Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 240637
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
237 AM EDT Mon Jul 24 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 305 PM EDT Sun Jul 23 2017

A few showers/thunderstorms possible across south central and south
eastern michigan through this evening. Quiet weather early this week
followed by a more active pattern for the end of the work week.

&&

.UPDATE...
Issued at 1044 PM EDT Sun Jul 23 2017

Shower activity has all but ended and have removed precipitation
from the forecast. Main forecast challenge tonight is cloud cover.
Fog imagery continues to show stratus over Northern Lower Michigan
working its way south. Expecting skies to become mostly cloudy
overnight as the stratus likely expands and works quickly south in
northerly flow of 20-25 knots. Not expecting fog given the wind in
the 1000-3000ft layer.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 305 PM EDT Sun Jul 23 2017

Not a ton of instability to aid in shower/thunderstorm development
with the greatest risk for any storms this afternoon remaining
mostly to the east/southeast of the Grand Rapids forecast area.
Ongoing showers...mainly over jackson county should exit by 5pm
or so with little/no severe threat expected before then. As the
showers move off...high pressure begins to build in with a
pleasant and less humid start to the work week expected. Cloud
cover should be abundant for most of the day Monday with Tuesday
seeing more sun than clouds.

.LONG TERM...(Wednesday through Sunday)
Issued at 305 PM EDT Sun Jul 23 2017

The main challenge in the long term deals with the timing and
strength of the convection Wednesday into Thursday.

Models are showing a series of mid level shortwaves arriving
Wednesday night. The atmosphere becomes moist and unstable during
the day on Wednesday with PWAT values forecasted to climb to close
to 2 inches and lifted index values down to at least -2 deg C.
However the cold front does not push in until later at night or
Thursday morning. Any stronger deep layer shear does not arrive
until after midnight and it is shown to weaken with time, which is
when the instability will be weakening.  Thus the severe weather
risk seems somewhat diminished at this time.  As a result will
continue to feature the potential for storms Wednesday into Thursday
with the highest POPs for Wednesday night.

The new High Res Euro supports a slower departure of the last mid
level wave to track through the CWA.  This model would favor keeping
a potential for showers/storms going into Friday.  The GFS is faster
and supports dry weather for Thursday night into Friday. I will hold
onto a risk for showers for the eastern CWA Thu night. Trends will
need to be monitored here.

Steady mid level height rises are forecasted for the weekend, which
should translate into a warming trend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 237 AM EDT Mon Jul 24 2017

Moderate confidence in MFVR ceilings materializing at most
terminals by 09Z. The greatest likelihood for fuel alternate cigs
below 2000 ft appears to be at JXN, LAN, and possibly GRR,
primarily in the 10Z-13Z timeframe. VFR conditions are expected
areawide after 16Z.

&&

.MARINE...
Issued at 1044 PM EDT Sun Jul 23 2017

Expecting the north flow to fill in over Lake Michigan tonight.
The Ludington buoy already has 4 foot waves and winds that have
gusted to 23 knots. The Northern Lake Michigan buoy has 25 knot
winds and 4 footers. Given the flow have opted to issue Beach
Hazards Statements and Small Craft Advisories for north of
Whitehall and south of Holland. The points will likely keep the
Muskegon and Grand Haven areas in a 2-4 foot wave range. It will
be close and we may have to add these two zones into the mix
overnight. Bottom line, expecting 3-6 footers north and south in a
northerly flow of 15-25 knots. North sides of north piers will
likely have strong structural currents tomorrow (Stearns, Mears,
north beach in South Haven).


&&

.HYDROLOGY...
Issued at 111 PM EDT Sun Jul 23 2017

No flooding concerns for the next 7 days. A frontal passage
Wednesday night into Thursday may bring thunderstorms but this is
not the setup that favors high basin average rainfall amounts.
Therefore, the rivers should behave for the foreseeable future,
especially with a cooler and drier pattern likely to follow for
late in the week and weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through this evening for MIZ037-043-064-
     071.

LM...Small Craft Advisory until 8 PM EDT this evening for LMZ844-845-
     848-849.

&&

$$

UPDATE...Duke
SYNOPSIS...Maczko
SHORT TERM...Maczko
LONG TERM...MJS
AVIATION...TJT
HYDROLOGY...Hoving
MARINE...Duke


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