Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 250553
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
153 AM EDT Tue Jul 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 327 PM EDT Mon Jul 24 2017

High pressure from Canada will bring cooler and drier weather
through Tuesday. Another cold front moves through on Wednesday
with a chance of strong thunderstorms. Then fair weather returns
for the end of the week.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 327 PM EDT Mon Jul 24 2017

The focus of the short term will be for Wednesday with convection
ahead of advancing cold front and amplifying upper trough possibly
including some strong to severe storms.

Sfc ridging holds on through early Wednesday with the earliest
chance for storms being across the northwest zones Wednesday
afternoon or evening. The front then sags through overnight with
strong sfc convergence being able to focus some storms. It appears
to be another overnight event when sfc based instability is
diurnally decreasing but also when low level jet is increasing.

Shear profiles and moisture transport would support the threat
for strong storms with heavy rain but we will have to watch trends
and see if the southward shift results in another miss for
southwest Lower Michigan.

Before then...we will have nice weather with low humidity. In
fact, with clear skies and winds going light, tonight could see
the coolest temperatures for the month of July to this point with
some of the cooler locations dropping down into the 40s.

.LONG TERM...(Thursday through Monday)
Issued at 327 PM EDT Mon Jul 24 2017

The digging mid level shortwave tracks eastward through Lower MI on
Thursday.  There will still be plenty of moisture and instability
around for showers and thunderstorms...mainly for the first half
of the day. Overall this system has trended stronger from previous
runs so confidence is relatively high for numerous/widespread
showers.

A secondary mid level shortwave tries to move for Friday.  Currently
this system is shown to be weak and the moisture limited. Will hold
off on adding any showers or thunderstorms to the forecast.

Relatively stronger subsidence arrives for Saturday and persists
into Monday.  Will keep the weather dry.  The thermal trough is now
shown to push out slower.  Thus any significant warming trend will
have to hold of until next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 153 AM EDT Tue Jul 25 2017

VFR conditions are still expected areawide through the day. To
address concerns from the previous forecast, fog later this
morning continues to appear unlikely around KJXN and KLAN.

&&

.MARINE...
Issued at 814 PM EDT Mon Jul 24 2017

Dropped both the Small Craft Advisory and Beach Hazards Statement
as conditions are improving. The South Haven and Port Sheldon
buoys both indicate conditions right near the threshold for
headlines at 3.9 feet. Current thinking is in the next hour or two,
the waves will fall below criteria, so let the headlines expire at
the end time of 800pm. Waves should be in the 1-3 foot range at
midnight and 1 foot or less by daybreak.

Light winds on Tuesday will bring quiet conditions out on the big
lake. Increasing southerly flow returns for Tuesday night into
Wednesday ahead of a cold front, followed by strong north flow
on Thursday.


&&

.HYDROLOGY...
Issued at 327 PM EDT Mon Jul 24 2017

A fair portion of the area has trended drier than normal over the
past 1 to 2 weeks. Late Wednesday into early Thursday appears to be
the only chance of appreciable rainfall over the next week. Local
amounts will depend greatly on the track of the potential
thunderstorm complex, though over an inch is possible where it does
track. This fairly progressive upper level shortwave trough and
associated surface front do not suggest much threat of excessive
rainfall.

&&

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

$$

SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...MJS
AVIATION...TJT
HYDROLOGY...CAS
MARINE...Duke



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