Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 200539
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
139 AM EDT Tue Jun 20 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 PM EDT Mon Jun 19 2017

Scattered showers and isolated thunderstorms will continue to
develop through Tuesday before fair weather returns Tuesday night
through Wednesday. Showers and thunderstorms are expected late
Wednesday night through Thursday night.

&&

.UPDATE...
Issued at 1019 PM EDT Mon Jun 19 2017

The rain showers over Lake MI continue to track southeast. They
are slowly dissipating. Enough momentum exists for some of these
to move inland over the next couple of hours. This update reflects
a small chance for measurable precipitation through 06z.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 325 PM EDT Mon Jun 19 2017

Primary short term fcst concerns involve determining convective
potential tonight through Tuesday and for late Wednesday night.

Sufficient instability has developed for showers and isolated
convection to continue to develop late this afternoon and evening.
Scattered convection over our se fcst area will continue to drift
slowly east and out of our area with a westerly flow lake shadow
resulting in dry wx over most of our fcst area for the next
hour or two.

However rgnl radar trends suggest that scattered showers and
isolated storms currently over eastern WI and western Lake Michigan
will move into our fcst area very late this afternoon through this
evening. This notion is supported by 3km nam and hrrrx higher
resolution guidance.

Scattered showers and isolated convection will develop again on
Tuesday. However tomorrow`s environment will be different with
little to no instability but stronger shear. Overall we expect
even less coverage of convection tomorrow but isolated stronger
storms may potentially contain gusty (but sub severe) winds.

Fair weather will return late tomorrow night through Wednesday
evening as a high pressure ridge builds in. However showers and
thunderstorms will develop early Thursday morning fueled by
forcing from a vigorous llj.

.LONG TERM...(Thursday through Monday)
Issued at 325 PM EDT Mon Jun 19 2017

Thursday and Thursday night look rather active with the potential
for some stronger storms and/or heavy rainfall.

Some type of MCS should be impacting the area Thursday morning with
a strong low level jet aimed directly at us, so will carry likely
PoPs. Typically in this setup a weakening trend of the convection
will take place by noon as the low level jet weakens, but if the low
level jet can be sustained through the day or if new diurnal
development fires on residual outflows/MCVs from the earlier
convection, we could have clusters of storms around all day long.

Then on Thursday night the sfc cold front is shown to sink slowly
south through the area. Scattered to numerous storms will continue
to be possible along/ahead of this front within axis/pool of PWATs
close to 2 inches and sfc dew pts around 70 sitting over the area.

As the sfc cold front settles southward on Friday, we should dry out
in the afternoon and probably remain relatively quiet Friday night
and Saturday. It looks like the front could try to bulge north again
on Saturday night and Sunday as a wave moves along the front, but
confidence in this scenario is low. The whole weekend could
potentially end up being dry with cooler/drier air mass gradually
filtering in from the northwest.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 138 AM EDT Tue Jun 20 2017

Our main focus with the 06Z forecasts is on the potential for more
pcpn on Tue.

Mid clouds left over from showers/storms over WI last evening are
now floating through the area. This should remain the case until
mid-late morning when diurnal cu/stratocu starts to move
in/develop ahead of the next short wave that will move through.

Models are in fairly decent agreement that a band of showers will
approach KMKG around 17z or so, and then push SE through the other
terminals thereafter. It looks like maybe 2-4 hours with the
threat. MVFR conditions will be possible. The thunder threat looks
too low at this time to mention at all. Winds will pick up around
this time also with some gusts to 25 knots or so.

Clouds will break up once the showers/wave move through. Wind
gusts will diminish toward 00z Wed.

&&

.MARINE...
Issued at 325 PM EDT Mon Jun 19 2017

Wave heights of 2 feet or less are forecast late this afternoon
through tonight. Wave heights of 1 to 2 feet are expected again
Tuesday although some 3 footers are possible by late morning through
the afternoon. Conditions will be tranquil Wednesday. Winds and
waves may ramp up on Thursday and thunderstorms may pose a hazard to
mariners late Wednesday night through Thursday night.


&&

.HYDROLOGY...
Issued at 159 PM EDT Mon Jun 19 2017

Two to over three inches of rain fell this past weekend which is
leading to higher river flows. The Flat River near Smyrna may reach
bankfull by midweek, but is the only site expected to do so.
Scattered showers and a few thunderstorms will be possible today and
Tuesday with less than a quarter inch of rain expected on average.
Additional heavier rains will become possible once again Wednesday
night through Friday and should lead to additional rises.

&&

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

$$

UPDATE...MJS
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Laurens
AVIATION...NJJ
HYDROLOGY...63
MARINE...Laurens



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