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Area forecast discussion
National Weather Service Grand Rapids Michigan
308 am EDT Wed Sep 18 2019

Latest update...

issued at 308 am EDT Wed Sep 18 2019

- warm and dry through Friday

- rain chances start on Saturday and will be likely on Sunday

- cooler weather expected early next week


Discussion...(today through next tuesday)
issued at 308 am EDT Wed Sep 18 2019

Fog and stratus has not been nearly the issue tonight as it was last
night for most of the area. Some fog/stratus is affecting the far
eastern portion of the area, likely due to less wind aloft and also
with a flow off of Lake Huron/Saginaw Bay for our NE counties. The
less extensive stratus should allow skies to become sunny earlier
than yesterday morning.

Other than the fog/stratus this morning, nothing much to deal with
through Friday. We will see temperatures warm a couple of degrees
each day as warmer air slowly advects in and upper heights build.
Some rain will try to approach on Thursday from the NW, and then the
GFS keeps trying to bring some isolated light rain showers Friday
afternoon. A front tries to lean in on Thursday, but all of the
support (low level jet and upper wave) stay far enough northwest to likely
keep US dry. The Friday chances from the GFS is likely the model
dealing with some diurnal instability. We believe Friday will be our
last fully dry day with little to no deep moisture return occurring
at that point yet.

Rain chances will start to appear on Saturday, but we are not
expecting a washout by any means. The upper ridge and associated
subsidence will move east by Sat morning. A lead short wave will
move in, and moisture return will be a bit better than Friday. We
can not rule out thunder on Saturday as some instability does
develop. Rain chances will become better Sat night and sun as the
low level jet moves in, and moisture return is much better at that

Severe weather threat is not looking very high right now, but
we are monitoring the situation. Right now, if showers and storms
are moving through Sat night and Sun morning, instability will not
have a good chance to build. If for some reason showers and storms
are limited early sun, and instability can build sun, things maybe a
little more concerning. Right now it looks like the chances of that
are lower.

The front will slip south of the area Sun night, but rain chances
will remain possible into Monday. This is because it takes until Mon
afternoon for a trailing wave to push through the area, and clear
the moisture and forcing out. Chances are better that Tue will be a
quiet and cooler day with high pressure building in behind the
weekend system.


Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 122 am EDT Wed Sep 18 2019

Fog was beginning to develop around southwest lower Michigan at this
time as good radiational cooling was underway. It is expected that
the fog will continue to expand over the next couple of hours.
This will likely lead to some impacts at the taf sites. How
widespread and significant the impacts become is uncertain at this
time. Much of the guidance suggests much less in the way of low
clouds and thick fog will occur this morning as compared to
Tuesday morning. Part of this may be because there is more wind
just off the ground...which would limit the fog/stratus. We will
feature a few hours of IFR/MVFR fog around daybreak. If we end up
with limited fog/stratus then conditions will reach VFR much
quicker for today as compared to yesterday.


issued at 308 am EDT Wed Sep 18 2019

We should remain headline free for the nearshore waters until we
come up to the weekend. Winds will start to slowly increase a
little, but should remain below Small Craft Advisory criteria. This
wind should help keep fog potential more limited than yesterday.

We see the potential need for headlines beginning likely for the
Saturday period and through much of Sunday as the frontal system
moves through the area, and winds and waves should increase enough.


GRR watches/warnings/advisories...


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