Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220248
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
948 PM EST Sun Jan 21 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 330 PM EST Sun Jan 21 2018

A strong storm system will cross Southern Lower Michigan late Monday
night.  This will bring rain to the region.  The rain will pick up
after midnight tonight and continue into Monday evening.  Then
colder air arrives late Monday night, changing the rain to snow.
Some areas will see light snow accumulations into Tuesday morning,
before it diminishes Tuesday afternoon.  Another system heads our
way by Friday night, bringing rain changing to snow Saturday night.

Temperatures will be up and down through the week.  Highs will
mainly be 40 to 45 Monday and Tuesday, cooling to 35 to 40 Wednesday
and Thursday.  Then back into the 40s Friday and Saturday, and
cooling once again by next Sunday.

&&

.UPDATE...
Issued at 947 PM EST Sun Jan 21 2018

No changes to the Dense Fog Advisory with several sites still
showing visibilities of 1/4 mile. The arrival of the more
persistent and heavier rain later tonight may mix out the fog a
bit, so it`s possible the advisory could be cancelled early if
visibilities improve.

Latest hi res models show the heavier/convective precip arriving
along I-94 around 09Z, and along I-96 toward 12Z, persisting
through about 18Z. Axis of heaviest rainfall appears to set up in
a band from South Haven and Holland, east-northeast across Grand
Rapids, to Lansing, St. Johns and Alma. Consensus is for total
amounts in this band of 1 to 1.5 inches, which increases
confidence enough to issue Flood Advisories for several river
forecast points (see FLSGRR).

Have added a slight chance of thunder to the fcst south of I-96
after 09Z, as a few hundred joules of elevated cape arrives from
the south.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 330 PM EST Sun Jan 21 2018

A very wet and dynamic system will move into the region late
tonight.  Many areas will see an inch or more of rainfall through
Monday evening, leading to hydro concerns.  On the back side of the
system some snow will fall, but accumulations are expected to be two
inches or less.

Low pressure will eject out of the Central Plains tonight and cross
Southern Lower Michigan late Monday night.  Plenty of Gulf moisture
gets wrapped up into this system with PW values climbing to around 1
inch.  Jet dynamics set up over the region by early Monday with a
coupled upper jet in place, leading to moderate upper divergence
throughout the morning and into the afternoon.  This coincides with
a low level jet noses into lower Michigan.  This scenario should
produce a very rain effective system starting late tonight and
continuing into Monday afternoon.

Much of the CWA should see near or over an inch of rain.  Localized
amounts approaching an inch and half are possible.  See hydro
discussion for more details on these concerns, along with snow melt
off.

Rain will change to snow late Monday night and continue in the
deformation zone on Tuesday morning.  Looks like a quick hitter
here, and along with temperatures near or just above freezing, and
snow falling on soggy ground, we may not see too much snow
accumulation. Areas north of I-96 stand the best chance to see
accums, but feel this area will see two inches or less.

In the meantime we will have to watch fog trends.  Areas already
have fairly low vsbys and fog should become more common into Monday.
A fog advisory is not out of the question later tonight and into
Monday.

.LONG TERM...(Wednesday through Sunday)
Issued at 330 PM EST Sun Jan 21 2018

The long term begins with some lake effect snow lingering from
Wednesday into Wednesday night. The lake effect does not look heavy
as delta t`s are marginal over Lake Michigan and moisture is
shallow. Any accumulations would be minor across Western Lower
Michigan.

850mb temperatures warm on Thursday taking any lake effect out of
play. A dry period is expected from Thursday into Friday as high
pressure shifts east through the area.

Friday night into Saturday rain showers are expected as a cold front
moves through the region. Saturday night into Sunday the
precipitation will mix with snow as colder air filters in behind the
front. Some light accumulations of snow are possible towards Jackson
on Sunday as a wave of low pressure is forecast to ride up the front
into the Eastern Great Lakes. The ECMWF would suggest a 1-3 inch
snow is possible next Sunday towards Jackson.

Bottom line a bit of an up and down long term period in regard to
temperatures with a warmer period Thursday and Friday. The warmer
period will have some snow on either end (Wednesday and Sunday).

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 709 PM EST Sun Jan 21 2018

Widespread LIFR/VLIFR conditions expected to persist tonight due
to stratus/drizzle/fog. Cigs/vsbys may improve a bit once the more
widespread and heavier rain develops after 10Z but conditions still
remaining IFR through most of Monday.

The heaviest rain will occur between 10z and 18z Monday and there
could even be some thunder during this time, especially near the I-94
corridor with the arrival of the elevated instability and 60kt
southerly low level jet. A period of LLWS may develop on Monday as
these stronger southerly winds at 2000 ft push through the area,
especially south and east of GRR.


&&

.HYDROLOGY...
Issued at 214 PM EST Sun Jan 21 2018

A complete melting of the natural snowpack is expected by Monday
in the Grand, Kalamazoo, and Muskegon river basins. This will
release a quarter to perhaps half inch of water. Rain totals on
Monday will mostly range between 0.6 and 1.2 inches (ECMWF and
ensemble have been consistently lower than GFS and ensemble).
Depth of frozen soil varies but overall expect the ground to
remain frozen enough to allow efficient runoff.

A number of river forecast points will likely rise above bankfull
in the upcoming week. There is a chance of minor flood stage being
reached at a few sites (of earliest concern are Holt and Eagle),
particularly if higher rainfall totals verify. A breakup of river
ice is expected, and any ice jams that form can cause
unpredictable fluctuations in water levels. Road closures are
possible in low spots near river banks. Water could also approach
buildings in flood prone areas.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 7 AM EST Monday for MIZ064>067-071>074.

LM...None.
&&

$$

UPDATE...Meade
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Duke
AVIATION...Meade
HYDROLOGY...CAS


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