Critique on the forecast - Today and Tonight

Early morning satellite imagery shows the upper low spinning away from Southeast Michigan but still
able to support a pattern of showers around the northwest flank of the system. Model analysis fields
indicate this is associated with a well-defined deformation axis wrapping around the system which
will efficiently wring out remaining moisture for a few more hours. Radar trends support model
depictions of the pattern leaving the Tri Cities dry at press time and then sliding southward and
shrinking eastward on a pace to exit the rest of the area around 8 am.

The continued eastward departure of the low will bolster northerly surface wind and cold advection
that is already in progress across Lower Michigan. The 00z model solutions are consistent with the
last several runs showing a pocket of 850 mb air at about 5C recovering to about 7C during the
afternoon. Sounding analysis translates that into highs mostly in the upper 60s with a boundary
layer mixing to 800 mb. This is about 15 degrees below normal highs that are still in the lower 80s
during the last week of July, but only approaching the record lowest max temp at DTW which is
68/1926 while FNT and MBS are in the lower to mid 60s.

High clouds stripping away reveal some breaks in the stratus over Lower Michigan during the early
morning. There could be some expansion of open sky for a few hours post sunrise but these will
quickly fill in as surface heating ramps up by late morning. Model soundings indicate enough
moisture for a generous cu response but with enough mid level subsidence to prevent showers. Expect
the afternoon cloud pattern to linger long enough into the evening to blend in with mid and high
clouds arriving with the next upper level height fall center in northerly flow aloft. The approach
of the upper wave will also sharpen surface pressure gradient enough to maintain a 5-10 knot wind
through the night. The combination of clouds and wind will then prevent temperatures from reaching
full radiational cooling potential and keep min temps in the 50s with the exception of the usual
cool spots that could touch the upper 40s by sunrise Tuesday.

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Remaining Remarks on the forecast - Tuesday through Sunday

Cool cyclonic flow will persist over the central Great Lakes from Tuesday into Friday as the upper
low remains over Ontario and Quebec. Weak upper shortwaves pivoting around the low will occasionally
brush across the area, bringing quick shots of moisture. Daytime heating will help us destabilize
each day with surface heating combining with cool air aloft ( h850 temps running just below 10C
through this period ) to steepen lapse rates. Temperatures will also run a bit below normal, with
highs only in the 70s ( compared to average highs in the low 80s ).

For Tuesday, models have been consistent with dropping a very weak upper wave down from Canada,
bringing a surge of low/mid level moisture with it. The shortwave and associated surface trough are
progged to work across the area during peak heating. Model forecast soundings lack a cap and show
lapse rates from the surface to 500mb ranging between 7 and 9 c/km. This should provide scattered to
numerous showers across the area, with a little better coverage expected north of M-59, closer to
the upper wave and cooler air aloft. Freezing levels are expected to run around 9000 feet with the
cooler airmass overhead. While the potential for thunderstorms will be low, thunderstorms or even
more vertically developed showers that develop will be capable of small hail.

Canadian upper low will lift north for the weekend, but medium range models are still in strong
agreement with keeping some troughing through the Great Lakes. While showers and thunderstorms will
still be possible, we should see some moderation in temperatures into the upper 70s or near 80 for
highs.

. . posted at 345 AM EDT Monday July 28 2014


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