Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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455
FXUS63 KGRR 291821
AFDGRR

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

LATEST UPDATE...
Hydro

.SYNOPSIS...
Issued at 330 AM EDT Mon May 29 2017

We will see another day with highs in the 70s on Memorial Day with
some scattered showers and isolated thunderstorms this afternoon and
evening. Coverage on the precipitation will not be widespread. An
upper low located over the northern Great Lakes will bring a fair
amount of cloud cover for Tuesday into Wednesday with isolated to
scattered showers at times both days. Highs on Tuesday and Wednesday
will cool into the 60s, which is below normal for this time of year.

&&

.UPDATE...
Issued at 1120 AM EDT Mon May 29 2017

Reduced POPs slightly, to 20% everywhere but the far NW CWA, near
Ludington, where I kept 30 POPs. Model soundings have come in dry
in the low levels, with mainly moisture above 5k feet. So expect
we will see diurnal clouds develop, but these will be fairly high
based. Some of the less vigorous afternoon showers may only be
virga, and those that do precipitate to the ground should be
isolated.

Left thunder in the forecast however. Due to the inverted V shaped
soundings, any storms that do form will likely produce brief gusty
winds to around 50 MPH. The synoptic wind will also pick up this
afternoon, occasionally gusting to 30 MPH.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EDT Mon May 29 2017

Main forecast focus in the short term in on cloud cover trends and
chances for showers and a few thunderstorms.

The Great Lakes region will be under the influence of an upper low
that will spin across the northern Great Lakes throughout the short
term. We are expecting precipitation at times through Wednesday
focused with upper shortwave troughs pivoting around the upper low.
Precipitation will be diurnally forced, with the bulk occurring in
the afternoon and evening hours the next few days. Simulated
reflectivity from the convection allowing models show the diurnal
trend as well. Best instability will be today with some lingering
low level moisture. Have showers and storms in the forecast for this
afternoon, but nothing more than scattered pops (30 pct). After this
evening just have isolated to scattered rain showers and left out
the mention of thunder as instability is forecast to be much less.

There will be a decent amount of sunshine today, especially from the
morning into the early afternoon. Clouds will become more prevalent
especially from tonight through Wednesday morning.

High temperatures will cool a bit each day early this week with
below normal highs in the 60s expected on Tuesday and Wednesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 330 AM EDT Mon May 29 2017

A warm front lifting north across the southern cwa will likely
produce showers/storms Thursday night and Friday. The best
instability is confined to areas south of I-94.

Forecast confidence next weekend is low due to quite a bit of model
spread. The major models generally show sfc high pressure building
south toward the Great Lakes, but also some troughiness aloft. By
Sunday the gfs shows a low moving from Manitoba southeast toward
Chicago which would bring some rain toward southwest Lower MI, but
the ecmwf doesn`t show any low. The Canadian on the other hand
strongly supports the GFS so that`s which way the forecast will lean
for now. We`ll include a chance of scattered rain showers late
Saturday into Sunday.

Highs will be a bit cooler than normal...a couple of degrees either
side of 70.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 157 PM EDT Mon May 29 2017

VFR conditions will continue through Tuesday. Winds will continue
to gust over 20 knots this afternoon before subsiding to around 10
knots tonight. There will be scattered showers and even an
isolated thunderstorm on Tuesday, but any reductions to visibility
will be brief.


&&

.MARINE...
Issued at 330 AM EDT Mon May 29 2017

Westerly winds are expected for much of the next couple of days with
an upper low spinning across the northern Great Lakes. Winds are
generally expected to be in the 10 to 20 knot range which should
keep waves below advisory criteria. 25 knot winds are located in the
1000-2000ft range though so we will need to keep an eye on the
forecast in case the winds over perform.


&&

.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...JK
SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...Ostuno
HYDROLOGY...Hoving
MARINE...Duke



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