Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 180138
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
938 PM EDT Sun Sep 17 2017

.UPDATE...

Clusters of showers and thunderstorms lingering along the primary
cold front are holding on near reservoirs of weak surface based
instability near Saginaw Bay and south of the Indiana border. Expect
the weakening trend to continue through midnight while the next upper
wave approaches. The wave can be seen in satellite imagery moving in
from northern Illinois at press time and which is expected to
produce a surface reflection along the cold front during the night.
Backing mid level flow and a slight uptick in low level jet forcing
will combine with some lift due to frontogenesis and DCVA to produce
another round of showers and isolated thunderstorms toward sunrise.
The latest model guidance supports scattered coverage - chance POPs
generally along and east of a line from Port Austin to Howell through
about mid Monday morning. Without the boost from daytime heating,
any new thunderstorms will be on the ordinary side of the spectrum
which will limit hazards to a brief heavy downpour.

&&

.PREV DISCUSSION...
Issued at 713 PM EDT Sun Sep 17 2017

AVIATION...

The initial cold front associated with low pressure moving through
the central Great Lakes is supporting bands of thunderstorms moving
into SE Michigan. There will be some weakening with the loss of
daytime heating and coverage will remain on the scattered side while
affecting the area mainly north of PTK. The primary cold front is
then expected to move down from northern Lower Michigan and reach
MBS shortly after midnight. This boundary will bring the best chance
of MVFR stratus as it moves southward across the region along with a
wind shift from westerly to northerly. There will also be some
potential for another round of showers and isolated thunderstorms
toward sunrise. A clearing trend will then develop during late
morning through Monday afternoon as high pressure builds into the
northern Great Lakes.

For DTW... Evening showers and storms are expected to dissipate or
weaken considerably before reaching DTW and will monitor trends
before adding them to the forecast, and the same for another round
of activity that is possible overnight toward sunrise. VFR will hold
until borderline VFR/MVFR develops Monday morning with the primary
cold front and associated northerly wind shift.

//DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms late evening and overnight.

* Medium for ceiling 5000 ft or less Monday.

PREV DISCUSSION...
Issued at 301 PM EDT Sun Sep 17 2017

DISCUSSION...

Warm mid September day across southeast Michigan, as temperatures
have pushed into the mid 80s. The 12z DTX sounding showed a
significant warm layer around 650 MB, which may be too much to
overcome to generate much in the way of showers and thunderstorms
this evening, especially with surface dew pts mostly in the lower
60s.  18Z SPC analysis does show SBCAPES of 1000-1500 J/KG over
western Lower Michigan, but quickly tapering off as one heads east.
The front is attempting to generate activity at the present time,
but mainly over northern Lower Michigan, closer to upper level
support, and approaching northern Indiana where better instability
resides. Planning on continuing with scattered/chance pops. On the
flip side, there does look to be an upper level PV filament
streaking out of northern Missouri, which tracks through the State
tonight, which could be enough to support an uptick in activity
despite the loss of surface/daytime heating, as a repositioning/
modest increase in the low level jet occurs overhead. 17z HRRR also
suggesting an increase in activity late tonight. Regardless, main
moisture axis exiting southeast Michigan around 12z, leading to a dry
day on Monday as 850-700 mb Theta-E min/surface ridging become
established, with PW values dropping under 1 inch.

Another surge of moisture to arrive late Monday night/Tuesday
Morning, as upper level energy comes out of the Four Corners region
this afternoon, and an upper wave/trough seen tracking along or
close to the southern Michigan border on Tuesday, per 12z
Canadian/NAM. Still, looks to be getting just marginally unstable
north of the Michigan border, with surface ridging holding on,
suggesting just low chance pops warranted at the moment. A good deal
of clouds and light early flow in low levels expected to hold maxes
in the 70s both Monday and Tuesday.

Main story in the extended timeframe is the expansive ridging over
the eastern CONUS bringing a continuation to the above normal
temperatures into next weekend.  A large trough will be situated
over western portions of the CONUS where it will stay through the
forecast period.  As ridging and surface high pressure remain over
the Great Lakes region, southerly winds will bring temperatures into
the 80s for all of this week.

MARINE...

A series of fronts are forecast to cross through the Great Lakes
region this evening and through the overnight period. The first
front will be the focus for some scattered showers and thunderstorms
during the afternoon and evening time frame for the open waters of
Lake Huron.  Post frontal winds will be shifting to a more westerly
direction around 5-15 kts. The secondary front will come during the
overnight hours in a more northerly direction and remain around 15
kts. The long fetch of northerly winds overnight could lead to some
higher waves along the shoreline of the Thumb on Monday morning. At
this moment conditions should remain under criteria for a small
craft advisory.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

UPDATE.......BT
AVIATION.....BT
DISCUSSION...SF/SP
MARINE.......AA


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