Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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696
FXUS63 KGRR 221524
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1124 AM EDT Thu Jun 22 2017

LATEST UPDATE...
Marine

.SYNOPSIS...
Issued at 326 AM EDT Thu Jun 22 2017

A cold front currently stretches from western Minnesota south to
northeast Nebraska. A warm front stretched from central Wisconsin
southeast to near Chicago. Thunderstorms were developing over Iowa
and Wisconsin and moving toward Lower Michigan.

The next 24-30 hours will be stormy until the cold front passes
through the state Friday. Several days of cooler weather will
follow with highs in the lower to mid 70s over the weekend.

&&

.SHORT TERM...(Today through Saturday)
Issued at 326 AM EDT Thu Jun 22 2017

Forecast concerns deal with convective trends through Friday
morning.

A robust low level jet continues to generate convection in Wisconsin
as it intersects the warm front that is in the vicinity. This
convection will continue for the next several hours as it moves
across the lake and the northern cwa. The larger MCS...if it makes
it...would arrive mid morning, but instability isn`t all that high
over the cwa yet so we may see some dissipation prior to arrival.

At this point, the higher chance of showers/storms will come this
evening ahead of the approaching cold front. Moderately strong shear
values around 35 knots may aid in some organization this evening as
they approach the cwa. Latest 3km NAM actually shows the convection
dissipating as it crosses the cwa after midnight. So does the WRF-
ARW. The GFS does give us some pcpn tonight, but even that weakens
quite a bit as it moves east. Given that this front is fairly strong
with decent shear, not ready to completely bail on the pcpn yet.

Skies will clear Friday behind the departing cold front. The airmass
will become cooler and drier and highs Saturday will only reach the
lower 70s.

.LONG TERM...(Saturday night through Wednesday)
Issued at 326 AM EDT Thu Jun 22 2017

Northwest upper flow will keep the region cool through Tuesday, with
a slight warm up possible by Wednesday.  A series of short waves
early in the week will produce scattered showers and possible
thunderstorms.

H8 temps hold around +6C Saturday night through Tuesday.  This will
keep us cool, with daily high temps mainly in the upper 60s to lower
70s.  This will be about 10 degrees below normal for this time of
year. The models disagree how long this pattern holds, with the
ECMWF hanging on to the cool northwest flow into Wednesday, while
the GFS becomes more zonal.  Will go optimistic and have Wednesday
warming into the mid and upper 70s.

As for rain chances, there will be several short waves that will be
passing through the mean flow early in the week.  Sunday and Monday
stand the best chance of seeing mainly afternoon scattered
showers/thunderstorms. These should be most commonplace inland from
the lake however, with an afternoon lake shadow likely. Highest POPs
over the eastern CWA.  Again, the models differ into the middle of
the week, but will bank on a more zonal flow and less chance of rain.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 721 AM EDT Thu Jun 22 2017

A slowly weakening MCS is moving east across Wisconsin and
northern Lower. We could see showers/storms through 17z, then a
dry period before more storms develop late this afternoon across
the northern taf sites and eventually this evening over the
southern taf sites. Mainly vfr conditions expected until after 06z
when mvfr cigs and perhaps ifr cigs develop.


&&

.MARINE...
Issued at 1122 AM EDT Thu Jun 22 2017

A marine fcst update has been issued to cancel the small craft
advisory and beach hazards statement. Numerous marine reports and
marine webcams indicate wave heights are in the 2 to 3 foot range.
Wave heights will not exceed 2 to 4 feet this afternoon.

&&

.HYDROLOGY...
Issued at 310 PM EDT Tue Jun 20 2017

The uncertain extent of coverage, location, and repetition of
thunderstorms Thursday morning and Thursday night makes the
rainfall forecast difficult. However, with PW values between 1.5
and 1.75 inches favoring efficient rain production (above the 90th
percentile for this time of year and approaching some June daily
record values in the DTX-area sounding climatology), and a tendency
for storms to repeat over parts of the area, it seems reasonable
that some spots could receive over 2 inches of rainfall. The most
favored area for significant rain totals will be north of I-96 and
perhaps closer to US-10.

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. Locations that saw heavy rain
last week will be more prone to have at least minor areal or street
flooding from heavy downpours on Thursday. As for rivers, the Rogue
near Rockford, 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...04
SHORT TERM...04
LONG TERM...JK
AVIATION...04
HYDROLOGY...CAS
MARINE...Laurens



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