Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191751

Area Forecast Discussion
National Weather Service Grand Rapids MI
151 PM EDT Wed Jul 19 2017


Issued at 330 AM EDT Wed Jul 19 2017

A weakening cold front will slip south through the area today with
widely scattered showers and storms. Many areas will remain dry.
Tonight into Thursday the front will remain across the Southern
Great Lakes as a warm front and will provide a focus for showers
and thunderstorms. Showers and storms look to be most prevalent
late tonight into Thursday across southwestern portions of the
state. A few more showers and storms are expected on Friday as the
warm front remains nearby. It will be warm and increasingly humid
with highs in the 80s each day.


.SHORT TERM...(Today through Friday)
Issued at 330 AM EDT Wed Jul 19 2017

Main focus of short term was on chances for showers and storms
with a frontal boundary nearby throughout the short term period.

Feel the threat of showers and storms today is fairly low given
the day will start off with a fair amount of cloud cover.
Instability should build across areas along and south of I-96
however with the threat of a few storms in this area this
afternoon and evening. Not expecting severe today although a
strong storm cannot be ruled out if we can get some sunshine
across the south.

Tonight, the expectation is a MCS will roll our way out of
Wisconsin and Northern Illinois. All of the models have some sort
of low level jet impinging on our area late. So, a MCS at the end
of its life cycle will be trying to move in. Cannot rule out a
severe threat given the strength the MCS will likely have upstream
and the fact that the NAM is showing 40-50 knots at 850mb/s at 12z

Showers and storms will linger into Thursday morning which will
likely temper our instability for Thursday afternoon. The low
level jet peels away as well so, expect precipitation to trend
down in the afternoon.

Wend dry Thursday night with the front sagging south and weak high
pressure building in. Friday afternoon we may see an increase in
showers and storms once again with the frontal boundary draped
just off to our southwest.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM EDT Wed Jul 19 2017

The unsettled and potentially active weather at the end of the short
term will continue into the beginning of the long term. The frontal
system that pushes through on Thu will be making a return to the
north Fri night. This occurs as a short wave in the zonal flow aloft
approaches, and a stronger low level jet pushes a surge of warm and
moist air over the area. An MCS is likely, with the exact track
still a bit uncertain.

Sat is a bit interesting with more showers/storms possible, most
likely late afternoon/evening. The interesting part is that we will
see somewhat of a phasing of two waves, one from the West and
another from the Northwest. There will likely be a break in the rain
after the Fri night MCS moves through. Another low level jet will
likely nose in with the srn wave, before the Nrn wave drops in. This
could become more interesting if the Nrn stream wave moves in
quicker and helps strengthen the Srn wave.

The stronger and more widespread storms should move out Sat night as
the sfc lows move by early Sunday. The NW upper trough will then
linger over the area Sun and early Mon. This will keep a chance of
rain in until later Mon when the upper trough axis moves east. Later
Mon through Tue should then be dry and seasonably cool as upper
ridging and associated Canadian sfc ridging builds over the area.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 151 PM EDT Wed Jul 19 2017

High probability for VFR conditions through 00Z. Also anticipate
VFR to MVFR ceilings from 00Z - 06Z for most terminals. An area of
showers and thunderstorms is expected to move eastward into
Southern Lower Michigan after 06Z with thunderstorms possible well
into the day Thursday. There is a small possibility that wind
gusts with these storms could exceed 40 knots, most likely in the
09Z - 13Z time frame.


Issued at 330 AM EDT Wed Jul 19 2017

Overall a fairly light wind regime the next couple of days. The
exception to the rule however will be late tonight into Thursday
morning. The NAM has a strong low level jet forecast that will
likely bring a short lived bump in the wave field over the lake.
For a time, southwesterly winds of 15 to 25 knots may develop.
Could see a brief period of 2 to 4 foot waves. Otherwise, waves
will be in the 1-3 foot range or less.


Issued at 325 PM EDT Tue Jul 18 2017

An active period is shaping up for the second half of the week.
Although most rivers are running near to slightly above average,
some may have considerable rises into the weekend with multiple
opportunities for thunderstorms. Favorable ULJ and LLJ dynamics will
be in play along with a weak surface boundary floating through the
region, coincident with some high PW values that may reach 2.00"-
2.25" at times. Any convection that develops could contain
torrential downpours with very efficient rainfall rates in this
environment. Exact placement is a tough call until the pattern is
captured by the high res convective allowing models. Interests along
area rivers and streams should pay close attention to trends later
this week.




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