Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 170514

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
114 AM EDT Sun Sep 17 2017


Looking for patchy MVFR fog to set up across the area once again as
airmass has changed little over the last couple days. Cannot rule
out a few IFR/LIFR obs around 11-12Z as temps bottom out this
morning. The exception is YIP who will have LIFR in the TAF due to
locally dense fog the last two mornings. We`ll burn off the fog this
morning and begin to transition to rain chances later in the day. A
band of showers along a cold front will reach MBS around 21Z before
slowly drifting SE through the other taf sites. Could see a few
thunderstorms early on and have expanded the PROB30 to FNT as well
as models seem to want to hold the forcing together at least to
them. Then with the loss of daytime heating and a weakening front,
the line of showers looks to dissipate so could end up dry from PTK
southward. Winds will shift from southerly to westerly behind the

For DTW...Light fog (MVFR) is expected to develop late tonight and
persist until an hour or two after sunrise. Mainly scattered clouds
today until moisture ahead of the cold front bring broken skies for
several hours. At this point, showers along the front look to be
isolated at best by the time it reaches the terminal so will have no
mention in the TAF.


* Medium for visibilities around 3SM in light fog Sunday morning.

* Medium for ceiling 5000 ft or less Sunday evening.


Issued at 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


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



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