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fxus63 kgrr 200657 
afdgrr

Area forecast discussion
National Weather Service Grand Rapids Michigan
257 am EDT Wed Jun 20 2018

Latest update...
synopsis/short term/long term/marine

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 at this time 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 06z tafs through 06z Wednesday night)
issued at 110 am EDT Wed Jun 20 2018

The main forecast concern overnight is the potential for showers from
roughly 8-12z at all taf sites. While short-term numerical model
guidance has been consistent in showing the development of
widespread showers this morning across central lower Michigan, I
suspect coverage will be lower than what is advertised. At this
point, the best potential for showers will be at kazo/kbtl/kjax
closest to the better moisture. A clap of thunder is also possible
as evident by lightning being observed over Lake Michigan (which
is surprising given a lack of appreciable instability). Given
that conditions are somewhat favorable for moderate to heavy
rainfall, IFR ceilings and possibly even visibilities are possible
in the strongest cells. I considered putting tempo groups for IFR
conditions into the tafs for kazo/kbtl but backed out given low
confidence in just how widespread the conditions may become. We
will have to wait and see how the activity evolves over the next
few hours. Regardless, I have vcsh in all tafs for at least a
short period of time this morning.

Outside of areas of precipitation, MVFR ceilings are expected
through the morning and early afternoon hours. Toward Wednesday
evening, clouds will clear from north to south leading to VFR
conditions at all taf sites.

&&

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...
Michigan...none.
Lm...none.
&&

$$

Synopsis...ostuno
short term...ostuno

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