Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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748
FXUS63 KGRR 221758
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
158 PM EDT FRI JUL 22 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 310 AM EDT Fri Jul 22 2016

An area of high pressure will control the weather today in
Southwest Lower Michigan. This feature will act to keep the
weather hot and humid. A thunderstorm or two could develop today
but most locations should remain dry. Not much change occurs as we
go through Saturday...but a wave of low pressure moves in for
Saturday night into Sunday night. Thus the risk for thunderstorms
will increase.

&&

.UPDATE...
Issued at 1050 AM EDT Fri Jul 22 2016

I have cleared the sky sooner and have lowered the risk of an
afternoon thunderstorm near I-94 this afternoon. This should allow
highs to get hotter than we were thinking earlier.

Two events working together have acted to dry the atmosphere over
us today. First the MCS yesterday and last night has well mixed
the atmosphere over us and brought in dry air through a deep layer
that will remain in place through tonight. The second part of this
is a weak but significant Canadian cold front slowly dropping south
across Southwest Michigan this afternoon. The front is currently
near Route 10. This air is not really cooler, but it is much
drier. Dew points currently in the lower 60s north of the front,
but afternoon mixing will lower those dew points into the 50s. So,
even though that front will bring surface convergence into our
central and southern CWA, the air is so dry it is hard to imagine
we would get anything more then isolated thunderstorms near and
south of I-94. Even that is questionable.

As for the heat advisory, I will continue it for this afternoon
but we may not reach 100 degrees at most locations as we were
thinking since dew points will be lower thanks to the MCS
yesterday and last night. Even so, we are expecting highs inland in
the mid 90s afternoon, this is the hottest air we have seen since
the summer of 2013. Lows last night were in the lower to mid 70s
so there was not much relief from the heat then either. So for
these reasons I will continue it this afternoon.

&&

.SHORT TERM...(Today through Sunday)
Issued at 310 AM EDT Fri Jul 22 2016

Will maintain the heat advisory. As the convective complex in
Illinois shifts south...the clouds here in MI will diminish
supporting increasing sunshine. The low level thermal ridge is in
place. Thus...we are more likely to see temperatures climb into
the 90s today as compared to Thursday. This thermal ridge remains
in the area Saturday. As a result we may need to extend the
headline. However...surface dewpoints are forecasted to fall of on
Saturday...somewhat offsetting the heat.

Will hold onto a low chance for storms across southern parts of
the CWA for today. The atmosphere remains unstable...with new
storms developing around Detroit. There is not large scale lifting
mechanism around to trigger widespread storms. Thus only a
localized storm or two appears possible.

Its hard to say with a lot of confidence how much if any storms we
see for Saturday night into Sunday. A mid level shortwave does
push into the Great Lakes region...but its forcing may not arrive
til after Sunday. There is a low level jet shown to arrive
Saturday night into Sunday. So with building instability and some
lift...we could see an increase in the thunderstorm activity then.
Will hold onto the relatively high pops then.

.LONG TERM...(Sunday night through Thursday)
Issued at 310 AM EDT Fri Jul 22 2016

The long term portion of the forecast will feature chances of storms
at the beginning and end of the period, with a quiet period in
between. We expect that temperatures will remain rather warm through
the period.

We will see chances for showers and storms from the end of the short
term linger into the long term beginning on Sun night. A strong
enough short wave will beat the ridge down enough over the area that
a cold front will slip through by Mon morning. This front will sink
south of the area on Mon, and take with it the core of the heat and
instability. Until it moves through, a chance of storms will remain
Sun night.

Drier weather will then settle in from Mon through most of Wed
as high pressure at the sfc builds through the state. Temps will drop
down a notch or so, but will remain very warm with max temps
expected to be well into the 80s. Heights will have lowered some,
but the noticeably cooler air will stay north of the area.

We will see rain chances increase then as early as late Wed, but
more likely Wed night into Thu. A short wave embedded in the
somewhat more zonal flow is expected to approach the area on Thu.
This will draw better moisture back up into the area from the
south.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 158 PM EDT Fri Jul 22 2016

VFR weather is expected the next 24 hours. Skies are expected to
be mainly clear. Winds will be westerly at 8-12 knots through this
afternoon, but become light and variable towards sunset. Nearly
calm winds are anticipated tonight.

&&

.MARINE...
Issued at 310 AM EDT Fri Jul 22 2016

The storms overnight resulted in strong and variable wind
conditions. The waves responded...especially over the southern end
of the lake and briefly came up to 5 feet. With no additional
strong/severe convection forecasted today...the waves will likely
settle down through the day. At this time will hold off on a SCA
and Beach Hazards. Will take another look prior to 6 am...and may
issue headlines if the waves do not diminish.


&&

.HYDROLOGY...
Issued at 1233 PM EDT Fri Jul 22 2016

Thursday rainfall amounts ranged from a tenth to three-quarters of
an inch across the whole area... a welcome sight for many.
Sunday`s thunderstorms will likely produce a similar range of
amounts, although locally higher amounts could occur if the storm
mode turns out to be more of a multicell cluster rather than
progressive linear like Thursday.

&&

.GRR Watches/Warnings/Advisories...
MI...Heat Advisory until 7 PM EDT this evening for MIZ044>046-050>052-
     056>059-064>067-071>074.

LM...None.
&&

$$

UPDATE...WDM
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...NJJ
AVIATION...Duke
HYDROLOGY...CAS
MARINE...MJS



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