Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 241806
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
206 PM EDT Wed May 24 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EDT Wed May 24 2017

The overall weather pattern suggests little overall change through
at least the middle of next week. We have a series of upper level
storms that move through the area between now and next wednesday
but the way they interact with the surface weather pattern will
for the most part mean only limited amounts of rainfall with
temperatures for the most part near normal. Sunshine is most
likely on Friday. The chances for measurable rain will be
greatest today east of Grand Rapids. Scattered showers are also
possible tomorrow, then scattered showers and afternoon
thunderstorms are possible over the weekend into Tuesday of next
week. At this point it no longer looks like an heavy rainfall
events over a large are is expected during this entire time
period.

&&

.UPDATE...
Issued at 1149 AM EDT Wed May 24 2017

The Great Lakes region is situated within a broad upper trough
which stretches from our area south all the way to the gulf coast.
Shortwaves are rotating around the trough and are affecting our
weather. One wave is lifting north out of the CWA this morning
and is associated with the more banded rain across Central Lower
Michigan. Expecting that rain to lift out to the north in the next
few hours.

The next wave is associated with a deepening surface low that
moves our direction from the Ohio Valley this afternoon and
evening. Showers and thunderstorms should fill in this afternoon
across Southern Lower Michigan ahead of this feature. A good break
in the cloud cover has developed across Southern Lower Michigan
which should add to instability there. Models all indicate CAPE
values increasing to 1000-1500 J/KG this afternoon which should be
more than enough for convection. Not expecting severe weather as
the deep layer shear decreases this afternoon. Main threats will
be locally heavy rainfall and cloud to ground lightning strikes.
Have likely to categorical pops (60-80 pct) across this south
towards evening.

Highs should top out in the upper 60s to around 70 degrees this
afternoon.

&&

.SHORT TERM...(Today through Friday)
Issued at 328 AM EDT Wed May 24 2017

We have that storm that I though yesterday could bring heavy rain
to areas south and east of Grand Rapids late this afternoon into
tonight but it now appears most of the heavy rain will be well
east of Michigan. The trowal feature now is mostly east of I-69
tonight and well east of the this area by Thursday afternoon.
Similarly the deformation zone with the mid and upper level system
does not get west of I-69. Still there is a decent surface low
that that tracks from Kentucky this morning to northern Ohio by
midday Thursday. So more than likely there will be some rain over
our southeastern CWA tonight from that.

I do believe we will see showers/thunderstorms over most of our
CWA today even so. There is enough instability (1000 to 1500 j/kg
of most unstable cape) during the midday hours (EL near the
tropopause) that it would seem to me scattered thunderstorms are
likely. Due to the southerly flow from 700 mb through 200 mb I
would seem any storms should move nearly due north today. Even so
it will not be raining most of the time. I do believe most areas
should see at least a 0.05 inches of rain but some very localized
areas could see near and inch of they got under the one of the
stronger storms (precipitable water is over an inch / which is
nearly double normal).

Beyond today our system pulls off to the northeast but we stay in
the upper level circulation through Thursday evening before
shortwave ridging moves in for Friday. So I would expect more
instability showers around Thursday. With the shortwave ridge
over the area Friday we should see sunshine during the day.

.LONG TERM...(Friday night through Tuesday)
Issued at 328 AM EDT Wed May 24 2017

Southerly flow should bring us warmer air for the weekend, but then
we should turn cooler again by Memorial Day and Tuesday.  Periods of
showers will be possible much of the extended period, but there will
be times when the showers should become more concentrated.

A cold front, with a wave of low pressure along it, should push in a
period of showers and storms into the region Saturday night and
Sunday. Given the current timing in the models, the SE CWA seems the
most favored for rain.

The other more concentrated period of pcpn should occur Monday
afternoon and evening when an upper low forms over the Northern
Great Lakes and spreads showers and a few storms into the area.

Otherwise we can not rule out random showers or storms just about
any day/night, but they will be more hit and miss then the times
mentioned above.

The holiday weekend will be mild, with highs in the 70s away from
Lake Michigan.  Then as the upper low takes shape, we will likely be
cooler into Monday and Tuesday.  In fact Tuesday could be quite
chilly with H8 temps diving down to around +5C.  We may stay in the
50s for highs Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 205 PM EDT Wed May 24 2017

Coverage of showers will increase this afternoon, with a few
tstms also possible through sunset. Cigs/vsbys should remain
predominately VFR through dark, although some lower vsbys may
occur if any heavy downpours pass over the terminals.

Cigs are expected to lower to IFR tonight with showers
continuing, particularly southeast of GRR and mainly after
midnight, as low pressure lifts north from Kentucky. However
guidance has been consistently too pessimistic with cig
trends/fcsts the last few days, so confidence in widespread IFR
tonight is not high.

MVFR conditions with scattered showers will linger into Thursday
morning, particularly east of GRR. Some IFR will remain possible
as well. Cigs are expected to improve toward/after 18Z Thursday.

&&

.MARINE...
Issued at 328 AM EDT Wed May 24 2017

There does not appear to be a strong enough gradient wind to cause
the surface winds to be strong enough for a small craft advisory
through Friday.


&&

.HYDROLOGY...
Issued at 1259 PM EDT Wed May 24 2017

Rivers over the southern portion of the forecast area (south and
east of Grand Rapids) continue to run above normal. Southern
sites will be the main concern for any flood potential over the
next several days.

Precipitation forecasts for today have trended downward slightly.
The greatest totals are expected near Lansing and Jackson, where
amounts will range from 0.50-0.70 of an inch. Amounts will trend
downward further north and west.

Long term precipitation forecasts bring waves of precipitation
through late this weekend into next week. The current pattern
would suggest that amounts could vary widely from point to point
with any adjustment in timing and placement. In addition,
scattered convection could play a role in locally heavy rainfall
at times. Therefore, immediate flood concerns have decreased with
the latest trends in forecast qpf. The upcoming week may need
to be monitored with respect to sites that are experiencing higher
than normal river levels.

&&

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

$$

UPDATE...Duke
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...Meade
HYDROLOGY...JAM
MARINE...WDM



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