Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181553

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1153 AM EDT Sun Mar 18 2018


SKC with wind gradually backing from WSW to WNW during the afternoon
and turning NE overnight as high pressure transits Ontario. There
may be just enough moisture in NE flow to support SCT low VFR, but
meaningful CIG not anticipated attm.

For DTW...Noise abatement issues with marginal NE flow will become
increasingly likely after about 23z and will continue through Monday.


* None.


Issued at 350 AM EDT Sun Mar 18 2018


Weak high pressure will move from the Plains into the Ohio valley
today while low pressure ripples along a polar front stalled over
the northern Great Lakes. These features will combine to produce
light westerly gradient flow which will guide mild air into the
region. Low level temperature fields in the models indicate the flow
will build the thermal ridge into central Lower Michigan early in
the day and expand it southward through the afternoon. Projections
of 925 mb temperature, as a measure of boundary layer modification
due to warm advection, rise from around 0C at 21Z yesterday to near
5C in the NAM/GFS and 7C in the RAP at 21Z today. A similar amount
of warming occurs up through 800 mb which is potentially the top of
the mixed layer according to RAP model soundings. The NAM and GFS
are closer to 850 mb which is the difference between high temps in
the lower 50s versus the mid 50s suggested by the RAP. Prefer to
lean the forecast toward the warmer end of the spectrum considering
how temperatures responded to full mid March sun yesterday afternoon
once the high clouds exited the region. The northern Thumb remains
the area with the greatest temperature forecast sensitivity
depending on the precise timing of the frontal passage. All of the
new model data point to a slightly slower wind shift, roughly 18 to
21Z, which will be long enough for that area to warm into the mid
and upper 40s, about as much as it can without a stronger wind and
with substantial snow cover still on the ground.

The shallow nature of the front under parallel flow aloft will make
it susceptible to differential heating between the land and water
over the southern Great Lakes. Higher resolution models show the
resulting lower surface pressure over Lower Michigan that will help
check southward progress of the front through the Thumb until
sunset. Surface cooling and pressure rises will then allow the front
to release rapidly southward across the Ohio border during the
evening. There is still no precipitation and minimal cloud cover
indicated in model data with the frontal passage. Falling
temperatures will then be the main result and will send readings
back below normal for Monday through the middle of next week. So
after reaching the lower to mid 50s today, readings will struggle to
warm out of the 30s for high temperatures through Wednesday.

The early to mid week below normal temperature pattern will be
supported by polar high pressure setting up shop over northern
Ontario. It will supply a continuous feed of cold air into the Great
Lakes enhanced by stronger gradient flow between it and low pressure
over the Tennessee Valley. Global model solutions remain in
agreement on that low pressure track although with some hint that
secondary development could occur Wednesday and extend northward
close to the Ohio border. Northwest flow aloft then maintains below
normal temperatures Thursday and Friday but with some upward
modification as gradient flow eases with weakening high pressure.
Reamplification of the long wave pattern then brings the next low
pressure system into the Great Lakes possibly next weekend. The
chance for a rain/snow mix would be the first measurable
precipitation in the area over a 10 day stretch since March 14th.


A weak area of low pressure will drop southeast from northern Lake
Huron to Lake Erie by this afternoon. The release of a weak cold
front south through lower MI will switch winds around to the
northeast this afternoon. High pressure building over Ontario will
drift slowly eastward through midweek. This will present a long
duration northeast flow set up and though winds don`t look to exceed
25 knots, the persistent onshore fetch will build significant wave
heights to several feet in the nearshore zones of Lake Huron and
potentially the Michigan waters of Lake Erie Monday and Tuesday.
Small craft advisories may be needed during this time.


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



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