Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 170958

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
558 AM EDT Sat Mar 17 2018


VFR conditions expected through the forecast as high pressure has
spread across the region. Only clouds to contend with will be cirrus
debris spreading northward from a low tracking east through the Ohio
Valley today. This will mainly be for the sites DTW/DET/YIP with
clear skies further north. Winds will be light, below about 7 knots,
through the period with some deviations in direction as the weak
pressure pattern makes adjustments.


* None.


Issued at 353 AM EDT Sat Mar 17 2018


A ridge of weakening and modifying surface high pressure will remain
over Lower Michigan today while a low pressure system slides nearby
to the south and a cold front stalls over the northern Great Lakes.
Mid and high clouds will be the only sign of the Ohio Valley system
over SE Michigan as they stream northward to at least the M-59
corridor, and possibly up to the I-69 corridor, before the system
shears toward the Atlantic coast. These clouds will result in some
decrease in surface heating initially while the Tri Cities and
northern Thumb receive full sun to jump start daytime heating from
morning lows in the teens. Even in the south, the timing of the
cloud decrease is expected to produce a late bump in surface heating
that will help high temperatures achieve guidance values in the
lower to mid 40s. The exception will be in the Thumb region where
onshore wind from Lake Huron and substantial snow cover will limit
readings to the upper 30s.

A broad region of high pressure over the Plains will edge into the
Great Lakes tonight. This will keep the sky clear and the wind light
for another round of efficient radiational cooling. Lows in the
lower to mid 20s are preferred and at the cooler end of the guidance
range across the area while readings in the upper teens will once
again be likely in the typically colder Thumb locations.

The front stalling over the northern Great Lakes today will be held
there tonight as a weak wave of low pressure ripples along the
boundary and within the northern stream upper level flow. The
passage of this system through Ontario will then allow the front to
move southward through Lake Huron and Lower Michigan but not before
a mild day unfolds over most of SE Michigan. This will be primarily
due to westerly low level flow and resulting warm advection on top of
the already mild high pressure air mass in place over the region. As
the surface low exits Georgian Bay, the cold front will release
easily southward over the cold Lake Huron water during the afternoon
but will otherwise leak more slowly through Lower Michigan under
parallel flow aloft. It is also getting to be that time of year when
differential heating between the land and water begin to play a
substantial role in the shape of the surface pressure pattern,
especially with shallow frontal boundaries. Higher resolution
versions of the models all show this well and are in reasonable
agreement on a late afternoon northeast wind shift in the Thumb and
Tri Cities. That will put a halt to the warming trend there after
highs in the mid to upper 40s. Moisture will be severely lacking with
this system which will lead to just patchy clouds with the frontal
passage and full sun to the south. The combination of low level warm
advection ahead of the front and mid March surface heating will boost
highs easily into the lower 50s with a few mid 50s possible toward
the Ohio border.

Passage of the front across the rest of Lower Michigan Sunday night
will bring temperatures back down below normal by Monday, a trend
that will last through the middle of next week. Highs in the 30s will
appear solid each day as the larger scale upper air pattern trends
out of the recent blocking pattern. The lower amplitude flow still
has the Great Lakes under influence of the colder northern stream
while the remnants of the Rockies upper low moves through the Ohio
Valley, and possibly as far south as the Tennessee Valley. The
farther south trend is shown in all of the global models which keeps
Lower Michigan dry for now, a trend that will be monitored cautiously
during the low predictability transition period in the larger scale


High pressure over the region will lead to fairly quiet conditions
over the eastern lakes into next week. Winds will be primarily out of
the northwest and stay below 20 knots through the weekend until a
weak cold front drops through Sunday producing a wind shift to the
northeast. High pressure returns quickly on Sunday from the northwest
which will keep the northeast flow going into the new week. Though
wind gusts look to remain below 25 knots Monday, the long fetch and
persistent northeast flow may lead to elevated waves heights in the
Lake Huron nearshore zones along the eastern Thumb Monday through


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



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