Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201123
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
723 AM EDT Sun Aug 20 2017

.AVIATION...

High pressure will bring VFR conditions throughout the forecast
period.  Light winds and good radiational cooling is generating
areas of shallow fog which will quickly dissipate after sunrise.
Light/variable winds will become southwest under 10 knots on the
backside of this high by mid/late morning with just a few diurnal
cumulus possible within a rather dry airmass. Weak surface flow and
daytime heating could bring a lake breeze up to or through DTW late
afternoon/evening backing winds more south southeast but would remain
under 10 knots. Light southwest flow tonight will bring increasing
dewpoints. Patches of high clouds from convection in the midwest may
make it over the taf sites, however, there should still be enough
radiational cooling to produce a bit more widespread fog in the 4-6
mile range towards sunrise Monday.

//DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 400 AM EDT Sun Aug 20 2017

DISCUSSION...

High pressure covering much of the country east of the Mississippi
during the morning will become centered more along the Atlantic
coast during the afternoon. This will ensure a sunny start to the
day across SE Michigan after some patchy and shallow fog around
sunrise. Light and variable wind will then take on a more southerly
component and help boost temperatures into the mid 80s most
locations. Model soundings indicate the boundary layer will be too
dry for anything more than a few cumulus but thickening cirrus is
expected late in the day as MCS debris drifts eastward from the
Plains. These clouds are timed too late to have an impact on
afternoon temperatures and then will thin during the evening and
allow some radiational cooling tonight. Guidance lows in the lower
to mid 60s look good.

Larger scale weather features in the Plains today will have an
increasing influence on Great Lakes conditions Monday and especially
by Tuesday. Mostly zonal flow aloft through the northern tier of
states is producing a classic lee side surface trough while the
upper level wave over central Canada is supporting a cold front as
far south as the Dakotas. These features intersect a warm front over
the Missouri valley that is the focus for low level jet forced MCS
activity. Ongoing nocturnal convection during the early morning is
expected to follow a standard daytime weakening trend while zonal
flow guides cloud remnants and any residual MCV into the southern
Great Lakes. The latest model solutions then look reasonable with
the slow eastward migration of the surface features into the Midwest
tonight. Some surface based convection in shown over the northern
Great Lakes this afternoon and evening while remaining capped
farther south toward Iowa and Illinois. This will set up the genesis
region for round 2 of low level jet forced MCS activity on the edge
of the 850-700 mb cap centered on Iowa, much farther east than
activity occurring early this morning. The strongest convection
should dive southeast along the instability gradient from there
while substantial cloud debris and even some MCV supported showers
could make it into Lower Michigan by late Monday morning into
afternoon.

A new round of short wave induced height falls is also projected to
develop over central Canada Monday into Monday night which will lead
to a pause in the eastward progress of the cold front. The Canadian
short wave will produce a surface wave along the front about at the
same time mid level monsoonal moisture is drawn into the westerlies
from the southwest states. A new round of deep warm/moist advection
will produce additional MCS development over the Plains and Midwest
as the low pressure system matures. The deepening upper wave will
provide strong forcing and a strong wind profile while the
instability axis/theta-e ridge spreads northward over the Great
Lakes ahead of the front. These large scale features will sustain
organized convection through Lower Michigan late Monday night
through Tuesday before the front exits eastward by Tuesday evening.

After the Tuesday frontal passage, global model solutions maintain a
sharper upper level trough, and even some signs of a closed low,
over eastern Canada by Wednesday. This will open the door for
stronger high pressure to develop over central Canada and spread
colder air into the Great Lakes Wednesday into Thursday. The latest
round of guidance temperatures now offer highs in the upper 60s in
the Thumb region by Thursday which match up better with 850 mb
temperatures in the 5-10C range. Modifying high pressure then holds
during the second half of the week and into next weekend.

MARINE...
High pressure centered over Michigan will gradually slide to the
east today maintaining a light mainly southwesterly flow through
Monday. Increasing moisture and a slowly advancing cold front will
bring showers and thunderstorms late tonight across northern Lake
Huron. This chance will spread south during the day Monday and
continue until the strong cold front sweeps through Tuesday
afternoon. Winds will then become strong from the northwest and
continue through the end of the week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....DRC
DISCUSSION...BT
MARINE.......DRC


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at www.weather.gov/detroit.



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