Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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674
FXUS63 KGRR 261925
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
325 PM EDT Wed Apr 26 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Hydro/Marine

.SYNOPSIS...
Issued at 325 PM EDT Wed Apr 26 2017

Multiple waves of showers and storms will move through portions of
the area from this afternoon through Thursday afternoon with a
system that will move through the region. Severe storms are not
likely, however some could become locally strong tonight with some
wind and hail, along with some locally heavy rainfall.

Conditions will dry out for a short period late Thursday through
early Friday. Another system will approach the area on Friday and
bring some chances of rain. A much better shot at widespread rain
will come late Saturday through Sunday as another expansive system
will tap quite a bit of moisture.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 325 PM EDT Wed Apr 26 2017

Our focus with this forecast package is on the waves of
showers/storms through Thu, and the chance of rain coming back in
for Fri/Fri night.

There is a dying line of showers over Central Lower that is at the
tail end of an upper vort moving NNE away from the area. This seems
to be just a bit too far north to tap 1000 j/kg of low level CAPE
over the srn portion of the area. This line seems to be some what of
a weak cool front that extends down S of the area. We can not rule
out another shower/storm popping up, but we do not expect widespread
showers/storms until after 00z tonight.

We are expecting a wave of showers/storms to arrive after 00z from
the SSW that are currently in Srn Il. These are associated with
another upper/sfc wave that will move NE through the evening. The
associated low level jet will nose up into the area and strengthen.
The sfc based instability that we see now will diminish, and this
wave will feature mainly elevated instability with it. This will
limit the severe potential with it. There is some decent shear with
healthy wind profiles up the column. The decent wind profiles will
keep an isolated wind threat in, if it could punch through the
stable near sfc layer. Heavy downpours will be possible too with
PWATS up around 1.5 inches.

We will likely see a lull in the rain for late tonight and early Thu
as the nose of the low level jet moves out, and the sfc low remains
to our west. Heavy widespread rainfall looks to stay over WI. We
will see the main cold front push through late Thu morning and early
Thu afternoon. This will likely develop a bkn line of
showers/embedded storms ahead of it with some diurnal heating taking
place before it pushes through. Forecast soundings do not not
support much of a severe weather threat with thin CAPE profiles. The
wind aloft however keeps a threat in before the front moves through.
The front looks like it should clear the CWFA by 19z Thu. A few
showers will remain in the afternoon to the NW as the upper wave
moves through.

We should end up dry Thu night with rain chances then increasing on
Fri again. The current upper system affecting us moves out, and the
leading short wave with the next upper system approaches. Low level
moisture is not exciting, but there may be just enough for a few
light rain showers to make it to the ground into Fri night. Thunder
chcs look too low with this to include in the forecast for now.


.LONG TERM...(Saturday through Wednesday)
Issued at 325 PM EDT Wed Apr 26 2017

Only small changes were made to the going grid forecast, as the
models are in good agreement and fairly steady. Active weather is
expected through much of the long range forecast.

Showers will be ongoing across Southern Lower Michigan Saturday,
with thunderstorms becoming possible Saturday night through Sunday
night. Widespread rain, could be heavy at times through the weekend.
Showers will continue into Tuesday.

Rainfall totals of one to two inches are likely Saturday night
through Sunday night with locally higher amounts possible.
Temperatures should be fairly close to normal through the long range
forecast period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 141 PM EDT Wed Apr 26 2017

VFR conditions this afternoon should give way to MVFR conditions
this evening or tonight, as showers and thunderstorms move across
the region. IFR levels are possible with any thunderstorms.
Moisture will be on the increase tonight, as 10-15 knot winds with
gusts to 30 knots blow out of the south southwest.


&&

.MARINE...
Issued at 325 PM EDT Wed Apr 26 2017

We are extending the Small Craft Advisory out through 06z Fri
morning with this forecast package. The initial advisory was mainly
for the winds out ahead of the system. We are now to the point that
the winds behind the system on Thursday need to be dealt with. These
will be the strongest Thu afternoon, and the waves will come down
enough finally Thu night.

&&

.HYDROLOGY...
Issued at 325 PM EDT Wed Apr 26 2017

Confidence continues to grow that we will have an increasing flood
risk as we head into the weekend and next week. The GFS, GEM, and
ECMWF all have been indicating a pattern that will produce
significant rainfall for our region, likely on the order of 2" to 3"
or more. When that much rain falls across the entire reaches of the
major basins - Grand, Muskegon, and Kalamazoo - there will be some
significant rises. Trends will continue to be monitored.

Smaller rivers and streams are going to be highly responsive to this
type of rain, with abrupt rises possible. Residents along smaller
rivers and streams should be aware of the risk for these types of
changes late into the weekend and early next week.

At this point it is too early to tell exactly how high the rivers
will get, but flood stage may be exceeded at many locations
potentially.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 2 AM EDT Friday for LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...63
AVIATION...63
HYDROLOGY...Hoving
MARINE...NJJ



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