Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 242257

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


The large high pressure system across the eastern Great Lakes will
maintain its influence across Se Mi tonight through Sunday evening.
Very dry air associated with this system will maintain mainly clear
skies. Its gradient will support an easterly component to the light

For DTW...During the overnight, the low level flow will turn
southeast across wrn Lake Erie. This trajectory will place metro
directly downwind of the lake influence. While the gradient may be
too strong to support fog, there is a chance that the moisture flux
off the lake will lead to some low clouds (based at or below 3k ft
given the expected inversion level). Both the RAP and HRRR are in
support of this, the timing of which being between daybreak Sun
through late morning. Still some question as to if the very dry
ambient airmass will support a solid BKN or OVC cig, so just
scattered clouds will be maintained in the TAF attm.

//DTW Threshold Probabilities...

* Low in ceilings below 5000 ft Sunday morning.


Issued at 330 PM EDT Sat SEP 24 2016


Anti-cyclonically sheared flow aloft this afternoon is supporting
weak subsidence through the troposphere. Near the surface,
east/northeast flow along the southern periphery of a surface high
over northern Ontario will continue to filter a dry/cool airmass
over Southwest Ontario into Southeast Michigan. A coincident weak
lake-effect response can be observed over southern Lake Huron and
Lake Erie. The dry nature of onboarding trajectories is limiting the
lake response to some cloud streamers. Short range guidance
soundings suggest the moist cloud depth will not be sufficient for
precipitation production within the progressively thinning cloud
field. Elsewhere, a batch of mid-cloud has completely succumb to the
deep subsidence over the region. Additional mid-cloud over northern
Lower Michigan will also cascade southeast over the area prior to
sunset while also thinning dramatically.

Skies will generally be clear tonight. The exception will be
locations near the Ohio border where lower-level moisture along the
old frontal boundary over northern Ohio and Indiana lingers
supporting a little more cloud. The ever drying surface layer in
conjunction with light winds and reasonable radiative cooling should
support a rather cool night - lows in the 40s outside the Metro
Detroit urban area.

Aggressively building ridge along the West Coast will shove the closed
low currently over the Continental Divide out onto the Northern
Plains tonight. Height falls forced by a deepening trough over
northern Alberta and Saskatchewan will coax the upper low
northeastward into southern Manitoba Sunday. The composite trough
structure will have an apparent negative tilt structure and the
associated cohesive PV anomaly will briefly lift to the northwest of
the Great Lakes region Sunday night. It will then undergo a
cycloidal redirection to the southeast early Monday, as a robust
upper-level jetlet in the main trough structure over the Canadian
Prairies surges along the resident tropopause undulation. The net
result is the main PV anomaly bulldozing east/southeast across the
Great Lakes region Monday.

During the reorientation transition, the remnant confluent PV
filament over upper Mississippi Valley will flip eastward across the
region Sunday night into early Monday - owing to wavelength
compression dynamics. This PV feature will force mass overturning
resulting in convection along the mid-level frontal corridor. While
ambient instability will be very limited precluding a free
convective release, expect the forced convection to be capable of
generating some thunder.

As the maturing rejuvenated development sequence occurs over Lake
Superior Monday afternoon, the mid/upper level jetlet will drive
significant drying at mid-levels along with appreciable isentropic
decent in the 292-298K layer. Wind speeds in excess of 40 knots
exist in this layer. Boundary layer mixing appears to reach roughly
5kft - supporting access to gust potential around 30 knots during
the afternoon hours.

The system undergoes a fairly rapid barotropic transition Monday
night, which will allow the low-level cloud field in the commahead
to centrifugally expand across Southeast Michigan after sunset.

Low pressure moving southeast across Lake Superior will bring the
continued chance for rain showers, with rumbles of thunder possible
Tuesday afternoon, as we work with weak instability. The chance for
precipitation will continue on Wednesday as the low centers over
Lake Huron. A drying trend is expected late next week as high
pressure builds back into the region. Temperatures will be on a
warming trend, peaking in the low to mid-60s early next week before
warming into the lower 70s by the week`s end.


Northeast winds of 5 to 15 knots will veer to the southeast late
tonight and then increase to 10 to 20 knots on Sunday. During the
day, the strongest winds will focus over the northern half of Lake
Huron. Winds will increase further Sunday night as the pressure
gradient strengthens in advance of an approaching cold front. Expect
wind gusts into the 25 to 30 knots range over parts of Lake Huron
with the southern expansion of 25 knot wind gusts possibly leading
to Small Craft Advisory criteria over parts of the nearshore marine

This cold front will bring showers to the area Sunday night into
Monday morning. In its wake, southwest flow will veer to the west
quickly with gusts approaching gale force over parts of the open
waters of Lake Huron, particularly during the Monday evening time


Low pressure lifting into Northwest Ontario on Sunday will swing 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 heavy
rain producing thunderstorms will be a limiting factor, thus no
flooding is expected.


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



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