windy and cool weather prevailed for the entire day.  Meanwhile, much warmer and more humid conditions were observed south of the front across Missouri into southern Illinois.  Central Illinois remained between the two contrasting airmasses, with the frontal boundary reaching a Jacksonville...to Effingham...to Robinson line by late afternoon. 

Instability parameters remained rather modest, with the evening upper air sounding at NWS Lincoln showing CAPE values of less than 1000J/kg.  However, large amounts of low-level wind shear were present in the vicinity of the warm front.  Surface winds were generally from the E/SE at around 10 kts, but quickly veered to the south and increased to 40 kts at around 3000 ft aloft.  This strengthening and turning of winds with height aided in the formation of rotating updrafts within many of the developing thunderstorm cells.

As a result, numerous supercell thunderstorms formed near the warm front between 4 PM and 7 PM...mainly southwest of a Canton...to Lincoln...to Decatur line.  A survey conducted by NWS Lincoln staff members on Saturday, April 16th uncovered evidence of three tornado touchdowns across parts of Menard and Mason counties. See a summary of the storm damage surveys conduced for April 15 here.

In addition to the tornadoes, numerous reports of funnel clouds and large hail were received.  Golf-ball sized hail (1.75" diameter) was observed at the Springfield airport, while hen-egg sized hail (2" diameter) occurred just west of Waverly in Morgan County.

As the evening progressed and the weak instability waned, the storms eventually congealed into a linear structure and began accelerating east-northeast.  The southern portion of the line produced gusty winds from south of Taylorville southeastward to Lawrenceville.  A gust to 53 mph was measured at the Flora airport, while a trained weather observer just east of Birds in Lawrence County recorded a 56 mph gust.

April 19 Review
An initial round of convection affected parts of central and southeast Illinois Tuesday morning, April 19.  This activity formed north of a warm front, as a low level jet stream brought in unstable air a few thousand feet above ground.  Hail from pea size up to the size of quarters, and locally heavy rain of 1-2" affected much of the area between 4 and 9 AM.

By mid afternoon a strong warm front shifted north to near the I-72 corridor.  Low clouds and northeast winds north of the front held temperatures in the 40s, while south of the front sunny skies and southerly winds pushed temperatures into the 70s with dew points in the 60s.  A high of 46 in Peoria and 80 in Springfield showed the sharp contrast across this front!  

Strong low level wind shear in the vicinity of this boundary provided a key ingredient for a rotating supercell to form in east central Missouri around 3 PM.  This storm tracked east periodically dropping up to baseball sized hail and cyclic tornadoes.  This cell skirted the southwest fringe of the ILX county warning area with hail and damaging winds affecting far southern Scott, Morgan, and Sangamon counties.  The southern part of this cell produced an EF3 tornado that caused significant damage in Girard.  Check out the St. Louis NWS storm summary page for details on this tornado.  Other storms developed during this time north of the warm front and produced copious amounts of pea to nickel sized hail northeast along the Illinois River valley.  Heavy rain with these storms also produced localized flash flooding.

As the main supercell tracked into Christian county the circulation broadened and a more linear thunderstorm structure began to form.  The system quickly grew upscale into a QLCS (quasi-linear convective system) which produced large hail, widespread damaging straight line winds, and brief tornadic spin ups along the leading edge.  Between 7 and 10 PM this line of storms tracked through eastern Illinois, downing trees and power lines and causing localized structural damage in the strongest wind gusts.  Very heavy rain rates also produced more localized flash flooding.  Damage surveys conducted the following day determined 6 tornadoes touched down, see the results
here.


April 22-27 Review
A persistent frontal boundary over the Ohio River Valley brought numerous rounds of showers and thunderstorms to the region from Friday, April 22nd through Wednesday, April 27th.  While much of central Illinois was spared from the strongest storms, our east-central and southeast Illinois communities received copious amounts of rainfall.  Locations along and south of I-70 generally picked up 6 to 8 inches of rain...with a few spots around Olney exceeding 9 inches!  As a result of the recent heavy rainfall, many rivers and streams rose above flood stage across Illinois.  Below is the 6-day accumulated SWOP rainfall map for the period:


Below are April rainfall statistics for several cities in central and southeast Illinois.

Peoria Top 10 Wettest Aprils (records began 1883)... 

1    8.66 inches in 1947
2    8.49 inches in 1950
3    8.32 inches in 1944
4    7.86 inches in 1893 
5    7.33 inches in 2011 
6    7.18 inches in 1970
7    7.17 inches in 1909
8    7.06 inches in 1983
9    6.92 inches in 1964 
10  6.88 inches in 1912 

Champaign-Urbana, IL Top 10 Wettest Aprils (records began 1888)...

