Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 160427
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1127 PM EST Mon Jan 15 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 313 PM EST Mon Jan 15 2018

Light snow will slowly diminish tonight for most areas away from
Lake Michigan as a system slowly begins to rotate away from the
area. Some lake effect snow showers will persist into Wednesday
morning.

The weather will quiet down for a couple of days in the mid-week
time frame with high pressure building in. Warmer weather is on the
horizon later this week into the weekend with highs expected to be
at least in the 40s. Rainy weather will move in later Saturday, and
will transition to snow on Monday as colder weather moves back in.

&&

.UPDATE...
Issued at 1127 PM EST Mon Jan 15 2018

Strong convergence is occurring in a zone from Holland east to
near Charlotte. Reflectivity has blossomed in the last hour or two
in this zone. The convergence is related to the strong temperature
contrast both to the north and south of the band of moderate snow.
Temperatures range from the middle teens in the snow band to near
and slightly below zero temps off to the north and south.

The NAMnest has a pretty good handle on this snow band at the
present time. It shows the band weakening with time tonight and
slowly sagging off to the south. Expectations are that we may see
an additional 1 to 3 inches of snow from Ottawa and Kent Counties
south through Allegan and Van Buren. The heaviest snow should
occur across Allegan and Van Buren counties. Therefore, the Winter
Weather Advisory was left as is.


&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 313 PM EST Mon Jan 15 2018

We are planning on dropping the Winter Weather Advisory for all
locations except Allegan and Van Buren counties with this forecast
package. Our main focus of the forecast is dealing with snow trends
into Wednesday morning before snow ends.

Light snow is ongoing over the area this afternoon, and has trended
down slightly for the most part compared to earlier. There is a
slightly enhanced band pretty much along I-96, mainly east of Grand
Rapids as of 20z. This is likely associated with a short wave
rotating through the upper low complex over the region. In addition,
some enhancement is occurring east of Lansing, likely due to some
enhancement off of Lake Erie with a SSE flow.

The light snow is not enough to justify keeping the headline for all
of the area, with only up to an additional inch expected at most
locations. The advisory that is in effect longer, will be kept for
Allegan and Van Buren counties through tonight. This is due to the
expected lake enhancement that occurs there this evening and part of
the overnight hours as the flow becomes onshore down there for a
bit. Some snow can be expected for the southern half of inland
areas, but again it should not be heavy enough to produce
significant enough impacts.

The upper system will depart the area Tue afternoon. This will leave
only some residual lake effect. The band will start out Tue
afternoon out over the lake with a N flow. This will gradually shift
onshore Tue night, before dissipating Wed morning. The upper flow
being anti-cyclonic at that time should limit the intensity a bit,
after the band loses it`s long fetch down the lake. Also, temps
aloft will be warming steadily to limit the instability. We will
eventually see clearing take place late Wed and more so Wed night
once what is left of the lake effect dissipates.

.LONG TERM...(Thursday through Monday)
Issued at 313 PM EST Mon Jan 15 2018

The main challenge in the long term deals with the amount of warmup
we see along the potential impacts from the next storm.

To start a backdoor cold front slips down from the north Thursday
Night supporting slowing down the warmup.  During Friday 925 mb
temps are forecasted to rise in the positive territory...which
should support temps at least above freezing.  Mid level confluent
flow has been increasing the past couple of runs across Ontario for
the weekend. This would support a high pressure system
there...possibly funneling shallow cold air in from the north for
the weekend here in MI.  Will need to monitor this trend...which
would have some impacts on the temperatures here in MI. So...will
still feature a warmup...but not as much as previously forecasted.

Models continue to show a powerful storm tracking through the
Southern Rockies and out into the Plains Sunday.  This system will
scoop up some Gulf moisture before it heads our way.  QPF should be
heavy at some point Sunday Night into Monday.  With the potential
for high pressure system to be centered over Ontario...there is an
elevated risk for a wintry mix for the CWA transitioning to rain as
the storm pulls in.  This would then be followed by the rain
changing to snow as colder air wraps in behind the departing storm
on Monday.  For now will not put zr/ip in the forecast for Sunday as
confidence is rather low...but it is a trend to monitor closely
given an increased risk for winter impacts.  Will need to monitor
the impacts to the rivers as well as the qpf looks to be potentially
heavy with this system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 701 PM EST Mon Jan 15 2018

Variable conditions are expected the next 24 hours as a weakening
trough of low pressure will be situated across the Southern Great
Lakes region. Conditions vary from MVFR to VFR for the most part
at 00z, with the IFR becoming less prevalent. The general thinking
is we will continue to see variable conditions as snow will weaken
and intensify at times through the period. Overall, though a slow
improving trend should be noted as we head from tonight into
Tuesday. Fairly widespread MVFR at least is in place and given the
time of year and time of day we should expected to see the MVFR
conditions continue or expand a bit into Tuesday morning. The
heating of the day and the weakening trough should tend to lift
ceilings a bit on Tuesday. We have the TAFs trending toward VFR
Tuesday afternoon. Winds will generally be under 10 knots through
the period.


&&

.MARINE...
Issued at 313 PM EST Mon Jan 15 2018

We will be letting the Small Craft Advisory go with the afternoon
forecast package. An offshore wind and diminishing winds are
bringing down winds and waves below criteria. The next period of
stronger winds and higher waves looks to begin around the Wed
afternoon time frame.

The nearshore forecast and marine headlines for the nearshore waters
from Manistee to St. Joseph will be coming to an end for the season
after the late evening forecast tonight. These products will be
resuming toward the beginning of April.


&&

.HYDROLOGY...
Issued at 313 PM EST Mon Jan 15 2018

Observations through Southwest Lower Michigan show overall stability
on area rivers. This is expected to be the case through the next few
days with highs near or below freezing through Thursday.

Next weekend`s temperatures may be a factor in raising concerns for
additional ice jams. Guidance places a strengthening system over the
Midwest, which results in strong southerly flow and temperatures in
the 40s through the area. Precipitation then streams in by early
next week, yielding amounts that exceed one inch through portions of
Western Michigan.

There is still plenty of time for forecast details to be worked out
and trends will need to be monitored over the next several days.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 7 AM EST Tuesday for MIZ064-071.

LM...None.
&&

$$

UPDATE...Duke
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...Duke
HYDROLOGY...JAM
MARINE...NJJ



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