Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 250019
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
819 PM EDT Sat Jun 24 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 315 PM EDT Sat Jun 24 2017

The area is looking at a an early fall-like pattern with cool
conditions by late June standards along with spotty shower activity.
This pattern will persist at least through Monday before we dry out
some and warm up a little.

Later this week, warmer air will return to the area. With the
arrival of the warmer air, a potentially wet period could take shape
with occasional rounds of showers and storms.

&&

.UPDATE...
Issued at 820 PM EDT Sat Jun 24 2017

I updated our grids, ZFP and actually our Near Shore forecast to
show showers likely and thunderstorms possible overnight tonight.

It seems to this forecaster that the upstream shortwave seen very
nicely on the IR/WV/VIS satellite loops is rather impressive
looking. It is heading toward SW MI from E IA and W IL/SRN WI.
The radar mosaic loop over the northern plain into the western
Great Lakes show and area of showers and thunderstorms assoicated
with this shortwave. The NAM12 18z thunderstorm probability
forecast (had 85 % for thunderstorms near MOP this afternoon) has
98% chance of thunderstorms in the MKG area between 06z and 09z.
In fact the SPC SREF 15z run also shows and enhanced chance of
thunderstorms west of US-131 in the 06z to 12z time frame Sunday
morning (late tonight and early Sunday). Also the HRRR/RAP/HiRes
ARW and HiRes NMM all show showers over our area in the 06z to 12z
time frame. This is all driven by that closed upper low forecast
to cross this area early Sunday morning. Model sounding all show
elevated instability in that time frame too. Most unstable cape
values rise to near 600 j/kg. Given all of this I am confident
enough update all of our forecast products to reflect likely
showers and possible thunderstorms overnight (not severe).

&&

.SHORT TERM...(This evening through Monday night)
Issued at 315 PM EDT Sat Jun 24 2017

The showers and scattered storms mainly over the NE portion of the
area this afternoon should tend to move east of the CWFA within the
next 2-3 hours. Unfortunately, the localized heavier rainfall is
affecting the Mt. Pleasant area which has been hit the hardest over
the last couple of days.

One short wave is about to exit to the east, leaving short wave
ridging to build in briefly. This will be short lived as another
weak wave, and a much stronger wave are moving toward the area from
MN/WI. These will arrive after peak heating, so diurnal instability
will be waning. We do think that the strength of the second wave
will be enough to carry rain chances in later this evening and
overnight.

Another break is order then Sunday morning, before a few
showers/storms will refire Sunday afternoon. This will be the case
as yet another short wave in the cyclonic flow aloft approaches the
area. There does look to be enough instability that thunder will be
possible once again. The westerly flow off of Lake Michigan will
once again shadow the western counties a bit, and allow for the best
rain chances to be over the E and NE.

Cyclonic flow aloft will remain Sunday night into Monday night. This
will mean bouts of showers with isolated thunder, focused on the
peak heating hours. Can not rule out a shower overnight Sunday
night. Monday night, we should tend to end all rain chances and
clear out as the upper low and jet lifts out as we become more anti-
cyclonic aloft.

.LONG TERM...(Tuesday through Saturday)
Issued at 315 PM EDT Sat Jun 24 2017

The big story in the extended is the potential for more heavy rain
during the latter half of the week.

Upper trough axis moves east Tuesday with shortwave ridging
returning Wednesday along with warming temperatures. We will also
see moisture return in southwest flow with chances for rain by
Wednesday afternoon. Surface low center tracks north of Lower
Michigan on Thursday with showers and thunderstorms along and ahead
of trailing cold front slowly pushing south through the forecast
area. The front stalls near southern Lower Michigan and another sfc
low tracks along it on Friday into Saturday with heavy rain and
flooding potential to be watched closely.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 741 PM EDT Sat Jun 24 2017

Skies have largely cleared behind the last shortwave but a much
stronger one is clearly seen on the IR/WV/VIS satellite loops
heading toward SW MI from E IA and W IL/SRN WI. The radar mosaic
loop over the northern plain into the western Great Lakes show and
area of showers and thunderstorms assoicated with this shortwave.
This has the potential for bringing a brief period of MVFR
cigs/VSBY in the 06z to 09z time period (more so for the I-96 than
the I-94) TAF sites. The NAM12 thunderstorm probability forecast
(had 85 % for thunderstorms near MOP this afternoon) has 98%
chance of thunderstorms in the MKG area between 06z and 09z. In
fact the SPC SREF also shows and enhanced chance of thunderstorms
west of US-131 in the 06z to 12z time frame Sunday morning. Also
the HRRR/RAP/HiRes ARW and HiRes NMM all show showers over our
area (mostly I-96) in the 06z to 12z time frame. Given all of this
I am confident enough so as to have put prevailing rain showers
in the GRR and MKG TAF in the 06z to 12z time frame. I put VCTS in
the MKG and GRR TAF as per the enhanced thunderstorm threat
there, then.

Behind that shortwave will be a brief clearing but like this
morning I could see MKG having MVFR cigs for a few hours. Once
again another shortwave moves in afternoon showers are possible
but mostly inland of US-131. Winds will be gusty tomorrow, just
like this afternoon and yesterday afternoon.


&&

.MARINE...
Issued at 315 PM EDT Sat Jun 24 2017

We have expanded the Small Craft Advisory and Beach Hazards
Statement north a couple of marine zones up to Pentwater. We will
see the winds and waves relax for a short time this evening. They
will ramp back up again overnight in association with the passage of
the next wave. The furthest north area will see the gradient a
little bit weaker closer to the core of the low.

It will be possible that additional headlines will be needed on
Monday, or an extension at the very least as the pattern remains
similar through then.


&&

.HYDROLOGY...
Issued at 1231 PM EDT Sat Jun 24 2017

The Chippewa River at Mount Pleasant crested at 14.77 feet Friday
night, about 10 inches below the record flooding of 15.58 feet in
September 1986. All river forecast points in our area have crested
as the water is being routed down through the Muskegon and Saginaw
river systems. Scattered showers Saturday through Monday should
have little effect on the rivers. Heavy rain potential may return
during the latter part of the upcoming week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Sunday evening for MIZ043-050-
     056-064-071.

LM...Small Craft Advisory until 8 PM EDT Sunday for LMZ844>848.

&&

$$

UPDATE...WDM
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Ostuno
AVIATION...WDM
HYDROLOGY...CAS
MARINE...NJJ


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