Clusters of showers and thunderstorms will continue to develop and lift east-northeast across northern IL overnight. Heaviest rainfall will likely be along and north of the I-88 corridor, though areas farther south will also see storms. A flash flood watch is in effect for much of northern IL through midday Saturday. Rainfall amounts of 1-2 inches, and likely some localized higher amounts, can be expected. This will likely result in flooding across portions of the area, as well as rises on area creeks and rivers.
No big changes to going forecast through tonight, though did
update digital forecast grids earlier to boost evening pops with
cluster currently moving across northern IL.
Surface frontal boundary remains just south of the forecast area
this evening, stretching roughly from near Kansas City to
Bloomington IL and Indianapolis. Cluster of storms were tracking
north of the front across north central IL at 745 pm, in
association with a low-amplitude short wave propagating though the
southwest flow aloft. While heavy rainfall remains the primary
concern, especially later tonight, cell about to exit southeast
Lee county has exhibited a bit of an elevated wind signature,
aided by stronger flow aloft, and presence of 40-50 kt deep layer
shear. Cooler, stable boundary layer will likely limit much of
this from reaching the surface, supported by decreasing inbound
winds in the lowest radar cuts as it approaches KLOT. Will
continue to need to monitor cells tracking along/south of the I-80
corridor this evening however, closer to the surface boundary.
Of course the real concern is for training thunderstorms into the
overnight hours, as southwest flow persists atop the low level
frontal zone, downstream of an upper trough translating across the
Plains. Region from southern IA into northern IL appears most at
risk for repeated rounds of storms overnight, highlighted by
current flash flood watch. No changes anticipated, with areal
extent of the watch looking good at this time.