Wednesday, July 12, 2017

Atmospheric Pattern Continues to Favor Heavy Rainfall

As mentioned earlier, a Flash Flood Watch will go into effect at 9pm for Winnebago, Boone, McHenry, Ogle, Lee, DeKalb and Whiteside counties.  It's appears as if the flooding potential may be a bit further south than where it was located late Tuesday night.  Which will be good news for those who are suffering from the significant flooding.

Thunderstorms are beginning to develop over Wisconsin and central/eastern Iowa this evening.  A few thunderstorms have reached severe limits, with a couple reports of very heavy rain near Cedar Rapids, IA.  These storms will continue to move east, but will then shift southeast as a cold front moves through Wisconsin.

As the front begins to shift south it will turn more parallel with the winds that are moving above in the atmosphere.  This type of set up is ideal for 'training' thunderstorms and typically is the cause of heavy rain events.  Like Tuesday night, it won't be a widespread event but for locations that do receive thunderstorms, rainfall rates of nearly one inch per hour are possible.  Right now, that highest risk looks to be over west-central Illinois and for some of our southern counties - Whiteside, Lee, Ogle and DeKalb.

The amount of moisture that is present in the atmosphere is significant this evening.  The image on the left is a current analysis of our precipitable water - or how much moisture the atmosphere is currently capable of holding.  Precipitable water values near two inches are found over west-central and central Illinois.  This is an extremely high amount of moisture and means that any thunderstorms that move through that area will be very efficient at producing heavy, possibly significant, rainfall. 

Thunderstorm coverage should begin to increase towards 9pm/10pm over western/northwestern Illinois.  It's important to remember that not everyone will experience heavy rain producing thunderstorms.  But those that do could see high rainfall rates.  So be prepared.

No comments:

Post a Comment