Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 201930
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EDT WED JUL 20 2016

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

.SYNOPSIS...
Issued at 256 PM EDT Wed Jul 20 2016

Hot and humid weather will moving 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.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 256 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 prolong expose 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 256 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
Monday.

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

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 146 PM EDT Wed Jul 20 2016

VFR weather is expected this afternoon and tonight. FEW/SCT
cumulus development is possible this afternoon with bases around
5000ft. Otherwise, the only cloud will be some cirrus debris
clouds from upstream thunderstorms through this evening. The
cirrus will have bases at or above 18,000ft.

Tonight upstream thunderstorms may lower and thicken the cloud
cover at times, but VFR conditions will continue. The weather may
become more active Thursday morning when some model data indicate
a few showers and storms drifting southeast through the area.
Confidence is not high in this precipitation so only have VCSH in
the TAF for Thursday morning (14z-18z).

&&

.MARINE...
Issued at 256 PM EDT Wed Jul 20 2016

Choppy waters, but below SCA criteria expected through Thursday
evening before a front drops in causing winds to relax somewhat.

&&

.HYDROLOGY...
Issued at 256 PM EDT Wed Jul 20 2016

&&

.GRR Watches/Warnings/Advisories...
MI...Heat Advisory from 1 PM Thursday to 7 PM EDT Friday for
     MIZ044>046-050>052-056>059-064>067-071>074.

LM...None.
&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Duke
AVIATION...Duke
HYDROLOGY...EBW
MARINE...JK


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