1    9.55 inches 1964
2    9.27 inches 1994
3    7.71 inches 1970
4    7.68 inches 1893
5    7.64 inches 1922
6    7.49 inches 1957
7    7.44 inches 1909
8    7.43 inches 1944
9    7.42 inches 2011 
10  6.94 inches 2009

Here are ranked April totals across Central & Southeast IL, courtesy of 
NWS Cooperative Weather Observers... 
Hutsonville.......... 13.74 inches (Wettest April & 2nd Wettest Month, records began 1946)
Olney 2S............. 13.31 inches (Wettest April & Month, records began 1890)
Robinson............. 13.18 inches (Wettest April & 2nd Wettest Month, records 1896-1911 & 2000-2011)
Lawrenceville........ 12.56 inches (Wettest April & Month, records began 2000)
Palestine............ 12.40 inches (Wettest April & 2nd Wettest Month, records began 1892)
Clay City 6SSE....... 11.87 inches (Wettest April & 4th Wettest Month, records began 1947)
Casey................ 11.78 inches (Wettest April & 6th Wettest Month, records began 1893)
Beecher City......... 11.37 inches (Wettest April & 2nd Wettest Month, records began 1974)
Effingham............ 11.12 inches (Wettest April & 4th Wettest Month, records began 1951)
Lawrenceville Airport 10.56 inches (Wettest April & 2nd Wettest Month, records began 2000)
Flora................ 10.49 inches (2nd Wettest April & 14th Wettest Month, records began 1893)
Mattoon.............. 10.23 inches (Wettest April & 3rd Wettest Month, records began 1948)
Sullivan............. 10.22 inches (2nd Wettest April & 4th Wettest Month, records 1899-1915 & 1992-2011)
Paris................. 9.99 inches (Wettest April & 12th Wettest Month, records began 1893)
Charleston............ 9.81 inches (Wettest April & 15th Wettest Month, records began 1896)
Neoga 4NW............. 9.60 inches (Wettest April & Month, records began 2005)
St David.............. 9.25 inches (2nd Wettest April & 6th Wettest Month, records began 2004)
Shelbyville Dam....... 9.00 inches (Wettest April & 4th Wettest Month, records began 1976)
Windsor............... 8.73 inches (3rd Wettest April & 28th Wettest Month, records began 1904)
Mattoon Airport....... 8.36 inches (Wettest April & 2nd Wettest Month, records began 2000)
Pana.................. 8.82 inches (4th Wettest April, records began 1890)
Danville.............. 8.17 inches (5th Wettest April, records began 1911)
Tuscola............... 8.02 inches (5th Wettest April, records began 1893)
Hoopeston............. 7.72 inches (3rd Wettest April, records began 1902)
Champaign-Urbana...... 7.42 inches (9th Wettest April, records began 1888)
Sidell 5NW............ 7.33 inches (3rd Wettest April, records began 1946)
Peoria Airport........ 7.30 inches (5th Wettest April, records began 1883)
Havana................ 7.27 inches (Wettest April, records began 1917)
Moweaqua.............. 7.21 inches (5th Wettest April, records began 1963)
Lovington............. 7.08 inches (Wettest April & 9th Wettest Month, records began 2000)
Ogden................. 7.02 inches (Wettest April & 8th Wettest Month, records began 2000)
Morrisonville......... 6.95 inches (2nd Wettest April, records began 1980)
Champaign Airport..... 6.90 inches (Wettest April & 7th Wettest Month, records began 2000)
Decatur............... 6.86 inches (11th Wettest April, records began 1894)
Clinton............... 6.70 inches (10th Wettest April, records began 1910)
Bloomington Airport... 6.69 inches
Newman 3W............. 6.46 inches (5th Wettest April, records began 1990)
Philo................. 6.37 inches (3rd Wettest April, records 1893-1915 & 2002-2011)
Kincaid 3W............ 6.29 inches (3rd Wettest April, records began 1973)
Sherman............... 6.24 inches (3rd Wettest April, records began 2000)
Decatur Airport....... 6.20 inches (Wettest April & 9th Wettest Month, records began 2000)
Springfield........... 6.18 inches (2nd Wettest April & 15th Wettest Month, records began 2003)
Chenoa................ 6.16 inches (8th Wettest April, records began 1944)
Stanford 2S........... 6.15 inches (Wettest April & 7th Wettest Month, records began 2004)
Princeville........... 6.08 inches (6th Wettest April, records began 1928)
Bloomington 5W........ 6.04 inches (2nd Wettest April, records began 1999)
Farmer City........... 5.83 inches (5th Wettest April, records began 1948)
Mason City 2N......... 5.81 inches (4th Wettest April, records began 1962)
Knoxville............. 5.78 inches (2nd Wettest April, records 1896-1906 & 1999-2011)
Roanoke............... 5.73 inches (2nd Wettest April & 10th Wettest Month, records began 2001)
Bradford 3 SSE........ 5.62 inches (4th Wettest April, records began 1980)
Morton................ 5.55 inches (2nd Wettest April, records began 1997)
Normal 4NE............ 5.49 inches (23rd Wettest April, records began 1893)
Springfield Airport... 5.46 inches (14th Wettest April, records began 1879)
Minonk................ 5.45 inches (10th Wettest April, records began 1895)
Altona................ 5.42 inches (2nd Wettest April, records began 2004)
Lincoln NWS........... 5.34 inches (18th Wettest April, records began 1906)
Jacksonville.......... 5.32 inches (23rd Wettest April, records began 1895)
Winchester............ 5.30 inches (6th Wettest April, records 1897-1905 & 1997-2011)
Congerville 2NW....... 5.01 inches (6th Wettest April, records 1935-1940 & 1991-2011)
Prairie City.......... 5.01 inches (3rd Wettest April, records began 2000)
Virgina............... 4.87 inches (13th Wettest April, records began 1963)
Mackinaw.............. 4.80 inches (25th Wettest April, records began 1940)
Athens 2N............. 4.33 inches (4th Wettest April, records began 2000)
Rushville............. 4.18 inches (47th Wettest April, records began 1890)
Galesburg............. 4.14 inches (39th Wettest April, records 1895-1909 & 1927-2011)
Beardstown............ 3.66 inches (57th Wettest April, records began 1890)
 


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