Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 180727

Area Forecast Discussion
National Weather Service Grand Rapids MI
327 AM EDT Fri Aug 18 2017

Synopsis/Short Term/Long Term/Marine

Issued at 327 AM EDT Fri Aug 18 2017

A breezy and cooler day with considerable clouds is in store
thanks to a low pressure system centered near Sault Ste Marie.
Although that system lifts out later today, another fast moving
disturbance may bring a few showers tonight into early Saturday,
mainly south of Interstate 96.

High pressure will provide mostly clear skies and warm
temperatures Saturday and Sunday, and probably into Monday as
well. Our next good chance of showers and storms is Monday night
and Tuesday with a strong cold front.


.SHORT TERM...(Today through Sunday)
Issued at 327 AM EDT Fri Aug 18 2017

Moist cyclonic low level flow will result in considerable
stratocu clouds today, although some breaks likely developing this
afternoon. The best chance of seeing some sunshine later in the
day, per low level rh progs, is south of I-96 and west of Hwy 131.
Most of the current light rain shower activity should end by
afternoon with perhaps the exception of U.S. 10 northward.

Another fairly amplified nrn stream shortwave will dive through
the region late tonight and early Saturday. Guidance is in good
agreement in showing the best qpf passing just south of Lwr MI
where better moisture will exist. However chance/sct pops still
warranted for areas along/south of I-96 and even a thunder threat
as guidance indicates 500 to as much as 1000 j/kg of MUCape.

Although clouds and a few showers/storms may still be present
south and east of GRR early Saturday, they should be gone by mid
morning. Subsidence/drying in the wake of the departing shortwave
will then lead to mostly sunny/pleasant conditions for the rest of
the day. Sunday looks sunny as well, and about 5 degrees warmer,
as southwest flow/weak waa develops at H8.

.LONG TERM...(Sunday night through Thursday)
Issued at 327 AM EDT Fri Aug 18 2017

The focus during the long term will be the cold front moving through
the Great Lakes Monday into Tuesday. That`s the period that has the
highest chance of seeing showers/storms. The gfs and ecmwf are in
pretty good agreement with the timing and track of the front and
both models show strong upper support in the form of a short wave
moving through the region. The upper flow will be transitioning to a
trough over the Great Lakes from the quasi zonal flow that we`ll see
over the weekend. There`s a decent shot of cooler air behind this
front that should see h8 temps fall from +16c ahead of it to +6
behind it. Shear values around 40 kts point toward a few
strong/severe storms potentially. A 30 kt llj is also progd to be


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 136 AM EDT Fri Aug 18 2017

Moisture associated with low pressure moving across Lake Superior
will result in a few showers this morning. MVFR cigs will slowly
move south too. Cigs will increase this afternoon as high pressure
builds into the Great Lakes and winds will diminish toward 00z.


Issued at 327 AM EDT Fri Aug 18 2017

Current buoy reports are showing 5-7 footers so the ongoing Small
Craft Advisory/Beach Hazard Statements are on track. Winds and
waves will stay up most of today, with a diminishing trend
beginning around 5 PM and waves falling below advisory criteria
by about 9 PM.


Issued at 329 PM EDT Thu Aug 17 2017

Localized rainfall amounts of 0.50" to 1.00" over the last 12 to 24
hours will not be enough to cause basin-wide concerns on area
rivers. Additional light rain for portions of the region Saturday
will not be cause for concern. Rivers will continue to remain well
within their banks through the weekend.


MI...Beach Hazards Statement through this evening for MIZ037-043-050-

LM...Small Craft Advisory until 9 PM EDT this evening for LMZ844>849.



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