Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211755

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


Issued at 330 AM EDT Mon May 21 2018

Low pressure moving northeast from Missouri will bring widespread
rain and cool temperatures today and tonight. Clouds will linger
in the wake of this system on Tuesday then sunny and warm weather
is expected Wednesday and Thursday. Memorial Day Weekend starts
out warm and humid with scattered showers and thunderstorms, then
ends up dry for the holiday.


Issued at 1122 AM EDT Mon May 21 2018

Rain is overspreading the area from the southwest, with embedded
thunderstorms expected to stay mainly south of I-94. Evaporative
cooling is expected with rain falling into surface air with
dewpoints in the 40s and 50s, which will keep temperatures in the
upper 50s to lower 60s for much of the day. Mid-level moisture
convergence will depart this evening allowing for a break in the
rain. MUCAPE values around 500 J/kg from parcels between 925 and
850 mb are still expected overnight as the main upper level trough
approaches. Scattered thunderstorms may develop then, mainly
near/south of I-96. Severe potential appears to be quite low due
to cold and stable air at the surface.


.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EDT Mon May 21 2018

Big slug of rain headed our way today as shortwave ejects
northeast from the Plains and draws up PWATs over 1.5 inches via
30kt low level jet. Will have categorical pops spreading in from
southwest to northeast this morning, then expect a persistent cool
rain this afternoon and evening which could even be heavy at
times once the higher h8 theta-e air arrives from the south.

Widespread rainfall amounts of one half to one inch are expected,
although some streaks of locally heavier amounts over an inch are
quite possible. MUCape progs argue against much coverage of tstms
this afternoon and evening, but will continue to carry a slgt
chance as some weak elevated instability does come through later
in the day and evening.

Heaviest/widespread rain departs after midnight, put expect some
lingering scattered showers and areas of drizzle/fog. Low clouds
will linger most of the day Tuesday, although some clearing may
develop later in the day especially over nrn and wrn sections.

Prospects for sunshine are much better on Wednesday (after patchy
morning stratus/fog dissipates) with drier air mass and sfc ridge

.LONG TERM...(Wednesday night through Sunday)
Issued at 330 AM EDT Mon May 21 2018

Chances for rain aren`t great during the long term, but probably
highest over the northwest cwa. Initially, high pressure over
Michigan will drift east late Thursday. Developing low pressure over
the Plains will generate showers/storms along the Mississippi valley
as the LLJ strengthens. An upper trough moving across the northern
tier of states will push the sfc low eastward and the precipitation
ahead of it will move toward the cwa.

The highest chance of precipitation looks to be late Saturday as the
trailing cold front moves across the cwa, but pops will linger into
Sunday as the upper support moves through.

Highs through the period will be in the 76 to 81 range.


.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 330 AM EDT Mon May 21 2018

May be dealing with areas of fog over Lake Michigan over the next
48 hours before high pressure delivers a drier air mass on
Wednesday. Otherwise winds and waves expected to remain below
advisory criteria.


Issued at 1127 AM EDT Sun May 20 2018

Many rivers especially in southern Michigan are running much above
normal for this time of year, with lowland nuisance flooding still
occurring at several points. Most river levels are falling.
Showers on Monday have the potential to produce around a half inch
of rain on average in southern Michigan, though it wouldn`t be
surprising if some locations picked up closer to an inch.
Depending on the basins where any heavier rain may fall, this
could prolong the nuisance flooding. The middle part of the week
will be dry, then rain chances return toward the end of the week.




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