Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201748
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
148 PM EDT Wed Sep 20 2017


.AVIATION...

Fog has finally cleared out the most of the area after hanging
around for most of the morning hours. TAF sites will continue to see
MVFR CIGS through the early afternoon before mixing attempts to
erode the low clouds around 21/22Z. A weak frontal boundary will push
northward across Lower Michigan today and stall out near MBS where
an instability axis will reside nearby. This could pose a threat of
convection, but chances still remain too low have include a TEMPO
group. Otherwise, light southerly winds 5-10 kts and CIGS improving
to VFR late this afternoon. Overnight could see some fog development
around 06Z and visibility further dropping by 11/12Z time frame.
Expect fog to develop over parts of the area overnight with MVFR/IFR
visibility. However, some drying out throughout the day today and
some higher clouds streaming across the area may be a limiting factor
to denser fog development.

For DTW...MVFR CIGS below 5000ft will continue to stream over the
area this afternoon before drying out and becoming VFR after 21Z
Development of fog is possible overnight but expect visibility to
remain MVFR through roughly 13Z before conditions improve.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5000 ft through this afternoon clearing to
  VFR this evening

* Low for in VSBY below 3SM overnight through roughly 13Z.

&&

.PREV DISCUSSION...
Issued at 344 AM EDT Wed Sep 20 2017

DISCUSSION...

Upper level low over Ohio is slowly drifting SE away from lower MI
as longwave ridge continues to strengthen overhead. The weakening
low has sent one final moisture surge, located along the 700-850mb
theta e gradient, northward which is about to pass over Saginaw Bay
as of 07Z. This appears to be its last gasp with any lingering
showers more of a mist out of the low stratus and fog due to the
abundant low level moisture in place. The low will fade away through
the day as ridging overtakes it.

Meanwhile further west, A strong shortwave rotating around the
longwave trough will get slung northeastward through the northern
plains into Canada with the aid of a 125+ knot jet. Though this will
be far removed from the Great Lakes, it will pull a warm front north
through lower MI today allowing a thermal ridge approaching 17C at
850mb into the state. It will also force a cold front into the
Midwest, draped from the western U.P. down through WI into IL. This
will be the focus for thunderstorm develop today into tonight west
of SE MI. The warm sector will provide us a fairly stout cap between
900-700mb which will likely prevent any storms from bleeding east
into our CWA. Models are keying in on a period after 09Z
tonight/Thursday morning where a wave tracking along the front
through Mid MI could bring a period of shower/storms to the Saginaw
region. Then the front will have inched closer to lower MI keeping
low chance pops around on Thursday as well. At this point thinking
is it will be difficult for showers to be able to break the cap and
majority of the area will remain dry through the forecast period.

Other main issue will be the heat. Models are being very consistent
with the ridge supporting 850/925mb temps of 17C/+20C respectively.
With dewpoints holding in the 60s limit nocturnal cooling, high temps
should easily make it into the mid 80s and possible upper 80s
Thursday through the weekend. These temps will be nearing 15F above
average for late September. Record highs for all 3 climate sites
(DTW, FNT, MBS) are all around 90F through this stretch. Something
to watch for.

MARINE...

South-southeast winds (generally under 15 knots) will persist across
Lake Huron through the end of the week as high pressure expands from
Quebec into the eastern Great Lakes. The winds across Lake St Clair
and Erie will have a more easterly component, but will be much
lighter. The winds will weaken slightly over the weekend as the high
pressure expands into Lower Michigan.

&&

.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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