Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 222029
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
328 PM EST Thu Feb 22 2018

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

.SYNOPSIS...
Issued at 328 PM EST Thu Feb 22 2018

A brief wintry mix will occur toward midnight.  Most areas will see
a very light glaze of ice, but it should be a bit more significant
toward Central Lower.  All areas will see the precipitation change
over to rain just prior to daybreak.  Then rain will end toward mid
day Friday.  After a quiet period Friday afternoon and night, rain
will move back in on Saturday and continue Saturday night.  Some
snow may mix in at the onset of the precipitation.  A risk of
thunderstorms will be possible Saturday night as warmer air surges
north.  More rain is expected into the middle of next week.

Daily temperatures are expected to remain in the 40s, with 50s
possible on Tuesday.  Nighttime lows will mainly be in the 30s.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 328 PM EST Thu Feb 22 2018

Will issue a winter weather advisory for the far NW CWA where a
wintry mix could lead to slippery roads by the morning commute. Rain
returns Saturday and Saturday night with thunderstorms also possible.

Low pressure will pass to the northwest of Lower Michigan toward
daybreak Friday.  The models have trended warmer with more of a SE
flow.  This should result in only a brief period of mixed pcpn.
However the duration will be longer the farther north one goes. Also
the steadier pcpn is expected to occur closer to the track of the
low, meaning the NW CWA will be most under the gun for steadier
pcpn, in combination of a longer duration where surface temps will
be below freezing.  Expect around 0.05 of an inch of glaze where the
advisory will be (Mason and Lake Counties), and lesser amounts to
the east and south.

The surface temps will be rising toward daybreak Friday from south
to north, ending the risk of freezing pcpn.  This occurs by 09Z over
the far south, to 15Z Fri in the north.  Rain will occur through the
rest of the morning, but as the low exits we will see a dry
afternoon.  Friday night also will be dry.

A more intense surface low will track NW of the area again Saturday
night.  Moisture flux arrives from south to north through Saturday,
and solidly in place by Saturday night.  The pcpn may start as a
period of rain/snow mix Saturday, but warmer air will surge in
changing it over to all rain. A 984 mb low will occlude into
Saturday night and a few isolated thunderstorms will be possible as
this front crosses the CWA Saturday night.  It will also become
quite windy late Saturday night as we see the lead edge of the cold
advection arrive.  This system moves through rather quickly so
rainfall amounts will be somewhat limited with a quarter to a half
inch of rain expected.  This may delay some of the rivers subsiding,
with the risk of thunder possibly adding a wild card to possible
localized heavier rains.


.LONG TERM...(Sunday through Thursday)
Issued at 328 PM EST Thu Feb 22 2018

500 mb flow pattern changes Sunday as strong wave moves from the
Central Plains into Ontario. Zonal flow/weak ridging will dominate
the extended period...as a closed low develops over California. That
system lifts out into the Central Plains and weakens Thursday...
which will give us a chance of precipitation Wednesday and Thursday
as the system approaches.  Models in good agreement through late
Tuesday...then they diverge in how they handle the upper low over
the southwestern US.

Cold air will return to the region Sunday on gusty northwest winds
as the initial system departs...with moderating temperatures
expected Monday and Tuesday.  A dry cold front will pass through
late Tuesday...bringing slightly cooler temperatures.  H8
temperatures fall below zero Sun morning as system passes overhead.
CMC doesn`t bring sub -10 C air into the region...rising above zero
Tue/Wed before falling back below zero on Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1215 PM EST Thu Feb 22 2018

Visible satellite imagery showing breaks in the cloud cover over
portions of West Michigan and continued clearing across far
southwest Michigan into adjacent areas of Illinois and Indiana.
VFR ceilings elsewhere. Radar indicating a few echos south of a
KAZO to KLAN line...with a few more shown from Milwaukee northeast
into northern Lower Michigan. Areal coverage and intensity of
radar returns has been decreasing over time. MVFR ceilings from
Central Illinois south and west will advect into the area later
this evening...but have above average confidence in VFR conditions
continuing through at least 00Z Friday.

Persistent southwesterly flow at mid levels will bring increasing
chances for precipitation at West Michigan TAF sites during the
latter portions of the upcoming forecast period. Models are
consistent in creating two areas of precipitation...one that will
remain south and east across Ohio and southern Indiana...and the
second which across Wisconsin and Upper Michigan. Still enough of
a threat exists to include mention of precipitation for all West
Michigan TAFs between 09Z and 18Z Friday.

There is some concern about precipitation type...as thermal
profile suggests the possibility of freezing rain for a brief
period around sunrise. Will keep the forecast all liquid for
now...but situation needs to be monitored and earlier onset of
precipitation could cause enough of a threat of freezing
precipitation to include in future forecasts.

&&

.HYDROLOGY...
Issued at 328 PM EST Thu Feb 22 2018

Water that ponded into low-lying areas and smaller rivers, creeks,
and streams is continuing to slowly make its way into the larger
rivers. Moderate to major flooding is expected to occur along the
Kalamazoo, Thornapple and Grand Rivers tomorrow into the weekend.
Water levels along the Grand River are expected to approach or
possibly exceed levels reached during the flooding in April of 2013.
Water levels along the Kalamazoo River, particularly near Comstock,
are expected to near levels that occurred in September 2008.

Please see the latest flood statement or river hydrographs for
details. Hydrographs are available by going to weather.gov/grr and
clicking on the "Rivers and Lakes" tab above the map.

A wintry mix of precipitation is expected late tonight through
Friday morning. This should not impact river levels or cause ongoing
flooding to worsen. Precipitation from a low pressure system over
the weekend will spread mostly rain into the area Saturday night and
Sunday. Amounts could exceed 0.25 inches, and could approach 0.50
inches near the Michigan/Indiana border. This may slow the receding
of waters and prolong river crests for rivers that crest over the
weekend. This precipitation is not yet accounted for in river
forecasts, as it is not expected to fall within 48 hours.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 3 AM to 10 AM EST Friday for
MIZ037-     038.

LM...None.
&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...MWS
AVIATION...MWS
HYDROLOGY...HLO



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