Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 270730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT TUE SEP 27 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 AM EDT Tue Sep 27 2016

A lengthy period of cool and unsettled weather is expected this week
and into the coming weekend. Low pressure over Lake Superior this
morning will move slowly south through the Great Lakes region Today
and Wednesday, then stall over Ohio for a few days. The low is
expected to move back to the north over the weekend. Clouds and
scattered showers associated with the low will continue to plague
the area with daily highs in the lower to mid 60s.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EDT Tue Sep 27 2016

Not much change from previous fcsts. As upper low drops south
through the state so will the deep moisture. That will cause the
coverage of showers to increase from north to south, particularly
over and downwind of lake Michigan.

Warm water temps around 22C combined with the incoming steep mid
level lapse rates related to the -20c cold core aloft should lead to
lake induced capes exceeding 1000 J/KG tonight and Wednesday. Low
freezing levels around 6000 ft will support the possibility of some
small hail, which already occured Monday evening in scattered
convection - per spotter reports in Muskegon and Ottawa counties.

A slight more western position of the low track is noted in the 00z
guidance and if this trend continues it could result in highest
pops/qpf being more over lake michigan and eastern WI tonight and
Wednesday morning as opposed to wrn lwr MI. A farther west track of
the sfc low would probably result in a quicker transition to
offshore flow, pushing the lake effect component toward Wisconsin.
This trend will need to be watched.

As we head into Wednesday night and Thursday, best pops/qpf
eventually shift to be located over southeast and south central lwr
MI. This is due to the combination of deformation zone rain band
pivoting around the north side of the closed upper low and
northeast flow off lake huron providing some lake enhancement.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EDT Tue Sep 27 2016

The models are coming into better agreement, holding the upper low
over the southern Great Lakes/Ohio River Valley through the end of
the week.  Rain chances will remain high through Friday night. It
appears the low will finally begin to drift northeast and weaken by
Saturday/Saturday night when the pcpn should gradually diminish.
Sunday and Monday appears mostly dry but cloud cover may hang on,
with an upper trough progged to extend back across the Great Lakes.

Daytime temps will not vary much from day to day with the upper low
dominating. Near normal highs of 65 to 70 can be expected with H8
temps holding 7C to 9C.


&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 147 AM EDT Tue Sep 27 2016

The main aviation concern into Tuesday will be brisk WSW winds
that will occasionally gust to 25 knots by daybreak and through
much of the afternoon.

Cloud ceilings will begin to lower from the north by late
afternoon and through the evening hours. This will also come with
scattered rain showers. An isolated thunderstorm will also be
possible, but was not added to the TAFs at this point. Some MVFR,
and possible patchy IFR, is expected to develop toward midnight.


&&

.MARINE...
Issued at 330 AM EDT Tue Sep 27 2016

Conditions will remain hazardous over lk MI due to west flow to 30
knots and waves to 10 feet. The risk for thunder and waterspouts
will increase this afternoon and tonight as the upper low arrives
and drops south across the lake. Winds are expected to become
offshore on Wednesday which should cause waves to subside.

&&

.HYDROLOGY...
Issued at 300 PM EDT Mon Sep 26 2016

River levels are around normal for this time of year. Lake effect
showers are possible this evening into Wednesday. Rain showers are
possible Thursday into Sunday. With less than a half inch of rain
expected through the end of the week, rivers and streams should
remain below bankfull into the weekend.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...Small Craft Advisory until 8 AM EDT Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...JK
AVIATION...JK
HYDROLOGY...63
MARINE...Meade


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