Day 1 of Chicago, IL (KORD)
A weak upper-level low approaching
from the northwest will provide clouds and intermittent showers and possibly weak
thunderstorms throughout the day 1 period. This will limit cooling tonight and
warming during the day tomorrow, but some breaks of sun are still likely, causing
temperatures to spike at times. Weak easterly winds off Lake Michigan will also
limit the diurnal temperature range a bit. Still, there will be just enough
daytime heating for very modest instability, not enough for any severe thunderstorms,
but perhaps enough to lead to more widespread convection in the late afternoon
and evening. Some of the showers and thunderstorms could bring briefly stronger
winds (beware as you’re forecasting for maximum sustained winds), but they won’t
be all that strong given very modest instability. It’s not clear if the lake
influence will inhibit storms via cooler temperatures or enhance them via any
lake breeze convergence. There will also be a band of showers late tonight/early
tomorrow morning, when the low will likely be achieved due to evaporational
cooling. Given the hit or miss nature of the storms, rainfall amount is quite
uncertain. Except for the GFS and MOS-X, most models appear to be too cool at
KORD recently, especially at night, so I recommend leaning toward the higher
side of model guidance. USL model has switched to KORD at http://www.microclimates.org/forecast/KORD/
and looks pretty reasonable today.
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