000
FXUS63 KGRR 260419
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1219 AM EDT Tue Sep 26 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 PM EDT Mon Sep 25 2017

One more day of hot weather is expected with highs on Tuesday
forecast to reach the upper 80s to around 90. Tuesday will mark the
7th day in a row of well above normal temperatures. A cold front
will pass through the region Tuesday night which may touch off a few
showers or a thunderstorm. The main story with the front however is
that cooler air will filter in behind it. Highs will be back to near
normal on Wednesday, cooling to below normal for Friday. Highs by
the end of the week will be in the 60s. So, for those looking for
relief from the heat, its on the way later this week. Precipitation
chances this week will be fairly small overall.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 328 PM EDT Mon Sep 25 2017

Main feature in the short term will be the cold front set to move
through the area Tuesday night. Otherwise, we will finally get a
reprieve from the heat as we head into mid week.

Chances for rain do not look all that high Tuesday evening through
Wednesday morning with the frontal passage. The main upper shortwave
trough associated with the surface cold front passes well off to the
north of the area. In fact, the shortwave stays mainly north of the
Straits of Mackinac. The ribbon of moisture with the front is fairly
narrow spatially and is not all that impressive with mainly 70 to 80
percent RH values in the 1000-700mb layer. Bottom line we have very
small chances (20-30pct) for precipitation in the forecast Tuesday
evening and Tuesday night.

As far as the heat goes, we should see a change in air mass occur on
Wednesday. 850mb temps drop from around +18C at present to +4C by
daybreak on Thursday.

Mainly clear skies are anticipated tonight, turning partly cloudy on
Tuesday before becoming mostly cloudy Tuesday night. Partly cloudy
skies are expected once again Wednesday into Wednesday night, with
some diurnal cumulus and lake generated stratocumulus.

.LONG TERM...(Thursday through Monday)
Issued at 328 PM EDT Mon Sep 25 2017

Normal temperatures for the end of September are in the mid-upper
40s for lows and mid-upper 60s for highs. We will fall right into
that range on Thursday with plenty of sunshine.

An upper-level trough and associated surface cold front passing
through the area Thursday night and Friday will enable scattered
showers to develop... first from mid-level moisture transport and
lift on Thursday night, then with a small amount of surface-based
instability on Friday under partly sunny skies (and partially
enhanced by warm Lake Michigan water). Rainfall amounts do not look
substantial, and most locations can expect less than a quarter of an
inch.

Temperatures will be several degrees cooler than normal Friday
through Sunday morning. Patchy frost is possible in the interior of
Central Michigan (north of Evart/Clare) Friday night and Saturday
night. Temperatures appear poised to rebound to the warmer side of
normal early next week as southerly flow resumes.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1219 AM EDT Tue Sep 26 2017

There will be scattered areas of fog again toward daybreak. It
seems like the I-94 TAFs stand the best chance of seeing some fog.
It may briefly go down to IFR at any one location, but for the
most part I`m expected light fog and MVFR vsbys.

Once the fog burns off by 13-14Z the rest of the day will be VFR.
A front will approach the region late, this will cause the
southwest winds to get a bit breezy to around 10 knots for MKG and
GRR into the afternoon.

The front will bring widely scattered showers and thunderstorms
after nightfall. Introduced vicinity thunder to MKG and GRR after
01Z. These will move toward the rest of the TAF sites after 06Z.

&&

.MARINE...
Issued at 328 PM EDT Mon Sep 25 2017

Southerly flow will continue both tonight and on Tuesday. We are not
expecting impacts from this wind as speeds are forecast to be in the
10 to 20 knot range. A cold front passes through the nearshore
waters Tuesday evening, with building waves behind it. By daybreak
on Wednesday waves are expected to be in the 2 to 4 foot range. On
Wednesday waves will peak in the 3 to 6 foot range. We will likely
need a Small Craft Advisory from early Wednesday morning possibly
around 600am through Wednesday night around midnight. Waves will
fall back below advisory criteria by Thursday morning.


&&

.HYDROLOGY...
Issued at 153 PM EDT Mon Sep 25 2017

Rivers are running around normal to much below normal for the time
of year. Meanwhile, the US Drought Monitor is indicating dry
conditions across Southern Lower Michigan. Rainfall is possible
Tuesday night and Thursday night into Friday but, less than a
quarter of an inch is expected. No river issues are expected into
the weekend.

&&

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

$$

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