Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201938

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
338 PM EDT Sun Aug 20 2017


Rather typical late summer conditions ongoing across Southeast
Michigan, as the area remains under the influence of weak but deep
anti-cyclonic flow. To the west, convective debris clouds from last
night`s action is beginning of overspread the region, while
thinning. Additional high clouds are expected to saunter overhead
through the evening hours.

The flow regime over the northern CONUS will undergo a modest
transition Monday and Tuesday as a strong cyclonic wave carves
southeast across central Canada into the upper Great Lakes region.
Along the periphery of the height falls, additional convectively
induced waves will influence the specifics across the western Great
Lakes region.

One such wave, a leftover MCV over eastern Iowa is evident in the
latest GOES imagery sequence. This dynamic feature will likely be
the focus for additional convective development along it`s
trajectory this evening into the overnight hours as it intercepts
richer near surface moisture. The increased moisture will advance in
an elevated fashion across Lower Michigan overnight as southwesterly
flow increases in advance of the MCV. As this moisture advection
process unfolds, elevated convection may continue to bubble eastward
across far southern Lower Michigan after midnight. Moreover, the
reservoir of moisture aloft will emerge at the surface through
diurnal mixing processes Monday and dewpoints will jump quickly.

Farther upstream over the central Plains, convection continue along
the edge of the mid-level cap. The NWP suite is challenged by this
ongoing activity. The best depiction thus far is by a few members of
the 20.00z NCAR Ensemble. Given the persistence of redevelopment,
expect new widespread coverage to develop near the current activity
near Omaha. This offers greater separation between the convective
waves and opens a window for continued advection of unstable air
into southern Lower Michigan early Monday. The additional
instability could facilitate new diurnal convective development
during the late afternoon hours. Regardless, a fair amount of cloud
cover is anticipated through the course of the day.

As the larger scale wave approaches Monday night, additional
widespread convection is expected upstream across the Mid and Upper
Mississippi Valley. The advancing cold front will collect the
activity and advance east across Michigan. The trend in the guidance
suite is to be quicker with the system, with the best chances for
showers and storms being overnight Monday night and during the first
half of Tuesday. The timing will likely limit severe weather

A closed upper low over eastern Canada midweek will keep northwest
flow in place over the region as an upper level trough slowly
translates eastward across the Eastern US through the end of the
week. Surface high pressure will slowly build into the Great Lakes
region midweek and remain in place through the end of the week.
These features will lead to a prolonged period of dry, cooler
conditions across Southeast Michigan through the end of the week.
Temperatures will fall slightly below average Wednesday through
Friday with highs in the upper 60s to mid 70s and lows in the upper
40s to mid 50s. Ridging will then build into the region next weekend
keeping dry conditions in place and bringing a slight warming trend
with highs approaching 80 by Saturday.



Light southwest flow to continue over the marine areas through
Tomorrow, with winds increasing on Tuesday ahead of a strong cold
front. This front coupled with increasing moisture will bring a
chance for showers and thunderstorms, with showers and thunderstorms
likely by Tuesday morning. Northwest winds behind the front will be
strong Tuesday evening, topping out around 30 knots over the open
waters Lake Huron before slowing decreasing on Wednesday.



A strong cold front moving through on Tuesday will likely triggers
showers and thunderstorms Monday night into Tuesday. Basin Averages
look to reside in the quarter inch to three quarter inch range, with
locally higher amounts possible in stronger thunderstorm activity.
At this time, no flooding is expected.


Issued at 112 PM EDT Sun Aug 20 2017


Dry airmass in place over southeast Michigan this afternoon with
high cirrus spilling over. Some moisture will attempt to work in
tonight, but likely struggle to saturate in the low to mid levels.
There looks to be another fog potential tonight with winds going
calm, but some uncertainty with opaqueness of high clouds around,
and will continue to highlight just 4-6 SM visibility reduction
around sunrise. Southwest winds 5-10 knots developing during Monday.
Additional moisture transport, but probably only enough to support
mid clouds, with a very low chance of showers/thunderstorms.

For DTW...There looks to be fog potential overnight with help from a
moisture push off Lake Erie, but high clouds around are expected to
help mitigate the fog somewhat.

There is a very low chance of a shower or vicinity thunderstorm
overnight through tomorrow as moisture comes up from the south. Best
chance looks to be late tomorrow afternoon, but even then, did not
feel it was worthy of prob30 at this time.


* None.


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



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