Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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584
FXUS63 KGRR 272339
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
739 PM EDT Tue Jun 27 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 324 PM EDT Tue Jun 27 2017

Quiet and comfortable weather will continue tonight into the first
half of Wednesday. Shower and thunderstorm chances will increase
Wednesday afternoon, and will be likely Wednesday night as a low
pressure system approaches the area. Some of the storms could be a
bit strong with hail, winds, and heavy rain all being threats.
Storms will continue into Thursday morning before diminishing some
as a front pushes south of the area.

Showers and storms will return late Thursday night and more so
Friday as another wave of low pressure moves up over the area.
Cooler weather will move in over the weekend with small chances of
rain possible.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 324 PM EDT Tue Jun 27 2017

Our main concern in the short term portion of the fcst is on pcpn
trends as rain moves in late Wed, and severe weather chances with
storms Wednesday night.

Quiet weather is expected through Wednesday morning across the area.
Ridging has taken over control over the area for the most part,
except for a few sprinkles across the far eastern portion of the
area this afternoon. This is a result of the upper jet and an
embedded short wave still nearby on the far wrn portion of the upper
low now east of the area. All areas will clear out once the diurnal
cumulus dissipate toward sunset.

Wednesday will start out clear, but will see an increase in cloud
cover by afternoon, and rain likely across the NW by evening.
Ridging will give way to a fairly decent short wave that is
currently located over the MT/WY area. This short wave will ride in
fairly quick due to the upper flow becoming more zonal as the upper
low departs. Strong moisture transport via a 60 knot low level jet
will begin to arrive Wed afternoon, and will be overhead Wed night.
The nose of the low level jet will be aimed more at Central and
Northern Michigan, where we expect the best concentration of storms.
Thunder chances look to come after 00z Thu when the more unstable
conditions arrive.

Some of the storms could become stronger, and heavy rain will be a
threat. Forecast soundings indicate some decent CAPE profiles in the
-10 to -30C layer based on elevated instability. The low level jet
will supply quite a bit of wind energy, and there is not a
significant inversion to entirely protect us with some better
updrafts. Heavy downpours will be a threat as Pwats will be climbing
to almost 2.0 inches. The good thing is the low level jet will be
progressive, so we do not expect much larger scale training.

The showers and storms will tend to diminish in coverage and
intensity a bit on Thu as the low level jet departs. The cold front
will be sinking south through the area, not likely moving out of the
area until the evening hours. This could produce some additional
convection if enough instability can build ahead of the front. This
will be focused more on the southern areas for Thu. There will be a
brief break Thu evening, before more convection tries to move in
toward daybreak Friday morning.

.LONG TERM...(Friday through Tuesday)
Issued at 324 PM EDT Tue Jun 27 2017

The main weather challenges deal with the timing and strength of any
thunderstorms in the long term.  Overall confidence is increasing on
strong/severe storms for Friday.

Models are coming into better agreement in supporting a round or two
of strong/severe storms on Friday.  The combination of stronger deep
layer shear of over 40 knots...plenty of instability and a
strengthening upper level jet support this potential.  Will increase
the POPs and QPF for this period.

For Friday evening...we are shown to hold onto some instability.
Will keep the risk for thunderstorms going.  Later at night the
atmosphere is shown to become stable.  As a result...will go with
only some rain showers then.

A warm front is forecasted by the High Res Euro to lift northward
back into the region on Tuesday.  Elevated instability is shown.
Will feature some thunderstorms then. The low level wind fields are
shown to be faster/about the same as the upper level winds. Commonly
this leads to slower moving storms.  This could lead to a heavy rain
risk.  The GFS though...is further south with the front and keeps it
out of the area.  Will keep a low chance for storms going in the
southern parts of the CWA.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 740 PM EDT Tue Jun 27 2017

I expect nearly clear skies tonight with winds becoming light from
the south. Most of the convection with the warm front tomorrow
will stay north of our TAF sites. It is not out of the question
MKG could see something during the afternoon so I put VCTS there
but that is the only place I put that. Elsewhere expect layered
clouds and gusty southwest winds (to 25 knots at times).

&&

.MARINE...
Issued at 324 PM EDT Tue Jun 27 2017

We will be issuing a Beach Hazards Statement and Small Craft
Advisory with this forecast package for Wednesday into Thursday.
Winds will begin to increase overnight tonight ahead of the next
incoming system that will arrive late Wed. Winds and waves will come
up enough to become a hazard on Wed from North to South. These winds
will remain up through Thu when the cold front will move through and
a weaker gradient will move in.


&&

.HYDROLOGY...
Issued at 324 PM EDT Tue Jun 27 2017

The Chippewa and Pine River warnings have been downgraded to
advisories with continued improvement. The Pine River levels are
dropping at a rate such that the advisory could potentially be
dropped by this time tomorrow. The Chippewa River will experience a
more gradual fall. The majority of river in a stretch from Ludington
eastward remain elevated, as well.

Additional rainfall is slated for late Wednesday into Thursday. This
midweek precipitation has the potential to delay improvement,
keeping rivers elevated. Additional rainfall could affect the area
again by Friday. Details in the exact placement of the heaviest rain
is still not certain, but the potential exists for more than 3
inches of rain to fall in some places over the next 5-7 days.

Further south, rivers are slightly above to near normal. Given
recent rainfall totals, river levels are almost certain to rise if
forecast precipitation amounts are achieved through the next week.
Those living near rivers should pay close attention to forecast
updates and monitor river trends closely.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from Wednesday morning through Thursday
     afternoon for MIZ037-043-050-056-064-071.

LM...Small Craft Advisory from 8 AM Wednesday to 2 PM EDT Thursday
     for LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...JAM
MARINE...NJJ



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