Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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829
FXUS63 KDTX 270343
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1143 PM EDT SUN JUN 26 2016


.AVIATION...

VFR conditions are expected through Monday evening. Tightening
pressure gradient in advance of approaching cold front will lead to
W/WSW wind gusts to around 25 knots during best mixing on Monday.
Winds will then veer to NW with the passage of this front Monday
evening. CIGS will thicken and gradually lower in the wake of this
front, but the chance of MVFR conditions appears to hold off until
06z or beyond attm.

For DTW...W/WSW wind gusts will approach cross wind thresholds in
the 28-30 knot range Monday afternoon, but probably average closer
to 25 knots. Veering winds behind a cold front will usher in lower
CIGS, possibly MVFR, Monday night.

//DTW Threshold Probabilities...

* Medium confidence in westerly winds gusting to 25 knots or greater
  tomorrow afternoon.

&&

.PREV DISCUSSION...
Issued at 346 PM EDT Sun Jun 26 2016

DISCUSSION...

The forecast reasoning provided in the updated AFD issued at 1545
UTC remains valid. Did make an adjustment to the pop forecast based
on the latest ARW and NMM, which is chance pops north and west of a
line from Bad Axe to Chelsea. The justification for likely pops
across the south and east continues to be a convectively unstable
thermodynamic profile in the presence of a synoptic boundary. The
area still remains under a marginal designation for severe weather
in swody1, a low end designator that highlights an isolated severe
thunderstorm will be possible. See the SWOMCD. The potential for
precipitation will likely end for all areas in the cwa by 01z this
evening.

Timing of the low level dewpoint gradient or "dry line" has sped up
a good 3 hours it seems in the recent guidance. Timing of the
boundary is through Saginaw by 06z tonight and through all of
southeastern Michigan by 09Z. The change in air mass will yield
surface dewpoints of around 60 degrees at daybreak, dropping into
the middle 50s by the afternoon.  With no true cold front moving
through the area and midlevel temperatures not taking a significant
hit, the pattern will support another warm day for southeastern
Michigan. Higher mixing heights will support an overachiever day
with temperatures Monday taking yet another run at the upper 80s to
90 degrees. Breezy conditions are forecasted with west winds of 30
to 35 mph likely.

The actual cold air advection event will occur Monday night as a
secondary cold front descends southward out of Canada through the
Great Lakes.  The second nocturnal cooling cycle will also throw its
support into the ring. Based on trends did include a chance pop for
the Thumb the latter half of Monday night and for the eastern cwa
during the first part of the day Tuesday. Nothing to get excited
about, just looking at a fair setup for some shallow cold air
advection drizzle or light sprinkles. Any liquid amounts will remain
very low.

Clouds, the main midlevel trough axis, and very developed shortwave
circulations overhead will ensure a cool day on Tuesday. With
northerly onshore flow over the eastern cwa, suspect temperatures
will remain the 60s for the northwastern cwa, likely creeping
into the lower 70s for the remainder of the cwa. This is a good 6
to 10 degrees below seasonal averages, and as a matter of
perspective, nothing significant.

Medium-range deterministic models and ensembles indicate baggy upper
trough for midweek tightening up into next weekend as upper low sets
up south of James Bay. Only notable precip chance at this time
appears to be in the Thursday night/Friday timeframe as a vorticity
lobe and surface front rotate through. Initial look ahead to the 4th
of July weekend: appears largely dry with near to below-normal
temperatures under upper northwest flow and surface high pressure.

MARINE...

Still a chance of thunderstorms into early evening hours, otherwise
favorable boating conditions with light southerly winds 15 knots
or less.  Tomorrow, westerly winds will become elevated in advance
of a stronger cold front. Gusts of 20 to 25 knot are expected along
the nearshore waters, with more stable profiles supporting lesser
winds over the open waters. A small craft advisory will be issued
for Saginaw Bay, Lake Saint Clair and Michigan waters of Lake Erie.
Winds will turn sharply to the northwest as the front drops through
the Central Great Lakes late Monday and early Monday night. Gusts
over much of Lake Huron are expected to reach around 25 knots. The
intrusion of colder air and long northerly fetch over the water will
allow wave heights to potentially build in excess of 4 feet over the
southern basin of Lake Huron. Additional small craft advisories may
be required Monday night into Tuesday.

HYDROLOGY...

Scattered thunderstorms are still anticipated to develop late this
afternoon, ending during early evening hours. The strongest
thunderstorms will produce torrential rainfall, which could exceed
an inch in isolated spots, leading to minor flood concerns in urban
areas.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 11 AM to 8 PM EDT Monday FOR LHZ421-422.

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

$$

AVIATION.....DG
DISCUSSION...CB/DT
MARINE.......SF
HYDROLOGY....SF


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



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