Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 170030
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
830 PM EDT Thu Mar 16 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 336 PM EDT Thu Mar 16 2017

A weak system will bring wintry conditions to much of Lower
Michigan during the day Friday. A very brief period of mixed
precipitation may occur before the bulk of the precipitation
moves east. It briefly turns mild early next week with
temperatures near 50 on Monday and a quick round of rain. Overall
conditions will average to near normal through the week with a few
snow showers Tuesday, as a system passes our northeast.

&&

.UPDATE...
Issued at 828 PM EDT Thu Mar 16 2017

All of the latest model guidence shows the precipitation starting
an hour to two later than we previously through so I updated the
grids a touch to slow the start time of the precipitation. The
Advisory will remain as I still believe we will see snow to sleet
and rain then to rain with some areas of freezing rain.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 336 PM EDT Thu Mar 16 2017

The primary concern will be another quick round of winter weather
moving in early Friday morning. A burst of snow is likely to
create hazardous driving conditions around the morning commute
into the early afternoon. Snow may be followed by a brief wintry
mix. Winter weather headlines will be issued to cover potential
impacts to the morning and mid-day commutes.

The main timeframe of concern progresses from west to east with
initial precipitation possibly starting as early as between 4-6
a.m. for the western CWA and running as late as 4 p.m. for far
eastern sections of the area.

This system can be seen on water vapor imagery taking shape over
southern Saskatchewan and Manitoba. The upper level and surface
features are vertically stacked, remain fairly weak and will
continue to dig southeast into the Great Lakes Region during the
day Friday.

Upper level ridging, along with surface and mid-level southerly
flow will result in warm air advection Friday morning. Moisture
deepens along the warm front with plenty lift in the DGZ capable
of resulting in a quick burst of snow for a few hours. One
inhibiting factor may be dry air near the surface. This may delay
the onset of snowfall, especially through central Lower Michigan,
but will be just enough to result in a short period of lower
visibilities and slick conditions at a time that will impact
morning commuters.

While mixed precipitation has been a concern over the last few
days, latest trends have lessened concerns for anything
substantial. Moisture depth rapidly decreases as mid and upper
flow turns westerly Friday afternoon. Additionally, trends have
been slightly cooler with the temperatures profiles through a bulk
of the activity. The warm air wedge is less pronounced and by the
time it does arrive, we see a downward trend in precipitation
intensity and surface temperatures gradually rise above freezing.
A brief period of freezing rain/sleet cannot be ruled out through
the middle of the day. The greatest chance runs through the
southern CWA with less than one-tenth of an inch of qpf to
contribute. Snowfall totals are likely to be 2 inches or less.

Northwest flow takes over Saturday with plenty of shallow moisture
hanging around. While temperatures are well below freezing aloft,
lift remains below the DGZ with above freezing surface temps. A
few sprinkles or drizzle will make for a gloomy, cool Saturday.

.LONG TERM...(Sunday through Thursday)
Issued at 336 PM EDT Thu Mar 16 2017

After a nice  day on Sunday, with highs in the mid and upper 40s, we
will see a cold front bring wet weather by late Sunday night into
Monday.

Then we will see a colder period move back in by Monday night and
last through Thursday.  Northwest upper flow develops behind the
cold front and H8 temps drop to -10C to -15C by Tuesday and
Wednesday. this will put high temps back into the 30s. A few light
lake effect snow showers may occur Tuesday. otherwise a Canadian
high pressure center drops into the Western Great Lakes, likely
mitigating any lake effect.

Rain and snow will be possible by Thursday in a warm air advection
pattern, behind the high

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 754 PM EDT Thu Mar 16 2017

There is an area of precipitation heading this way, and it should
bring IFR and maybe even LIFR conditions to the area by late
Friday afternoon (drizzle, fog etc). On the leading edge there
will be a band of moderate to heavy snow (about an hour worth at
any one location) that will cross the TAF sites mid morning but
that will change to sleet, freezing rain then rain by early to mid
afternoon. The drizzle kicks in by late afternoon. On the up
side, at least though 09z expect solid VFR across all of the TAF
sites, and if the precipitation slows down enough, maybe we can
push that to 12z. Actually there is an issue with the models being
to fast on the start time. The latest runs area 1 to 2 hours
slower than runs early in the day. I wrote the tafs to account of
a slower arrival of the precipitation.


&&

.MARINE...
Issued at 221 PM EDT Thu Mar 16 2017

Will issue a small craft advisory north of Holland staring early
Friday morning.  South winds will increase overnight, reaching
around 20 knots prior to daybreak.  Winds will then slowly diminish
late Friday as the winds turn to the west. This will lead to a
brief lull in the rough conditions much of Friday night

We will likely need another small craft advisory by early Saturday
morning through Saturday evening when northwest winds kick up to
around 20 knots leading to building waves again.


&&

.HYDROLOGY...
Issued at 206 PM EDT Thu Mar 16 2017

Minimal melt water and runoff from recent snowfall combined with
minor additional snow and rain amounts Friday should not yield any
appreciable rises on area rivers and streams. The next prospect
for any significant rainfall may hold off until the end of next
week. Until then, we do not anticipate any hydrologic concerns.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 4 AM to 4 PM EDT Friday for MIZ037-
     038-043-044-050>052-056>059-064>067-071>074.

     Winter Weather Advisory from 8 AM to 4 PM EDT Friday for MIZ039-
     040-045-046.

LM...Small Craft Advisory from 8 AM to 7 PM EDT Friday for LMZ846>849.

&&

$$

UPDATE...WDM
SYNOPSIS...JAM
SHORT TERM...JAM
LONG TERM...JK
AVIATION...WDM
HYDROLOGY...Hoving
MARINE...JK



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