Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 111140
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
740 AM EDT Fri Aug 11 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Fri Aug 11 2017

Scattered showers and storms will remain possible today across
Southwest Lower Michigan along and ahead of a cold front. The front
should press east of the area during the afternoon hours ending the
threat of rain towards Lansing and Jackson towards early evening.
Dry weather is then expected over the weekend as high pressure
gradually works in from the west. Highs will be a bit cooler than
normal for this time of year with 70s expected for highs today,
Saturday and Sunday.

&&

.SHORT TERM...(Today through Sunday)
Issued at 330 AM EDT Fri Aug 11 2017

Main concern in the short term period pertains to chances for
showers and storms today. Cold front at 300am stretches from
Northern Lake Michigan across portions of Southern Wisconsin into
Eastern Iowa. The front will progress to the east through the course
of the day, moving through the eastern portion of our forecast area
towards Lansing and Jackson between 18z and 22z. It is during this
time frame when I feel the best chances for redevelopment will
occur. Moisture will remain ahead of the front with surface dew
points in the mid 60s. NAM is probably overdone in its instability,
but we may be able to build CAPE values into the 1000-2000 j/kg
range once again at max heating. The NAMnest and the HRRRx are not
bullish on additional showers/storms this afternoon, so went with
consensus which is isolated to scattered pops in the east this
afternoon. Deep layer shear values are below 30 knots this afternoon
so not expected severe weather.

Expecting dry weather the remainder of the short term as high
pressure gradually builds into the Great Lakes region. Partly cloudy
skies will trend towards mostly clear as we head from tonight into
the weekend.

.LONG TERM...(Sunday night through Thursday)
Issued at 330 AM EDT Fri Aug 11 2017

We gradually work out of a blocking pattern into next week.  The
main impact to this change will be temps returning to above normal
levels by Wed/Thu.

The upper low that will be parked over Eastern Canada will finally
move east toward the middle of next week.  This will bring weak
upper ridging to the Great Lakes by Tuesday night.  Until then the
northwest flow will keep the region near to slightly below normal on
Monday and Tuesday, with above normal temps developing under the
ridge into Wed and Thu.

This pattern supports an overall dry regime.  We will have to watch
for isolated showers/storms Sunday night and Monday with a short
wave passing through, but most areas stay dry.  Then a more
progressive pattern takes shape for the latter portion of the week.
A cold front may reach the Upper Midwest by Wed night and Thu and
another chance of mainly isolated showers and storms could move in.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 740 AM EDT Fri Aug 11 2017

Some dense fog and VLIFR conditions have developed at KMKG this
morning. This should be fairly short lived with conditions
improving steadily this morning. Other sites may see some MVFR
conditions this morning, especially KGRR and KLAN. Otherwise
expecting a trend to VFR by midday.

An isolated shower or thunderstorm is possible at KBTL, KLAN and
KJXN this afternoon between 18z and 23z. Have VCSH wording in the
TAF right now as the thunder threat is very isolated. Looking for
VFR conditions tonight.

&&

.MARINE...
Issued at 330 AM EDT Fri Aug 11 2017

Will hold off for now, but it appears we will need Small Craft
Advisories and Beach Hazards Statements tonight into Saturday
evening as north flow increases behind the cold frontal passage. We
may even add these headlines later this morning. At this point the
headlines are a later second into third period forecast. After
another look later this morning we may issue. 3 to 5 foot waves look
likely especially up towards the points.


&&

.HYDROLOGY...
Issued at 1036 AM EDT Thu Aug 10 2017

River levels are around normal for the time of year. This is much
below bankfull. Less than a half inch of rain is expected this
afternoon through Friday, with a low chance of showers next Tuesday
and Thursday. Therefore, no river impacts are expected through next
weekend.

&&

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

$$

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



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