Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211929

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EDT Mon May 21 2018

Synopsis/Short Term/Long Term/Marine/Hydro

Issued at 329 PM EDT Mon May 21 2018

Showers and possibly a thunderstorm lingering into Tuesday morning
will end as high pressure delivers clearer skies and warmer
temperatures for the middle portion of the week. It will likely
start feeling more humid toward the end of the week ahead of the
next low pressure system approaching from the upper Midwest.
Sporadic showers and thunderstorms appear possible between Friday
and Saturday night. The passage of a weak cold front and re-
establishing high pressure on Sunday and Memorial Day will likely
provide pleasant weather.


.SHORT TERM...(This evening through Wednesday night)
Issued at 329 PM EDT Mon May 21 2018

Rain and a couple thunderstorms will become more scattered this
evening as the best low-level moisture convergence departs to the
northeast. Will keep chances for precipitation going through the
overnight into the mid morning as scattered showers and perhaps a
couple thunderstorms develop from from lingering low-level moisture
and increasing MUCAPE as the upper level wave and surface low move

Dense fog is possible near the lakeshore especially near South Haven
on Tuesday morning as winds become northwest and advect lake fog

Low level stratus will be slow to mix out on Tuesday and this may
keep the temperatures held back in the mid 60s. Skies will clear out
by Tuesday night and Wednesday. Wednesday looks like the start of a
warm period for the second half of the week.

.LONG TERM...(Thursday through Monday)
Issued at 329 PM EDT Mon May 21 2018

This looks like a very warm pattern for Southwest Michigan. This
could be the warmest afternoon temperatures so far this year
actually. Over the weekend a system on the southern branch of the
polar jet (which will be north of us) will very likely bring showers
and thunderstorms. Details for that our sketchy this far out in

We have a series of strong Pacific storms that will force a mean
upper trough off the west coast into next week.  That in turn forces
a ridge  upstream over the western and central CONUS.  Meanwhile a
closed upper low over the Southwest CONUS get`s Henry Ruled out of
there and tops the upper ridge Thursday (all models like this
track). It then dives southeast into the southern Ontario and the
northern Great Lakes over the weekend. It seems to me the GFS is
weakening this system way to fast. So the ECMWF is very much
preferred by this weekend.

Another thing to watch for next week is the tropical system the GFS
has been forecasting in nearly every run since the 8th at 12z coming
into the Gulf of Mexico around the 25-27th.  Over the pas few days
the ECMWF has picked up on it too.  This could bring a lot of
subtropical moisture into our area the middle of next week.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 155 PM EDT Mon May 21 2018

There is little question all TAF sites will have rain into this
evening and cigs will go IFR by early tonight. As the rain
continues to saturate the boundary layer air this will, by itself,
lower the ceilings. Also, helping the cause for lower ceilings,
there is a solid area of IFR cigs over Iowa and northern Illinois
and southern Wisconsin at 1740z that is moving east with the storm
system. So one way or the other cigs will go IFR by 06z, if not
much sooner at all SW MI taf sites.

There is a chance of thunderstorms, mostly for the I-94 tafs and
more so for the I-69 / I-94 taf (JXN) late this afternoon into
late evening. For that I have VCTS in the AZO, BTL and JXN tafs
this evening.

As for visibilities, I would expect 3sm to 5sm in rain and fog
this afternoon and evening. After the rain ends later this
evening, it is more than possible we could see fog or even dense
fog and winds go light and variable after midnight as the surface
low tracks west to east between I-94 and I-96. I did no put IFR
fog in the tafs for Tuesday morning as I am not sure about it but
it is something to consider.


Issued at 329 PM EDT Mon May 21 2018

Areas of dense fog are possible as winds go light tonight then shift
northwest Tuesday morning. Winds and waves will likely remain below
small craft advisory criteria.


Issued at 329 PM EDT Mon May 21 2018

Total rainfall amounts with the rain through tonight will be less
than an inch for most locations. River forecasts this morning taking
these amounts into consideration produce small rises at the more
flashy locations. Most rivers seem to simply exhibit a slower fall
after the previous rains over the weekend.

Once the rain moves out tonight/early Tuesday, we should remain dry
until at least Friday, if not later. This will allow rivers to
recover a bit more before rainfall returns over the holiday


LM...Dense Fog Advisory from 8 PM this evening to 10 AM EDT Tuesday
     for LMZ844>848.



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