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Area forecast discussion 
National Weather Service Grand Rapids Michigan
728 am EDT Tuesday Sep 16 2014

Latest update...

issued at 319 am EDT Tuesday Sep 16 2014

An area of high pressure will build into the region today from the
west. This system will help to create areas of dense fog this
morning. The fog will dissipate later this morning giving way to
mostly sunny skies and below normal temperatures. A weak cold
front will slip south of the region Wednesday night. Then a very
strong high pressure system will build down from the north for the
end of the week.


Short term...(today through thursday)
issued at 319 am EDT Tuesday Sep 16 2014

The main challenge deals with the potential for dense fog early
this morning. Overall it looks like most locations will see dense
fog this morning. As a result I issued a dense fog advisory.

Thick fog already exists in places...especially north of
Interstate 96 as of 3 am. Hrrr RUC shows the skies temporarily
clearing out across Southern Lower Michigan with the thick fog building
southward through the remainder of the night. The fog is shown to
slowly dissipate late this morning. As a result with an elevated
risk for hazardous conditions for the morning commute and at bus
stops...I decided that an advisory would be the best way to go.

The remainder of the forecast is relatively quite with a weak dry
cold frontal passage Wednesday night.

Long term...(thursday night through monday)
issued at 319 am EDT Tuesday Sep 16 2014

The main focus of the long term portion of the forecast continues to be
the system that is forecast to move through the area this weekend and
the associated precipitation chances with it.

We should see one more dry and quite mild day at the beginning of
the period on Friday. The far northwest corner could see a low chance of some
rain late on Friday afternoon. We will see an upper ridge in the
process of weakening as it moves east into the area during the day
on Friday. This will keep most of the area dry. Increasing srly return
flow will bring a nice surge of warmth into the area.

The threat of rain will gradually increase starting Friday night and
will peak on Sat night. We will see the initial surface low with the
next front stay well north into Canada...taking with it the best low
level jet and moisture transport with it. The front will approach
the area late on Sat and then move through the area on Sat night and
into the first part of sun. We could see another very mild day on
Sat if we see a decent amount of sunshine and h850 temperatures in the middle
teens c.

The interesting thing about the frontal passage will be that some of
the models are indicating that some remnants from the tropical
system Odile could interact with the front. This could lead to a bit
more rain than currently forecast as the models typically under forecast the
amount of heat and moisture with systems of a tropical origin that
become extra-tropical. This will be something to watch.

We should dry out during the second half of sun as we see the dry
slot move through the area. We could see one more mild day on sun
before the cold conveyor belt wraps into the area on Monday. The models
are showing h850 temperatures dropping down close to zero c on Monday. There
is fairly decent agreement with the strength and timing of this low
and the cold air behind it. We have added some lake effect rain
showers for Monday along the shore with an expected north-northwest wind.


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 716 am EDT Tuesday Sep 16 2014

Dense fog will continue to impact taf sites for much of the
morning with many sites in southwest Michigan LIFR to start. Conditions
will generally start improving after 14z...but IFR could easily
persist through 15z. By 18z enough mixing expected to allow for
conditions to improve to VFR. Will need to monitor the fog
potential for later tonight. Right now the potential is too low to
add it to the forecast.


issued at 319 am EDT Tuesday Sep 16 2014

May end up with waves approaching Small Craft Advisory criteria
Wednesday night into Thursday around Big Sable Point as a stronger
northeast flow develops. Will continue to monitor this potential.
Otherwise the marine forecast looks quiet at this point.


issued at 319 am EDT Tuesday Sep 16 2014

Will need to monitor the heavy rain potential over the weekend as
a cold front moves through and taps tropical moisture. Otherwise
no major rain systems expected through Friday.


GRR watches/warnings/advisories...
Michigan...dense fog advisory until 11 am EDT this morning for miz037>040-



short term...mjs
long term...njj

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