Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 202343
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
643 PM EST Tue Feb 20 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 329 PM EST Tue Feb 20 2018

Rain will continue tonight and occasionally be heavy, especially
southeast of a Grand Haven to Mt. Pleasant line.  Around an
additional inch of rain is likely overnight, which will only worsen
flooding over the region.  The rain is expected to turn into a
wintry mix toward daybreak Wednesday.  A light glaze of ice could
occur on elevated surfaces such as car tops and trees.  The
precipitation will end Wednesday morning, with some sunshine
expected into the afternoon.

Another system is expected to give us a wintry mix again Thursday
night into early Friday, but it is expected to change to all rain
later Friday.  Then another good chance of rain arrives Saturday
night into Sunday.

Temperatures are expected to remain above normal, with daytime highs
mainly 40 to 45 into next week, and lows mainly in the mid 20s to
lower 30s.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 329 PM EST Tue Feb 20 2018

The last wave of heavy rain will come tonight as the cold front
comes through.  Some areas will see another inch of rain.  The
precipitation will end as a light wintry mix late tonight into early
Wednesday.

The cold front will come through with plenty of upper support
tonight.  Precipitable water values of 1.25 to 1.5 inches and the
lift from the upper and low level jet will make for a very efficient
rain maker overnight.  Given the timing of all these features coming
together, the SE half of the CWA, from roughly Grand Haven to Mt.
Pleasant southward will see the heaviest rainfall of around an inch,
with some areas exceeding that.  This will only add to the flooding
woes, perhaps pushing some rivers to a moderate flood when we see
crests by later this week and into the weekend.

Cold low level air rushes in later tonight, while levels closer to
5k ft remains warm.  This should result in a brief period sleet
and/or freezing rain after midnight until about daybreak.  Given the
warm rains that have warmed the ground, not expecting that roads
will become slippery.  Instead any ice accums will be on cars, or
aloft in the trees, and road signs.  Drier air will be pushing in
from the NW and GRR and points NW will see the pcpn end by 12Z.  A
lingering wintry mix to the SE of GRR should still occur into
Wednesday morning, but this too will be brief with little impact
expected.

Skies will quickly become partly sunny behind the pcpn from NW to SE
on Wednesday, and even mostly sunny by the end of the day.  It will
be much cooler tomorrow behind the front with highs mainly in the
30s.

Fairly quiet weather will continue Wednesday night and Thursday,
although some light snow or flurries may occur as a system moves to
our south.  High temps Thu mid 30s to lower 40s.  The next decent
chance of pcpn won`t move in until late Thursday night with low
pressure moving NE out of MO.  Forecast soundings suggest snow
initially, but then warm air aloft moves in overnight which could
switch the pcpn to freezing rain.  The Friday morning commute could
be impacted.

.LONG TERM...(Friday through Tuesday)
Issued at 329 PM EST Tue Feb 20 2018

There are two main weather systems of concern in the long term
coming through the southwest flow aloft: One on Friday and another
on Saturday night. Fortunately the QPF progs do not look excessive
with either system. Temperatures will remain above normal.

The first system on Friday brings some light freezing rain in the
morning changing to rain before ending in the afternoon. Latest
guidance has less than a quarter inch of QPF. The warm conveyor belt
rains stay south through the Ohio Valley and the area of wintry
precip with the mid level shortwave passes through Wisconsin and
Upper Michigan.

The second system impacts the area on Saturday night and Sunday
morning but also shows signs of potential QPF bifurcation for Lower
Michigan. A very similar set up to the first system is shown, with
convection preferring the Ohio Valley region and the swath of snow
in the colder air tracking through Wisconsin. In between, we see
scattered showers in the warm sector Saturday night, possibly
starting as snow especially north of I-96, followed by a cool down
on the back side of the system on Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 643 PM EST Tue Feb 20 2018

Heavy rain will be moving east overnight but some areas of IFR are
possible through 06Z. Generally MVFR conditions through 18Z
Wednesday then becoming VFR by Wednesday afternoon.

&&

.HYDROLOGY...
Issued at 329 PM EST Tue Feb 20 2018

Very little has changed in the last 24 hours. Widespread rainfall
amounts of 1 to 2 inches fell overnight Monday into Tuesday morning.
These amounts, in addition to snowmelt and frozen surface layer,
resulted in rapid feedback on area streams and rivers. All rivers
are being impacted by some magnitude of river rise and/or flooding.

Most notable impacts are along the Looking Glass River near Eagle.
Emergency management reported several roads closed in Watertown and
Eagle Twp, various road along the river, flooding in Wacousta Park
and homes threatened and/or impacted in/near Grand Ledge and Fowler.
The river is forecast to continue to rise overnight, possibly
achieving record levels of around 10.5 feet late Wednesday evening.
Given record event type levels, reference data is limited to the
type of impacts that could occur beyond previous events. All
residents should continue to heed advice from local official, while
maintaining vigilant to river levels and keep up with latest
forecasts.

The Grand River basin will also take on plenty of water from smaller
streams and tributaries. Several sites along the Grand River will
reach moderate flood level, while Comstock Park could reach over 17
feet, which is slightly below 2013 levels.

Additional rainfall this evening through early Wednesday morning is
expected to generally range from 1 to 2 inches. Embedded storms
could result in periods of heavy rain, possibly enhancing localized
rainfall totals. The greatest totals are likely to fall over
Southern Lower Michigan, in places already impacted by last night`s
heavy rain. River rises will continue through the end of the week
with larger rivers cresting over the weekend. Areas away from
rivers, such as low lying, flood prone locations, will also run the
risk of minor flooding, at least until rain exits Wednesday.

&&

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

$$

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


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