Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210736
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
336 AM EDT Mon Aug 21 2017

.DISCUSSION...

Main bulk of unsettled weather will take place in the first portion
of the forecast before things dry out.  An upper level low,
currently situated over the Hudson Bay, will rotate down across
Ontario through the beginning of the week.  A large trough
associated with this low will come across the Great Lakes region as
an associated surface low forms out over the northern plains and
travels east towards the area.  This system will bring in increasing
chances for rain and storms to Southeast Michigan beginning late
this afternoon through Tuesday.  As the surface low begins to form
out to the west today, southerly winds over the area will start to
bring in more moisture resulting in another warm and more humid day.
This humid airmass will be brief as the cold front brings in cooler
and drier air by Wednesday.

Some patchy areas of fog are expected to develop as more moisture
rich air filters in, before fig dissipates shortly after sunrise.
Earlier this morning, there was some thunderstorm activity that
fired over eastern Illinois and has been slowly moving
east/southeast. This will bring in some cloud debris to portions of
the CWA through the morning. This afternoon there will be a slight
chance for rain and a few isolated storms as surface based activity
may develop as a result of diurnal heating and increasing moisture
advection into the area. Better chances look to be over northern
portions of the CWA before chances increases over the entire CWA
coming into Tuesday. However, this does not bode too well for people
wanting to enjoy the partial solar eclipse over Southeast Michigan
as there looks to be clouds hanging around, although there is
potential for a few breaks in those clouds.

Chances increase overnight and into Tuesday as a cold front
approaches the area. This front will be in place to the north of the
area today before sagging across the CWA tomorrow. There is also a
thunderstorm complex, currently situated over western Iowa, which
will move eastward during the early morning hours. Lots of
uncertainly with this complex and how it holds together. This may
also help in developing some activity over the area later today.

Cold front looks to be pushing eastward across the area starting
early Tuesday morning before quickly moving through by Tuesday
evening.  This will provide the focus for rain and storms during the
day. Severe weather looks to stay minimal as instability stays lower
due to cloud cover and early timing.  Cooler and drier air then
filters in behind the departing cold front Tuesday night. Quiet
weather then comes back into the picture for the remainder of the
week as high pressure moves in over the area from the northwest.
Temperatures cool off slightly back into the 70s for the second half
of the week before warming slightly back to near 80 this weekend.

&&

.MARINE...

A weak front will stall over northern to central Lake Huron while
producing light and variable wind today before moving back northward
tonight ahead of the next low pressure system. Light southerly wind
will continue over the remainder of marine areas until increasing
from the southwest tonight as low pressure deepens while moving into
the Straits region. Wind and waves will remain below SCA thresholds
leaving widespread showers and thunderstorms along and ahead of the
front as the primary marine weather impact before the frontal
passage. Strong northwest wind behind the front will have gusts
reaching 30 knots over the open waters of Lake Huron Tuesday night
as colder air spills into the region. As it stands now, the wind
pattern will be from the northwest direction enough to keep the
highest waves offshore of the southern Lake Huron nearshore zones
before veering toward the north and weakening during Wednesday. The
incoming air mass will be cold enough to produce enough instability
over the water for marginal waterspout potential Wednesday into
Thursday.

&&

.HYDROLOGY...

A low pressure system developing over the Plains states today will
reach the Straits region by Tuesday morning and pull a strong cold
front through Lower Michigan. Moisture/humidity will increase
considerably ahead of the front and provide fuel for numerous
showers and thunderstorms late tonight through Tuesday. Basin
average 24 hour rainfall totals are expected to be in the 0.25 to
0.50 inch range with locally higher amounts near 1 inch possible
where multiple thunderstorms occur. The potential for flooding is
expected to be limited by the fast movement of the associated cold
front which is projected to exit eastward by Tuesday evening.

&&

.PREV DISCUSSION...
Issued at 1151 PM EDT Sun Aug 20 2017

AVIATION...

Increasing low level moisture, aided initially by southeast flow
from western Lake Erie, will bring some potential of MVFR fog late
tonight. Otherwise, expect scattered to broken middle level clouds
between 10-15kft with perhaps scattered diurnal cumulus on Monday
close to 5-6kft. The increasing moisture (and instability) will
bring some potential of widely scattered convection late Monday.

For DTW...Other than patchy shallow MVFR fog late tonight, expect
generally VFR conditions. The one caveat will be a small potential
of a shower or thunderstorm in the vicinity after 20z-21z Monday
afternoon/evening. Confidence remains too low to include in forecast
attm.

//DTW THRESHOLD PROBABILITIES...

* Very low for a thunderstorm impacting terminal 20z-00z Monday.


&&

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

$$

DISCUSSION...SP
MARINE.......BT
HYDROLOGY....BT
AVIATION.....DG


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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