What
luck with the storms arriving at ~0530 UTC last night, causing day 6’s low to
be 68F and precip to be 0.08”. Intermittent showers continued after 06z, with
0.22” counting for day 7. There was a very strong precipitation gradient in the Chicago area, with almost nothing to the northwest and up to 1" to the south and southeast. Cloudy skies have kept it from really warming up and
winds from blowing, with a high of 73F and max wind of only 10 kt so far. There could still be brief stronger winds with a subtle boundary over western Illinois as of 2230 UTC, visible as the cloud edge on satellite, before 06z tonight. Clouds
cleared out in the past hour, but the sun is going down quickly and it’s
unlikely to get any warmer. Mostly clear overnight will promote some
radiational cooling, but the low will be at the end again (Saturday 06z) due to
a re-inforcing cold front and continuous cold advection tomorrow, despite winds
preventing quick radiational cooling again. The high might be at the start
(Friday 06z), especially if there are some mid-level clouds around that time that
could briefly warm it up or stop the nighttime cooldown. Temperatures will warm
up with sunshine initially tomorrow, but with cold advection aloft, the warmup
will slow down quickly by early afternoon, with the daytime surface heating leading
to modest instability and increasing cumulus-type clouds. The clouds will build
into scattered showers, which could bring up to 0.05” of rain. With the steep afternoon
lapse rates and dry low-level air, any showers will lead to pronounced evaporative
cooling and a gust front that would briefly enhance the already overall stronger
winds tomorrow. Note that although it is currently cooler than some of the models, that is due to the thick high cloud shield, which models tend to underestimate its effect in slowing the daytime warmup. The
high cloud shield will not be present tomorrow. Clouds will be more
cumuliform, and at least earlier in the day, rather scattered.
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