Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 230730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT Fri Jun 23 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 AM EDT Fri Jun 23 2017

A cold front will push south through the area this morning bringing
rounds of showers and thunderstorms. Cooler and less humid air will
filter in behind the front this evening and tonight. Lows tonight
will dip into the upper 50s with highs on Saturday only making it to
around 70 degrees. The cooler conditions will persist into Sunday as
well with highs around 70 once again. After a dry night tonight,
small chances for showers and a scattered thunderstorm return to the
forecast for the weekend.

&&

.SHORT TERM...(Today through Sunday)
Issued at 330 AM EDT Fri Jun 23 2017

We will be dropping the areal flood watch with this forecast
issuance as the heavier rain is winding down across Central Lower
Michigan. This area is covered by Flood Advisories and Flood
Warnings at this time. South of that area, we are expecting more
transient showers and storms as the cold front is finally on the
move south. The front stalled across Central Lower Michigan earlier
in the night resulting in rainfall totals in excess of 5 inches
across portions of Isabella County. Showers and storms will work
south into the I-96 corridor before day break and move south of I-94
around noon. Skies will turn partly cloudy this afternoon as deep
layer RH values below 50 percent late this afternoon and evening.

A quiet night tonight will be followed by a return to more unsettled
weather this weekend. Not expecting a washout, but diurnal
instability will build each afternoon with a chance for showers and
a few storms both Saturday and Sunday. The upper pattern will
feature northwest flow with embedded shortwaves working through the
area.

.LONG TERM...(Sunday night through Thursday)
Issued at 330 AM EDT Fri Jun 23 2017

The long term period starts off with a mid to upper level trough
over the Great Lakes Region.  Models are in decent agreement in
tracking it slowly east Sunday night into Tuesday.  The latest GFS
is quicker with this features departure.  So it looks unsettled with
the cold core system overhead and relatively warmer lakes around.

Mid level heights rise steadily into Wednesday as warm air advection
strengthens.  Will need to monitor the risk for showers and
thunderstorms as the warm front lifts north.

Another mid level low/trough drops out of the Canadian Prairies for
Thursday resulting in height falls for MI. We could see
thunderstorms developing by the end of the period.

I did warm up temperatures slightly during the warm air advection
period as we commonly see values that end up higher than forecasted
in those regimes this far out.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 212 AM EDT Fri Jun 23 2017

A cold front stretches from a little north of KMKG to near KMOP at
06z. Showers and thunderstorms are located along and north of the
front. The front will sag south through the night and be near the
I-94 TAF sites in the 12z to 15z time frame. MVFR ceilings will
become more widespread through the remainder of the night and
possibly even dip into the IFR category towards 12z. Showers and
thunderstorms will gradually drop south through the area between
06z and 12z. The showers and storms should be pushing south and
east of the area around 15z or so. After 18z, VFR weather is
expected.


&&

.MARINE...
Issued at 330 AM EDT Fri Jun 23 2017

Some borderline small craft advisory conditions are possible this
morning as the low level jet is situated over the southern half of
Lake Michigan. The Port Sheldon buoy is at 3.6 feet at the present
time while winds at the MKG ASOS are gusting to 25 knots. Feel these
winds and waves will be short lived this morning and will not issue
a SCA. Winds and waves should remain below criteria tonight and
tonight, with addition borderline SCA conditions Saturday into
Sunday.

&&

.HYDROLOGY...
Issued at 300 PM EDT Thu Jun 22 2017

Locally heavy rainfall and perhaps minor areal flooding appears
possible Thursday evening/overnight. PW values will rise over 1.75
inches this evening as sharply higher-dewpoint air at 850 mb is
advected from the south. These PW values are in the range of
daily records for June in the DTX-area sounding climatology. Higher
moisture content in the column of atmosphere will favor more
efficient rain production. With a tendency for storms to repeat over
parts of the area tonight, it seems reasonable that some locations
could receive over 2 inches of rainfall within a few hours. The most
favored area for significant rain totals Thursday night appears to
be north of I-96.

The tendency for flooding to develop will depend on local antecedent
conditions. While May and early June were rather dry, last week`s
rainfall ranged from 1.5 to locally over 5 inches in areas north of
South Haven, Hastings, and Lansing. In addition, areas along and
north of M-20 saw between 0.5 and 1.5 inches of rain Thursday
morning. Places that saw heavy rain last week will be more prone
to having at least minor areal or street flooding. As for rivers,
the the Flat near Smyrna and the Maple near Maple Rapids are running
high after last week`s rain, and will be less tolerant of any
additional heavy rain that falls within their basins. Above bankfull
rises are possible, so people with interests along those rivers
should monitor the situation.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...MJS
AVIATION...Duke
HYDROLOGY...CAS
MARINE...Duke


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