What a day in the
WxChallenge today. Squall line amazingly pushed ~150 mi east of models with the
leading edge arriving at KSTL before the start of day 5. This meant that
despite a 72F peak and 23 kt wind surge ahead of the squall line, as expected,
none of that counted for day 5. Instead, high temperature and peak wind were
only 70F and 18 kt respectively during daytime! Even with some of the squall line
before day 5, there was still 3.90” for day 5, only stopping an hour ago, and ~8”
in past 2 days with flash flooding across the region this morning.
All the rain has
pushed off to the east as drier air as come in. Even as surface high pressure
approaches, lingering low-level moisture trapped underneath a subsidence
inversion in an otherwise dry atmosphere will lead to at least a scattered to
broken layer of low-level clouds throughout the night that will inhibit
radiational cooling despite light winds. Low clouds are the most difficult to
predict; in cases with marginal moisture like tonight into tomorrow, a little
more or less saturated would make the difference between a solid deck of low
clouds and mostly clear skies. This is making the temperature forecast trickier
than earlier expected. Even tomorrow, the low clouds will likely struggle to
break up, causing a cooler high temperature. Actually, if the clouds are thick
enough, the high could occur at the beginning (Wednesday 06z) instead of
tomorrow afternoon. There is also a decent chance of the low occurring at the
end (Thursday 06z) even if it stays rather cloudy due to subtle cool advection
via northeasterly surface wind.
Note that this
rather cloudy scenario I am favoring is leaning more towards (but not going
completely toward) the NAM 3-km and HRRR, which have a better handle on the
current low-level cloud cover from western Missouri to Minnesota, though might
be a bit overdone. Some other global models like ECMWF and GFS are underestimating
the current cloud cover and show relatively clear sky in St. Louis tomorrow,
while the CMC is in between. The clearer models are showing a larger diurnal
temperature range (especially cooler for the high) than the cloudier models.
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| Source: Penn State Meteorology |
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| Source: PivotalWeather |
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| Source: Meteogram Generator |
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