Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 151628
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1128 AM EST Thu Feb 15 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 323 AM EST Thu Feb 15 2018

Fog and drizzle will persist this morning then rain showers will
move through this afternoon as low pressure tracks south of
Michigan. A cold front comes through tonight with rain showers
changing to snow showers. Colder weather with periods of snow
showers will continue into the weekend.

&&

.UPDATE...
Issued at 1127 AM EST Thu Feb 15 2018

We issued a dense fog advisory until 22z for areas along/south of
I-96. Widespread dense fog should persist until the cold front
sweeps through late this afternoon.

UPDATE Issued at 750 AM EST Thu Feb 15 2018

Dropped the Dense Fog Advisory as current obs show all reporting
sites are half mile or greater visibility. Some patchy quarter
mile visbilities are possible in the next couple hours but not
widespread enough to keep the advisory going.

&&

.SHORT TERM...(Today through Saturday)
Issued at 323 AM EST Thu Feb 15 2018

Will keep the dense fog advisory as is for now, but we will watch
obs later this morning to see of it needs to be extended later.
Steadier showers moving in later this morning across the southern
half of the forecast area should help dissipate the dense fog.

Other forecast issue is timing change over as the steadier precip
ends tonight and transitions to lake effect snow showers Friday
morning. Not expecting much accums as inversion heights are around
5 kft then crash as sfc ridging builds in Friday afternoon.

Light snow with some lake enhancement expected Saturday afternoon
as northern stream shortwave trough approaches. Light accums are
possible.

.LONG TERM...(Saturday night through Wednesday)
Issued at 323 AM EST Thu Feb 15 2018

The models are coming into better agreement into the extended
periods, however there are still various timing issues.

A short wave crosses the CWA Saturday evening.  Once this passes the
snow will come to an end late Saturday night.  Accums will general
be under an inch, but localized two inches will be possible toward
the higher terrain in Central Lower.

A warming trend will begin Sunday night as a surface boundary moves
slowly into the Western Great Lakes.  Flow ahead of this system will
be southerly, bringing the warm air.  We should begin to see the
chance of pcpn late Sunday night or Monday morning.  If it arrives
early enough we could see light freezing rain at the onset,
otherwise rain should be the pcpn type.  Decent rains could occur
Monday afternoon and night as the surface boundary only sags through
slowly, being parallel to the upper flow, along with deep SW flow.

The timing differences really show up late into Tuesday/Wednesday as
to when the front finally moves through.  General consensus has it
pushing SE of the area on Tuesday, then turning colder Tuesday night
into Wednesday.  The steadiest rains should push off with the front,
then as the colder air returns the rain should switch to snow
Tuesday afternoon or Tuesday night.  Not an overly cold air mass, so
it looks doubtful we will see any lake enhancement to the snow, but
it should continue lightly into Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 628 AM EST Thu Feb 15 2018

IFR and LIFR conditions can be expected through 18Z across much of
southern Lower Michigan. Then IFR and MVFR will continue into the
evening and overnight. Winds will be southwest around 10 to 15
knots this morning and turn northwest around 10 knots tonight.


&&

.HYDROLOGY...
Issued at 1059 AM EST Thu Feb 15 2018

Snow water content in the Grand River basin is about 1.5 inches,
and about a half inch of it is expected to melt today. The
Looking Glass River near Eagle and Sycamore Creek in Holt may rise
out of bank over the next couple days in response to this
snowmelt. Ionia may do the same. Ice on the rivers will continue
to cause short term fluctuations. A low confidence of heavy rain
with a medium confidence of total snowmelt Mon to Tue will likely
keep river levels elevated with an outside chance of more
substantial flooding.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 5 PM EST this afternoon for MIZ050-
     056>059-064>067-071>074.

LM...None.
&&

$$

UPDATE...04
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...JK
AVIATION...Ostuno
HYDROLOGY...CAS



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