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February 20-21 Heavy Rain/Flooding/High Wind Threat


Hoosier

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having a hard time remembering the last time we had a flash freeze with the kind of standing water likely to be in play

Not quite flash freeze but 12-12-10 here went from hours of heavy rain to heavy snow and dropped into the teens by that night. The freeways were absolute skating rinks even 2 days later.

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But December 27, 2008 saw temps soar into the 60s...that is an example of a torch.

We were having such a winter wonderland prior to that too. Wave after wave. Then one came in as snow, turned to pingers, freezing rain, and then...rain. and was all downhill from there.

Still bitter about that one since it was perfect Christmas weather up until literally midnight, Christmas Eve morning... :underthewx:

 

Not quite flash freeze but 12-12-10 here went from hours of heavy rain to heavy snow and dropped into the teens by that night. The freeways were absolute skating rinks even 2 days later.

Yeah, that was BAD. I got my truck stuck out in front of Ford Field in all the ice while I was on my way to get tickets to the "Minnesota Snowbowl" after their dome collapsed and they decided to play the game in Detroit.

The way the snow was plastered to everything days later was really awesome looking too.

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Two words: ice jams!

The rivers will be overwhelmed.

This is not good at all. One thing that may limit things somewhat over northern IL southern WI and southern lower MI is that if the GFS is close (hopefully) with 2m temps, they only top out in the 40s. Farther south though, where well into the 50s is likely, snowmelt will be further accelerated. So while flooding will be a big problem north with the forecast rain amounts, places farther south and east that may end up slightly lower on the rainfall side could see similarly bad problems with the more rapid snowmelt. Also any intense convection in those areas would up the ante.
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I mentioned this in the southern ON thread ... the most costly impacts from rain and snowmelt on Thursday would likely not be river flooding but roof collapse risk for flat-roofed structures such as small apartment buildings and commercial areas, and large-scale urban ponding as water collects in parking lots and underpasses. The snow load on flat-roofed buildings is probably already quite large but add the weight of the rainfall to that and I'm sure there will be some widespread damage. People would have some time between the last of the snow on Wednesday and the onset of the rainfall to clear away some of the roof snow, as for large parking lots, like shopping malls, clearing storm drains might save some trouble.

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I mentioned this in the southern ON thread ... the most costly impacts from rain and snowmelt on Thursday would likely not be river flooding but roof collapse risk for flat-roofed structures such as small apartment buildings and commercial areas, and large-scale urban ponding as water collects in parking lots and underpasses. The snow load on flat-roofed buildings is probably already quite large but add the weight of the rainfall to that and I'm sure there will be some widespread damage. People would have some time between the last of the snow on Wednesday and the onset of the rainfall to clear away some of the roof snow, as for large parking lots, like shopping malls, clearing storm drains might save some trouble.

 

Very good point. 

 

Hopefully with the sun and wind the next two days some of that snow can be melted and sublimated away. Of course it takes longer on flat roofs.

 

NAM has heaviest axis of rain over the IL river valley towards NW OH.

 

NAM_221_2014021718_F84_PCPIN_72_HR.png

 

If this storm bombs out like the EURO showed, it could go further west and bring even more warm air up.

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Very good point. 

 

Hopefully with the sun and wind the next two days some of that snow can be melted and sublimated away. Of course it takes longer on flat roofs.

 

NAM has heaviest axis of rain over the IL river valley towards NW OH.

 

NAM_221_2014021718_F84_PCPIN_72_HR.png

 

If this storm bombs out like the EURO showed, it could go further west and bring even more warm air up.

I miss the old Geos :lol:

 

Seriously though...with the water stored in our snowpack...a bit of sublimation means next to nothing. Need to avoid the heaviest rain and warmest temps here.

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