Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 110751
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
351 AM EDT Wed Oct 11 2017

.DISCUSSION...

The broad swath of showers is making its way through the state early
this morning with the upper wave now crossing over Lake Michigan.
Good isentropic lift will help maintain these showers through early
this morning as the wave lifts closer to Michigan. PW value on the
00Z sounding last night was 1.05 inches with the expectation for
that number to increase through the early morning hours as the mid
level flow around this low pressure draws additional moisture into
lower Michigan. Moisture which will wrap around the north side of
this low pressure system shown in the the 850-700 theta-e axis
remaining over Michigan. The trailing deformation will keep showers
in the forecast through this afternoon as the center of the surface
low pressure drifts eastward across IN/OH. Positioning of the
surface low and tightening pressure gradient will bring some gusty
east/northeast winds throughout today as well. Bulk of the rain
should move off with the wave by this evening with the exception of
some light rain showers or drizzle forming off the lakes given the E-
NE winds.

Ridge axis will drift over the Great Lakes on Thursday keeping some
lower level moisture trapped and lead to mostly cloudy conditions.
Flow returns out of the south along a boundary lifting north. Do not
expect much in the way of rainfall from this, but a few scattered
showers could develop late Thursday afternoon and evening given the
amount of low level moisture present.

An upper trough begins to dig across the Intermountain West by the
end of the week as warm air advection streams into the area under
mid to upper level southwest flow. Temperatures will warm up
slightly into the upper 60s and 70s for Friday. The next round of
likely rain chances enter the forecast late Friday night across
Central Michigan along an elongated frontal boundary pushing south
across the state under a 150 kt jet passing through western Great
Lakes and southern Ontario. Prefrontal showers will bring increased
rain chances across the Thumb and Tri-Cities through early Saturday
morning and then further south throughout the day.

The boundary stalls out in lower Michigan on Saturday as the upper
trough digs across the Intermountain West and ejects out into the
Plains. Uncertainty still remains with this system, but it is
looking like the aforementioned trough will eject out of the plains
with associated surface low deepening as it crosses the mid
Mississippi Valley and into the Great lakes late Saturday night.
That stalled boundary will lift northward as a warm front putting
the forecast area in the warm sector as a cold front pushes east
across Michigan Sunday afternoon bringing more showers,
thunderstorms, and gusty winds through Sunday evening. Cooler start
to the beginning of next week as colder air enters behind the front
arrives with high temperatures in the upper 50s and lower 60s.

&&

.MARINE...

Brisk to moderate northeast winds will continue across all marine
areas today north of low pressure tracking into the Ohio valley.
Gusts to 25 knots will be common at times.  Localized higher gusts
to 30 knots likely across Saginaw Bay given some degree of
channeling within this favorable trajectory.  The onshore flow will
contribute to wave heights reaching 5 to 8 feet across western
portions of lake Huron, while waves build to 3 to 5 feet over the
western lake Erie basin.  Small craft advisories will remain in
place through the duration of the daylight period.  Winds shift to
easterly tonight and remain brisk. The gust potential will ease, but
wave heights remain elevated through this period.  Therefore, small
craft advisory conditions will now extend into early Thursday for
the nearshore waters and outer Saginaw Bay.

Prevailing east to southeast winds Thursday and Thursday night will
maintain moderate wave action, particularly across the northern half
of lake Huron.  Waves generally at 4 to 7 feet over that corridor.
Developing southerly winds become more modest by Friday, downstream
of an advancing frontal boundary.  This boundary will bring
potentially more unsettled conditions heading into the weekend.
Periodic rounds of showers, with isolated thunderstorm potential
during this time.

&&

.HYDROLOGY...

A widespread area of light to intermittently moderate rainfall will
continue across the region throughout the daylight period.  Rainfall
will taper off in both intensity and coverage during the late
afternoon and early evening period.  Rainfall totals between three
quarters of an inch and one inch are expected, with the potential
for localized higher amounts.  This amount of rainfall occurring
over more than a 6 hour period will mitigate greater flooding
concerns.  Some ponding of water on roadways and poor drainage
flooding of low lying areas will be possible through the latter half
of the day.

There will be a low chance of rain Thursday, but of little
consequence.  Brief period of dry conditions into Friday, before
conditions turn more unsettled again for the weekend period.  There
is the potential for multiple rounds of showers, with possible
thunderstorms as a frontal boundary stalls near the region.  Some
uncertainty yet in the positioning of this front, which will dictate
placement of the higher rainfall potential.  Rainfall amounts in
excess of an inch will be possible across portions of southeast
Michigan this weekend.

&&

.PREV DISCUSSION...
Issued at 1144 PM EDT Tue Oct 10 2017

AVIATION...

Recent radar trends suggest rain will be moving into the terminals
around the start of the TAF period (06Z), the result of low level
moisture transport preceding and upper level trough.  Residual low
level dry air will allow ceilings to initially be VFR at the onset
of rainfall. Model soundings suggest that increasing low level
moistening through both advective processes and increasing rainfall
intensity will lead to a rapid drop in ceilings into the IFR and/or
low end MVFR range by 10Z. Low clouds amidst persistent rain and/or
drizzle will then persist through much of the day Wednesday. In
addition, northeast winds will increase through the morning as the
sfc low lifts into the nrn Ohio Valley. Boundary layer cooling from
the rain will suppress the gustiness of the winds to some degree.
The tightening gradient over srn Mi late tonight into Wed morning
does however suggest some gusts over 20 knots are possible. The
strongest winds will likely be at MBS as the northeast winds funnel
down Saginaw Bay.

For DTW...There have been some embedded thunderstorms this evening
across northern Illinois. The better mid level instability is still
expected to slide south of metro Wednesday morning suggesting the
chances for thunderstorms will be quite low. Northeast winds will
persist through the TAF period with the track of the sfc low passing
south of the state.

//DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 ft after 10Z.

* Low for thunderstorms Wednesday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 4 PM EDT Thursday for LHZ421-441>443.

     Small Craft Advisory until 8 PM EDT this evening for LHZ422.

Lake St Clair...Small Craft Advisory until midnight EDT tonight for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until midnight EDT tonight for LEZ444.

&&

$$

DISCUSSION...AA
MARINE.......MR
HYDROLOGY....MR
AVIATION.....SC


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