Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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076
FXUS63 KDTX 171901
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 141 PM EDT Sun Sep 17 2017

AVIATION...

Main focus for this TAF period will be the chance for showers and
thunderstorms this afternoon and evening, increasing cloud cover,
and post frontal winds shifting to the north overnight into tomorrow
morning. Best chance for thunderstorms ahead of the initial front
look to be at MBS, FNT, and PTK. The front looks to weaken as it
moves through southeast Michigan and the loss of daytime heating
will also help scatter out the rain and thunderstorms moving through.
Will leave out a tempo -TSRA group at the remaining TAF sites at
this time. Winds will begin to veer from to the west later tonight
and then to the north by tomorrow morning. MVFR CIGS will begin to
pass over by the morning as well.

For DTW...Do not anticipate the line of showers and thunderstorms
reaching DTW at this time, so will keep them out of the TAFs for
now. Increasing clouds associated with a low pressure system and
associated front will bring a low stratus deck overnight to at or
below 5000ft. Post frontal winds will bring northerly winds by
morning around 15/16Z.

//DTW THRESHOLD PROBABILITIES...

* Medium for ceiling 5000 ft or less Sunday evening and overnight.

* Low for showers and thunderstorms this evening.


&&

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

$$

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


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