Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 130348
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1148 PM EDT Thu Oct 12 2017


.AVIATION...

While the better low level moisture convergence (and IFR status) is
now sliding into the thumb, a region of fog has enveloped much of
metro Detroit in its wake. Recent model soundings, aided by
observations just to the west and southwest suggest increasing
southerly flow may actually cause fog/low clouds to lift northeast
of the terminals just prior to daybreak, leading to a VFR cloud deck
through the remainder of the morning. Most likely, ceilings and
visibility will remain highly variable during the course of the
morning hours.

For DTW...Fog and low clouds may struggle to hold through into
daybreak as south-southwest low level flow increases and thick 4k ft
cloud deck lifts overhead from the south.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5000 ft this morning and afternoon.

* Low for visibilities at or below 1/2 SM this morning.

&&

.PREV DISCUSSION...
Issued at 905 PM EDT Thu Oct 12 2017

UPDATE...

A sfc trough axis will lift into the thumb region tonight amidst
developing low level southerly flow. This will cause the region of
drizzle to become more focused across the Port Huron and thumb
regions during the course of the night. The 00Z DTX sounding
revealed a shallow inversion based near 800 ft, capped by a much
deeper inversion based near 6k ft. Some erosion of the low level
inversion to the southwest has caused some loss in the shallow
stratus deck, likely to push into portions of Se Mi tonight. While a
higher cloud deck will support the current cloudy forecast, there
have been some brief breaks and thinning of these clouds upstream.
This may offer enough boundary layer cooling to support areas of fog
tonight. The current forecast has a good handle on these factors.
Thus no evening update will be issued.

PREV DISCUSSION...
Issued at 317 PM EDT Thu Oct 12 2017

DISCUSSION...

Moist low level airmass remains in place (12z DTX sounding indicated
8 C dew pt at 925 and 850 MB), as inverted surface trough/return
moisture arches north in between the Central and Eastern Great
Lakes. With low clouds socked in all the way west through the Midwest
and south of the Ohio River, a cloudy forecast tonight seems like a
sure bet, with potentially enough low level moisture/isentropic
ascent/slight cooling of the boundary layer for some very light
rain/drizzle and fog.

Strong upper level trough/energy tracking through the Pacific
Northwest, with the positive tilted trough moving into the Northern
Plains on Saturday. Moisture axis/850-700 MB Theta-E ridge folding
over into southern Lower Michigan Tonight-Tomorrow morning, with the
axis then lifting to Saginaw Bay Saturday afternoon as warm front
pulls north. Looks like a tight low level baroclinic zone will
subsequently set up over southeast Michigan on Saturday, with maxes
around 60 degrees in/around Saginaw Bay, with temps around 80 degrees
toward the Ohio Border based on 925 mb temps reaching AOA 20 C.

Main moisture axis with cold front looks to be tracking through
around 12z Sunday, and looks to be out ahead of the excellent large
scale forcing/mid level cold pool (-29 C at 500 MB), and thus little
in the way of instability. Regardless, 60 knots at 850 MB will have
to be watched closely, but looks like there will be a stable
warm/dry bubble around that level. Even if no thunderstorms/convection
develops along the front, should be a pretty good wind pop behind
the front with good cold air advection advertised Sunday morning.
Although, the very good (28-30 MB) 6 hr rise/fall pressure couplet
will be displaced north over the U.P., and thus planning on just
advertising wind gusts on Sunday to around 40 MPH for now, in line
with our local SREF weighted probabilistic guidance. But wind gusts
to 45 mph certainty possible across the Thumb Region, per 12z
operational Euro, as the surface low continues to rapidly deepen as
it tracks into Quebec.

A chilly overnight period is expected Monday morning as temperatures
dip down into the upper 30s across most of SE MI, and lower 40s
across the Metro Detroit urban areas. While MOS guidance suggests
clearing skies Sunday night into Monday morning, upper-level
troughing and embedded shortwaves seen in long-range guidance may
act to keep cloud cover around which would keep lows in the lower
40s. As a result, opted to leave out the mention of frost
possibilities despite dew points nearing the freezing mark across
Flint to the Tri-Cities.

Upper-level ridging is then expected to move in from the Central
Plains to the Great Lakes throughout Tuesday and will hold across
the eastern half of the U.S. through most of the week, bringing dry
conditions and plenty of sunshine to the area. Additionally, WAA
will increase starting Tuesday through the weekend, which will push
daytime highs back into the mid to upper 60s starting Wednesday.
Temperatures in the lower 70s are not out of the question across the
Metro Detroit region if temperatures overachieve. Overall, quiet
weather is expected for most of the extended period as temperatures
warm-up throughout the week.

MARINE...

East to southeast flow will continue over Lake Huron through
tonight, with weaker northeasterly flow across Lake St. Clair and
the western shores of Lake Erie as weak high pressure slowly builds
across the region. Winds will veer to south southwesterly Friday
ahead of an approaching frontal boundary that will impact the waters
this weekend with periodic rain. A surge in winds will be possible
late in the weekend as an area of low pressure develops along the
frontal boundary and tightens the pressure gradient. Small craft and
gale force conditions will be possible.

Small Craft Advisories will remain in effect for the nearshore
waters of southern Lake Huron and outer Saginaw Bay through tonight
for waves of 3-5 feet. Waves over the open Lake Huron waters will be
higher at 5-8 feet. Wave heights will subside Friday and into
Saturday, before increasing again Sunday in response to the
developing area of low pressure.

HYDROLOGY...

A frontal boundary will approach southeast Michigan this weekend,
with an area of low pressure developing along it for the latter half
of the weekended. This frontal boundary will bring another round of
showers and periods of steadier rain to the region, along with
possible thunderstorms. There still remains some uncertainty as to
how far east the frontal boundary reaches in proximity to southeast
Michigan, which may determine the location of highest rainfall
amounts. Regardless, rainfall amounts in excess of one inch will be
possible across at least a portion of southeast Michigan this
weekend.

&&

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

$$

AVIATION.....SC
UPDATE.......SC
DISCUSSION...SF/AM
MARINE.......SF
HYDROLOGY....SF


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