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Hydrologic Outlook

Hydrologic Outlook

Hydrologic Outlook
National Weather Service Lincoln IL
334 AM CDT Tue Jul 25 2017


An extremely moist air mass will be in place across central
Illinois Wednesday night. An area of thunderstorms is expected to
move across southeast Iowa during the evening hours, then track
across central Illinois late evening and overnight. This area of
storms is expected to be through the area by midday Thursday, with
rain continuing further south.

Present indications are that rainfall amounts of 1 to 3 inches are
likely in areas along the I-74 corridor, potentially as far south
as Havana and Lincoln, especially between late Wednesday evening
and sunrise Thursday. Locally heavier totals are a significant
concern, given the tropical air mass in place and the potential
for storms to repeatedly move across the same areas. This would
likely cause significant rises on area rivers. The Illinois River
is already rising due to heavy rains that occurred over northern
Illinois recently, and this amount of rain would likely result in
a faster and higher rise.

There has been some uncertainty as to the exact location of the
heaviest rain potential. Be sure to monitor later forecasts for
updates on this situation, as there is potential for flooding to
occur late Wednesday night into early Thursday.



Hydrologic Outlook

Hydrologic Outlook
National Weather Service Chicago IL
422 AM CDT Tue Jul 25 2017 /522 AM EDT Tue Jul 25 2017/


Thunderstorms are expected to return to the area by Wednesday
night, with the return of a very humid air mass which will
support the potential for heavy rainfall. There remains
uncertainty as to where the heaviest rainfall will occur, though
there is some signal from numerical model forecasts that locations
south of a Dixon, to Joliet, to Valparaiso line may be most
favored for higher rainfall amounts, potentially of 1 to 3 inches.

Given the wet antecedent conditions from recent heavy rainfall,
areas that receive additional heavy rainfall Wednesday night and
early Thursday will likely be more susceptible to flooding than
normal. This would likely cause additional rises on portions of
the Kankakee and Illinois Rivers, where rises have already
occurred due to recent rains.

Those with hydrologic concerns in these areas should maintain a
close watch on actual rainfall amounts and river stage forecasts.
Be sure to monitor later forecasts for updates on the heavy rain
and flooding potential Wednesday night into early Thursday.



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