Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211746
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
146 PM EDT Thu Sep 21 2017


.AVIATION...

Ample moisture and diurnal mixing will aide in the development of
some scattered to broken VFR cu this afternoon. Winds will be out of
the south at 5-10kts with light and variable winds at times. There
is a slight chance for convection to develop along an instability
axis rotating into the the area that will affect MBS. The building
ridge and strengthening cap will be the limiting factor for any
convection to develop. There is be potential for lower VSBYs from BR
to develop again tonight with ample surface moisture and calm winds.
However, high clouds streaming over the area overnight could help
limit the development of any dense fog.

For DTW...Low end VFR of scattered to broken clouds could develop
this afternoon. CIGS are expected to be around to slightly above 5000
ft today and tonight. BR is possible tonight, but do not anticipate
any dense fog development.

//DTW THRESHOLD PROBABILITIES...

* Low in ceilings at or below 5000 ft today and tonight.

* Low in fog development tonight.

&&

.PREV DISCUSSION...
Issued at 347 AM EDT Thu Sep 21 2017

DISCUSSION...

For a fairly quiet pattern this week, there are a few things to talk
about. First and foremost we are in the midst of a very warm stretch
of weather today through Tuesday where temperatures will reach the
mid to upper 80s each day. A few 90 degrees obs will not be out of
the question either today through Saturday as impressively strong
ridge sets up over the Great Lakes. In addition, there will be a
chance of thunderstorms this afternoon and again on Wednesday.

Upper level pattern will be dominated by a deep trough over the west
coast and resultant ridge over the eastern conus. We`ll have a
chance of thunderstorms this afternoon as a weakening cold front
slides through northern MI, over top the ridge as it builds further
north into the region. Elevated mixed layer will fold over into the
region with the front around the ridge. Will be no shortage of
elevated instability where model CAPE forecasts exceed 2000 J/kg.
The surface ridge and warm air layer between 900-700mb will amount
to a decently strong cap which may prevent most locations from
seeing any storms today. Better chances through mid MI were mid
level short wave activity will pivot through. Will take several
hours through the afternoon to break the cap even up there, so best
time will be between 18Z-00Z. Any remnant shower/storm activity will
trickle eastward and fade away likely by about midnight. These
storms are not expected to be severe as shear is almost nil. We`ll
have a high CAPE environment with good mid level lapse rates so
likely a pulse type day with some potential for small hail.

As for the heat, the temperature profile within the ridge (building
to around 590 dam) will be very summer like. 850/925mb temps will
increase to around 17/22C respectively. This should easily allow
highs to reach into the upper 80s. Locations away from the lakes
will have a chance to hit 90 as the slight easterly component to the
wind may be enough to keep temps down a degree or two. Add to it
the air is not exactly dry as dewpoints will will be in the 60s and
even near 70 at times. That typically makes it harder to really
maximize highs. Above average temperatures will persist through
about next Wednesday.

Pretty steady forecast heading into the weekend through about
Tuesday. High pressure parks over the region with the west coast
trough only slowly drifting eastward. Next real opportunity for
precipitation will come on Wednesday as the vort max embedded in the
trough finally ejects out through the northern plains sending a cold
front through lower MI.

MARINE...

South-southeast winds will persist across the lakes today through
Friday as high pressure remains anchored over the eastern Great
Lakes and weak surface troughing holds over Lower Mi. Peak winds
around 15 knots are expected over the open waters of Lake Huron. The
high pressure will expand across Lower Mi over the weekend. This
will result in a weakening of the winds.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....AA
DISCUSSION...DRK
MARINE.......SC


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