Wednesday, July 26, 2017

Updated Wednesday Storm Threat

10:45pm Update: Heaviest of the rain has now moved east of I-39, with only isolated showers showing up further to the west.  Flash Flood Warnings remain in effect for Stephenson, Jo Daviess, Carroll and Whiteside counties until 2am, Flood Advisory for Ogle and Lee counties until 12:30am, Green and Rock counties until 11:30pm and for Winnebago County until 3am.  Any additional rainfall this evening should remain light.

10:00pm Update: Flood Advisory issued until 3am for Winnebago County.  Rainfall totals up to, two inches of rain have already fallen over parts of the county.  It's possible that an additional two inches of rain could occur under the heavy rain showers.

9:00pm Update: Flash Flood Warning has been issued for Stephenson, Jo Daviess, Carroll and Whiteside counties until 2am.  A Flood Advisory has been issued for Ogle, Lee and far SW Boone counties until 12:30am and a Flood Advisory has been issued for Green and Rock counties until 11:30pm. 

Rainfall rates of one to two inches per hour have been recorded with the incoming storms.  These storms are moving to the east around 30mph, so
the heavy rain won't last too long.  But when it comes down, it will be very heavy.  Our overall severe threat is decreasing, with heavy rain our greatest threat.

(10:02:30 PM) nwsbot: Local Storm Report by NWS MKX: Brodhead [Green Co, WI] trained spotter reports HEAVY RAIN of M1.80 INCH at 09:05 PM CDT -- fell in 80 mins.

(8:50:17 PM) nwsbot: Local Storm Report by NWS MKX: 3 ENE Monroe [Green Co, WI] awos reports HEAVY RAIN of M1.94 INCH at 08:35 PM CDT -- measured at the monroe airport (keft) in one hour.

 (8:47:58 PM) nwsbot: Local Storm Report by NWS DVN: 1 N Savanna [Carroll Co, IL] law enforcement reports FLASH FLOOD at 08:15 PM CDT -- mudslide over portion of rt 84 north of savanna. area currently deemed unsafe.

Cloud cover Wednesday afternoon held temperatures down in the upper 70's and low 80's, but the heat index reached close to 90 degrees in many spots.  That's because the dew point temperature quickly warmed into the mid 70's. 

Most of Wednesday afternoon has been quiet, just cloudy.  Showers and thunderstorms have been developing along and ahead of a cold front to the north and west this afternoon.  Most of the thunderstorms have been sub-severe, with locally strong winds and heavy rainfall.  Our severe threat Wednesday evening is on the lower end, however, a few of the stronger storms could produce locally strong wind gusts over 50 mph. 

The complex of thunderstorms over eastern Iowa have been steadily marching east and are expected cross the Mississippi River around 7pm, affecting Carroll, Whiteside and Jo Daviess counties first.  Most of the storm reports that we have received from the storms in Iowa have been reports of very heavy rain, over an inch within an hour.  Because dew point temperatures are so high, any thunderstorm that move in will be capable of producing heavy rainfall.  And I think through the evening that is going to be the biggest threat to the Stateline.

Storms have been fairly progressive, moving to the east between 30 and 35 mph.  So the threat for storms to repeatedly move over the same area is low, but the threat for very heavy downpours remain high.

Thunderstorms should be moving east and south of the Stateline roughly after 2am, with skies remaining cloudy through Thursday morning.

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