Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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632
FXUS63 KGRR 220402
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1202 AM EDT Tue May 22 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
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.

&&

.UPDATE...
Issued at 1120 PM EDT Mon May 21 2018

Light showers continue to progress to the east across the forecast
area in advance of the upper shortwave which is to our west in
Wisconsin. Expect scattered showers to continue through the night.
In addition, the models continue to indicate the chance for a few
thunderstorms in the south between 06z and 12z. A weak low level
jet will slide across Southern Lower Michigan during that time
frame and isolated thunderstorms will be the result. Any storms
will remain below severe levels given weak instability. Threat
for storms will mainly be in the southern two rows of counties in
the GRR forecast area or south of BIV/GRR/LAN.

Moist air mass is in place with winds that are light. A low will
slide into the area overnight with a very baggy surface gradient.
Thinking areas of fog are certainly possible along and south of
I-96. The threat for dense fog is up for debate, but not out of
the question certainly. A marine dense fog advisory continues for
most of our nearshore waters. As the winds shift to the west late
tonight, expecting the fog to thicken up over the lake and
potentially advecting inland along the shore into Tuesday morning.

&&

.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
through.

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

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
time.

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 06Z TAFS through 06Z Tuesday night)
Issued at 1145 PM EDT Mon May 21 2018

Conditions will deteriorate to IFR and then primarily LIFR
overnight through mid morning Tuesday due to deteriorating cigs
and visbys and showers and fog. Conditions will slowly improve to
MVFR Tuesday afternoon as cigs/visbys improve. Further improvement
from MVFR to VFR will occur during the mid to late evening hours
Tuesday.

&&

.MARINE...
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.


&&

.HYDROLOGY...
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
weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Dense Fog Advisory until 10 AM EDT Tuesday for LMZ844>848.

&&

$$

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



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