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000
FXUS63 KGRR 221918
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
318 PM EDT Tue Aug 22 2017

LATEST UPDATE...


.SYNOPSIS...
Issued at 315 PM EDT Tue Aug 22 2017

An unseasonably strong cold front has moved through Southwest
Michigan early this afternoon. The air is cold enough that it is
kept our air temperatures from rising significantly this
afternoon. Several additional pushes of colder air from central
Canada will move into Michigan over the next few days keeping
temperatures around 10 degrees below normal into the weekend. On
Thursday as the coldest air moves into the area, we could see
showers on the cold front. With the air so cold and Lake Michigan
being so warm, we could even see a few lake enhanced light rains
showers Thursday. Canadian Polar air will be brought in behind
that front and the surface high that follows will take until
Monday to get east of the area when a slight warm up will begin.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 315 PM EDT Tue Aug 22 2017

Little question the next few days will be much cooler than both
what is normal for this time of year and what we have had over the
past week or so. The only real question is will the air be cold
enough and moist enough for lake enhanced rain showers. As it
turns out it will be on Thursday so we continued to add showers to
our zone and grids.

The core of the polar jet will be over central lower Michigan
Wednesday, so areas over our northern CWA just may see a few
sprinkles (not actually in our forecast). On Thursday a decent
shortwave dives into the eastern CONUS trough and that pushes the
polar jet core south of Michigan. It also brings 850 temps to near
5c, which is 15c colder than the mean Lake Michigan surface
temperature. There is just enough moisture between the surface and
700 mb to allow lake enhanced showers. Inland the air is unstable
enough being on the cyclonic side of the polar jet for showers
there too. Any showers would be light. A few cold air funnels are
also possible. Largely for the same reason.

The passage of the secondary cold front has a line of showers with
it but that should gone by 5 to 6 pm so I believe skies should
become mostly clear tonight. Temperatures should fall into the
upper 40s north and lower to mid 50s south. Thursday night should
be the coldest with clear skies and light winds, I could see
locations like Leota having lows in the mid to upper 30s.
Elsewhere this is likely to be coldest night with almost all
inland locations having lows in the 40s. The last time GRR had a
low below 50 was on the 2nd of June (46).

Bottom line... pref- fall like weather for a few days.

.LONG TERM...(Friday through Tuesday)
Issued at 315 PM EDT Tue Aug 22 2017

Mid level ridging will dominate the weather across the region
through most of the period.  As a result...expect dry conditions
with below normal temperatures. Surface high pressure will bring
fall like temperatures Friday morning through Saturday
morning...with a slow but steady warm up from Saturday through
Tuesday as the high moves to the east and southerly winds redevelop.

The tropical system expected to develop over the western Gulf of
Mexico in the next few days could impact the local weather Monday
onward...but uncertainty is high as the longer range models are
handling the remains of this system differently. Widespread rainfall
could be in store for West Michigan in the latter part of next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 103 PM EDT Tue Aug 22 2017

Radar shows a narrow line of showers along cold front north of
KGRR. Band of clouds associated with these showers showing up
well on visible satellite imagery. Widely scattered showers have
also developed in deeper moisture ahead of the front. The front will
move steadily southeast this afternoon and rain chances will
decrease significantly once it passes any particular location.

Will continue MVFR ceilings for the rest of this afternoon...with
a clearing trend expected around 00z Wednesday. Some of the short
range models indicate an increase in low level moisture between
09 and 12Z Wednesday...but will not include this in the TAFs at
this time.


&&

.MARINE...
Issued at 315 PM EDT Tue Aug 22 2017

I will keep all headlines as is but will add water spouts to our
forecast on Thursday since since the air is unstable enough.


&&

.HYDROLOGY...
Issued at 1240 PM EDT Tue Aug 22 2017

Area rivers are around normal levels for the time of the year and
well below bankfull. Rainfall over the past 24 hours has mostly been
under an inch, and only minor river rises have been observed. No
significant precipitation is expected Wednesday through the weekend,
so no river issues are expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Wednesday afternoon for MIZ037-
     043-050-056-064-071.

LM...Small Craft Advisory until 6 PM EDT Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...MWS
AVIATION...MWS
HYDROLOGY...63
MARINE...WDM