Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 240830
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EST Tue Jan 24 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 AM EST Tue Jan 24 2017

Rain will end this morning across central and eastern portions of
the state with dry weather expected this afternoon. Our next weather
maker will move out of Colorado this morning, through the plains
today and tonight and take aim on our area for Wednesday.
Precipitation will spread into Western Lower Michigan tonight in the
form of a rain and snow mix. The precipitation will be the most
widespread on Wednesday with a mixture of rain and snow across
Central Lower Michigan and mainly rain across Southern Lower
Michigan. Colder air will flow in behind the system for Thursday and
Friday on northwest winds. Lake effect snow returns to the forecast
for the end of the week and into the weekend.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EST Tue Jan 24 2017

The main forecast concerns revolve around precipitation type and
determining whether light accumulations of snow are possible in the
late tonight and Wednesday time frame.

The current light rain across eastern portions of the forecast area
should wind down through the course of the morning hours as the
convergence it is associated with wanes. We are expected a dry
afternoon with plenty of low clouds.

The focus shifts to the incoming system for tonight and Wednesday.
The precipitation looks delayed a bit from last night`s model runs
by 6 to maybe 9 hours. Much of the evening hours may end up being
dry. Precipitation spread in overnight with the threat of both a
cold rain and light snow. The heavier precipitation looks to remain
west so not expecting anything significant in terms accumulations.
Any accums tonight would be less than a half inch it appears.

On Wednesday a mix of rain and snow will continue across Central
Lower, while trending to all rain in the southern half of the
forecast area. Accumulations across the high ground of Central Lower
may be around an inch on Wednesday.

Colder air gradually filtering for Wednesday night and Thursday
should turn the precipitation over to all snow. Some light
additional accumulations are possible, on the order of a dusting to
around an inch.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EST Tue Jan 24 2017

Forecast concerns during the long term deal with lake effect snow.

We`ll see a return to colder weather during the extended period. H8
temps Thursday night will be around -10c to start and then slowly
fall to around -12c Friday morning as northwest flow aloft draws
down colder air. Both the gfs and ecmwf show a deep trough aloft
moving toward the lake by 12z Friday. Inversion heights will rise
and lake effect snow will develop as over-lake instability will be
more than sufficient to produce snow. We boosted pops over guidance
considerably from Friday through Sunday.

As the Friday trough moves east during the afternoon, the ecmwf
shows another quickly moving southeast across Wisconsin. That should
result in another flareup of snow showers Friday evening.

Another deep trough moves in Saturday night and Sunday resulting in
more snow.

Several inches of accumulation certain seems possible with the
activity aloft and h8 temps remaining in the -12c to -14c range
through the weekend. H8 temps will warm above -10c Sunday night and
Monday as the deep upper trough moves east and southwest flow
develops.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 226 AM EST Tue Jan 24 2017

Latest neph analysis shows cigs around 400 feet across the cwa.
Visibilities are generally 4-7sm and little change to those are
expected through mid morning. By noon though the light rain should
be ending and cigs will climb to at least 1k ft and steadily
improve during the afternoon, but still remain mvfr. Fog will
likely develop again after 00z.

&&

.MARINE...
Issued at 330 AM EST Tue Jan 24 2017

Main concern are winds that will be on the increase in the wake of a
surface low passing through the area on Wednesday. Southwest winds
will increase Wednesday afternoon, with stronger northwest winds
increase Wednesday night. It appears will we need Small Craft
Advisories Wednesday afternoon into Thursday, but will hold off for
now given its late third and into the fourth forecast period. Waves
will likely be building into the 4 to 7 foot range into Thursday
morning.

&&

.HYDROLOGY...
Issued at 1209 PM EST Mon Jan 23 2017

River levels are in the process of generally falling with the
recent lack of appreciable rainfall over the past few days and
with the ice having moved out with the warm temperatures.

River levels will likely stabilize or even rise a little with
more precipitation expected through Wednesday. No significant
rises are expected, and no major flooding is expected. We are
looking for up to around or just over half an inch with rain
tonight, and rain/snow Tue night/Wed. The precipitation could fall
as mostly snow up north, limiting immediate runoff into the
rivers.

Conditions will become colder at the end of the week and beyond.
Lake effect snow showers will become likely, with little to no runoff
expected after Thursday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...04
AVIATION...04
HYDROLOGY...NJJ
MARINE...Duke



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