Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 161749
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
149 PM EDT Sat Sep 16 2017


.AVIATION...

Diurnally driven scattered clouds have started to develop this
afternoon across southeast Michigan. Thinking CIGS will settle in at
VFR for all TAF sites and will remain scattered throughout the
afternoon before clearing out after 0Z. Winds will remain light and
out of the south. Fog will most likely develop again overnight. Some
uncertainty remains around how thick the fog may get again with
incoming clouds ahead of a cold front Sunday night, but it looks
like clouds could mitigate fog from the extent we have seen the last
couple of days. Expect fog to break rather quickly after 12/13Z
tomorrow.

For DTW...Looks like scattered clouds will develop and be at or
below 5000ft and begin to clear out around sunset. Fog again could
redevelop overnight and bring with it some MVFR visibility with
potential to be slightly lower, but will again burn off rather
quickly around 12/13Z

//DTW THRESHOLD PROBABILITIES...

* Medium for ceiling 5000 ft or less during afternoon.

&&

.PREV DISCUSSION...
Issued at 314 AM EDT Sat Sep 16 2017

DISCUSSION...

Mid level anticylonic flow associated with an upper ridge over the
eastern Great Lakes will influence Se Mi into Sunday. This will
allow sfc high pressure to remain anchored over the ern Great Lakes.
Model soundings suggest moisture quality will be a little more
shallow today in comparison to yesterday. This should support less
of a diurnal cu field. With a similar airmass in place today and the
expectation for full sun, afternoon high temps into the low 80s are
expected. Light southeast winds off the lakes late in the day will
boost boundary layer moisture, possibly leading to some fog late
tonight (especially downwind of Lake Erie). The strength of the
gradient flow atop the shallow nocturnal stable layer will be the
main limiting factor for more widespread fog potential tonight.

A mid level trough axis forecast to lift from the northern plains
into northern Ontario on Sunday will drive a sfc cold front into wrn
Lower Mi. Diurnal heating will support modest daytime
destabilization, while convergence along the front will likely be
enhanced in the lee of Lake Mi. Se Mi will remain under a little
more influence from the mid level ridge over the ern Great Lakes.
Thus, dry weather will prevail through the daylight hours over most
if not all of the forecast area. Slight low level warming under
southerly flow ahead of the front will support Sun highs into the
80s despite some increasing cloud coverage during the afternoon.

The front will slowly push into Se Mi Sun night. With the upper wave
driving this front lifting well north of the state and persistent
mid level ridging across the ern Great Lakes, this front will weaken
as it slowly works its way east into Se Mi. This and the loss of
diurnal instability supports mainly low chance-type pops with this
front Sun night. Weak sfc high pressure will expand across the nrn
Great Lakes on Monday, dragging the remnants of the sfc front south
of Detroit during the day. Daytime temps will be a little cooler in
the post frontal airmass on Monday (especially if low clouds persist
well into the afternoon).

A highly amplified pattern across North America is forecast during
the course of next week, featuring long wave trough amplification
across the wrn US with downstream ridging across the east. There are
some indications in the model solutions that some short wave
impulses will lift into Lower Mi on Tuesday within a broad region of
warm air advection. The approach of Jose on the east coast will
likely cause mid level ridging to persist across the eastern Great
Lakes, thereby reducing the chances for convection across Se Mi on
Tues. The forecast for the remainder of the work weak will feature a
dry forecast with high temps likely well above mid-late September
averages in light of strength of the upper ridge forecast over the
ern US.

MARINE...

High pressure remains over the Great Lakes for the bulk of the
weekend resulting in favorable boating conditions. Winds will be out
of the south at or below 15 knots which will keep waves heights in
check. A low pressure system lifting north of the lakes today will
push a weak cold front through the Central Great Lakes Sunday
evening and night. Scattered showers and thunderstorms will be
possible with this frontal passage. Winds will flip to northerly
behind the front by Monday morning, but still remaining at or below
15 knots.

PREV DISCUSSION...
Issued at 322 PM EDT Fri Sep 15 2017

Discussion...

With very little change in the overall airmass across the region,
this afternoon`s conditions will basically be repeated on Saturday.
There will be a little less residual low level moisture around, so
shallow fog during the early morning hours will be more limited in
most locations. Once that burns off, mostly sunny skies and south
winds 5 to 10 mph will bring temperatures into the lower 80s across
most of the region by afternoon.

The high pressure ridge will shift slightly east late Saturday into
Sunday as a weak cold front approaches from the west. This will lead
to additional warm air advection as south-southwest flow increases
somewhat. So, even with an increase in upper level cloud cover by
late in the day, expect temperatures to climb into the lower 70s
once again with some locations most likely reaching 85 degrees for
high temperatures.

The cold front then works into Southwest Lower Michigan from Sunday
evening into the overnight, bringing a chance of showers or isolated
thunderstorms to the area. Lack of quality moisture across the area
should limit coverage substantially and have no plans of increasing
precipitation chances above the going 20-30 percent in any notable
way.

After the front passes through in the morning, Monday`s high
temperatures will moderate slightly lower, particularly for areas
north of the I-69 corridor where highs will be in the lower 70s. For
the southern counties, upper 70s are expected Monday. Slight chance
for a round of showers on Tuesday as a weak mid-level disturbance
moves over the southern Great Lakes. Following this, an upper ridge
will build into the region Wednesday and into the weekend. With this
setup, SE Michigan can expect a mainly dry period with daily high
temperatures in the upper 70s. Overnight lows will fall into the
upper 50s to lower 60s.

MARINE...

High pressure remains over the region heading into the weekend
resulting in favorable boating conditions. Winds will be out of the
south through the weekend, mainly at or below 15 knots which will
keep waves heights in check. A weak cold front will swing through
the Central Great Lakes Sunday evening and night, triggering
scattered showers and possibly a thunderstorm. Winds will shift
northerly behind the front early next week, but still at or below 15
knots.

&&

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

$$

AVIATION.....AA
DISCUSSION...SC
MARINE.......DRK


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