Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 212345
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
645 PM EST Wed Feb 21 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 327 PM EST Wed Feb 21 2018

Quiet weather will continue tonight and Thursday.  Then a wintry mix
is expected to arrive Thursday night into Friday morning.  Quiet
weather returns for Friday afternoon and night.  Temperatures will
remain slightly above normal with daytime highs in the upper 30s to
mid 40s, and lows in the 20s to around 30.

Daytime highs in the 40s are expected to continue through the middle
of next week.  A solid chance of rain is expected by Saturday night,
and then rain and snow should return by Tuesday night and Wednesday.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 327 PM EST Wed Feb 21 2018

A wintry mix will settle over the region Thursday night, but it`ll
be fairly short-lived, exiting already toward noon Friday.

Period of concern in the short term runs from about midnight
Thursday night through about noon Friday.  Low pressure in MO will
lift NE toward Chicago by daybreak Friday, and toward the Straits by
Friday afternoon.  Initially the easterly flow will prevent the low
levels from warming ahead of the system, while warm air aloft
arrives first overnight Thursday night.

If the pcpn arrives early enough, forecast soundings favor snow,
with perhaps a mix only toward I-94.  But as the warm air aloft
continues to flow in, more sleet and freezing rain will develop into
late evening when the pcpn is more likely.  This is then replaced
with just rain toward daybreak Friday as the boundary layer warms.
Even though the pcpn should be light, headlines may be needed for
this event as a glaze of ice will be possible in time for the Friday
morning commute.  At this point it would appear the highest chance
to see a more substantial ice accumulation would be across Central
Lower, our northern two rows of counties. Up to a tenth of an inch
of glaze will be possible there.  With the recent warmth and rain,
the wild card will be the road temps and whether we see ice on the
roads and the potential for slippery roads. Elsewhere the ice accums
are expected to be less as the duration of icing will be less,
generally just 4 to 6 hours.

As mention the pcpn will trend to plain rain toward daybreak Friday,
although it may take until mid morning across Central Lower. Then as
the low passes the pcpn will end by 18Z Friday.

In the meantime, tonight and Thursday will remain quiet.  I did
remove the low POPs that we had for this period since the moisture
looks too shallow. Then once the Thursday night/Friday system moves
out, Friday night looks quiet again.

.LONG TERM...(Saturday through Wednesday)
Issued at 327 PM EST Wed Feb 21 2018

The focus in the long term continues to be with the potential for
more rain from the system that comes through the region on Saturday
and Saturday night. Currently we are expecting only around a quarter
to possibly as much as one half inch of QPF which should have little
impact on the rivers, but this will need to be watched.

Current projection is for the sfc low and wintry precip to track
west of Michigan through Wisconsin which brings the warm sector into
our area. However the warm sector gets pinched off quickly as the
sfc system occludes, with the axis of highest PWATs and QPF staying
off to our southeast. The highest amounts near a half inch are
projected around Jackson, but if that axis of heavier rain over Ohio
were to shift farther north it could be a hydro concern.

There may actually be a brief period of snow as the precipitation
begins on Saturday morning before temps warm.

Breezy and turning cooler on Sunday on the back side of the
departing system, then a mainly dry and quiet pattern settling in
for the early to middle part of next week with high pressure.
Temperatures are expected to remain above normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 645 PM EST Wed Feb 21 2018

Ceilings around 1500 to 2500 feet AGL across central and southern
Lower Michigan will clear out this evening with VFR conditions
expected into Thursday afternoon. By late afternoon MVFR
conditions will return across the southern areas from near AZO to
JXN as lower stratus clouds move north.

&&

.HYDROLOGY...
Issued at 327 PM EST Wed Feb 21 2018

Most recent observations along some of the smaller streams have
indicated that levels are nearing their peaks. Most smaller streams
and rivers will do so between now and Wednesday evening. Larger
rivers continue to rise with the greatest impacts to come later in
the week and into the weekend. Overall, observed river levels have
line up fairly well with forecast trends and most adjustments have
been minor with each update.

Areal flooding will subside through the evening or has already
subsided, while the greatest concern going forward will exist along
the larger rivers through the weekend. Particular focus will be on
the Red Cedar River and Grand River as rises continue to impact the
Lansing area and water funnels downstream to Grand Rapids. River
levels in Lansing and Grand Rapids will be among some of the
historical crests. Levels in Grand Rapids could come close to 2013
levels, while levels around Lansing will be most comparable to 1975.
Many roads and locations along each of the river are already
impacted and will only continue to see waters rise this weekend.

Various other rivers through Southwest Lower Michigan continue to
experience minor to moderate flooding. Impacts expressed in previous
discussions remain valid and recent advisory/warning products can be
referenced for impacts specific to each river and site.

Light rain is expected to bring about one-tenth of an inch of
precipitation late Thursday into Friday. This will have no impact on
current forecasts. The next system will come over the weekend, late
Saturday into Sunday with around one-quarter to around three-tenths
of an inch. These amounts may stall improvement slightly. However,
this system will be one to watch, as higher precipitation amounts
are just south of Lower Michigan and any northward adjustment could
further impact forecasts. For now, no additional impacts are
expected.

&&

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

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Meade
AVIATION...Ostuno
HYDROLOGY...JAM



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