Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231955

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
355 PM EDT Wed Aug 23 2017


Quiet stretch of weather at least through the weekend as expansive
area of high pressure tracks across Ontario and the northern Great
Lakes before stalling slightly over Quebec and the NE conus for a
couple more days. Positioning of the high will send steady feed of
cool and dry air into the region. This will result in temperatures
remaining a few degrees below normal for the coming week. Normal
highs are around 80 and lows are around 60.

The mid levels are a bit more exciting with a compact vort max
diving through southern MI Thursday. This wave is the next trough to
rotate around the dominate upper level low lifting NE out of western
Quebec. This wave will increase cloud cover over SE MI Thursday
morning with a small chance of seeing some isolated showers in the
afternoon. The early morning clouds may prevent any shallow fog from
developing. Moisture depth is thin with PWATs only around a half
inch. Better chance of precip will occur across the eastern Thumb as
northern flow behind the trough axis excites lake effect clouds and
possibly some showers as cool air advects over the warm lake.

After Thursday the high will take a firm grasp over the area with a
mid level shortwave ridge working into the Great Lakes. Upper level
flow becomes very weak across much of the country as strong
westerlies emerge across Canada. This is where model solutions start
to diverge. A mid level wave will cut off over the Midwest and try
to drift into the state but may take a few days with no steering
flow. One thing to watch will be remnants of the developing tropical
system Harvey over the western Gulf of Mexico. Airmass will be quiet
dry early next week when the trough tries to drift across lower MI,
but if the system finds itself a bit further north and east after
making landfall, the trough may be able to tap into it for moisture.



The pressure gradient is forecasted to weaken considerably tonight
in response to surface high pressure finally building into the
central Great Lakes. Northwest winds tonight are expected to ease
into the 15 to 20 knot range. A secondary cold front structure is
expected to push southward and release off of Lake Huron during the
day on Thursday. Winds are forecasted to veer to the northeast
during the afternoon and range between 10 and 15 knots. Cooler air
and lift along ahead of this boundary may create a favorable
environment for waterspouts, especially where any land breeze
development is possible. High pressure will eventually settle
overhead by Friday, bringing enough dry air to inhibit cloud
formation and produce favorable wind and wave conditions through the


Issued at 156 PM EDT Wed Aug 23 2017


The combination of cool northwest flow with relatively moist
antecedent boundary layer moisture and full vegetation green-up has
led to a bkn layer of boundary layer cumulus over all of southeastern
Michigan today. The area remains under a favorable sector for strong
upper level confluence as evidenced in recent water vapor imagery.
Progged moisture progs depict a high amount of lower theta e
advection from the due north overnight off of a backdoor type frontal
structure. This drying in concert with loss of diurnal heating will
cause cumulus dissipation this evening. One question for Thursday
morning is prospects of near surface radiation fog development with
cool temperatures at daybreak. The unknown with fog potential hinges
on the the amount of high cloud that will be in place ahead of
the shortwave set to  dig through southeastern later Thursday
afternoon. Attm, preference was to hold back on fog given the tenuous
dependence on said cloud deck in forecast soundings. The forecast
sides with more of an opaque midcloud Thursday.


* Moderate for ceiling 5000 feet or less this afternoon.


Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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