Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 142310
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
710 PM EDT Thu Sep 14 2017

.AVIATION...

VFR during the evening will be under borderline cumulus/altocumulus
lingering for a couple hours after sunset. As these clouds dissipate
and surface wind decouples, timing and coverage of fog will be the
primary aviation weather concern through Friday morning. Using a
combination of upstream observations from last night and locally
this morning, expect onset timing shortly after midnight for the
prone areas such as FNT, PTK, and YIP likely with less than 1 hour
of MVFR before quickly transitioning to IFR and LIFR. The potential
for dense fog of a 1/4SM or less remains in play for all areas
subject to timing and coverage refinements in later updates. The
possible exception could be MBS where higher visibility could result
from wind near 5 knots during the night. Model soundings then
indicate surface based moisture will be shallow enough to follow a
standard trend for dissipation mid to late Friday morning. This will
be followed by VFR under scattered cumulus and light south wind
through Friday afternoon.

For DTW... VFR under scattered cumulus will give way to fog
development overnight through mid Friday morning. Quick IFR
formation is likely just after midnight and 1/4SM or less is
possible toward sunrise through early Friday morning.

//DTW THRESHOLD PROBABILITIES...

* Moderate for visibility 1/2SM late tonight through early Friday
  morning.

&&

.PREV DISCUSSION...
Issued at 329 PM EDT Thu Sep 14 2017

Discussion...

A ridge of high pressure will remain in place through the upcoming
weekend. This will lead to a continue mild (to warm) stretch of
weather with highs climbing into the lower 80s in many locations
both Friday and Saturday while low temperatures build from 55-60
early Friday morning to the lower 60s in many area by early Sunday
morning.

There will be a continue chance of late night fog, especially
tonight, as low level moisture values remain rather high as the
remnants of Irma only gradually shifts to the east late today and
tonight. Patchy fog may even be possible late Friday and Saturday
nights as flow remain very weak under the aforementioned ridge of
high pressure. With the longer nights of early fall, these ideal
radiative cooling conditions may be enough to produce additional
bouts of minor fog formation.

An upper level shortwave exiting the northern plains toward Hudson
Bay will drag a cold front through SE Michigan Sunday night into
early Monday, bringing with it a chance for showers for the entire
region. The front is progged to slow and weaken just to our south,
which could lead to a slight chance of more showers into Tuesday for
areas near the Ohio border. Temperatures Sunday will be above
average in the lower to mid 80s, while post-front temperatures
Monday and Tuesday will be slightly cooler in the mid to upper 70s.

Model guidance then shows an upper ridge building into the area mid
next week. However, the models diverge on the timing and placement
of the ridge axis. The ECMWF solution places a strong ridge axis
directly over the Great Lakes from Wednesday through Friday which
would result in dry conditions for Michigan. On the other hand, the
GFS solution places this ridge axis to our east with a possible
disturbance and chance of rain on Thursday. For now, we will keep
low chance of precipitation mid-late week until we see more
agreement between model solutions.

MARINE...

Light and variable winds tonight will become increasingly southerly,
reaching into the 10 to 20 knot range by Saturday ahead of a weak
cold front, which looks to be moving through Sunday evening,
potentially triggering a few showers. Weak northerly flow to follow
the passage of the front early next week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....BT
DISCUSSION...DG/TF
MARINE.......SF


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at www.weather.gov/detroit.



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