Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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158
FXUS63 KGRR 130522
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1222 AM EST Wed Dec 13 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 322 PM EST Tue Dec 12 2017

Lake effect snow continue along the lake shore with scattered snow
showers inland. A clipper will move across the state Wednesday
bringing accumulating snow to much of southwest Lower Michigan. Yet
another clipper will move across the state Friday bringing more snow
to the region.

&&

.UPDATE...
Issued at 946 PM EST Tue Dec 12 2017

No major changes to the ongoing forecasts for the evening. Lake
effect snow bands continue generally west of Highway 131. Radar
estimates rates up to an inch per hour in the main band around
Zeeland. Estimated accumulations since 4 pm are approximately 2 to
4 inches across western Ottawa...much of Allegan except the far
east...and also for Van Buren to western Kalamazoo counties. The
main band was pushing inland with persistent bands developing
further west. Satellite imagery shows colder clouds overspreading
the ongoing lake effect near the lakeshore...with temps down to
-26 deg C. Could be some seeding from these clouds helping out
 with keeping the lake effect relatively organized.

The next storm moves in for tomorrow...with models speeding it up
somewhat. The 7am start time still looks good though. There seems
to be better agreement in not shifting the band north of Grand
Rapids and Lansing. Widespread 4 plus inches look likely at this
point.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 322 PM EST Tue Dec 12 2017

Forecast concerns deal with ongoing lake effect snow and the next
clipper arriving tomorrow morning.

Lake effect continues along the lake shore where visibilities have
briefly fallen to less than a mile throughout the day. Conditions
remain very favorable for lake effect snow to continue tonight.
Cross sections show that lift is centered in the DGZ through much of
the evening. Expect several inches more snow in the warning area.

We discontinued the advisory for Lake and Newaygo counties and the
warning for Kalamazoo county, but kept the warnings going overnight
along the lake shore.

The next system is a clipper that will move from Minnesota across
northern Illinois. HiRes models indicate snow will develop around
12z along the lake shore and spread inland. For that reason, we
extended the winter storm warning until Wednesday evening and issued
a winter weather advisory for the non lake shore counties...also
until Wednesday evening.

Pretty good pressure advection was noted with this system and a
deformation axis will likely set up near a MKG-LAN line. We`re
looking at 5 to 7 inches of snow with this system within 40 miles of
this line with lesser amounts in the northeast and far southwest
cwa.

Colder air will be brought south behind the departing clipper and
more lake effect snow can be expected Thursday and Thursday night.

.LONG TERM...(Friday through Tuesday)
Issued at 322 PM EST Tue Dec 12 2017

Fast flow regime continues through the extended with the usual model
differences in timing and amplitude of embedded shortwave features.
Fairly high confidence for Friday with a clipper and quick shot of
arctic air bringing some snow into Saturday morning.

Warm advection pattern is already underway by Saturday evening as
Plains low makes a run at Lower Michigan on Sunday into Monday.
Forecast confidence decreases here as low track is uncertain and
whether Gulf moisture transport reaches here, along with precip type
if it does. Did not deviate from blended POPs here...although they
are not representative of 12Z operational ECMWF, which would be
higher across the southern half of the forecast area.

Once that low gets past it looks like temperatures drop again with
some lake effect snow in west flow on Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1222 AM EST Wed Dec 13 2017

The lake effect snow showers will continue to diminish, however
as they move inland there could be a brief period of IFR at MKG
and GRR.

Then a clipper approaches toward daybreak. The steadiest snow is
expected to be from I-96 northward. This leads to MKG, GRR and LAN
feeling the most impact as compared to the I-94 TAF sites. This
will be a prolong snow. Periods of IFR can be expected along I-96
from about 14Z to 00Z. Meanwhile it now seems that the I-94 TAFs
may only should only see brief periods of IFR mainly in the
afternoon.

After 00Z the snow will let up and all areas return to VFR or
MVFR.


&&

.MARINE...
Issued at 322 PM EST Tue Dec 12 2017

Wind continues to slowly subside and most locations are under gale
force. Therefore, we discontinued the gale warning and issued a
small craft advisory through Wednesday afternoon. Waves will
continue to be well above 3 feet through tonight.

&&

.HYDROLOGY...
Issued at 1028 AM EST Tue Dec 12 2017

Rivers are running near normal levels. No flooding or significant
rises in river levels are expected. Snow is forecast periodically
through the week.

Temperatures have been around to below freezing for a week and
similar temperatures are expected to persist through the end of this
week. This should allow some ice to begin forming on area rivers,
especially on the Muskegon River in Central Lower Michigan.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning until 11 PM EST this evening for MIZ037-043-
     050-056-064-071.

     Winter Weather Advisory from 7 AM this morning to 11 PM EST this
     evening for MIZ038>040-044>046-051-052-057>059-065>067-
     072>074.

LM...Small Craft Advisory until 4 PM EST this afternoon for
     LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...04
SHORT TERM...04
LONG TERM...Ostuno
AVIATION...JK
HYDROLOGY...63
MARINE...04



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