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Area forecast discussion 
National Weather Service Grand Rapids Michigan
629 PM EST Thursday Dec 18 2014

Latest update...

issued at 240 PM EST Thursday Dec 18 2014

Light snow and freezing drizzle are expected to diminish overnight.
Quiet weather is expected through the weekend with some sun on
Friday. Highs will be in the 30s over the weekend with a warm up
into the lower 40s early next week.

Unsettled weather is expected next week...with multiple
opportunities for both rain and snow. Rain or snow will be possible
beginning Sunday afternoon into Sunday night. Then a period of rain
is expected Monday and Tuesday. Colder air should arrive about
Tuesday night which should change the precipitation to snow which
should continue into Christmas day.


Short term...(this evening through Saturday night)
issued at 240 PM EST Thursday Dec 18 2014

Main concern is drizzle/freezing drizzle this afternoon lasting into
the evening. Surface boundary has stalled roughly along a Holland to
Grand Rapids to Lansing line. Temperatures south of this boundary
have been slow to rise...but expect a slow climb above freezing the
rest of this afternoon. Short range guidance including the hrrr
shows the boundary dropping south to I-94 by 10 PM. There is a
narrow window for freezing drizzle again this evening as
temperatures begin to fall. Precipitation is most likely to occur
over far southwest lower Michigan where speed convergence of winds
off Lake Michigan will supplement boundary convergence. Light snow
will also continue to be possible early tonight in the vicinity of
the boundary.

Otherwise no significant weather is expected through Saturday night
with high pressure in control.

Long term...(sunday through thursday)
issued at 303 PM EST Thursday Dec 18 2014

Still a fair amount of uncertainty as to the details of the storm
system expected to impact the region just prior to Christmas and
into Christmas day.

The models have trended further north with the surface
taking it across northern lower Tuesday night. They are also
hinting at an East Coast low which may Transfer energy from the
Great Lakes low. Bottom line...this appears to be a slow moving
storm and a few wobbles either way will be make a difference on
timing precipitation type.

The storm becomes negatively tilted by Tuesday night which should
favor a quicker arrival to the colder air. Best bet right now is
that this moves in Tuesday night. So expecting a wet Monday and
Tuesday...followed by a cool down and a switch to snow Tuesday
night. And even though some of the storm/S energy may shift to the
East Coast...we should remain under a moist cyclonic flow lingering
into Christmas day. This should result in light snow continuing
right into the Thursday. 800 mb temperatures should be around -8c by Christmas
day so expect Lake Michigan will help enhance the snow a bit. All
in all it appears a white Christmas is a good bet for much of SW Michigan.

Until then...I added probability of precipitation to Sunday afternoon and evening...mostly
along and north of I-96. Models show a sharpening warm front moving
north into the area with decent isentropic lift ahead of it. Would
expect some light snow with this...although accums should remain
under an inch. Then warmer air arrives late Sunday night/Monday
when the precipitation should switch to rain.


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 623 PM EST Thursday Dec 18 2014

A couple of aviation hazards exist into Friday. To start IFR/MVFR
conditions exist throughout the region. There is a boundary
shifting south of kgrr and klan. Taf sites south of these
locations are expected to see IFR this evening. Drier air will
filter in from the north as the boundary eventually pushes south
of these locations and should allow for VFR conditions to return
by Friday. However the boundary will be slowing down...and that
could prolong the impact conditions into Friday.

Icing will exist in the clouds into Friday and possibly Saturday. At
the surface...freezing drizzle could mix with snow at times south
of the boundary. This evening through 04z appears to be the most
likely timeframe for freezing drizzle.


issued at 240 PM EST Thursday Dec 18 2014

No concerns at this time. Winds and waves will continue to subside
this evening and stay low into the weekend with high pressure in


issued at 240 PM EST Thursday Dec 18 2014

No significant Hydro impacts expected for the foreseeable future.


GRR watches/warnings/advisories...


short term...tjt
long term...jk

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