Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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394
FXUS63 KDTX 221004
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
604 AM EDT THU SEP 22 2016

.AVIATION...

SE Michigan airspace will largely remain south and east of ongoing
convective activity focused along a frontal boundary through the
daylight period.  There remains at least a low potential for a
shower/thunderstorm to impact MBS.  Otherwise, simply a steady
stream of high cloud given our downstream potential from this
activity.  A modest southwest wind through the evening.  Frontal
boundary slides across the area tonight.  This will lead to an
expansion of low stratus as winds become northeasterly during the
early morning period. Potential exists for CIGS to fall below
1000 ft.

For DTW...Some increase in high cloud expected today, but skies will
remain clear within the lowest 5000 ft.  Any thunderstorm
development expected to remain north of the airspace through
tonight.  Frontal passage expected Friday morning, bringing an
increasing potential for some low stratus development.

//DTW Threshold Probabilities...

* Low for CIGS below 5000 ft Friday morning.

&&

.PREV DISCUSSION...
Issued at 351 AM EDT Thu SEP 22 2016

DISCUSSION...

Trend in upstream convection and cloud cover overnight has been for
a thinning of clouds (including cirrus) as they approach stable
airmass over Southeast Michigan, while convection has been mostly
dying off by the time it reaches Lake Michigan. This trend should
continue through the early morning hours, however may see a few
showers or perhaps even a thunderstorm brush the Saginaw Valley or
Thumb. Global and hi-res models then take the shortwaves generated
from the overnight convection over IA/MN/WI into central and
northern Lower Michigan by this afternoon. This will focus chances
for precipitation over the northern portion of the state, and keep
pop mention confined to areas already mentioned.

Forecast soundings for today look stable and very warm, with H850
temps in the 14-16C degree range and H925 temps in the low 20s, as
we reside on the south side of the frontal boundary stalled over
northern Michigan and Lake Huron. Big story for today will end up
being well above normal temperatures as the calender officially
turns to fall. Cirrus may limit sunshine we see today making
temperature forecast a little more complex, especially since
coverage is harder to judge based on overnight trends of erosion.
Did not go with forecast temps quite as high as MET guidance with
potential for high clouds, but forecast temps are now in the low 80s
for the Thumb and Saginaw Valley ranging to the mid/upper 80s for
the rest of the area.

GFS/Euro still in line with a strong shortwave trough dropping
through Ontario late today and tonight as it pivots around the upper
low over Hudson Bay. This will push the front southward into Central
Lower Michigan tonight and southern Lower Michigan Friday. Coverage
of precipitation along the front will decrease as it drops into
Southeast Michigan as the boundary loses support from right entrance
region forcing and low-level jet, and surface trough ahead of the
upper wave slides east along the front late today and exits
overnight. Strong Canadian high pressure will become centered over
Ontario Friday and expand into the Central Great Lakes Friday
through Saturday, exerting a stabilizing influence which will only
help to decrease precipitation chances. Chances for thunderstorms
looks to end Friday evening. Cannot rule out a shower Friday night
and Saturday as 925mb front remains over Southeast Michigan, but
most of the weekend looks dry. Much cooler temperatures are expected
after today however, with max temps falling back into the upper 60s
and 70s Friday through Sunday.

Last few rounds of medium-range models (GEM/GFS/Euro) have shown
wide variations with how they handle the upper low dropping down the
west coast, and whether or not it becomes and then stays phased with
upper energy pushing through the Gulf of Alaska. This leads to
significant timing differences, both model to model and run to run,
with the timing of the next cold front and precipitation chances
over Southeast Michigan. Little change was therefore made to Monday
through Wednesday forecast.

MARINE...

Frontal boundary draped across northern Lake Huron today will sag
southward through early Friday.  This frontal passage will bring a
transition to moderate northeast flow. The long fetch of onshore,
unstable flow over southern Lake Huron and into Saginaw Bay will
result in increasing wave heights.  This will likely reach small
craft conditions across portions of the nearshore waters and Saginaw
Bay Friday and Friday night.  High pressure building into the region
will lead to diminishing wind speeds and a corresponding reductin in
wave heights by Saturday.

&&

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

$$

AVIATION.....MR
DISCUSSION...HLO
MARINE.......MR


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