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Area forecast discussion
National Weather Service Grand Rapids Michigan
1001 PM EDT Thu Jun 21 2018

Latest update...

issued at 310 PM EDT Thu Jun 21 2018

A large area of low pressure will slowly move across the Northern
Ohio valley during the next couple of days. Chances for rain and
perhaps a thunderstorm will increase tonight from south to north and
then shift eastward Friday. Rain chances will decrease Saturday
night as the low moves east. Highs will be around 70 Friday and
climb into the 80s early next week.


issued at 1000 PM EDT Thu Jun 21 2018

The band of rain which gave Berrien County the heavy amounts
earlier has been diminishing and shearing out while moving
northeast and encountering drier air and the confluent upr lvl
flow. However additional bands of rain are expected to develop
overnight on northeast periphery of the upr low, and several of
the hi res cams show a fairly healthy band of rain pivoting up
toward the I-94 corridor around daybreak. Our going fcst has pops
ramping up to likely in that area after 09-10z, so no fcst changes
needed at this time.


Short term...(this evening through Saturday night)
issued at 310 PM EDT Thu Jun 21 2018

Main item of interest is a large low seen on visible imagery over
far northwest Missouri. A band of showers and storms pivoting around
the low extend from western Wisconsin south through Kentucky. Some
of this rain has produced localized flooding in northern Illinois
where precipitable water values approach 2 inches. As the low moves
east, that band of rain/storms will move north across the southern
counties. Forecast values of pwat climb to around 1.5 inches south
of I-96 Friday and so we'll need to watch out for the heavy rain
potential. The southern cwa has already received around an inch of
rain recently and additional heavy rain could lead to flooding, as
mentioned in the Hydro section below. I don't see the northwest cwa
getting much rain from this system, but the east could see some rain
since the forecast track of this low will start to move northeast
once it gets to Ohio. The models have been consistent on the track
of the low for several model runs and confidence is fairly high that
we'll see rain over much of the cwa from late tonight through
Saturday. Rain chances will diminish Saturday night as the low moves
away from Michigan.

Temperatures will be cool for mid June with highs around 70
tomorrow, but a rebound will occur Saturday and temperatures will
climb into the mid to upper 70s.

Long term...(sunday through thursday)
issued at 310 PM EDT Thu Jun 21 2018

High pressure over the Great Lakes will result in mostly dry weather
Sunday through Tuesday, model are hinting at a decent chance of rain
Tuesday night through Wednesday as another low moves from the plains
east across lower Michigan. Both the ECMWF and GFS are in
surprisingly good agreement with the track of the sfc low and the
accompanying upper trough. Timing wise, the ECMWF is a bit quicker,
but the result is basically the same. We'll have likely pops during
this period for showers/storms.

Highs during the period will be in the lower to mid 80s.


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 745 PM EDT Thu Jun 21 2018

While bands of heavy rain are not too far to our southwest, we
remain VFR with a feed of dry low level air coming in from the
east. That dry air will make it difficult for the bands of rain to
spread north, so have held off on bringing sub-VFR conditions
into the area until Friday afternoon. Will feature prevailing MVFR
conditions after 16-18z Friday, although IFR vsbys are possible
if/where bands of heavy rainfall develop.


issued at 310 PM EDT Thu Jun 21 2018

East winds 10 to 15 knots will produce waves 1 to 2 feet tonight and


issued at 1108 am EDT Thu Jun 21 2018

River levels are running near normal, and are steady or slowly
falling. No flooding is expected.

Periods of rain will be possible today through Saturday. Scattered
to numerous showers and thunderstorms may develop. Generally expect
less than an inch of rain, with locally heavy rainfall possible with
the storms. This may result in localized flooding where storms form
and train over the same locations.


GRR watches/warnings/advisories...



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