Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251930
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EDT Tue Apr 25 2017

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

.SYNOPSIS...
Issued at 330 PM EDT Tue Apr 25 2017

The dry and warm air mass that has been over the area the past few
days will gradually come to an end through Wednesday evening as a
system slowly pushes in from the West. This system will have waves
of low pressure move along it, and bring periods of showers and
storms through Thursday afternoon. There is a small chance of severe
weather, however heavier rainfall will likely be a better threat.

A mainly dry period can be expected from Thursday night through
Friday night as the area will be in between systems. Another bigger
system that will have plentiful moisture from the Gulf will move in
over the course of the weekend and bring more rain to the area.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 330 PM EDT Tue Apr 25 2017

Our main issue in the short term forecast period is determining pcpn
trends through the period, and hazards associated with any storms
that will push through the area.

We will start to see some chances of rain showers move in across the
NW corner of the CWFA late tonight and Wed morning. This are will be
on the far Ern periphery of the best moisture transport moving
across WI and IL tonight with a 35 knot low level jet associated
with a short wave moving NNE. Instability in our area is pretty much
zero, so we do not expect thunder through Wed morning.

We expect that a few showers/storms could pop up Wed afternoon
across the area. A better chance of more widespread showers/storms
will come in mid-late evening across the Wrn half of the area.
Instability builds Wed afternoon with dew points approaching 60
degrees, and sfc temps in the 70s across most of the area that does
not see clouds/rain showers in the morning. Sfc based CAPE`s look to
approach 1000 j/kg across the SE portion of the area which could
approach 80 degrees. The limitation is that forecast soundings
indicate that we could be capped around 8-10k feet. If something was
to develop, deep layer shear values are fairly impressive, in the 40-
50 knot range. This could provide some severe weather with strong
winds or large hail.

A more organized line of showers/storms comes through mid-late
evening into the overnight hours. A fairly strong short wave moves
up Lake Michigan, and looks to have a 50+ knot low level jet
associated with it. Instability in general will be on the wane some.
This looks like the biggest threat would be a swath of heavier rain
in a short period of time.

The Wed night wave will move through, and the cold front will
progress east a bit into the central portion of our area. At this
time, it looks like the main wave moves through, and brings another
low level jet across the area. The models have a look to them of
another swath of heavier rain with limited instability available.
The swaths of heavier rains will be tough to pin down at this time,
but there are good signals they will be around the area. We should
see all the rain move out by Thu evening as the entire system lifts
out of the area by then.

.LONG TERM...(Friday through Tuesday)
Issued at 330 PM EDT Tue Apr 25 2017

Active weather pattern will continue into the long term period with
one main low pressure system forecast to move through the area
between Saturday and Monday. The heaviest rain looks to be during
the Saturday night through Sunday night period with 850mb dew points
surge to around +10C. The ECMWF also shows solid 850mb moisture
transport during this time as well. Heavy rain is quite possible
over the weekend with periods of showers and thunderstorms. One to
two inches of rain appears possible at this point, but we will
refine that as the event gets closer.

Friday into Friday night will be somewhat of a quieter period as we
will be in between systems. The weekend system is an upper low that
pivots through the area, so we are looking for plenty of cloud cover
along with periods of rain. Temperatures will be seasonable with
highs in the upper 50s to lower 60s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 217 PM EDT Tue Apr 25 2017

VFR weather is forecast the next 24 hours with cloud bases at or
above 4000ft through the period. There will be some times, namely
this evening and again into the midday hours of Wednesday, when we
see ceilings around 4,000-5,000ft. Otherwise, mid and high clouds
are expected with bases at or above 10,000ft.

Winds will be from the south-southeast around 10 knots this
afternoon and evening. An increase in wind is expected late
tonight and into Wednesday, picking up into the 10-20 knot range
with gusts to around 25 knots.


&&

.MARINE...
Issued at 330 PM EDT Tue Apr 25 2017

Winds will be on the increase tonight and remain up through
Wednesday as the gradient ahead of the incoming system presses into
the area. The winds will be nearly parallel to the shoreline, or
even offshore a bit, which should limit the waves some. Also, the
warmer air over the cooler waters will limit wave generation also.
We will make a last minute decision at press time whether it will
require a Small Craft Advisory or not.

&&

.HYDROLOGY...
Issued at 330 PM EDT Tue Apr 25 2017

In spite of conditions drying out over the last few days, rivers
remain higher than normal across the area and a few decent
widespread rain events may prime them once again for a flood risk.
The Muskegon and Grand River basins in particular are running at
about the 75th percentile for this time of year. Rainfall amounts
Wednesday into Thursday could be locally heavy and the western
reaches of those basins may experience rises. Additional significant
rain this weekend over especially the central and western reaches of
those basins may cause some above bankfull rises and we will have to
monitor closely for a flood risk on the main stem rivers.

&&

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

$$

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


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