Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 291932
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
232 PM EST Tue Nov 29 2016

LATEST UPDATE...
Hydro

.SYNOPSIS...
Issued at 322 AM EST Tue Nov 29 2016

A very deep low pressure system stalled over northwest Minnesota
this morning has pushed an occluded front through the area. This
will bring gusty surface winds and a period of mostly clear skies
to the area. It will be unseasonably warm too with highs in the
upper 50s. Tonight the cold air starts coming back in. That will
bring a period of showers to the area but winds will diminish.
The air more typical of late November moves back in Wednesday
night into Thursday with lake enhanced rain showers. Some wet snow
is possible over the higher elevations over northern sections.
Friday will see the showers diminish to sprinkles but it will
remain seasonably cool.

&&

.SHORT TERM...(Today through Thursday)
Issued at 322 AM EST Tue Nov 29 2016

The main issues are the chances for showers tonight into Thursday
as the cold air comes back in. There is also the issue of
potential change to snow Wednesday night into Thursday.

As typical of a strongly occluded frontal system the dry slot
will move through the area today. Skies should for the most part
become mostly sunny by mid morning across the area. It will be
breezy and unseasonably mild with highs pushing 60 degrees. Given
we have current temperatures at 3 am in the lower 50s over the
southern and central sections that should not be hard to do.

Tonight a 150 to 160 knot jet core rotating around the base of the
upper level system (currently over MO), creates a wave on the
front that tracks over Lake Michigan early tonight. The warm
advection lift ahead of that system will surely bring a period of
showers to the area. There is marginally enough instability for
thunderstorms over Lake Michigan this evening so I put isolated
thunderstorms in the zones near the lake shore for that. Since we
are still mostly in the warm air yet, it will remain unseasonably
mild tonight.

However after this system tracks through the area the cold air
does come back in. During the day time Wednesday we get a sort of
dry slot but not as strong as today so I do not think there will
be much in the way of showers around Wednesday. Wednesday night
into Thursday we do get the deeper moisture back with westerly
winds. This is a great lake enhanced precipitation set up. I and
very confident areas near and west of US-131 will see rain showers
Wednesday night into Thursday. I pushed pops up to likely but I
think the could be near 100% actually. That bad news for snow
loves is the freezing level will not be quiet low enough to get
much snow out of this event. I could see some wet snow over the
higher elevations in northern counties through.

.LONG TERM...(Thursday night through Monday)
Issued at 322 AM EST Tue Nov 29 2016

Colder air invades the area through the latter portion of the week,
which should produce some light lake effect snow. Then big question
marks come into the forecast for the end of the weekend and into
early next week.

As the upper low moves into Quebec, the Great Lakes region will
continue to see northwest upper flow.  This will continue to bring
in cooler air for late in the week and into the early weekend.  H8
temps should become cold enough for some lake effect snow showers by
late Thursday night, and this should be assisted by cyclonic flow.
Inversion heights suggest the DGZ will only be marginal moist enough
for some snow, so expect what occurs will be on the light side, with
perhaps some minor accums toward LDM/Baldwin on Fri night.  Surface
and weak upper ridging would suggest the lake effect will diminish
Saturday.

By Sunday and Monday there is poor agreement in the models, with the
ECMWF becoming much more amplified and bringing surface low pressure
out of the Western Gulf Saturday night, and heads it toward the
Great Lakes by Monday.  The GFS is much slower with a surface low,
being over the Dakotas Monday with less of a Gulf influence.  These
differences make a huge impact on the temp regime over the region
too.  It seems to make sense that a slower solution is the way to
go, if we indeed become significantly amplified.  This would also
favor a warmer solution Sunday night into Monday.  For now will have
a forecast showing snow arriving late Sunday, then mixing with and
changing over to rain Monday.  However significant tweaks may be in
the offering as we move closer to this system.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 110 PM EST Tue Nov 29 2016

VFR weather dominates the area at 18z, the exception being MKG
where some moisture off of Lake Michigan is producing a ceiling at
1900ft. Expect these clouds to dissipate or lift soon with MKG
becoming VFR as well by mid afternoon. A gusty south wind will
continue this afternoon with winds of 15-25 knots common.

This evening a disturbance will move into the area from the
southwest out of Illinois. The disturbance will bring clouds, the
chance for scattered showers and an isolated thunderstorm. At this
point have VCSH in the forecast as the precip should be scattered.
The threat for storms looks too low to include at this point, but
not out of the question. The main impact from the disturbance is
that it will likely slide MVFR clouds into the area overnight.
Some model indications even show an IFR deck developing late
tonight into Wednesday morning. Winds will be much lighter
overnight into Wednesday on the order of 5-10 knots.


&&

.MARINE...
Issued at 322 AM EST Tue Nov 29 2016

At this point I will leave the marine headlines as they are but I
could see extending the SCA into mid evening as it may take awhile
for the winds and waves to fall below criteria.


&&

.HYDROLOGY...
Issued at 232 PM EST Tue Nov 29 2016

Rainfall amounts ranged from roughly a half inch in the greater
Lansing area to over 2 inches in Oceana county. The only rivers
making a run toward bankfull are Sycamore Creek at Holt (cresting
Wed morning) and Maple River at Maple Rapids (cresting this
weekend). Very minor flooding in low lying areas adjacent to the
rivers is expected. Heavy precipitation is not anticipated until
at least next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 1 AM EST Wednesday for LMZ847>849.

     Small Craft Advisory until 7 PM EST this evening for LMZ844>846.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...Duke
HYDROLOGY...CAS
MARINE...WDM



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