Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 140358
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1158 PM EDT Sun Aug 13 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 PM EDT Sun Aug 13 2017

A cold front will gradually ease southeast into Southwest Michigan
Monday night, only to return back north as a warm front Tuesday
night.  This system will bring a chance of showers and storms to
Central Lower Michigan Monday, that will then spread across all of
the region Monday night.  With the front still over the area, we may
continue to see widely scattered showers and storms Tuesday and
Tuesday night, but these should largely be along and south of I-96.
Good chances of rain should continue Wednesday and Thursday before
we finally dry out into the weekend.

Daytime high temperatures will mainly be 80 to 85 each day.  However
more humidity will move into the area for Tuesday and linger until
about Friday.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 328 PM EDT Sun Aug 13 2017

A short wave will pass through late Monday night and bring a surface
cold front into the area. The front is then expected to stall over
the CWA by Tuesday, returning north as a warm front by Tuesday
night.  This system will bring a few showers and storms to the area,
with a peak across Central Lower tomorrow afternoon and evening.

After a quiet night the front and the upper wave will begin to
impact SW MI on Monday with increasing lift.  I increased the POPs
for Monday, mainly across Central Lower to account for the moisture
pooling that occurs ahead of the front.

These showers and storms will drift across the entire CWA Monday
night as the short wave moves through.  Not seeing as favorable
moisture pooling however, so will keep POPs in the chance category.

The upper support is lost into Tuesday and Tuesday night as the
short wave moves east.  However the front stalls over the southern
CWA Tuesday, then it lifts north Tuesday night.  Expect widely
scattered showers and storms mainly along and south of I-96 and
isolated POPs to the north.

Instability is not overly strong, nor is there much upper jet
dynamics, so severe weather is not expected.  And due to the
scattered nature of the showers and storms, most areas will see a
quarter inch or less through Tuesday night.

Expect a bit more cloud cover through the short term so increased
overnight mins and lowered daytime highs slightly for most areas.

.LONG TERM...(Wednesday through Sunday)
Issued at 328 PM EDT Sun Aug 13 2017

Mid level flow this week will transition from a blocky pattern with
a persistent low over northern Quebec...to a more progressive
pattern. This will bring a series of systems through the northern
portion of the country...allowing warmth and moisture to move
farther north and increasing rain chances.

First system will move through Wednesday...helping to kick out the
Quebec low.  A series of weak shortwaves is then indicated by all
models in the Thursday to Saturday time frame.  Mid level ridging
then reasserts itself across the northern plains by Sunday.

Rain chances will be highest Wednesday night into Thursday...with a
break on Friday.  Another wave of precipitation is then expected
Friday night into Saturday.

Warm and muggy conditions are expected Wednesday...with highs in the
lower and middle 80s.  A few upper 80s would not be out of the
question if sufficient breaks occur in the clouds.  Slightly cooler
temperatures...from the upper 70s to lower 80s...are then expected
from Thursday through Sunday.

Wednesday and Thursday morning will be muggy...with lows from the
middle 60s to near 70.  Lows will be closer to 60 degrees for the
rest of the extended period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1130 PM EDT Sun Aug 13 2017

Vfr conditions will continue at all the terminals through Monday
evening. Winds will be light and variable overnight and then
become southerly at around 5 to 10 kts late Monday morning through
Monday evening.

Isolated showers may develop Monday into Monday evening but there
is not enough potential in them to warrant mention in any of the
terminal fcsts at this time. We do expect some scattered showers
and perhaps a few thunderstorms to move in from the west after 06Z
Tue.

&&

.MARINE...
Issued at 328 PM EDT Sun Aug 13 2017

Winds and waves will be fairly low through the short term.  Boaters
and beach goers will have to monitor the thunderstorm risk however
from Monday through Tuesday night and beyond.


&&

.HYDROLOGY...
Issued at 1136 AM EDT Sun Aug 13 2017

Rivers continue to run near or below normal. There is little or no
immediate concern for flooding.

Chances for rain continue to show more promise in the second half
of the work week. Amounts are questionable given the differences
in guidance. At this time, long term forecast rainfall amounts
are highest west of Lake Michigan with 1+ inch totals most likely
over Wisconsin, trending lower as the crow flies east.

&&

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

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...MWS
AVIATION...Laurens
HYDROLOGY...JAM
MARINE...JK



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