Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 280725
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
325 AM EDT WED SEP 28 2016

.DISCUSSION...

Pronounced Upper Level Ridging building into Ontario today sending
the upper level low over Western Great Lakes south into the Ohio
Valley.

Detroit was able to reach 70 degrees yesterday, as the DTX sounding
indicated a 850 mb temp of 7 C. 850 MB temps will start the day
even a touch warmer, but there will be more clouds and the wind
direction will be flipped, out of the southeast. Developing
showers will also put an end to the warming, and another run at 70
degrees appears to be a long shot for Detroit Metro area, and will
follow guidance mostly in the mid 60s along/south of M-59. Areas
north of M-59 stand a better chance of reaching into the upper 60s
to near 70 degrees as showers look slower to arrive north.

Strong upper wave/shortwave tracking though northeast Illinois this
morning will be rounding through the northern Ohio Valley today, as
the parent circulation/500 MB low tracks south through Indiana.
Expecting numerous showers along with a few thunderstorms this
afternoon into this evening, as there will be large scale
ascent/pv advection, solid moisture advection (PW values
increasing to around 1 inch), along with the daytime instability
generated, as mixed layer capes reach around 500 J/kg (per 00z
nam) as surface dew pts push into the 50s. With limited
instability and 0-6 KM bulk Shear of 20-25 Knots, no severe
weather is expected. Although, 0-1 km shear ramping up late in the
day could allow for some organization, and at the very least small
hail remains possible.

With the main upper level circulation dipping south into Kentucky by
Thursday morning, moisture will only increase over southeast
Michigan, as Atlantic Moisture is tapped and pulled Westward into
the Central Great Lakes with strengthening deep layer Easterly Flow.
PW values progged to reach around 1.5 inches, with 850 mb dew pts of
10 C. Unfortunately, timing and locations of the spokes of energy
rotating on the outer fringe of circulation Thursday-Friday is
difficult, and pin pointing the exact axis of heavy rain over
southern Lower Michigan within the deep moisture plume is a
challenge, and will continue to broad brush pops with high likely
for now. Isolated thunderstorms will be possible from time to time as
showalter index hovers around zero and mid level lapse rates (700-500
mb) oscillate around 6.5 C/KM.

Still unsettled/showery for Saturday and possibly into Sunday as 500
mb low slowly tracks into Lower Michigan and then into the Eastern
Great Lakes. The 00z Euro came in slowest (amongst GFS/Canadian) with
the progression of the upper level system, drawing the
uncertainty with the second half of the weekend.

&&

.MARINE...

A large area of surface low pressure now over northeastern Wisconsin
will push southward down the long axis of Lake Michigan before
emerging over portions of the Ohio River Valley by this evening. As
a result, surface wind directions will respond by becoming easterly.
Surface winds today will remain relatively weak before the east
winds increase tonight into the 20 to 30 knot range. Small craft
advisories will be in effect beginning tonight, then persisting
through the week and possibly into the weekend. This is expected to
manifest itself with wave heights in the 5 to 7 or 6 to 8 foot
range for a long duration at the end of the week.


A steady flow of moisture around the east and northeast side of this
upper low will maintain very unsettled conditions across the central
Great Lakes with widespread shower activity and embedded thunder at
times. Waterspout chances will increase today as the chance for
convection increases. In fact, there appears to be a pretty decent
chance at a few waterspouts over parts of the area today as over
water instability becomes rather impressive. This seems most likely
over parts of Lake Erie where the coverage of showers and/or storms
will be most robust.

&&

.PREV DISCUSSION...
Issued at 1158 PM EDT Tue SEP 27 2016

AVIATION...

Showers expanding into the FNT to MBS area have been light enough
for VFR to hold and this will continue through the night before the
pattern shifts back to the west. There could be a brief occurrence
of MVFR ceiling at MBS considering recent observations from MOP but
there really should not be a window for development much more to the
east of MOP. Rain and lower clouds will then consolidate near the
south end of Lake Michigan during the morning before moving back
into SE Michigan during late morning through afternoon. This will be
due to low pressure developing over Indiana which will be reflected
by wind backing and increasing from the east over the region. The
moisture surge combined with daytime heating will make thunderstorms
possible but coverage is expected to be too low to include in the
longer time ranges of the forecast.

For DTW... VFR above 5000 ft will persist through the morning.
Showers are then expected to increase in coverage during the
afternoon which will make MVFR restriction more likely through the
day. Plan to continue holding off on mention of thunder at longer
time ranges in the forecast although isolated coverage remains
possible over D21. Light and variable wind becoming light northeast
during the morning is expected to approach 10 knots while shifting
toward E-SE as a potential negative factor for preferred SW traffic
operations.

//DTW Threshold Probabilities...

* Medium for ceiling at or below 5000 ft after 16Z.

* Low for thunderstorm potential after 19Z.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 PM this evening to midnight EDT Friday
     night FOR LHZ421-422-441>443.

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

$$

DISCUSSION...SF
MARINE.......CB
AVIATION.....BT


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at www.weather.gov/detroit.



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