Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191921

Area Forecast Discussion
National Weather Service Grand Rapids MI
321 PM EDT Sat May 19 2018

Synopsis/Short Term/Long Term/Marine/Hydro

Issued at 320 PM EDT Sat May 19 2018

Showers and thunderstorms will be possible into this
evening, mainly east of Battle Creek and south of Lansing, before
drier weather pushes in behind a frontal boundary tonight. Areas of
fog are possible overnight as soils remain very saturated from
recent rainfall. A frontal boundary will remain near the border with
Indiana Sunday and Monday, providing a chance for showers each day.
Temperatures will remain below normal the next few days, with highs
in the 60s.


.SHORT TERM...(This evening through Monday night)
Issued at 320 PM EDT Sat May 19 2018

Frontal boundary (denoted by west wind shift occuring across West
Michigan) will work east across Lower Michigan this afternoon and
early this evening as low pressure continues to track towards SE
Michigan. Ahead of the front, SPC mesoanalysis shows about 1000 J/Kg
of SB CAPE has built within peaks of sunshine east of Battle Creek
and south of Lansing (roughly). This area will be the primary region
for convective initiation as we head through early evening as the
frontal boundary works through. Could see a briefly strong updraft,
producing 40 mph winds and small hail at best, but storms should be
pulsy and short-lived with little shear to organize. Areas behind
the front (including Grand Rapids) are expected to remain dry for
the remainder of today. Front should work into the Detroit-area by
8PM, providing dry weather for the second half of the evening for
West Michigan.

Upper trough working across Manitoba and Ontario will push another
cold front down into Lower Michigan tonight, before it stalls just
south of the MI border early Sunday morning. Drier air moving in
aloft and stable thermal profiles within moist layer from surface to
H850 will limit potential for precipitation. Will maintain dry
forecast through the overnight hours, but would not be surprised to
see a few sprinkles associated with the frontal boundary as it drops
southward. Areas of fog may form tonight, especially near/south of
Grand Rapids where soils remain more saturated and closer to where
front will settle late and lighter winds will reside. For areas
north of Grand Rapids, north winds behind the front keep atmosphere
mixed much of the night before building high pressure allows
atmosphere to decouple late. This will provide a more limited window
for fog to form with sunrise just after 6AM, and expecting only low
coverage there in favored locations and where winds go light for
several hours.

Waves ejecting out of a loose upper trough over the Plains will then
track through Lower Michigan and the Ohio Valley on Sunday. Stalled
frontal boundary near the MI border will become a focus for showers
and thunderstorms Sunday morning through Sunday evening as waves
ride over the top of it. Appears most activity will stay south of
the area closer to the surface front and instability gradient, but
we could see some showers over southern Michigan along the 925-950mb
frontal slope. Harder to time convective rounds tomorrow, but will
continue to favor the first half of the day and the southern portion
of the forecast area as higher res models key in on a decaying storm
complex from Iowa just brushing the area. Will have to watch
potential for overnight convection to develop further north than
expected and watch track of any MCVs that are generated to see if
increase of pops or expansion northward is warranted. Chances for
thunder continue to look low given only weak elevated instability
along/south of I-94, and will keep thunder mention out of forecast.

May see coverage of rain/showers increase Monday as convergence and
forcing increase along the front and its position is nudged
northward by low pressure lifting into the Ohio Valley. Model
solutions have not been consistent enough with frontal placement,
timing of small waves, and track/timing of surface low to lend high
confidence in forecast Sunday night through Monday night, however,
and will leave chance-range model blend pops in the forecast.

Moisture-laden atmosphere the next few days will keep max temps
below normal and min temps near to above normal.

.LONG TERM...(Tuesday through Saturday)
Issued at 320 PM EDT Sat May 19 2018

To start the period...mid level ridging will be pushing in from the
west on Tuesday.  Heights will continue to rise right through
Thursday. This will support a moderating trend to the temperatures
and generally dry weather.  Above normal temperatures look likely to
arrive during this period.

Models are in relative agreement on tracking a digging mid level
wave in from the northwest for the end of the week.  Southerly low
level winds out ahead of this feature are expected to draw up
abundant moisture.  With decent instability expected to develop
along with strengthening deep layer shear...there is a risk for some
organized convection to develop.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 131 PM EDT Sat May 19 2018

Abundant low level moisture will keep the potential for low clouds
and fog going for the forecast period. Ceilings and visibilities
could increase for a few hours this afternoon...but will likely go
back down tonight as temperatures lower.

The atmosphere was destabilizing at this time...mainly toward KLAN
and KJXN. A few thunderstorms could develop in that region before
heading east during the afternoon. Will need to monitor the risk
for a few showers/storms later tonight tracking in from WI/IL.
Currently the potential appears too low to put them in forecast
for now.


Issued at 320 PM EDT Sat May 19 2018

A frontal boundary will drop through Michigan tonight,
bringing an increase in north winds. Wave heights north of Whitehall
are expected to become hazardous to small craft this evening, and a
Small Craft Advisory is now in effect through Sunday morning. Winds
will turn east and become lighter Sunday afternoon through Sunday
night as the front slips south of the area. Offshore flow will
quickly allow wave heights to subside tomorrow afternoon. Quiet
marine conditions are then expected through Tuesday.


Issued at 320 PM EDT Sat May 19 2018

River levels are high across southern Lower Michigan. The rivers in
central Lower Michigan are near to a little above normal. The
Portage River near Vicksburg is in minor flood, otherwise no river
flooding is ongoing. We are not expecting significant amounts of
rain, with less than an inch of rain expected through the week. This
may lead to a slowdown or pause of the river level falls, but no
new flooding.


LM...Small Craft Advisory from 10 PM this evening to noon EDT Sunday
     for LMZ848-849.



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