Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 200744
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 1155 PM EDT Tue Sep 19 2017

AVIATION...

Low level moisture remains high across southeast Michigan, with
surface dew pts holding in the 60s. Mid/high clouds have thinned out
in spots, which has allow for lower ceilings toward LIFR in spots.
However, still not totally confident the ceilings will drop below
400 ft or in the development of dense fog, as a light easterly wind
remains and transient mid/high clouds persist. Will continue to
monitor trends before 6z issuance, but anticipating going with IFR
conditions overnight into early tomorrow morning. Ceilings will then
be slow to lift on Wednesday, and probably going to take most of the
day to dissipate the High MVFR clouds during the afternoon with weak
surface winds persisting.

For DTW...Difficult ceiling and visibility forecast overnight, and
likely to dip into IFR with LIFR possible by sunrise.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5000 ft through early tomorrow afternoon,
  then decreasing confidence late tomorrow afternoon.

* Low for cigs/VIS to fall below 200ft and/or 1/2sm 8-14z.


&&

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

$$

DISCUSSION...DRK
MARINE.......SC
AVIATION.....SF


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