NWS Lincoln, IL -- SWOP event summary

November 3-5, 2024

A slow-moving cold front interacted with an unseasonably moist airmass to produce periods of rain across central and southeast Illinois from the evening of Sunday, November 3rd through the evening of Tuesday, November 5th.  Beneficial rainfall amounts were recorded across the entire region...with the heaviest totals in excess of 3 inches focusing from Lincoln and Champaign southwestward to the Saint Louis metro.

The synoptic pattern featured a prominent upper-level trough of low pressure over the Rockies with deep-layer southwesterly flow noted downstream from the Southern Plains northeastward to the Great Lakes.  The image below shows 500mb heights (black lines) and winds (blue shading) during the evening of November 4th.  Note the strong southwesterly flow from Texas to Illinois.

500MB CHART 6PM CST NOVEMBER 4

At the surface, a frontal boundary extended from the Great Lakes southwestward to Texas...with a 1004mb low analyzed over northern Missouri.  Winds that had been southeasterly earlier in the day had veered to southerly ahead of the slowly approaching front, helping transport copious Gulf of Mexico moisture northward into the region.  12am November 5th dewpoints were in the lower to middle 60s, more typical of April or early May rather than the first of November.

SURFACE MAP 12AM CST NOVEMBER 5

Mesoanalysis from the evening of November 4th showed near record amounts of moisture within the atmospheric profile.  The 6pm CST upper air balloon sounding from NWS Lincoln measured precipitable water of 1.24, which was near the 99th percentile for the date.  Meanwhile late-evening RAP analysis from the Storm Prediction Center (SPC) suggested even higher values on the order of 1.70 to 1.80 advecting northward from the Ozarks.  These values would represent all-time record moisture content for November 4th and 5th.

PRECIPITABLE WATER  12AM CST NOVEMBER 5 

Thanks to impressive thermal and moisture transport from the southwest, the atmosphere became modestly unstable during the evening of November 4th.  Mixed-Layer Convective Available Potential Energy (MLCAPE) values peaked at 250-500J/kg.  Given strong forcing, favorable upper jet dynamics, ample moisture, and the noted instability...a few thunderstorms developed within the broad area of showers ahead of the front.  Severe weather did not occur: however, some of the cells produced gusty winds in addition to heavy downpours.  Below is an image depicting MLCAPE values (solid lines).  Note the highest values in excess of 500J/kg (red line) focused across the Ozarks...with a pocket of greater than 250J/kg further north across central Illinois.

MLCAPE 12AM CST NOVEMBER 5 

While the heaviest rainfall mostly occurred on November 4th, the very slow eastward movement of the front allowed showers to persist across much of the area until finally clearing out from west to east during the evening of November 5th.  Storm total rainfall was both impressive and highly beneficial...and will significantly mitigate the antecedent drought conditions.  The highest totals in excess of 3 inches were focused along and southwest of a Lincoln to Champaign line...with portions of southern Sangamon and Christian counties getting more than 5 inches.  

NOVEMBER 3- 5 RAINFALL MAP