Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 210530

Area Forecast Discussion
National Weather Service Grand Rapids MI
130 AM EDT THU JUL 21 2016


Issued at 330 PM EDT Wed Jul 20 2016

Hot and humid weather will move into the region over the next
couple of days. Afternoon heat index values will rise to around
100 both Thursday and Friday. A very warm a humid night on
Thursday will not allow for much relief to the hot conditions.
Within this stifling air will come periodic thunderstorms. The
best chance of storms will come Thursday evening, but widely
scattered storms will be possible Thursday and Friday. A weak cold
front drops through the area Friday evening which will give the
area a slight break from the very hot and humid weather.

The weekend into next week remains warm with daytime highs mainly
85 to 90, but the humidity should be less. Another period of
scattered storms should occur Saturday night through Sunday night.


Issued at 1021 PM EDT Wed Jul 20 2016

Latest HRRR guidance keeps the area dry through 12z Thursday, but
have maintaied a small pop around Ludington after 5 am to cover
the small chance that some of the late night activity over nrn
Wisconsin will sneak into that area toward daybreak.

Other possibility is new scattered showers or tstms developing in
a north/south fashion over lk mi/wrn lwr mi toward daybreak on
the leading edge/gradient of the incoming higher pwat/theta-e


.SHORT TERM...(This evening through Friday night)
Issued at 330 PM EDT Wed Jul 20 2016

Will issue a heat advisory starting Thursday afternoon and extend
it into Friday evening when front brings some relief. Storm
chances will be within the short term too, with the best chance
coming Thursday evening.

Temps will continue to warm as the upper ridge to our west builds
our way into Thursday. It does flatten out into Friday, but
little relief will occur until a surface front comes through
Friday evening. Many areas across southern lower, and away from
the lake will see low to mid 90s both days, along with dew points
in the 70s. This pushes heat index readings toward or exceeding
100. So will issue a heat advisory for both days. Also being a
factor, will be the very warm and humid night on Thursday, not
allowing people to recover from the Thursday heat, but jumping
right back into stifling heat Friday. We could struggle to reach
the 100 degree criteria in some spots if we see widely scattered
storms, along with debris clouds, but it will be very humid and
uncomfortable, and even dangerous if prolonged exposure occurs.

As for the storms...this is a ridge rider type set up. MCSs will
largely be triggered by nocturnal low level jets. Tonight`s jet
is progged to set up over WI and the U.P. Some of these storms
should slip over the ridge and into the GRR CWA tomorrow morning.
But they should weaken as they get farther removed from the LLJ.
Expect these to remain widely scattered into the area, so will
only have 30 POPs over much of the CWA. The jet weakens through
the day and the storms should too.

Another nocturnal LLJ develops Thursday night and noses into
Lower MI, and should bring our best chance of storms. Some of
these storms could be severe with the bulk shear values around
25-30 knots. At this point it appears the MCS develops over
central/northern lower and sags south through the night.

Some of these storms could survive over the southern CWA into
Friday. But with a weak front dropping in, the storms will push
south.  This front will also give us some relief from the heat.

.LONG TERM...(Saturday through Wednesday)
Issued at 330 PM EDT Wed Jul 20 2016

Heat and humidity will remain in place over the weekend, with the
upper ridge slowly dampening out. The flattening of the ridge will
be due to a shortwave trough moving east along the U.S./Canadian
border. Highs over the weekend will be around 90.

The shortwave will pivot a low pressure system through the Great
Lakes over the weekend with a warm front lifting into the area
Saturday night. A cold front will sweep through the area on Sunday.
The upper system will then move through the area on Monday. Chances
for showers and thunderstorms will exist from Saturday night through

High pressure will build in for Tuesday and Wednesday and have a dry
forecast in place those two days.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 127 AM EDT Thu Jul 21 2016

Dewpoints will increase into the lower 70s today and we may see
some haze develop. There is a potential for thunderstorms this
morning and again tonight. The potential this morning is pretty
low and depends on what happens to the cluser of storms moving
toward Wisconsin currently. If they move southeast across
Wisconsin, it`s possible the outflow from them may produce a storm
or two across Lower Michigan. The better chance of storms will
occur after 03z. Included a vcty comment late in the period.


Issued at 1021 PM EDT Wed Jul 20 2016

Strongly considered issuing a Small Craft Advisory and Beach
Hazard Statement this evening for areas north of Whitehall for
Thursday - due to strengthening southerly flow. However confidence
is still somewhat low on exact behavior/strength of the low level
jet. This will be monitored overnight and headlines may still be
needed for Thursday with the 4 am issuance.


Issued at 332 PM EDT Wed Jul 20 2016

The main hydro concern through the end of the week will be localized
flooding due to heavy rainfall. Showers and storms are expected
mainly Thursday afternoon into early Friday morning. With low
confidence in coverage, the pattern will continue to support some
locations not seeing enough rain and some locations getting too much
too quickly.

Basin-average rainfall of a half inch to 1 inch is forecast, but
strong thunderstorms could produce localized rainfall totals well
over 1 inch. As is typical with summer convection, rainfall totals
will probably vary substantially over short distances.


.GRR Watches/Warnings/Advisories...
MI...Heat Advisory from 1 PM this afternoon to 7 PM EDT Friday for



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