Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 161911

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
311 PM EDT Sat Sep 16 2017


Temperatures have reached or exceeded 80 degrees just about
everywhere in southeast Michigan, as of 3 PM, as upper level ridge
remains in place today. Dry mid levels, as 12z DTX sounding revealed
a 700 mb dew pt depression of 29 C, and CU field has been limited
this afternoon. Surface moisture/dew pts remain elevated in the lower
60s, which continues to highlight the potential for patchy fog
tonight with winds going calm.

850-700 MB Theta-E min more or less holding through early tomorrow
afternoon, before moisture advection ramps up, with main moisture
axis with cold front arriving during the evening (per 12z
NAM/Regional GEM/Euro). Precipitable water axis at or above 1.75
inches sliding through. Upper level support will be tracking into
Ontario, with just modest height falls extending south into southern
lower Michigan. None-the-less, sufficient leftover diurnal
instability, SBCAPES between 1000-1500 J/kg, coupled with low level
convergence likely sufficient to generate showers and a few
thunderstorms (0-6 km bulk shear under 20 knots suggests nothing
close to severe), with local probabilistic SREF weighted guidance
even indicating numerous pops for evening hours. Mid level lapse
rates look adequate at best. Trended forecast to high scattered pops.

Upper level energy/disturbances ejecting out of the Central Plains,
moving through early next week, but embedded within the back drop of
an amplifying upper level ridge by Mid Week, as very large trough
encompasses North America along and west of the Rockies. Very warm
mixed layer to spread into lower Michigan late in the work week with
strengthening and deep southwest flow. 850 MB temps reaching and
slightly exceeding 20 C suggests high temperatures of 90 degrees
could come into play. Morning fog/low clouds could always derail the
forecast, and a more conservative approached will be utilized due to
the time of year.



Favorable boating conditions through most of the weekend as a high
surface pressure is anchored over the Great Lakes. Light south winds
of 5-15 kts will allow wave heights to remain around 2-4 ft through
Sunday.  A weak cold front will be pushing through southeast
Michigan Sunday evening and overnight in response to low pressure
system lifting to the north through Ontario. A few scattered showers
and thunderstorms will be possible with the passage of the front in
the later evening overnight time frame. Winds will turn northerly
behind the front and remain around 15 kts or below by Monday


Issued at 149 PM EDT Sat Sep 16 2017


Diurnally driven scattered clouds have started to develop this
afternoon across southeast Michigan. Thinking CIGS will settle in at
VFR for all TAF sites and will remain scattered throughout the
afternoon before clearing out after 0Z. Winds will remain light and
out of the south. Fog will most likely develop again overnight. Some
uncertainty remains around how thick the fog may get again with
incoming clouds ahead of a cold front Sunday night, but it looks
like clouds could mitigate fog from the extent we have seen the last
couple of days. Expect fog to break rather quickly after 12/13Z

For DTW...Looks like scattered clouds will develop and be at or
below 5000ft and begin to clear out around sunset. Fog again could
redevelop overnight and bring with it some MVFR visibility with
potential to be slightly lower, but will again burn off rather
quickly around 12/13Z


* Medium for ceiling 5000 ft or less during afternoon.


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



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