Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191756
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
156 PM EDT Mon Jun 19 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 317 AM EDT Mon Jun 19 2017

Scattered showers and a few thunderstorms will be possible today
and Tuesday as cooler air filters into the region. Otherwise,
partly sunny conditions will hold for many areas. After a dry day
Wednesday, thunderstorms may move into the region Wednesday night
through Thursday night. Another possibility for storms exists late
in the weekend.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 317 AM EDT Mon Jun 19 2017

Primary focus is on coverage of any showers and thunderstorms today
and Tuesday. The H500 shortwave trough will move through during peak
heating today as surface based CAPE climbs to 1000 J/kg with
essentially no CIN. There is also a reasonable amount of instability
in the -10C to -20C layer should any convection develop. A sampling
of RAP bufkit soundings show decent moisture availability from the
LCL (2500 ft) to about 30k ft. This is also reflected in GFS and
ECMWF deep layer RH values of around 80% this afternoon.

An assessment of the HRRR/HRRRX, NAM 3km, and WRF-ARW reveals a
common thread with convective development. The most likely time
frame for development is after 16Z and lasting into late evening.
Convection should be scattered in nature east of US 131 with little
if any activity near and west during the day. With westerly H850
winds and sfc winds, there may be a protective lake shadow in
place. However, additional storms in eastern WI may survive the
trip over the lake in time for a late evening arrival along the
lakeshore, especially north of Muskegon.

For Tuesday, much less sfc based instability will be present as well
as less deep layer RH. That said, a 50-60 kt mid level jet core in
association with a secondary H500 trough will be coming through mid
afternoon. Any showers and storms that can fire in this environment
may have potential for gusty winds that mix down. But the main
limiting factor to strong storms developing appears to be the
general lacking of sfc based instability.

.LONG TERM...(Wednesday night through Sunday)
Issued at 317 AM EDT Mon Jun 19 2017

We continue to think that the potential exists for an occasionally
active and unsettled weather pattern over the next week. Multiple
rounds of showers/storms will be possible at times through next
Sunday.

The first threats will come beginning Wed night and linger through
Fri morning. We will see upper heights build a bit that will bring a
warm front into the area Wed night. This looks to touch off a round
of storms with strong moisture transport aimed at Lower MI via a 50
knot low level jet. Another wave will approach Thu night, but may be
a little further south as the boundary will likely sink south in the
wake of the Wed night/Thu am wave.

We will likely see a break in the action then much of Fri and Sat.
We see enough of a ridge in the zonal upper flow and the sfc
boundary will sink far enough south to keep the area dry and mild.

The break in the active weather looks to come to an end by Sat
night. Another better organized upper wave comes through the zonal
flow aloft. This will bring another low level jet through the area,
resulting in another wave of storms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 156 PM EDT Mon Jun 19 2017

Will carry thunder in the TAFs through about 20Z east of GRR/AZO.
After 20Z, most of the convection near BTL/LAN/JXN will have moved
off to east as the westerly flow continues to send stable lake MI
air farther inland. Any shower/tstm could create IFR or lower
conditions, possibly even with some small hail, but these would
probably be very brief based on the small cell size noted on
radar.

More tstms are floating east from Wisconsin, but these should
tend to weaken as the come across lake MI. Will therefore only
carry VCSH into the evening hours before all of this activity
weakens with sunset.

Otherwise VFR tonight into Tuesday morning. Gusty west winds this
afternoon diminishing to 5-10 kts tonight, but increasing/becoming
gusty again after 14-15Z Tuesday. More widely scattered
showers/isolated storms will likely develop on Tuesday,
particularly in the afternoon.

&&

.MARINE...
Issued at 317 AM EDT Mon Jun 19 2017

Waves of 1-2 ft are expected today and may get a bit higher
tomorrow with 1-3 footers. It appears waves of 3-5 feet are
possible Thursday as SW winds increase.


&&

.HYDROLOGY...
Issued at 317 AM EDT Mon Jun 19 2017

Conditions are drying out but rivers have responded to recent
heavy rainfall. The Flat River at Smyrna may exceed bankfull and
the Rogue River below Rockford has come close after a swath of
2"-4" of rain fell across the region (locally higher). The Grand
River has also risen but will stay within its banks. Additional
rainfall for the second half of the week will need to be monitored
for additional rises on the rivers.

&&

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

$$

SYNOPSIS...Hoving
SHORT TERM...Hoving
LONG TERM...NJJ
AVIATION...Meade
HYDROLOGY...Hoving
MARINE...Hoving



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