Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 212328
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
728 PM EDT Sat Jul 21 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Sat Jul 21 2018

The Great Lakes will remain under the influence of an upper low from
tonight into Sunday. Showers will continue off an on as well as a
few thunderstorms especially this evening. We will begin to dry out
into Monday as the upper low begins to move off to the east. High
temperatures will remain in the upper 70s for Sunday and Monday.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EDT Sat Jul 21 2018

Showers will remain likely from late this afternoon through the
evening as a diurnal boost is given to the precipitation. Heating of
the near surface layer with cooler air aloft is resulting in pockets
of showers and even a few thunderstorms. CAPE values as expected
have risen to above 1000 j/kg. Any storms will remain below severe
levels but will be capable of short duration locally heavy rain.

Expecting the showers and storms to taper of as we approach midnight
with a lull in the precipitation overnight. On Sunday, a vorticity
maximum is forecast to rotate in out of the east. This should bring
another round of showers and possibly some stratiform rain to the
GRR forecast area.

Sunday night through Monday night the upper low should gradually
lose influence over our weather with showers diminishing in coverage
and intensity.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EDT Sat Jul 21 2018

Mainly dry weather is expected from Tuesday through Wednesday as a
weak surface ridge of high pressure slides through the area.

Both the ECWMF and the GFS show a cold front sliding through the
area Wednesday night into Thursday. We may need to bump chances for
showers and storms up a bit during this time frame going forward.

Friday and Saturday the forecast looks a bit unsettled with an upper
trough sliding in overhead. The pattern would be conducive for some
afternoon showers and storms with cooler temperatures in place
aloft.

The warmest days of the next 7 will be on Tuesday and Wednesday with
seasonable temperatures either side of those two days.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 728 PM EDT Sat Jul 21 2018

Isolated thunderstorms will continue this evening with brief
periods of IFR. MVFR and VFR will prevail through the evening then
ceilings will lower to IFR overnight and into Sunday morning.
WInds will be northeast to east at 5 to 10 knots.

&&

.MARINE...
Issued at 330 PM EDT Sat Jul 21 2018

A strong north wind flowing down the western side of Lake Michigan
has produced 7 footers at the Wilmette IL buoy. These waves will
make a run at our nearshore waters tonight. Almost in the sense of a
swell from the western side of the lake gradually filling in and
building on our side of the lake. At this point have decided to not
issue a Small Craft Advisory as the conditions will be marginal.
Will forecast 2-4 footers in the northern two zones near the points
and in the far southern zone south of South Haven. The higher waves
will be confined to the tonight portion of the forecast with waves
falling already by daybreak. The area of most concern will be in the
far south towards St. Joseph. Waves will continue to diminish from
Sunday into Monday as the gradient becomes more slack.


&&

.HYDROLOGY...
Issued at 1249 PM EDT Sat Jul 21 2018

River levels are around to a little below normal for the time of
year. Most of Southwest Lower Michigan had an inch of rain or less
this weekend, with isolated values to near 2 inches. This has
resulted in steady or slowly rising river levels. More rain is
possible into Sunday, with locally heavy rainfall possible in any
thunderstorms. Main stem rivers are not expected to flood, but any
of the smaller rivers or creeks that get a thunderstorm or 2 may
have quick hitting rises and minor flooding.

&&

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

$$

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



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