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216
FXUS63 KGRR 171929
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EDT Thu Aug 17 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Hydro/Marine

.SYNOPSIS...
Issued at 329 PM EDT Thu Aug 17 2017

Showers and thunderstorms will exit to the east through late this
afternoon and early evening. Clouds and a few showers will linger
behind as cooler, drier air works into the region tonight into
early Friday. Temperatures will trend upward over the weekend.
There will be a quick shot at showers and a few storms, mainly
along/south of I-96 overnight Friday into early Saturday. Otherwise,
much of the daytime hours should be dry through Monday. The next system
approaches the region Monday into Tuesday, bringing in the next
chance of precipitation.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 329 PM EDT Thu Aug 17 2017

The main focus is within the first few hours of the period with
respect to this afternoon`s thunderstorm chances.

The bottom line is that much of SW Lower has likely avoided the
severe weather once again. We are not completely out of the woods
over the eastern CWA, but a few factors have continued to limit
chances. Plenty of cloud cover resulted from this morning`s
showers and storms, largely keeping surface instability in check.
Water vapor shows dry air with plenty of subsidence working in
from west to east behind the front.

CAPE values are under 1000 J/kg through much of the forecast
area. However, where skies have been partly to mostly sunny over
Indiana/extreme Southern Michigan, indices have pushed 2000 J/kg.
Meso analysis continues to place effective shear of 40-50 kts
over the southeastern CWA, mainly toward Lansing and Jackson.
Albeit more robust than reality, high res guidance has done a
decent job in timing/placement of showers and storms over Central
Lower. All-in-all, while severe weather cannot be ruled out, the
window is quickly closing and the likelihood of anything becoming
severe this evening is becoming doubtful.

Low and mid level moisture hangs around through tonight and the
first part of Friday. Clouds and a few shower may linger on the
back side of the system. Moisture finally evacuates by mid to late
Friday afternoon, hinting that clouds may begin to break.

A quick moving shortwave then moves to our south late Friday night
into Saturday. Showers and a couple of thunderstorms are possible,
but this should all be out by mid morning Saturday. Much of the
day will dry out to mark the beginning of improving conditions for
the weekend.

.LONG TERM...(Sunday through Thursday)
Issued at 329 PM EDT Thu Aug 17 2017

Mid level flow pattern transitions from a weak ridge early Sunday to
northwest flow by Tuesday as a persistent low redevelops over
Quebec. High pressure will dominate Sunday..but warmer temperatures
will return for the first part of the work week as southerly flow
strengthens.  A frontal boundary will try to move through the region
Monday but have little success.  A second front...aided by a short
wave moving southeast from Canada...will push through the region
Tuesday.

Rain chances will increase Monday into Tuesday ahead of the frontal
boundary...with dry weather is expected from Wednesday through the
end of the work week.

Significantly cooler air will move into the region for the latter
half of the week.  While 850 mb temperatures will approach 20
degrees C early in the week...several of the longer range models
indicate that those readings will fall into the 6 to 8 degree C
range.  As a result...above normal temperatures early in the week
will become below normal for the end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 113 PM EDT Thu Aug 17 2017

Radar showing latest wave of showers and thunderstorms over
southeastern Michigan...with widely scattered showers from
northwest Lower Michigan across Lake Michigan into Wisconsin.
Short range model guidance suggests that the best chances for
widespread showers and thunderstorms will at KJXN and KLAN from
19Z to 22Z. Will keep a vicinity wording at the remaining TAF
sites as chances are non zero.

Ceilings are ranging from below 1 kft AGL at KMKG to around 1.5
kft AGL at KAZO/KLAN/KBTL to at or above 5 kft AGL at KGRR and
KJXN. Upstream ceilings in the 1.5 to 2.5 kft AGL range are
widespread...with below 1 kft AGL over northwest Lower Michigan.
Will keep a MVFR ceiling area wide this afternoon...with the
exception of KMKG...where IFR ceilings will likely continue.

Should see some temporary improvement in ceilings to possibly VFR
conditions this evening as evident over Wisconsin over the past
few hours...but expect a return to MVFR later tonight. The rain
chances will increase as the lower ceilings return...which was
depicted well in the current forecast.


&&

.MARINE...
Issued at 329 PM EDT Thu Aug 17 2017

Small craft and beach hazard conditions will be present through
Friday. Southerly winds of 20-25 kts will shift out of the west,
giving rise to waves that will build between 6-8 feet in some
locations. Winds will gradually die down through Friday evening,
which should allow waves to subside. Headlines will continue
through Friday.

&&

.HYDROLOGY...
Issued at 329 PM EDT Thu Aug 17 2017

Localized rainfall amounts of 0.50" to 1.00" over the last 12 to 24
hours will not be enough to cause basin-wide concerns on area
rivers. Additional light rain for portions of the region Saturday
will not be cause for concern. Rivers will continue to remain well
within their banks through the weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from 6 PM EDT this evening through
     Friday evening for MIZ064-071.

     Beach Hazards Statement through Friday evening for MIZ037-043-
     050-056.

LM...Small Craft Advisory until 9 PM EDT Friday for LMZ846>849.

     Small Craft Advisory from 6 PM this evening to 9 PM EDT Friday
     for LMZ844-845.

&&

$$

SYNOPSIS...JAM
SHORT TERM...JAM
LONG TERM...MWS
AVIATION...MWS
HYDROLOGY...Hoving
MARINE...JAM