Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 101200
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
700 AM EST Wed Jan 10 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Wed Jan 10 2018

A increasing southerly flow of air will take hold today across the
Great Lakes region ushering in warmer air. The warm air will result
in areas of fog as higher moisture air is pushed over a melting snow
pack. The fog may become dense in spots through Thursday. Today and
Thursday rain showers can be expected along with temperatures that
will push into the 40s today and into the lower 50s on Thursday. On
the leading edge of the precipitation this morning, with some low
level cold air hanging on, some light freezing rain or drizzle can
be expected. By early afternoon enough warming should have taken
place to change any light freezing precipitation over to all rain. A
cold front will push through Lower Michigan Thursday night bringing
a transition back to a period of brief freezing rain before changing
over to snow. Some accumulating snow is expected late Thursday night
into Friday morning.

&&

.SHORT TERM...(Today through Friday)
Issued at 330 AM EST Wed Jan 10 2018

Main focus in the short term is on 1) dense fog potential today
through Thursday, 2) a chance for some light freezing precipitation
this morning, 3) the transition back to a mix of precip Thursday
night, before 4) some accumulating snow occurs late Thursday night
and Friday.

As for the dense fog, some of the most dense fog that can occur is
when higher dew point air is advected over a melting snow pack. This
situation sets up for much of the next 24 to 36 hours or through the
day on Thursday. Some of our high resolution guidance is indicating
areas of dense fog from this afternoon through tonight and into
Thursday. One mitigating factor is the strong winds just off the
surface with 50-60 knots just 1,000 to 2,000 feet off the ground. At
this point not confident enough to issue a dense fog advisory but
that is something that is certainly possible going forward. We will
be monitoring the evolution of 1/4 mile visibilities.

The light freezing precipitation this morning looks to be just that,
light. QPF totals in the models are on the order of a few hundredths
of an inch in spots. Moisture overviews show a shallow moisture
layer with a DGZ that is quite high. Vertical motion in the shallow
moisture layer has the distinct look of freezing drizzle. Given the
models very consistently showing rain showers moving through left
the mention of freezing rain vs drizzle, but the main takeaway is
this should be a light event. No headlines planned for the freezing
rain/drizzle this morning. We will monitor conditions this morning.
The other item of note is the fog may deposit some moisture on the
cold ground that may result in icy spots. By midday, most of the
area will have risen above freezing taking.

A cold front will plow through the area Thursday night resulting in
a changeover of precipitation from rain to snow. There will be a
brief period where we could see some freezing rain again. The
freezing rain looks light and brief however given the strength of
the front.

The main concern is that a wave on the front late Thursday night and
Friday morning will result in a swath of snow through our area.
Could see a couple of inches of snow in Grand Rapids, with higher
amounts to the south and east. Thinking Lansing and Jackson could
see totals of 2 to 4 inches before it comes to an end.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM EST Wed Jan 10 2018

Confidence has become much stronger that we will miss out on much
of, if not the entire snowstorm that will be ongoing Fri night into
Saturday. Good model consensus now exists in taking the heavier
swath of snow now through Ohio. This is the result of the developing
upper low digging a little further south, and the sfc front/upper
jet being a tad farther east when the wave lifts NE. This will
result in our area being cold once again, with some lake effect
closer to the lakeshore with an almost due N low level flow.

The cold air and lake effect near the shore will remain through the
weekend. The threat of snow will increase by Mon a bit. A fairly
strong upper low will dive SE over the area. This will deepen the
moisture and help to boost lake effect a bit ahead of it. Once the
wave passes, colder air will be reinforced with the low level NW
flow behind it bringing in -20C air at H850. Lake effect will become
re-established for the western half of the area.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 700 AM EST Wed Jan 10 2018

Poor aviation conditions are expected the next 24 hours.
Widespread IFR and LIFR conditions are in place at 12z across the
area and conditions will only slowly lower through the day and
into tonight. We will likely see ceilings drop to around 200ft
today and remain there for tonight. Visibilities will dip to below
1 mile today with the potential to trend toward 1/4 mile. Have
VCSH in the forecast today. There is the potential for some light
freezing drizzle or freezing rain this morning, but have decided
to leave this out of the forecast given somewhat low probabilities
of occurrence. Winds will be southerly the next 24 hours at 10-20
knots.

&&

.MARINE...
Issued at 330 AM EST Wed Jan 10 2018

Left the marine headlines as is with this forecast issuance, that
being a Small Craft Advisory north of Holland into Friday morning.
At some point though going forward we will be transitioning the
southern two zones, south of Holland, into the Advisory as well.
Northwest cold air advection develops right around 00z Friday and
higher waves begin pushing into areas south of Holland around 03z on
Friday. So, headlines look good right now for the strong south flow
that develops today and persists through Thursday. 5 to 8 footers
are expected in the southerly flow. The south end of the lake on
Friday looks to hit the 6 to 10 foot range.


&&

.HYDROLOGY...
Issued at 127 PM EST Tue Jan 9 2018

Expect river rises to commence with snowmelt over the next couple
days. Melt rates could be especially high on Thursday when high
temperatures around 50 will be possible. Warm temperatures should
limit the ice jam threat. The Grand River basin has an estimated
snow water equivalent of 1-2 inches over much of the area. We
expect bankfull might be exceeded in spots later this week and
this could also be the case for smaller streams elsewhere across
Southwest Lower Michigan.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 10 AM EST Friday for LMZ846>849.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...NJJ
AVIATION...Duke
HYDROLOGY...TJT
MARINE...Duke



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