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Area forecast discussion 
National Weather Service Grand Rapids Michigan
707 PM EST Friday Feb 27 2015

Latest update...
aviation

Synopsis...
issued at 305 PM EST Friday Feb 27 2015

The center of a large high pressure system will pass just south
of Michigan late tonight into middle afternoon Saturday. This will
bring and end to the snow showers over western and central
sections early this evening. Skies should be partly cloudy
overnight with lows near zero. Skies should become mostly sunny by
afternoon Saturday with highs in the lower 20s. An upper level
system passing over Michigan Sunday will bring a period of light
snow to the area. Accumulations should be in the 1 to 3 inches
range with southern areas seeing the 3 inches and central sections
near I-96 seeing the inch. Temperatures will rise to near freezing by
afternoon. A storm from the Southern Plains will bring a mix of
snow... freezing rain and rain Tuesday as temperatures rise to
near 40

&&

Short term...(this evening through Sunday night)
issued at 305 PM EST Friday Feb 27 2015

The main issue we are watching in the short term is the snowfall
expected on Sunday. Otherwise we will see slow moderation to our
unusually cold temperatures through the weekend...each day will be
warmer than the previous day (through sunday).

The primary driver for the snow event Sunday is the a jet streak
from the southern stream that comes into phase with the next northern
stream shortwave. This causes the southern branch jet streak to
strengthen from around 120 knots Saturday evening to near 170
knots as it passes south of Lake Erie Sunday night. That sort of
strengthening causes strong fgen which slopes northward from near
700 mb near FWA to near 400 mb over htl as the jet streak moves
through. Of course that sort dynamic demands a low to middle level
response which is to lift air northward toward Michigan as this
jet feature moves through. So...the key to where the heavy snow
falls really is just where the axis of the jet streak is. Since
the jet streak axis is just south of Michigan that is where the
heaviest snow is likely to fall. Still there is middle level lift
over lower Michigan so we will see some light snow from this
event. I am thinking around an inch near GRR to 2 to 3 inches just
south of Interstate 94. Cold air following the jet streak will
lead to a Shallow Lake effect snow shower event Sunday night but
this will be not much more than flurries since inversion heights
will be below 5000 feet.

Otherwise the lake effect snow band moving onshore today will
dissipate by early this evening leaving partly cloudy skies
tonight. The clouds in from the southwest winds off Lake Michigan
will keep the temperatures from falling like last night so lows
will be milder.

Saturday should see some clearing by middle afternoon as winds become
more southerly and not off Lake Michigan anymore. Saturday night
will see increasing middle and high clouds as the system snow heads
this way.

Long term...(monday through friday)
issued at 305 PM EST Friday Feb 27 2015

Main focus of the forecast continues to be the system expected to come
through during the Monday night through Tuesday night time frame. There are
only minor changes to the thinking with regards to this system.
Those changes are mainly the result of the exact track of the low.

We continue to expect precipitation to develop as snow late Monday night...after
a quiet period on Monday with high pressure overhead. Precipitation is expected
to start out as snow across the entire County warning forecast area overnight Monday night into
early Tuesday morning. There is fairly good model consensus that temperatures
aloft will warm above freezing by Tuesday afternoon...allowing p-types
to change over to some sleet and/or freezing rain for most of the
area. This will likely be brief where temperatures come above freezing Tuesday
afternoon and evening...which is currently expected to occur along
and south of I-96.

Areas north of I-96 could end up remaining all snow/sleet/freezing
rain north of the low track where temperatures could potentially stay below
freezing the entire time. This could be where a decent amount of
icing could take place.

We can expect fluctuations in the track of the low and placement of
p-types for at least another 24 to 48 hours. This is due to the fact
that the energy that will affect this system is still well over the
Bering Sea...west of Alaska. Once it moves over the continent and
into the radiosonde observation network...better sampling should take place. The other
main part of this...the low over the Pacific northwest...is already
starting to be sampled better.

We should see a quick burst of Arctic air follow this system coming
in on Wednesday and holding into Thursday. Some lake effect will be possible at
that time. A quick moderation comes late next week as the northern branch
of the jet lifts back north of the area. We will see a wrly flow
over the area with the next clipper system potentially staying north
of the border.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 705 PM EST Friday Feb 27 2015

No changes to previous thinking. There is a slight chance for
MVFR ceilings to develop at some of the terminals later tonight...but
any ceilings that develop should remain 2500 feet above ground level or higher...and
therefore above fuel alternate thresholds.

&&

Hydrology...
issued at 1202 PM EST Friday Feb 27 2015

The Battle Creek site (btcm4) on the Kalamazoo river has shown
some erroneous data through the morning hours. This has been
determined to be caused by the extreme cold that settled in
overnight. It has since shown signs of returning back to its
original reading as a result of the sunshine this afternoon.
Coordination with local officials has not revealed any need for
concern.

While area streams and rivers have been stable for several weeks
now a rather active period and gradual warming trend is expected.
This does not necessarily raise alarm but we should heed specifics
as temperatures begin to increase and precipitation approaches.
Total precipitation through the next seven days is anticipated to
remain under an inch. The real question comes on Tuesday...as to
the extent of warmth...precipitation amounts and precipitation
type. That said...we would need a meaningful amount of moisture
in a short period of time...coupled with an extended period of
warmth to create instability in the current ice cover. As of
now...no real issues are expected but rivers will be monitored
through the next week.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...none.
&&

$$

Synopsis...wdm
short term...wdm
long term...njj
aviation...tjt
hydrology...jam

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