Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191747
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
147 PM EDT MON SEP 19 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Mon Sep 19 2016

A warm day is expected today with high temperatures rising into the
78 to 83 degree range across much of the area. Normal highs this
time of year are in the upper 60s. The warm air is flowing into the
region on southerly winds ahead of a cold front. The front is
expected to touch off scattered showers and thunderstorms from late
afternoon into this evening. The best chances for storms will be
this evening across West Central Lower Michigan up towards
Ludington. The front will sag south tonight and weaken. Showers and
storms will come to an end overnight. A dry day is expected Tuesday
with highs once again up near 80.

&&

.UPDATE...
Issued at 1123 AM EDT Mon Sep 19 2016

Severe potential continues to look low, but if it were to occur,
it should be across Central Lower during the early evening hours.

Instability will peak by late afternoon with the front approaching
Central Lower at that time. The best low level convergence
continues to be progged to our west as the front gradually
weakens as it heads our way. Feel the window for stronger storms
will be a short one...generally between 5 and 10 PM. Thereafter we
will lose the strongest instability and storms will gradually
diminish by late evening.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EDT Mon Sep 19 2016

Main concern in the short term pertains to storm chances this
afternoon and evening, storms again Wednesday afternoon and fog this
morning.

Regarding today`s convective threat, overall is not too impressive
given a lack of instability and better dynamics. The upper wave
driving the front is well to the north across the Lake Superior
region. Instability is not impressive either, likely peaking in the
500-1000 j/kg range. The one factor that is quite noteworthy is the
0-6km bulk shear values on the order of 40-60 knots for areas along
and north of I-96.

Expecting some storms to develop along the front this afternoon and
evening, drifting south with time. The strongest storms will likely
be towards evening up near Ludington. Not out of the realm of
possibilities we see an isolated severe storm given the strong
shear. Damaging winds will be the main threat. The storms should
become even more scattered and dissipate overnight as the boundary
sags south.

Storms Wednesday afternoon will likely be confined to West Central
Lower Michigan once again up towards Ludington. A little bit more in
the way of instability is noted, over 1000 j/kg. Deep layer shear
is much weaker however when compared to today.

As for the fog this morning, thinking patchy is a good way to
describe it. Winds are increasing just off the surface as the
gradient builds in and this will likely keep the fog largely in
check. Visibilities are bouncing up and down due to the wind aloft.
Thickest fog will be in the southeast CWA where the wind builds in
last.

.LONG TERM...(Wednesday night through Sunday)
Issued at 330 AM EDT Mon Sep 19 2016

Chances for pcpn during the long term aren`t that great and mainly
center around a slow moving cold front will sag south across the
cwa.

Initial zonal flow aloft will transition toward a ridge over the
Plains and a trough across the East Coast. A sfc low moving
northeast across Wisconsin will provide the initial push for the
cold front to move south Wednesday night and Thursday. Highest pops
will be over the northwest cwa. It`s more than possible that the
southern cwa remains dry through much of this period.

A large area of high pressure over Ontario will build south and the
cold front will slowly move south on Friday across the cwa and kind
of wash out as it goes. The western part of the front across the
Wisconsin will begin to become active Friday night and Saturday as
it moves north in response to a Plains low. But the lack of any real
moisture over the cwa suggests that we may remain dry through the
weekend as is reflected in the low pops.

Above normal temperatures are expected through the period with highs
around 80 Thursday slowly falling to highs in the lower 70s by
Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 147 PM EDT Mon Sep 19 2016

VFR conditions should prevail into this evening then scattered
showers and thunderstorms will bring isolated MVFR and IFR but
coverage will be low, so the TAFs will have VSH or VCTS. The
storms should be gone by 06Z.

Winds will be southwest today with gusts to 20 knots at times
then blo 10 knots tonight.

&&

.MARINE...
Issued at 1123 AM EDT Mon Sep 19 2016

Tweaked the headlines a bit. First off I removed the areas south
of South Haven. With the flow more southerly, this area should not
see small craft advisory conditions.

Also, extended the current advisory into the overnight period,
north of South Haven. Winds are only expected to diminish slowly
as the front moves in tonight, and hazardous waves will not
subside until close to daybreak Tuesday.


&&

.HYDROLOGY...
Issued at 1129 AM EDT Sun Sep 18 2016

The river advisory continues on the Sycamore Creek at Holt this
morning. River obs are reflecting that rises are beginning to
slow, which signals that the site is nearing its peak. The river
should top out around sunset and will begin falling late this
evening. Dry conditions will allow the river to continue to fall
through Monday.

A frontal boundary will bring additional rainfall Monday night.
Overall amounts are expected to be light (around 0.25" or less),
but brief bouts of locally heavy rain cannot be ruled out.
Flooding concerns are low at this time with a side note: Due to
near/above normal river levels, basins affected by any heavy rain
could see quick response times, mainly consisting of within bank
rises.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...Small Craft Advisory until 6 AM EDT Tuesday for LMZ845>849.

&&

$$

UPDATE...JK
SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...Ostuno
HYDROLOGY...JAM
MARINE...JK



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