Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 100400
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1200 AM EDT Tue Oct 10 2017


.AVIATION...

Quiet weather over southeastern Michigan with weak surface ridging
in place and virtually zero thermal advections to speak of. Upper
level confluence will strengthen by morning as the entrance region to
the upper level jet axis will snap into place directly over the
Great Lakes. Uncertainty exists as to the likelihood of fog
overnight. Rap soundings have been bouncing around a fair amount in
not only saturation but also with the surface inversion structure.
RAP forecast soundings remain not nearly as bullish in amount of
near surface saturation but given a couple of obs with Haze concerns,
lack of mixing will lead to some br/fg. Will continue a MVFR fog
mention.

For DTW...Expecting some fog to develop late Tonight, just not sure
how dense it will become with the shallow moisture. Otherwise, could
see MVFR stratus track in from the north Tuesday morning.

//DTW THRESHOLD PROBABILITIES...

* Low for cigs at or below 5000 ft late tonight into Tuesday morning.

* Very low for cigs/vis aob 200 ft and/or 1/2SM from 10-13z.

&&

.PREV DISCUSSION...
Issued at 348 PM EDT Mon Oct 9 2017

DISCUSSION...

An outstanding fall day is unfolding around SE Michigan this
afternoon. Under plenty of sunshine, highs are solidly in the mid to
upper 70s which are 10 to 15 degrees above normal for early October
but well short of records in the mid to upper 80s. A cold front over
the northern Great Lakes will then move through the region tonight
and bring quite a change for Tuesday. The front remains too lean on
moisture for rain but will bring clouds and cooler air after fully
exiting into Ohio Tuesday morning. Observations indicate just some
fragile bands of low clouds within the frontal zone over the
northern Great Lakes today, along and north of the surface wind
shift and are modeled to remain in a similar relative position in
the frontal zone during the night. This is important for potential
fog development overnight as there is also a lack of high clouds
upstream which will allow some radiational cooling of the relatively
moist boundary layer over SE Michigan. Timing the frontal passage
shortly after midnight in the Tri Cities and northern Thumb regions
will likely prevent fog coverage there in favor of low clouds. A
later wind shift farther south will bring the greatest coverage of
fog along and south of the I-69 corridor and especially through the
Detroit metro area to the Ohio border. The wind shift to the
northeast will then scour out remaining surface moisture by mid
Tuesday morning leaving varying amounts of low cloud coverage within
the frontal inversion for the rest of the day. Expect these clouds
will have greater coverage near the Ohio border while mid and high
clouds associated with both the front and the next upper wave cover
points north through the afternoon. Prefer guidance temperatures in
the 60s considering the cooler northeast flow that will be in place
along with the clouds.

As the front settles toward the Ohio valley, the stage will be set
for it to interact with the next low pressure system and produce a
generous rainfall event Tuesday night through Wednesday. The upper
wave is observed moving through the central Rockies today and is
already producing significant lee side surface cyclogenesis over the
southern Plains. There is good model agreement to then bring the
system into the mid Mississippi valley during Tuesday while tapping
deep moisture from the Gulf region that will supply a pattern of
isentropic ascent over lower Michigan Tuesday night. The upper wave
is then projected to move directly over the region early Wednesday
with a surface low track south of the Ohio border through the day.
There is some variation in solutions on the surface low track and
character while agreement is solid in the formation of a mid level
theta-e trowal axis over SE Michigan as a sign of the dynamic
support within the wave. Model QPF offering 12 hr totals around 1
inch then look reasonable ending Wednesday afternoon. The potential
for excessive rainfall will be limited by a northward push of the
dry slot and the fast movement of the system.

Upper-level ridging aloft and surface high pressure will influence
the Great Lakes Thursday into Friday which will bring dry conditions
and will allow temperatures to slowly ramp up through the weekend.
Wind direction will shift from the northeast to the southwest
Thursday into Friday, which will allow warmer air to push daytime
highs into the lower 70s Friday afternoon. WAA will continue to ramp
up Friday into Saturday, as noted in the 850 mb thermal maps, where
temperatures averaging 6C Friday morning increases to 15C Saturday
morning. An increase in warmer air and a chance to see periods of
extended sunshine will allow daytime highs to peak in the mid to
upper 70s, and even the lower 80s across Metro Detroit Saturday
afternoon. For reference, normal daytime high temperatures reside in
the lower 60s across SE Michigan for mid-October.

The next likely chance for rain and thunderstorms will come to
Michigan Saturday into Sunday, however, confidence regarding timing
and intensity remain low as discrepancies between long range models
are prevalent. The GFS pushes the warm front and an associated LLJ
across Central Michigan which produces precipitation across the Tri-
Cities to thumb. As low pressure pushes northeast from northern
Illinois into Central Michigan, rain chances eventually spread
across the Metro Detroit region, with PoPs continuing through early
Sunday as a cold front sweeps through the state. The ECMWF model
produces rain chances from the warm front early Sunday. The center
of the low pressure center is north compared to the GFS run, pushing
northeast from southern WI into northern lower Michigan, which drags
the associated cold front through the state early Monday morning.

Cool and dry air will filter in behind the cold front Monday into
Tuesday, which is expected to return temperatures back to seasonal
values.

MARINE...

A cold front dropping south through the region will bring an
increase in north-northwest winds across lake Huron Tonight. Winds
will be topping out between 20 to 25 knots over the open waters of
Lake Huron by Tuesday morning. This trajectory will build wave
heights to 4 feet over greater over southern lake Huron, which
should impact the nearshore waters as well. Winds will then ease a
bit late Tuesday and Tuesday night, while shifting to north.
However, easterly winds on Wednesday will increase back into the 20
to 25 knot ranges, as low pressure tracks through the Ohio Valley.
Additional small craft advisories will likely be needed.

HYDROLOGY...

Widespread rainfall is expected Tuesday night into Wednesday as a
low pressure system tracks through the Ohio Valley. Rainfall
totals around 1 inch appear likely, but the rainfall will occur over
a longer duration, roughly 12 or more hours. Thus, no flooding is
anticipated, but standing water on the area roadways and in the
flood-prone low lying areas and area roadways should be expected.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 2 PM EDT Tuesday for LHZ421-441-442.

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

$$

AVIATION.....CB
DISCUSSION...BT/AM
MARINE.......SF
HYDROLOGY....SF


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at www.weather.gov/detroit.



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