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Area forecast discussion 
National Weather Service Grand Rapids Michigan
330 am EST sun Nov 23 2014

Latest update...
synopsis/short term/long term/marine

Synopsis...
issued at 330 am EST sun Nov 23 2014

Warm and wet weather can be expected for the area for today through
most of the day on Monday. Temperatures will reach into the 50s for
most locations...and periods of rain will occur from this afternoon
through Monday afternoon. Rain will change over to snow late Monday
afternoon into Monday evening. Accumulating snow will be likely
across the area Monday Night.

Lake effect snow showers will be ongoing then Tuesday morning. More
snow accumulations will be expected before the snow showers diminish
later in the day. Another wave of low pressure will move through the
area on Wednesday and bring another chance of snow. Colder air will
then move in for Thanksgiving with some lake effect possible.

&&

Short term...(today through tuesday)
issued at 330 am EST sun Nov 23 2014

The main concerns in the short term portion of the forecast are the
rainfall trends through Monday...and then the transition to snow
Monday evening along with lake effect thereafter.

We continue to expect that the more widespread rain will move in
this afternoon and will continue through tonight. There is a short
wave this morning that is sparking a few showers across the southern
portion of the County warning forecast area. We will then see the rain become more
widespread this afternoon as the wave across eastern Texas will be driven
north-northeast toward the area tonight. Strengthening moisture transport ahead
of this wave from the Gulf of Mexico will assure the entire area
will see rainfall later today and tonight.

We will see the rain let up a bit Monday morning...before more precipitation
moves back in across the area Monday afternoon and Monday evening. The
wave tonight will move away from the area...and we will see another
wave currently moving into The Rockies skirt by just southeast of the area.
The models all place the deformation portion of this wave over the
area. Precipitation with this will remain rain until likely just after 00z
for most of the area before the sufficiently cold enough air moves
in and changes all precipitation to snow.

We do believe that all of the area will see the potential for a
couple of inches of snow from this...before precipitation transitions over to
lake effect overnight Monday night. Some of this lake effect could be
fairly healthy as yet another short wave moves in from the west
overnight and early Tuesday morning. Good cyclonic flow and the cold
pool aloft will lead to inversion heights at least around 10k feet.
This will help to enhance the low level convergence over the
area...and produce some decent bands of lake effect. There will be
some SW enhancement in the evening with the deformation band. This
will then transition to more of a wrly mean low level flow by
daybreak on Tuesday. In addition...brisk winds will be blowing the snow
around creating impacts for the Tuesday morning commute.

The snow showers should then diminish in coverage and intensity
later on Tuesday. The wave moving through in the morning will be east of
the area in the afternoon and the area will become under the
influence of short wave ridging. Inversion heights will sink to
around 5k feet or so with low level convergence diminishing.



Long term...(tuesday night through saturday)
issued at 330 am EST sun Nov 23 2014

Below normal temperatures are likely for the upcoming Holiday period
although confidence remains low regarding the extent and amount of
lake effect snow.

Although 500 mb troughing tends to persist over Canada and the northern third
of the Continental U.S. Including the the Great Lakes region... we are on the
southern fringes of this longwave trough. Medium range guidance actually
develops a flatter/more zonal aloft by next weekend. The result of
this is more more in the way of surface ridging and anti cyclonic
flow at the surface... which indicates that the lake effect over the
Thanksgiving weekend should be generally on the light side.

The best chance for some accumulating snow... although probably not
too significant... appears to be Wednesday night into Thanksgiving
day. 150kt Pacific upper jet spins up a surface low over the Minnesota/WI area on
Wednesday. The warm advection ahead of the low brings a diminishing
trend to Our Lake effect on Tuesday night and Wednesday. However as
the system moves slowly east into Michigan Wednesday night then off to the
east it helps tug down colder 800 mb air around -15c for Thanksgiving
day.

So perhaps we will see an inch or two of synoptic snow with the low
itself Wednesday night followed by a few more inches of lake effect
on Thursday. The problem here is that the models are not in good
agreement on the evolution/track of the surface low which will dictate
the low level flow on the back side on Thanksgiving.

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1152 PM EST Sat Nov 22 2014

Conditions have improved this evening with VFR and MVFR conditions
expected to continue overnight...although a trend towards lower
ceilings and visibilities is possible after about 10z. Rain should
hold off until Sunday afternoon when IFR/LIFR conditions should
become widespread. Winds will be southwest tonight then go more
southeast on Sunday around 10 knots.



&&

Marine...
issued at 330 am EST sun Nov 23 2014

We will be maintaining the going headlines for the nearshore waters
with this forecast package. Winds and waves are somewhat marginal this
morning...however they are close to criteria. This will remain the
case through the first half of today before a little better mixing
takes place and allows for better winds to reach the surface.

The bigger concern will be the potential gales from Monday afternoon
through early Tuesday. The latest trends show the potential for higher
end gales to be possible with the cold air advection. A gale watch
is out for this period already...so things are well covered.

&&

Hydrology...
issued at 330 PM EST Sat Nov 22 2014

General thinking has not changed very much. Storm total rainfall
by Monday afternoon should be on the order of 1.00"-1.50" across
the entire County Warning Area. Factoring in a melt-off of 0.50"-1.00" liquid from
the snowpack...and substantial river rises are highly likely. The
12z GFS is probably overdone with >2.00" of total rainfall from
South Haven to Grand Rapids by Monday afternoon. Using this as the
worst case scenario...many rivers would reach or exceed bankfull
and a few forecast points could come close to minor flood stage.
Again...this is not being forecasted but nevertheless should give
some reference should the worst-case scenario unfold with 2" of
rain and a complete snow melt especially across the western Grand
River/Muskegon river basins. No flooding is currently
forecasted. The colder weather moving in for Tuesday and beyond
may help slow or even reduce the amount of river rise that would
normally occur with that much liquid flowing into the river basins.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...gale watch from Monday morning through Tuesday morning for
lmz844>849.

Small Craft Advisory until 10 am EST Monday for lmz844>849.

&&

$$

Synopsis...njj
short term...njj
long term...Meade
aviation...ostuno
hydrology...Hoving
marine...njj

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