Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221717
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1217 PM EST Thu Feb 22 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EST Thu Feb 22 2018

Surface high pressure over the area this morning will result in
mostly cloudy skies and afternoon temperatures slightly above
normal between 35 to 40 degrees. The next system comes through the
area tonight into Friday morning. This will bring the threat of
some light freezing rain, possibly mixed with sleet and snow over
northern sections late tonight into mid morning Friday. It will
warm enough that all areas will see just rain showers my mid to
late morning Friday. That will be followed by a surface high
Friday night into Saturday morning. However a much stronger system
from the southern plains deepens rapidly and comes through
Southwest Michigan Saturday night. This time it should be warm
enough that most areas will just have rain showers. Our northeast
sections could see a little freezing rain Saturday night however.
This system moves out of the area by Sunday evening.

&&

.UPDATE...
Issued at 1159 AM EST Thu Feb 22 2018

Models are trending warmer for the pcpn tonight. We may still
see light ice accums north of I-96, and we will continue to
monitor whether an winter weather advisory is needed.

UPDATE Issued at 406 AM EST Thu Feb 22 2018

On farther consideration, it seemed to me our hourly temperature
grids were to cold tonight given the cloud cover so I updated the
temperature, dew point, relative humidity and weather grids from 7
pm this evening till 7 am Friday morning. In so doing we now have
freezing rain mostly near and north of Route 10 overnight into
Friday morning.

&&

.SHORT TERM...(Today through Saturday)
Issued at 328 AM EST Thu Feb 22 2018

Our main forecast issues for this forecast package is the threat
of freezing rain and sleet late tonight into the mid morning hours
of Friday. The question is will there be enough ice to warrant a
Winter Weather Advisory. Since for the most part the energy with
this system bifurcates Southwest Michigan (north and south of
here), we do not get much in the way of total precipitation
amounts. Also considering air temperatures should go above
freezing today and skies will be cloudy tonight I wonder if air
temperatures will even get below freezing over most of our CWA
tonight in the first place. Based on the questionable nature of
the freezing rain in the first place and even if it happens is
likely to have minimal impacts, I do not intend to issue an
advisory.

As for the "BIG PICTURE", we still have large upper level high
over the Southeastern CONUS with our Polar Vortex upper low
displaced southward into Hudson Bay with a deep trough over the
western CONUS. This creates a "Train track" set up for surface
lows to follow toward the Great Lakes area. This pattern finally
breaks down early next week, but until then we will continue to
see systems coming out of the western trough into the Great Lakes.

The next system bifurcates us tonight into Friday, meaning the
deep moisture and southern stream energy stay south of us and the
jet lift event on polar jet core will stay north of us. We get
minimal amounts of precipitation with this sort of set up. So,
while it is likely we will see some light precipitation between
midnight and sunrise, it will be light, mostly less than a tenth
of an inch.

Once that comes through we wait for the next system which is
talked about in the Long Term discussion.

.LONG TERM...(Saturday night through Wednesday)
Issued at 328 AM EST Thu Feb 22 2018

The ecmwf continues the trend it started yesterday in that`s it
quickly moving toward the gfs solution for the storm moving through
the Great Lakes this weekend. The reason for this is the development
of the upper trough on the ecmwf.

The ecmwf sfc low is roughly 10mb lower than the 00z run yesterday
and is now only 10mb higher than the gfs. Both tracks take the low
through Wisconsin which places the cwa in the warm sector. However,
this system will occlude around the time it gets to Lake Michigan
and so the warmest air will be pushed off to the southeast. Models
also indicate the heaviest precipitation will remain southeast of
the cwa on the convective side and well to the northwest on the cold
side. We`re looking at around a quarter inch of pcpn possible
Saturday night and early Sunday. It`s also possible that there could
be some mixed precipitation in the form of snow/sleet/freezing rain
over the northeast cwa Saturday evening before warmer air moves in.
The low is progd to deepen as it moves by and so Sunday could be
rather breezy.

Mostly dry weather is expected from late Sunday through early
Wednesday when the gfs develops another low in Oklahoma and moves it
toward the Great Lakes. The ecmwf isn`t remotely close to the gfs
with this system nor is the canadian model so we`re not going
overboard with pops.

Highs in the mid 40s are expected during the extended which is
roughly 10 degrees above normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1215 PM EST Thu Feb 22 2018

Visible satellite imagery showing breaks in the cloud cover over
portions of West Michigan and continued clearing across far
southwest Michigan into adjacent areas of Illinois and Indiana.
VFR ceilings elsewhere. Radar indicating a few echos south of a
KAZO to KLAN line...with a few more shown from Milwaukee northeast
into northern Lower Michigan. Areal coverage and intensity of
radar returns has been decreasing over time. MVFR ceilings from
Central Illinois south and west will advect into the area later
this evening...but have above average confidence in VFR conditions
continuing through at least 00Z Friday.

Persistent southwesterly flow at mid levels will bring increasing
chances for precipitation at West Michigan TAF sites during the
latter portions of the upcoming forecast period. Models are
consistent in creating two areas of precipitation...one that will
remain south and east across Ohio and southern Indiana...and the
second which across Wisconsin and Upper Michigan. Still enough of
a threat exists to include mention of precipitation for all West
Michigan TAFs between 09Z and 18Z Friday.

There is some concern about precipitation type...as thermal
profile suggests the possibility of freezing rain for a brief
period around sunrise. Will keep the forecast all liquid for
now...but situation needs to be monitored and earlier onset of
precipitation could cause enough of a threat of freezing
precipitation to include in future forecasts.

&&

.HYDROLOGY...
Issued at 327 PM EST Wed Feb 21 2018

Most recent observations along some of the smaller streams have
indicated that levels are nearing their peaks. Most smaller streams
and rivers will do so between now and Wednesday evening. Larger
rivers continue to rise with the greatest impacts to come later in
the week and into the weekend. Overall, observed river levels have
line up fairly well with forecast trends and most adjustments have
been minor with each update.

Areal flooding will subside through the evening or has already
subsided, while the greatest concern going forward will exist along
the larger rivers through the weekend. Particular focus will be on
the Red Cedar River and Grand River as rises continue to impact the
Lansing area and water funnels downstream to Grand Rapids. River
levels in Lansing and Grand Rapids will be among some of the
historical crests. Levels in Grand Rapids could come close to 2013
levels, while levels around Lansing will be most comparable to 1975.
Many roads and locations along each of the river are already
impacted and will only continue to see waters rise this weekend.

Various other rivers through Southwest Lower Michigan continue to
experience minor to moderate flooding. Impacts expressed in previous
discussions remain valid and recent advisory/warning products can be
referenced for impacts specific to each river and site.

Light rain is expected to bring about one-tenth of an inch of
precipitation late Thursday into Friday. This will have no impact on
current forecasts. The next system will come over the weekend, late
Saturday into Sunday with around one-quarter to around three-tenths
of an inch. These amounts may stall improvement slightly. However,
this system will be one to watch, as higher precipitation amounts
are just south of Lower Michigan and any northward adjustment could
further impact forecasts. For now, no additional impacts are
expected.

&&

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

$$

UPDATE...JK
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...04
AVIATION...MWS
HYDROLOGY...JAM



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