Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 291928

Area Forecast Discussion
National Weather Service Grand Rapids MI
328 PM EDT FRI JUL 29 2016

Synopsis/Short Term/Long Term/Hydro/Marine

Issued at 328 PM EDT Fri Jul 29 2016

Showers with a few thunderstorms will remain possible, and even
likely at times through Saturday before diminishing Saturday night.
Severe weather is not expected, but some locally heavy rainfall
will be possible.

Drier weather can be expected for Sunday and Monday with mild
temperatures. Chances for rain will increase late Tuesday and
linger into Wednesday as temperatures start to become very warm
again. This warmer weather will last through Thursday before a cold
front with showers and storms will come through on Friday.


.SHORT TERM...(This evening through Sunday night)
Issued at 328 PM EDT Fri Jul 29 2016

Our main focus in the short term is trying to determine rainfall
trends with the upper system that is slowly meandering through the
Great Lakes.

We are watching a couple of different areas of showers and/or
storms this afternoon. One is a band of lighter showers across just
north of I-96, and the other extends from NW of Chicago to I-80
across Indiana. The showers in our area likely can be attributed to
the deformation area of the wave across Nrn Illinois, while the
storms SSW of us are likely just ahead of the wave itself
interacting with diurnal heating.

The convection to our SSW will try to move across the srn counties
as the wave moves E/NE this evening and tonight. It will tend to
diminish a bit before it gets here as it would arrive after peak
heating and should lose it`s punch. We could still see some locally
heavy rain out of it, but the bigger threat should stay south of us
before diminishing.

We expect that sct showers will continue over the central portion of
the area this afternoon, and likely expand a bit this evening and
tonight as the best deformation with the wave moves across the area.
Instability is very weak for this area, so it should be mostly
showers with only a rumble or two of thunder. Heavy downpours will
be possible there, but the rainfall rates should not be as high
being further removed from the deepest moisture south.

We will see at least one more wave move through Saturday afternoon/
evening that will bring more showers/storms to the area. The SE half
of the CWFA looks to have the best threat Saturday afternoon where
the wave will track. Instability looks to be a little bit better due
to the upper wave being almost overhead and some decent low level
moisture remaining. Fcst soundings show better CAPE profiles for
some large hail. Locally heavy rains will also be possible with
light wind profiles aloft.

This may linger into Saturday evening, but should move out during
the course of the night with the entire long wave moving out.
Conditions will then dry a bit for Sunday and Sunday night with
a decent amount of sunshine expected and mild temps.

.LONG TERM...(Monday through Friday)
Issued at 328 PM EDT Fri Jul 29 2016

Ridging at the sfc and aloft will lead to dry/mostly sunny weather
for Monday, and probably most of Tuesday and Wednesday as well.
However the ECMWF is suggesting the possibility of some storms with
an approaching warm front and shortwave Tuesday afternoon/night so
will need to have some small pops for this. Main chance at this time
is over the western and srn sections of the CWFA.

Expect a warming trend next week as heights rise... reaching well
into the 80s to near 90 by midweek. Dew points/humidity levels
should also come up by midweek. Models have trended slower with the
cold front and associated convection late next week and are now
showing it coming through late Thursday night and Friday.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 200 PM EDT Fri Jul 29 2016

VFR conditions will generally prevail through evening outside of
the widely scattered shower/tstm activity. However if any of
these cells do impact an airport, the vsbys could go IFR or even
LIFR due to localized heavy rainfall. For now have used VC
terminology in the TAFs through evening, but will issue an AMD if
it looks like heavy showers will impact any of the terminals.

A more widespread rainfall could develop later tonight into
Saturday morning so went with predominately MVFR conditions with
persistent showers after midnight. Confidence is still somewhat
low as to the the timing, areal extent, and intensity of this
rain, but the thunder risk should be low enough to leave out of
the TAFs overnight. The thunder threat could redevelop Saturday


Issued at 328 PM EDT Fri Jul 29 2016

We continue to expect that we will not need marine headlines through
the weekend and into early next week. Winds are up around 15 knots
this afternoon, but in an offshore regime. This will limit the wave
action. The offshore flow will continue through most of the weekend.
This will tend to drive down water temps at the shoreline from their
current mild levels.


Issued at 328 PM EDT Fri Jul 29 2016

Thunderstorms the past two days have primarily been heavy rain
threats, and this will continue to be the case into Saturday. A slow
moving trough with weak vertical shear will continue to promote
isolated to scattered slow-moving storms. No substantial dry air can
be found in the deep convective layer, and precipitable water values
are still around 1.5 inches which is near the 90th percentile for
late July climatology. Slow moving storms Thursday into Friday
produced a number of isolated reports of rainfall greater than 2.50
inches, along with street and parking lot flooding several inches
deep. We will continue to stay alert for the isolated flooding
threat through Saturday.


.GRR Watches/Warnings/Advisories...


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