FXUS63 KGRR 201806
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
206 PM EDT Wed Jun 20 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 257 AM EDT Wed Jun 20 2018

Showers and a few thunderstorms can be expected today across the 
southern half of Lower Michigan. Some local flooding is possible
as heavy rain combines with slow moving storms. The showers should
diminish this afternoon with a spell of dry weather beginning
tonight and lasting through Thursday.

&&

.SHORT TERM...(Today through Friday)
Issued at 257 AM EDT Wed Jun 20 2018

Some potential for localized heavy rain this morning across the
southern half of the forecast area. Precipitable water is close to
1.9 inches and storms are slow moving. Downpours across Berrien
County ATTM show MRMS instantaneous precip rates spiking over 3
inches an hour with rain gage reports showing 1.5 inches in 45 
minutes. This area of rain is progged to expand north and east
this morning and we will have to watch for areas of training and
backbuilding.

The rain should begin to taper off this afternoon as weak sfc wave
translates east and sfc front sinks south in its wake with drier
air advecting in from the north. Fair weather with comfortable
temperature and humidity follows for Thursday, then moisture
spreads north again Thursday night and Friday as next sfc wave
approaches.

.LONG TERM...(Friday night through Tuesday)
Issued at 257 AM EDT Wed Jun 20 2018

Rain will continue Saturday and into early Sunday as a cut-off low 
pressure system drifts through the Great Lakes. Model guidance 
continues to shift the heaviest rainfall ever so slightly southeast 
with each new run which isn't surprising given the lack of real 
synoptic "guidance" (e.g. cut-off lows sometimes drift wherever 
they please). At this point I still feel confident in the chance 
for precipitation this weekend but the heaviest just may stay 
outside of our area depending on the final track of the system. 

A compact (and rather potent) shortwave trough will swing through 
the Great Lakes Sunday and provide the "guidance" to kick the low
east into Canada. Breaks in cloud cover with diurnal heating will
promote pockets of modest instability ahead of the upper-level 
wave supporting the possibility of a few thunderstorms Sunday 
evening. However, coverage looks fairly limited at this point in 
time. 

The area will then become dominated by a large high pressure system 
early next week with dry and seasonable temperatures expected. 
Another low pressure system may impact the area toward the end of 
next week, but we won't worry about the details of such at this 
point in time. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 207 PM EDT Wed Jun 20 2018

Lower ceilings remain across Southern Lower Michigan as of 18z.
MVFR and even IFR ceilings are in place along and south of I-96. An
improving trend should be seen this afternoon and early evening 
with all TAF sites becoming VFR by 00z as the low clouds push
south. A mid deck of clouds with bases at or above 10,000ft will 
likely be in place tonight into Thursday morning.

&&

.MARINE...
Issued at 257 AM EDT Wed Jun 20 2018

Winds and waves will be relatively light the next couple days.
Winds will mostly be offshore, so waves will be highest away from
shore.


&&

.HYDROLOGY...
Issued at 1234 PM EDT Tue Jun 19 2018

Recent rainfall has resulted in a slight rise on a few area rivers. 
With river levels running near normal, no flooding is expected.  

More rain is possible today through Wednesday night and again Friday 
through Saturday night. Scattered to numerous showers and 
thunderstorms may develop. Generally expect less than an inch of 
rain, with locally heavy rainfall possible with the storms. This may 
result in localized flooding.

&&

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

$$

SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...Borchardt
AVIATION...Duke
HYDROLOGY...63
MARINE...Ostuno