Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221754
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
154 PM EDT Mon May 22 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 AM EDT Mon May 22 2017

For the most part expect periods of showers and slightly cooler
than normal temperatures this week into Memorial Day Weekend.

Today through we may actually see a little sunshine from late
this morning into early this evening before the clouds and showers
move in from the next storm system. That storm is rotating around
the larger departing storm. Meanwhile a more significant storm
develops on the stalled front over the Ohio Valley by Tuesday
evening and rotates northward toward Michigan on Wednesday. If the
storm gets this far north it could be very wet here during the
afternoon and evening. That system will be slow to move out so
expect scattered showers into Thursday before another brief dry
period moves in on Friday. Then another system may bring showers
with it during next weekend.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 325 AM EDT Mon May 22 2017

We are watching two features, the sunshine for this afternoon and
the storm that may impact our area on Wednesday. This one could
be a real soaker of it gets far enough north.

We may actually see some sunshine this afternoon! That is the
result of surface ridging between the departing occluded front
and the in coming developing surface low (currently over
Minnesota). There will be low to mid level warm advection ahead of
that system today so that warming should clear the clouds out by
late morning. It will not last through as a shortwave rotating
around the larger departing storm develops a surface low that
moves into our area tonight and stalls over our area Tuesday.

It stalls over our area thanks to a 100 knot plus jet core
currently digging southward over the western plains on the back
side of the large upper trough over the central United States. As
that digging jet gets closer to the surface front it forms a
surface low over Kentucky early Wednesday morning that gets
captured by the developing upper low over SE Iowa by mid morning
Wednesday. That puts Michigan in deep southerly flow from 850 mb
through 250 mb. That in effect drives that new surface low north
toward Michigan. The only real question is just how far north it
gets (models are not in total agreement on just how far north and
west that storm will go). Still there is enough agreement to go
with likely pops over our Southern CWA. All of the models and most
of the ensembles of the those models as well as previous runs of
those models show the rain getting to at least I-96 by late
afternoon Wednesday.

There is enough mid level instability (surface based on Tue) so
that a few thunderstorms are possible both tonight into Tuesday
night. The system coming up from the south may bring enough
instability with it for more thunderstorms south of I-96
Wednesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 325 AM EDT Mon May 22 2017

Good agreement continues in the models showing a stacked low over
the Lower Great Lakes Wed night.  Deep moisture lingers over the
region, so I`ve raised POPs.  However conditions look better as we
work through the latter portion of the work week.  By Thursday the
low should be moving into the Eastern Lakes, and the showers should
not be as prevalent across SW MI.

Upper ridging gradually moves in by Friday night.  This feature may
not completely clear the region out, because a short wave attempts
to break down the ridge.  So after a mainly dry Thursday night and
Friday, we could see hit and miss showers Friday night and into the
start of the Memorial Day weekend as the upper wave slides through.
At this point the best chance for scattered showers seems to be
south of I-96 with some residual moisture lingering.  Many areas may
stay dry, depending on how strong the upper ridge is able to be.

There is some timing differences by Sunday, but it appears the ridge
slides off to the east, leading to a better chance of rain by then.
Again the ridge`s trends will need to be monitor.  But if trends
continue the eastward movement of the ridge, it would allow a cold
front to push into the Western Great Lakes by Saturday night,
increasing the chance for rain by Sunday.

Temperature-wise we will stay cool through the work week with the
low in the vicinity, but warmer air, closer to normal, will arrive
just in time for the holiday weekend, when temps should push into
the 70s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 153 PM EDT Mon May 22 2017

The main aviation issue this afternoon is the winds as we will
continue to have gusty west winds of 15 to 25 knots through early
evening. Sfc wind speeds will drop below 10 knots after 00z.

Rain showers are expected to push in rapidly from the southwest
later today and tonight, particularly north of a line from AZO to
LAN. Rain will be most persistent/heaviest at MKG and GRR, and
MVFR cigs/vsbys should develop at these terminals by 06Z tonight.
There is even a risk of some IFR later tonight, especially at MKG.

Meanwhile, farther southeast, JXN is expected to remain VFR
tonight into Tuesday with little or no rain. The AZO/BTL/LAN TAFS
are sort of tricky since they`ll be on the srn edge of the lower
MVFR/IFR cigs later tonight and could go either way - or
fluctuate between VFR and MVFR once the rain moves in.

&&

.MARINE...
Issued at 325 AM EDT Mon May 22 2017

At this point I plan on leaving our marine headlines as is. It
would seem to me winds will be lighter tonight into Wednesday.


&&

.HYDROLOGY...
Issued at 125 PM EDT Mon May 22 2017

River systems in Southern Lower Michigan are running above normal,
while river levels in Central Lower Michigan are around normal.
Tonight through Thursday, unsettled weather will bring up to an inch
of rain. This should keep levels elevated, but not expecting
flooding to result. The following forecast is based on observed and
forecast 24 hour precipitation.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 10 PM EDT this evening for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...Meade
HYDROLOGY...63
MARINE...WDM


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