Update: Heavy rains/potential flooding expected across the Chicago area overnight

As the wide band of showers and thunderstorms spreads east over our area overnight, there will be an enhanced threat of flood-producing downpours in some of the stronger storms. “Training” of storms (storms forming and repeatedly tracking over the same locations) could also give high rainfall totals. Rainfall totals may easily exceed an inch in many areas and some locations in northeast Illinois and northwest Indiana could record over 3-inches.

Following is a recently-issued Mesoscale heavy rainfall discussion that includes our area…

Updated at 10:45PM CDT...

Graphic for MPD #0328

Areas affected...Eastern IL...Northern/Central Indiana...Western
Ohio

Concerning...Heavy rainfall...Flash flooding likely

Valid Tuesday 1012PM CDT to Wednesday 4:12AM CDT 



Summary...Complex of storms over north-central Illinois will track
eastward into portions of Indiana and potentially western Ohio.
With very saturated soils and high streamflows, flash flooding
will be possible through the overnight hours.

Discussion...Regional radar mosaic from the area shows an
organized line of thunderstorms across east-central Illinois into
portions of northwest Indiana. This complex of storms is working
within a favorable area of upper level ascent /right entrance
region/ of a jet streak over New  York. Additionally, at 03z,
there remains a zone of higher MUCAPE of about 1500-2000 J/kg
across much of the outlook area, which is also where the greatest
effective shear exists (40 to 50 kts). PWs of 1.3 to 1.6 inches
were noted on the latest TPW blended product.

The 00z hi-res guidance is poorly representing this feature, with
the bulk of the models too far north with its initialization. The
models are also too slow and dissipate the complex too quickly
compared to what's happening. The 01z HRRR did seem to be doing
the best, though isn't strong enough and likely is under-doing the
QPF potential. Through 08-09z (3 to 4AM CDT), there's potential for an additional
1-2" with localized 3" amounts possible.

Looking at the KILX radar estimates, hourly rates approaching 1.5"
appear likely, and there have been a few mesonet observations that
show above 1 inch (1.44" in Pekin, IL in 1 hr). As this line
tracks east along the best effective shear and MUCAPE gradient, it
should move over areas that are saturated and wet with recent
heavy rainfall events from earlier today but also in the last
several days. In the last 12 hours, recent thunderstorms have
dropped between 1 and locally 3" of rain across portions of
north-central Indiana. Streamflow data from the National Water
Model shows very high / above normal flows from eastern IL through
north central IN and western OH. Also, the top 40 cm soil
saturation is running around 70-80 percent.

With very saturated soil conditions and with the additional
rainfall moving into the area, instances of flash flooding will be
likely.

Graphic for MPD #0325

MESOSCALE PRECIPITATION DISCUSSION 0325

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

840 PM EDT TUE MAY 28 2019



AREAS AFFECTED......SOUTHEAST NE...NORTHEAST KS...NORTHERN



MO...SOUTHERN IA...NORTHERN AND CENTRAL IL...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID until 1138PM CDT

SUMMARY...ADDITIONAL FLASH FLOODING WILL CONTINUE THIS EVENING AS

CONVECTIVE CLUSTERS, INCLUDING SUPERCELLS, BECOME MORE WIDESPREAD.

HOURLY RAINFALL RATES BETWEEN 1 AND 2 INCHES ARE LIKELY, WITH

EMBEDDED HEAVIER RATES UNDERNEATH THE STRONGEST CELLS. RAINFALL

TOTALS OF 3 TO 5 INCHES ARE ANTICIPATED IN SCATTERED AREAS THROUGH

11:30PM CDT.

DISCUSSION...UNSEASONABLY ROBUST UPPER LEVEL FORCING, OWING TO A

SHORTWAVE APPROACHING FROM THE CENTRAL PLAINS ALONG WITH

RIGHT-ENTRANCE REGION UPPER JET FORCING VIA THE 250 MB JET STREAK

OVER THE UPPER MIDWEST-UPPER GREAT LAKES REGION, COMBINED WITH A

TYPICAL WARM SEASON THERMODYNAMIC ENVIRONMENT WILL CONTINUE TO

SUPPORT UPSCALE GROWTH OF CONVECTION WITH AN ELEVATED FLASH FLOOD

THREAT THROUGH THE EVENING HOURS. MUCAPES BETWEEN 1000-2000+ J/KG

ACROSS THE OUTLOOK AREA, ALONG WITH PW VALUES NEAR 1.75", WILL

MAINTAIN THE POTENTIAL FOR 2+ INCH/HR RAINFALL RATES. MOREOVER,

SOUTH-SOUTHWEST LOW-LEVEL INFLOW OF 35-40 KTS WILL VEER MORE

SOUTHWESTERLY THIS EVENING, ALIGNING NEARLY PARALLEL TO THE MEAN

850-300 MB FLOW. THIS WILL LIKELY INCREASE THE UPWIND PROPAGATION

POTENTIAL WITH TIME, THEREBY ENHANCING THE THREAT FOR CELL

BACK-BUILDING AND TRAINING.

FLASH FLOODING WILL BECOME INCREASINGLY LIKELY AS THE EVENING

PROGRESSES, GIVEN THE UPSCALE GROWTH AND VIGOR OF THE CONVECTION,

ALONG WITH THE WET ANTECEDENT SOILS. THREE HOURLY FLASH FLOOD

GUIDANCE (FFG) ACROSS MUCH OF THE OUTLOOK AREA IS BETWEEN 1-1.5

INCHES, WITH AREAS LESS THAN AN INCH. MOST HIGH-RES CAM GUIDANCE

INDICATE POCKETS OF 3-5 INCH TOTALS THROUGH THE MPD OUTLOOK PERIOD.

 

Notice: you are using an outdated browser. Microsoft does not recommend using IE as your default browser. Some features on this website, like video and images, might not work properly. For the best experience, please upgrade your browser.