Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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860
FXUS63 KGRR 232026
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
326 PM EST Thu Feb 23 2017

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

.SYNOPSIS...
Issued at 255 PM EST Thu Feb 23 2017

A storm system in the panhandle of Texas will strengthen as it
tracks through Lower Michigan on Friday. This system will create
winter weather conditions to the northwest of its track and spring
like conditions to the southeast. Some of the thunderstorms on
Friday could be severe for southwest parts of the state. As the
storm goes by a colder airmass will arrive for later Friday night
and into Saturday.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 255 PM EST Thu Feb 23 2017

The main challenges deal with the impacts from the winter weather
and thunderstorms.

Nearly all models are trending colder across my northern counties
with this storm. Initially we are still looking at rain for the
onset. Then...forecast soundings later tonight show a deep
slightly subfreezing isothermal layer. Based on this...I do
feature a period of snow with accumulations of 1 to 3 inches. The
period of snow could be heavy...so if it trends colder...more snow
could fall. Then the elevated warm layer arrives. That will mix
the weather types up. Will continue to maintain the mention of
sleet and freezing rain as well with up to a quarter inch of
ice...especially elevated surfaces. We may need to expand the
winter headlines further south. Slick roads...especially
overpasses and some power outages look possible for impacts.

Then for late Friday night and into Saturday...model trends are
also colder here. With the trowal passing through and temperatures
below freezing... there will be a window for potential impacts. We
may need winter weather headline for western parts of the CWA as
lake enhanced moisture could support increased snow rates.

Severe weather looks possible for Friday into the evening...mainly
south of a Lansing to Holland line.  The main period looks to be
during the mid afternoon through the evening hours. This is when
the instability will be most favorable. Overall not a lot of
instability is forecasted...but the deep layer shear will be
plenty favorable for organized convection. Forecast soundings do
show some capping for a while for the afternoon. But that
eventually breaks down ahead of the advancing cold front. A narrow
line of convection with possible damaging wind gusts looks likely
with an isolated tornado possible. Strong convective winds gusts
could lead to power outages. Any stronger storm could focus the
damage.  The morning convection could be strong as well with
rather steep mid level lapse rates around.



.LONG TERM...(Sunday through Thursday)
Issued at 255 PM EST Thu Feb 23 2017

High pressure to the South of Michigan will keep a weak wave mostly
North of Lower Michigan Sunday into Sunday night. Might see a quick
burst of light snow. Another couple of waves will pass nearer to
Lower Michigan and bring precipitation for Monday night into
Thursday. With daytime temperatures mainly in the 40s and lows near
and below freezing Monday through Wednesday, a mix of precipitation
types is possible. The grids had more rain than the neighbors, so
mixed in more snow. Confidence in precipitation occurring is high
while confidence in precip type is low.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1251 PM EST Thu Feb 23 2017

Clouds moving in from the North and the West have bases mainly in
the MVFR range. Coverage will vary through the afternoon from
scattered to overcast. Ceilings and visibilities will lower this
afternoon/evening as rain showers move in from the West. IFR
conditions should occur overnight and through tomorrow.
Isolated thunderstorms overnight should become scattered on
Friday.


&&

.MARINE...
Issued at 255 PM EST Thu Feb 23 2017

The wind will increase this evening and gusts over 30 knots look
possible. Thus will keep the Small Craft Advisory going. With an
offshore component...the wave heights will largely remain under
criteria.

As the surface low tracks through the region Friday afternoon and
evening there will likely be a lull in the hazardous winds and
waves.


On Saturday conditions look likely to approach gale force winds.
In addition with northwest cold air advection the waves should
build considerably.

&&

.HYDROLOGY...
Issued at 255 PM EST Thu Feb 23 2017

Repeated showers and thunderstorms on Friday may produce rainfall
totals in excess of 1 inch in parts of the area. There are several
rivers which will be susceptible to rises above bankfull if their
respective basins receive that much rainfall. This includes both
small basins with quick response times and main stems with longer
response times. Will have to monitor rainfall totals closely on
Friday.

In the longer term, there is a low confidence but plausible scenario
in which additional rainfall amounts in excess of a half inch on
Tuesday sustain high river levels.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from midnight tonight to 11 AM EST
     Friday for MIZ037>040-044>046.

LM...Small Craft Advisory from 10 PM this evening to 11 AM EST Friday
     for LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...63
AVIATION...63
HYDROLOGY...CAS
MARINE...MJS



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