Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 241654
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1254 PM EDT SAT SEP 24 2016


.AVIATION...

Now that left over low level moisture has mixed into scattered
cumulus deck, expect dry northeast flow from high pressure to the
north/northeast to maintain VFR conditions from this afternoon on
into Sunday. This northeast flow, generally 10 knots or less, will
weaken tonight and veer to the east and southeast on Sunday as the
high shifts gradually eastward across southeast Canada.

//DTW Threshold Probabilities...

* None.

&&

.PREV DISCUSSION...
Issued at 402 AM EDT Sat SEP 24 2016

DISCUSSION...

The narrative for the entire weekend is a dry one complete with
idyllic early autumn weather that will be spot on to seasonal
averages.

The center of dominant surface high pressure will slide slowly
southeastward today across portions of Ontario south of James Bay. A
solid surface ridge axis will exist along the southern periphery of
this anticyclone and will only slowly retreat out of the central
Great Lakes by Sunday afternoon. A highly amplified mid to upper
level ridge axis will then become the dominant from Sunday
afternoon through Sunday evening. This trailing upper level
feature will block any precipitation from making it into the area
prior to late Sunday night.

The question for today is on clouds. Would rather not get into some
long winded diatribe, but the consensus of the data supports holding
onto a persistence of clouds today. The two main reasons are: 1.
evolving low level southeasterly flow trajectories will support
little to no dry air advection especially with a Lake Erie
influence. 2. Even if clouds were able to break will need to contend
with upper level stretching deformation high cloud that will be
streaming down from the northwest. Did remove the pops for this
afternoon over Monroe County with slower than previously expected
due easterly flow. Rather, did introduce a chance for a shower
back across Monroe County the latter half of tonight as some lake
effect activity may push onshore. Highs today are expected to
range from the middle 60s in the Thumb to the low 70s in
southwestern Lenawee County.

An ideal radiative cooling environment is expected to develop
tonight with clear skies and the influence of the surface ridge
axis. Favored the cooler MAV guidance which suggests 50s in the
urban core areas and 40s in many of the rural, outlying locations.

Off of a cool start Sunday morning, temperatures are expected to
rebound into the lower 70s across all of southeastern Michigan. It
really will be an ideal day with high cloud beginning to spread
across the region during the afternoon hours.

Sunday night and Monday System. Details continue to sort themselves
out, particularly with the timing of individual potential vorticity
maxima and complex mergers. Ultimately though, the wavelength of
the governing features are great enough and at such a high
amplitude the difference and the uncertainty doesnt have that much
of an effect on the sensible weather forecast. The latest thinking
is that the system will have a significant negative tilt as the
closed upper level low digs into the Great Lakes. This degree of
tilt will shunt the best warm advection support and height falls
well to the north and east of southeastern Michigan. This will
lead to what should be a small time window for precipitation as
the cold or occluded frontal forcing flashes across the area. The
organization of the frontal forcing is very good per cross section
analysis with a brief period of deep upright ascent. The
potential exists for some sharp cyclonic vorticity advection
across southeastern Michigan Monday afternoon. That will need to
be watched for some possible thunderstorm potential. Right now,
timing appears too early and cloud cover too opaque to be in phase
with any instability. Timing most of the precipitation across
southeastern Michigan between 12-18Z Monday.

One last item that will be monitored is what the magnitude of
west winds will be Monday afternoon in the wake of the cold
front. Mixing depths are going to matter and would like more
timing details to sort it out. Ballparking west winds at this
time to be 20 to 25 knots.

MARINE...

Northeast winds in the 5 to 15 knot range today will veer around
to the southeast Tonight. Wind speeds will then increase into the 10
to 20 knot range tomorrow, with the highest winds across the northern
third of Lake Huron. Winds gusts look to top out around 25 knots
Sunday evening, with showers likely late Sunday night into Monday
morning as a cold front moves into the Central Great Lakes, clearing
the area Monday afternoon. Winds shifting to the west behind the
front, generally holding in the 15 to 25 knot range into Monday
night.

HYDROLOGY...

Low pressure lifting into Northwest Ontario on Sunday will track a
cold front through lower Michigan Monday morning. Showers are likely
late Sunday night into Monday, with rainfall totals of a quarter to
half an inch. The progressive nature of the front and lack of
instability/thunderstorms will be limiting factor, and thus no
flooding is expected.

&&

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

$$

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


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at www.weather.gov/detroit.



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