Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 202024

Area Forecast Discussion
National Weather Service Grand Rapids MI
324 PM EST Mon Feb 20 2017

Synopsis/Short Term/Long Term/Marine

Issued at 324 PM EST Mon Feb 20 2017

Low pressure will bring some rain Tuesday with fair and warm
weather for Wednesday. A storm on Friday could bring high winds
along with rain changing to snow by Saturday.


.SHORT TERM...(This evening through Wednesday night)
Issued at 324 PM EST Mon Feb 20 2017

The only weather maker in the short term is a sfc trough
extending south from low tracking way up into Canada over the next
24 hours. Bulk of precip will hold off until very late tonight
with showers moving through during Tuesday morning and exiting the
eastern zones during the afternoon. QPF with this should be a
quarter inch or less as gulf moisture transport is disrupted by
separate southern stream low that remains along the Gulf coast.

Wednesday and Wednesday night will see a clipper passing well to
the north with no measurable precip expected from it. Max temps on
Wednesday once again expected to be near records although
southwest flow could temper maxes across western zones. Moisture
is lacking Wednesday night and F-gen forcing is way off to the
north, so slight chance POPs from the model blend were dropped.

.LONG TERM...(Thursday through Monday)
Issued at 324 PM EST Mon Feb 20 2017

The main challenge in the long term deals with the impacts of the
storm system for the end of the week.  Overall confidence is lower
than normal as far as the track and intensity of this storm and thus
the impacts go.

The models are generally showing a mid level trough tracking out of
the western U.S Thursday and deepening it into a closed low as it
tracks through the Great Lakes Region Friday into Saturday.  A
shallow cooler airmass will be in place ahead of this system...which
raises the risk for freezing rain for northern zones at some point
Thursday night into Friday.  Currently the models are slightly too
warm for this to happen and it will not be in the forecast.  However
with a strengthening nearly stationary warm front overhead and a low
level jet with gulf moisture advecting in...all this should spell
some heavier rain..which could last for several periods.   With
elevated instability in place...thunderstorms should occur as
well...especially further south.  Deep layer shear is strong and
that could spell organized thunderstorms with a severe
potential...mainly for far Southern Lower MI late Thursday Night
into early Friday Evening.  As a result severe weather and heavy
rain impacts are possible.

As colder air gets drawn into this developing system...a transition
to snow should occur.  This should happen from northwest to
southeast through the CWA Friday Night.  Wrap around moisture may
support accumulations for the lake enhanced coastal regions late
Friday Night into Saturday.  We could see some slick road impacts
from this.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1243 PM EST Mon Feb 20 2017

VFR weather is to prevail through the evening...but conditions
will change overnight and Tuesday morning. Low level moisture will
be on the increase ahead of an approaching low pressure system.
This will raise the risk for low cloud formation...especially
after midnight. Then rain moves in and that should impact mainly
the western TAF sites later tonight. There could even be a few
thunderstorms around late tonight and early Tuesday. Low clouds
and drizzle could be widespread Tuesday morning with IFR and lower
impacts possible.

Will need to monitor the low level wind shear potential for
tonight as a low level jet moves in.


Issued at 324 PM EST Mon Feb 20 2017

Small Craft Advisory in effect overnight then winds and waves
subside Tuesday afternoon.


Issued at 100 PM EST Mon Feb 20 2017

Basin average rainfall through tomorrow is expected to be ranging
from a couple tenths of an inch over the Grand and Kalamazoo River
basins to perhaps a half inch across the western reaches of the
Muskegon River basin. This rainfall should not lead to any
appreciable rises on the main stem rivers. More substantial
rainfall is possible Thursday night through Friday as a
strengthening storm system approaches the Great Lakes. The
placement of this heavier rainfall is still in question, but
models are indicating an inch or more possible where it does set
up. Both small stream and main stem river rises look likely if
this pattern holds.


LM...Small Craft Advisory until 11 AM EST Tuesday for LMZ844>849.



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