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561
FXUS63 KGRR 260345
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1145 PM EDT Sun Jun 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 319 PM EDT Sun Jun 25 2017

More cool and showery weather will be likely through Monday evening
as an expansive area of low pressure sits over the region and brings
weak waves to the area. Much of the period at any one location will
not be raining. The chance will remain at all times through Monday
evening, especially in the afternoon and early evening hours.

Temperatures will warm back up a bit then Tuesday and Wednesday as
the system moves out of the area. The warmer temperatures will be
accompanied by occasional threats for more widespread showers and
storms from late Wednesday into next weekend.

&&

.UPDATE...
Issued at 907 PM EDT Sun Jun 25 2017

Based on radar trends and the consistent forecasts for rain
showers as the next upstream shortwave moves through the area I
increased to pop to likely across the area tonight, from west to
east, with the movement of the shortwave. Rainfall amounts should
mostly be less than a tenth of an inch. Instability for the most
part is marginal for thunderstorms but I do have them possible
near the lake shore as the water is warmer than the air, which is
odd in late June but it is none the less true.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 319 PM EDT Sun Jun 25 2017

Our main focus in the short term is on the continued shower/storm
chances through Monday night as the upper low continues to spin over
the region and send down short waves through the area. The weather
looks fairly quiet through the rest of the short term after the
system should move out Monday night.

Plenty of diurnal cloud cover away from Lake Michigan, with showers
north of I-96 this afternoon so far. A sfc trough is dropping south
through the area with a few showers along it. We expect a few storms
will become possible from now through mid-evening with enough sfc
based instability available to justify the mention. Severe weather
is not expected, but some pea-sized hail and cold air funnels will
be possible.

The coldest of the air aloft will come in later tonight and linger
through Mon evening. This will spell more of the same as the past
couple of days, but bring lake effect/enhancement into play. The air
will be cold enough to bring delta t`s up to around 13-15C. This
could enhance some of the showers along the lakeshore. Forecast
soundings show thunder could remain possible over the lake with
EQL`s up well above the -20C isotherm and decent lake-induced CAPE.
Inland, the peak heating hours will bring the most showers. Thunder
threat inland does not look great with temps being held down in the
50s and 60.

We will finally see the upper jet lift NE of the area later Mon
night as a strong wave moving through late Mon will finally take it
out of the area. We should dry up the shower chances, and finally
warm up some.

.LONG TERM...(Wednesday through Sunday)
Issued at 319 PM EDT Sun Jun 25 2017

The long term period is looking stormy.  The main challenges deal
with the timing of the storms along with their impacts.

To start the period...a low level jet will be arriving from the
southwest Wednesday afternoon into Wednesday night.  This is
associated with a mid level wave...which will be pushing in from the
west.  The combination of an unseasonably moist
airmass...instability and lift will support a round or two of
thunderstorms.  Mid level lapse rates are forecasted to steepen up
as we go through the night along with an increase in the deep layer
shear.  All this suggests a risk for some severe weather.  Locally
heavy rain is possible given the high PWAT airmass that moves in.

For Thursday...there is some uncertainty as far as how far south the
cold front shifts. The front ends up becoming nearly parallel to the
mid level flow supporting the uncertainty. Will keep a risk for
storms going for now. The GFS keeps this boundary over the CWA and
shows and afternoon mid level wave moving in.  That...combined with
abundant instability would support some severe weather.
However...considerable uncertainty exists on this setup.

Then for Friday into Saturday...a mid level low drops out of the
Canadian Prairies and into the Great Lakes Region. That combined
with an unseasonably moist airmass supports additional storms...some
of which could be severe.  Heavy rain could occur as well.  There
are model timing differences.  The faster GFS would push the main
axis of storms and heavy rain off to the east by Saturday while the
High Res Euro shows the mid level low still to the west of Lower
Michigan on Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1123 PM EDT Sun Jun 25 2017

Vfr conditions will continue at all the terminals overnight with
scattered light rain showers that should gradually taper off
overnight. West winds will increase considerably by mid to late
Monday morning and gust to around 25 kts from late morning through
the afternoon into early evening before subsiding.

Scattered showers are expected at all the terminals Monday
morning and afternoon. Isolated thunderstorms may also develop
Monday afternoon but there is not enough potential to warrant
mention in the terminal fcsts at this time. Conditions should be
mainly vfr Monday although brief reductions to mvfr are possible
in heavier showers.

&&

.MARINE...
Issued at 319 PM EDT Sun Jun 25 2017

No change needed to the marine headlines after the earlier
expansion. Winds will come down slightly for a little bit this
evening, before coming back up overnight with the next wave. Winds
will stay up in the Small Craft/Beach Hazards category through Mon
evening before dropping off.

We will see temps drop off enough aloft combined with the relatively
warmer waters of Lake Michigan to bring a waterspout threat
beginning overnight tonight, and lasting through Monday evening.


&&

.HYDROLOGY...
Issued at 319 PM EDT Sun Jun 25 2017

Rain heavy enough to affect river levels is not expected until
Wednesday afternoon at the earliest. This will allow river levels to
fall the next few days. We will enter a potentially wet period from
Wednesday afternoon into the weekend.

At this point it looks like heavy rain and thunderstorms will be
mostly likely Wednesday evening into Thursday morning and again
Friday morning into the evening. The combination of these two events
could produce amounts over 3 to 4 inches in some areas. We will
continue to monitor forecast trends over the next few days for
specifics on amounts and locations where the heavier rain is
expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Monday evening for MIZ037-043-
     050-056-064-071.

LM...Small Craft Advisory until midnight EDT Monday night for
     LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...Laurens
HYDROLOGY...Ostuno
MARINE...NJJ