Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 240730

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT SAT SEP 24 2016

Synopsis/Short Term/Long Term/Marine

Issued at 330 AM EDT Sat Sep 24 2016

High pressure north of Lake Huron will provide fair weather today
and tonight. A cold front will pass through the state on Sunday
night and early Monday, bringing showers and a few thunderstorms.
Breezy and cool weather will follow behind with front on Monday with
scattered showers and highs only in the 60s.


.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat Sep 24 2016

Main issue in the near term is cloud trends. Higher potential for
sunshine today - especially this afternoon - as surface ridging and
drier air press southward through the region. Diurnal cu schemes are
not particularly strong today, scattered at best, although there
should be some high cloudiness streaming in from the northwest.

Increasing clouds expected Sunday from west to east, although a good
chance for areas east of GRR to remain sunny much of the day. Low
chance pops arriving late in the day for MKG/LDM areas.

Nighttime frontal timing/limited instability (MUCAPEs below 500
J/KG) should keep thunderstorm coverage/chances fairly low Sunday
night. However the probability of showers will be high as axis of
high PWAT air over 1.5 inches precedes the front.

Upper low/cold pool aloft support scattered showers on Monday and
perhaps even some thunder as steeper mid level lapse rates arrive. A
very fall like day for sure.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat Sep 24 2016

We are looking at a period of cool and unsettled weather for at
least the first portion of the long term. We will see the wrn trough
that will drive the sfc front through in the short term, try to
close off over the Great Lakes as additional energy dives in. This
will drive the jet south of the area, bringing the cold pool aloft
and cyclonic flow overhead. This will keep the threat for showers in
through Wednesday. Some lake enhancement will be likely with plenty
of over water instability with Lake Michigan still in the lower 70s.

There has been decent agreement that the area would see conditions
dry out and temperatures moderate beginning Thursday. This was the
result of a strong enough wave rotating around the upper low, and
taking it east of the area. This was never a sure thing considering
we are dealing with an upper low that is always tough to forecast
the movement. We are starting to see some evidence that this low may
not kick out as quick as earlier expected, and linger around the
region. We are not adding rain chcs yet for Thu and/or Fri, but will
be monitoring. If the low takes longer to kick out, temps will
remain cooler than advertised right now.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 158 AM EDT Sat Sep 24 2016

Our main aviation focus is on the lower cloud cover that is in
place, especially along I-94 early this morning. The cigs along
I-94 are in the 2-3k ft range. This is the back edge of the lower
cloud cover that plagued the area on Fri. This is fcst to slowly
sink south later this morning, and should be south of the I-94
terminals by 16z.

Once this cloud cover moves out, some diurnal cumulus will be
possible with mid clouds also floating by. This should generally
remain the case then through 06z tonight, with the diurnal clouds
dissipating around sunset. An E/NE wind will likely hold up
through the period.


Issued at 330 AM EDT Sat Sep 24 2016

Offshore flow will keep wave heights below advisory criteria through
the weekend. Waves will begin to build Sunday night with the passage
of the cold front and westerly wind shift/increase, then significant
wind/wave action is high confidence Monday in cold advection/
cyclonic flow pattern.

Wave heights could easily approach 10-12 feet Monday afternoon
considering how warm the water still is (72F at the srn lk mi buoy).
This will create very steep lapse rates/deep mixing over the water.
Will also need to monitor waterspout potential although at this time
is appears the winds may be too strong on Monday. Gales
watches/warning may eventually be needed for Monday.


Issued at 1032 AM EDT Fri Sep 23 2016

Hydro concerns are minimal through the weekend, as little rain is
expected and river levels are around normal for the time of year.
Showers and thunderstorms are expected Sunday into Monday night with
additional rain possible Tuesday into Wednesday. Around 1 inch of
rain is expected and therefore rivers and streams should remain
below bankfull through the week.


.GRR Watches/Warnings/Advisories...


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