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000
FXUS63 KGRR 201744
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
144 PM EDT Wed Sep 20 2017

LATEST UPDATE...
Aviation

Ridging will maintain VFR conditions and dry weather through the
afternoon and early evening. Low pressure tracking through central
Canada will drive a frontal boundary through the area tonight and
Thursday. This will increase moisture over west Michigan, but the
front will weaken as it encounters the ridge over the area,
keeping chances for precipitation very low tonight. Best
potential still looks to reside at MKG and GRR, but confidence in
occurrence is very low. Increase in cloud cover should help
mitigate the threat for dense fog. Will favor MVFR visibilities
late tonight and Thursday morning for most location, with IFR more
likely to occur at BTL, AZO, and JXN.

.SYNOPSIS...
Issued at 244 AM EDT Wed Sep 20 2017

A weak area of high pressure will track through the region today
providing the area with mainly dry conditions after a foggy start.
Tonight a cold front will be weakening as it tracks in from the
northwest. This feature will dissipate over the area on Thursday.
It will become increasingly moist so a few showers or
thunderstorms may occur. Summerlike conditions are expected for
the end of the week.

&&

.SHORT TERM...(Today through Friday)
Issued at 244 AM EDT Wed Sep 20 2017

Fog/status will prevail around the region to start the day. The
fog should thicken up somewhat as we go toward daybreak. At this
time the cloud cover that is in place appears to the limiting the
coverage of dense fog. So will not go with a headline at this
time. There were a few light rain showers in the eastern zones
around Mount Pleasant. Will hold onto a low risk for showers to
start the morning there.

Tonight the cold front that featured an active line of storms
yesterday in the Upper Plains...will be moving into Michigan from
the northwest. This feature will be weakening with time and is
expected to dissipate over the area on Thursday. What it does do
is draw in increasing amounts of moisture with PWAT values close
to 1.75 inches. So it may very well feel muggy. The low level
thermal ridge folds in as well. High temperatures will be topping
out in the mid to upper 80s Thursday and Friday. The atmosphere
each day will become quite unstable as well. Deep layer shear will
be weak so any storms should be pulse in nature.  With the
boundary of the dissipating front still around on Thursday will go
with a risk for thunderstorms. Will keep it dry for Friday with no
real focusing mechanism around along with the main axis of
moisture shifting north of the CWA resulting in falling PWAT
values.

.LONG TERM...(Friday night through Tuesday)
Issued at 244 AM EDT Wed Sep 20 2017

A dome of high pressure will create mid summer-like conditions this
weekend across Lower Michigan. Highs in the mid to upper 80s coupled
with dewpoints in the mid 60s will feel hot and humid.

We`re running with a dry forecast through the period too. The
exception to that is next Tuesday afternoon. Both the ecmwf and gfs
show a strong short wave ejecting out of the western US trough and
pushing the northern portion of the Great Lakes ridge eastward. This
allows a cold front to move close to Lake Michigan Tuesday. We`ll
continue with a slight chance of showers/storms Tuesday afternoon
across the northwest cwa. The higher chance of pcpn will come
Tuesday night if current model trends hold.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 134 PM EDT Wed Sep 20 2017

&&

.MARINE...
Issued at 244 AM EDT Wed Sep 20 2017

The easterly surface winds will veer today and tonight as a
weakening cold front nears. This system will dissipate over the
area on Thursday. The combination of offshore flow and a
relatively weak pressure gradient will act to keep the wave
heights low today. Tonight and Thursday the pressure gradient will
be weakening. So despite an increasing fetch...the warm air
advection and weakening front will support only low wave heights.


&&

.HYDROLOGY...
Issued at 330 PM EDT Tue Sep 19 2017

Rainfall this morning was fairly light and occurred south of a line
from Holland to Lansing. Most rainfall totals were under 0.10
inches, but a few locations did pick up more than 0.25 inches.
Weakening low pressure tracking south of the area will continue to
provide a chance for showers south of I-96 today. Rainfall this
afternoon and evening will be even more hit and miss than this
morning. A few locations in Ingham, Jackson, and Calhoun counties
could pick up more than a tenth of an inch of new rainfall, however.
A weak frontal boundary will provide the next chance for showers or
a thunderstorm Wednesday night into Thursday. High confidence then
exists with very warm and dry conditions late Friday through the
weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...HLO
HYDROLOGY...HLO
MARINE...MJS