Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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017
FXUS63 KGRR 300055
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
855 PM EDT Mon May 29 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 325 PM EDT Mon May 29 2017

The region will stay cool Tuesday and Wednesday with highs in the
60s to around 70. This compares to average highs in the 70s for
this time of year. Scattered showers, or even a thunderstorm, will
dot the landscape from Tuesday afternoon into mid day Wednesday,
then the precipitation will exit Southwest Michigan.

It appears a better chance of showers and storms move back into
the area Thursday night through Friday night. Next weekend looks
mainly dry. We should continue to see slightly below normal
temperatures, with highs mainly in the upper 60s to mid 70s.

&&

.UPDATE...
Issued at 856 PM EDT Mon May 29 2017

I am watching an area of showers over central Lake Michigan moving
largely toward the east (heading toward MKG). There is a
significant twist in the H20 vapor image loops and there is also
a 400 mb PV feature with this area of showers too. The instability
is feeble at best but the model sounding show the air to be more
moist in that area so it just may be the area from MKG to LDM will
see a few showers over the next 3 to 4 hours.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 325 PM EDT Mon May 29 2017

The upper low over the Superior region will continue to drift
slowly east. Several short waves pass through between now and mid
day Wed, bringing shower chances.

Weak lift remains over SW MI into tonight. Cannot rule out an
isolated shower or storm over the NW half of the CWA, but 20 POPs
should cover these.

A better chance of showers and storms will arrive Tuesday
afternoon as a short wave pinwheels around the upper low and into
SW MI by evening. Another short wave arrives Wed morning. So this
leads to carrying slightly higher POPs from roughly 18Z Tuesday
through 18Z Wednesday. Will keep the mention of thunder in the
forecast for Tuesday afternoon and evening, as the daytime heating
and chilly air aloft leads to decent lapse rates. Same is true
toward I-94 on Wednesday, until the final short wave comes
through. Expect the scattered pcpn will be east of the area after
18Z Wed, with the exiting short wave. Skies will begin to clear
behind the wave into the evening.

Wednesday night will be mostly clear and cool with lows dipping to
the 45 to 50 range.

.LONG TERM...(Thursday through Monday)
Issued at 325 PM EDT Mon May 29 2017

Showers and thunderstorms will be on the increase Thursday night and
Friday as area of isentropic ascent in overrunning pattern sets up
across Lower Michigan, although it appears that the bulk of the
precip could remain just to our south where one or more clusters of
convection form along a well defined sfc boundary Thursday night
into Friday night.

There is lower than average confidence in the forecast over the
weekend as ensemble spread remains large. The majority of solutions
suggest a Canadian sfc high will be centered across southern Canada
or the northern Great Lakes with a sfc low tracking across the
stalled sfc boundary south of Lower Michigan. Dry northerly flow
should result in fair weather over much of the weekend although
southern zones could be in the northern edge of the rain at times.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 720 PM EDT Mon May 29 2017

VFR conditions will continue through Tuesday (and well beyond
then). A cold core upper low over the area will bring afternoon
showers to the area tomorrow as it did today. Also, as today
there, will be a "lake shadow" to the convection. Locations like
GRR and MKG will very likely see no showers. On the other hand,
AZO,BTL, LAN, and JXN have a better chance of having one of those
showers. Even then through I would expect VFR conditions to rule.
Like today tomorrow will be breezy with gust to near 25 kts at
times. The showers are expected to dissipate with sunset
tomorrow.


&&

.MARINE...
Issued at 325 PM EDT Mon May 29 2017

Winds have come up today and waves will continue to gradually
build tonight. Not expecting we will reach small craft advisory
criteria, but it will become rougher on the lake by midnight.
These choppy waves will continue into Tuesday, but diminish by
late afternoon and into the evening. Lower waves can be expected
Tuesday night through Wednesday night.


&&

.HYDROLOGY...
Issued at 206 PM EDT Mon May 29 2017

No hydrologic concerns for a few days. Small rivers and streams
may be susceptible to rises Thursday night into Friday if
convection materializes across the region. PWAT values are
expected to increase to 1.25-1.50" across southern Lower MI during
that time. Hard to see this becoming a problem on mainstem rivers
unless widespread, training thunderstorms occur. We`ll keep an eye
on trends.

&&

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

$$

UPDATE...WDM
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Ostuno
AVIATION...WDM
HYDROLOGY...Hoving
MARINE...JK



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