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Area forecast discussion 
National Weather Service Grand Rapids Michigan
654 PM EST Sat Feb 28 2015

Latest update...

issued at 311 PM EST Sat Feb 28 2015

Our departing polar high will allow for a mostly clear evening
across most of the area but clouds will increase after sunset. Light
snow is expected after midnight near and south of Interstate 94.
There will also be a lake snow band moving inland north of
Muskegon to near Ludington but that snow will stay close the Lake
Shore...not getting to much farther east than US-31. A cold front
will move through the area Sunday night bringing snow showers with
it but accumulations will be mostly less than an inch. The air
behind this cold front is not as cold as that past several fronts
so temperatures will make it into the middle 20s on Monday with
partly cloudy skies. The system on Tuesday will bring a mix of
snow...sleet and freezing rain. The precipitation may become all
rain over southern and central areas in the afternoon. Some
accumulation of snow is expected from this storm. Cold air with
some lake effect snow will follow for Wednesday. A warming trend
starts Friday. Temperatures should be in the middle 30s in the
afternoon by Saturday.


Short term...(this evening through Monday night)
issued at 311 PM EST Sat Feb 28 2015

I am not expecting much snow from the event tonight into Sunday
night. Most areas near and north of Interstate 96 and east of
US-131 will see little more than flurries from this event. Likely
our Northwest Lake shore will see the most snow from this event
due to the southwest flow event between midnight and midday
Sunday. Otherwise the system snow will largely stay south of

As it turns out the northern stream jet streak diving into the
eastern Continental U.S. Upper level trough is stronger and as a result in
nudging the system moving through this area farther south...
something we have seen happen more than once this winter so far.
The result is most of meaningful snow from this system will be
near and south of Interstate 80. The jet streak I wrote about
yesterday is not forecast to track just south of I-80 but it does
strengthen to 170 knots south of Cleveland by sunrise Monday
morning. Going that far south means the deep moisture and lift
will stay south of Michigan with this system.

Even so we do get short warm advection snow event around midnight
till around 6 am Sunday morning. The snow has to overcome all of
the dry air at lower levels so do not expect much from this and it
should not get any farther north than intestate 96. Mixing ratios
near 700 mb rise from below .5 g/kg to near 1.5/kg and the condensation
pressure deficits fall to near 10 mb south of Interstate 96 around
midnight...and below 2 mb near Interstate 94... that should be
enough of a short period of light snow over our southern half of
our County Warning Area.

Meanwhile as the system brings more moisture farther north... that
will be enough to allow a southwest flow event to develop from
north of Muskegon to Ludington by midnight and last into middle
morning Sunday. All of the high resolution models show good lift in
the dgz. I have to admit the best lift through is really shallow
and near the base of the dgz so I am thinking this will not a big
event either.

The initial warm advection lift event passes east of the area by
middle morning Sunday. The system snow will be south of our County Warning Area for
the most part Sunday. The northern stream cold front comes through
Sunday night with snow showers but the lift is not all that great
and mostly below the dgz so not much from this event either.

Monday the cold air comes back in but this air is not nearly as
cold as the past few events.... even it will be deep enough and
cold enough for lake effect clouds so I expect partly to mostly
cloudy skies.

The southern stream system heads our way Monday night. I do not
expect snow to start until after sunrise Tuesday.

Long term...(tuesday through saturday)
issued at 311 PM EST Sat Feb 28 2015

The main item of interest in the long term remains the system that
is expected to affect the area from Tuesday into Tuesday night. As
expected...we continue to see fluctuations in the exact track.

The main batch of precipitation will come through the area during the day on
Tuesday. There is good agreement that we should see a decent burst of
snow across the area as the precipitation develops. The snow will then
transition over to some sleet and freezing rain as temperatures aloft warm
above freezing and surface temperatures remain below freezing for a period.

The best bet right now is the the northern third of the County warning forecast area should see
mainly snow with some mixture of precipitation possible. The central portion
of the County warning forecast area will see snow transition to freezing rain and
sleet...but how long is in question. This area could see temperatures warm
enough and change over to all rain for a period. Southern areas have a
good chance at seeing precipitation transition over to rain.

The period of different p-types is still a bit in question. It all
has to do with how quick the northern stream system comes in and phases
with the southern stream wave. The quicker it comes in...the more the
warmer air will get shunted south of the area. The slower the northern
stream is...the better the chance we will see warmer air move in. Being
that the energy that will dig the northern stream wave is still north of
the Bering Strait...more fluctuations in the track of the system can
be expected.

We will see a glancing shot of Arctic air move in behind the system
for the Wednesday/Thursday time frame. This will produce some lake effect as
the flow aloft becomes cyclonic Wednesday night and Thursday morning. Lake
effect should not be too significant as the dgz is quite low to the
ground...the open portion of Lake Michigan is becoming limited...and
inversion heights are not all that high.

We will see a moderation in temperatures then for the end of the week and
the beginning of next weekend. The upper jet lifts north of the area
by Thursday night. There will be a couple of waves riding along the
jet...that should remain mainly north of the County warning forecast area. Return flow will
set up and we should see temperatures closer to average with mainly dry

Week two...(sunday March 8th through Saturday March 14th)

Support and confidence is increasing that the area will see a return
to more average conditions over the next couple of weeks after the
record cold February. It is even possible that the area could see
its first period of Spring weather with a period of above average
temperatures beginning during the week of Mar 9th.

Global model ensembles are latching on to a pattern change. Once the
strong trough lifts out this coming Thursday...we will see a more zonal
flow set up with the Arctic air remaining north in Canada.
Eventually toward the 10th...a long wave trough is forecast to develop
over the eastern Pacific as a strong low in the central Pacific phases
with a trough diving south from north of Alaska. This then helps to
push the western upper ridge toward the area and bring Spring-like
warmth to the area.


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 653 PM EST Sat Feb 28 2015

Main changes this update were to delay the onset of lower ceilings and
precipitation. This is based on latest model guidance and observations
that indicate MVFR ceilings still well upstream over Iowa and Illinois.
There is a chance that fuel alternate ceilings at inland terminals may
materialize even little later still than what is in the tafs. The
mkg terminal may see this transition much sooner being next to
Lake Michigan...and due to the fact that the nearby Lakeshore
observation from ldm at 2335z reported bkn025.

Overall certainty in timing transitions to MVFR and fuel alternates
remains low and may require relatively frequent taf amendments


issued at 1132 am EST Sat Feb 28 2015

Conditions on area rivers and streams remain stable. This is
expected to continue to be the case through at least the next
couple of days.

The pattern will become more active as we get into
the second half of the weekend and into next week. The extreme
cold that has been all too stubborn will begin to release its grip
on the region. As a result...gradually warmer temperatures will
make their way in through Tuesday. While there is some question to
the extent of the warmth it is still not anticipated to create
many issues as cold air quickly moves back in during the middle
of the week. Total precipitation amounts should hover around a
half inch through the next seven days with most of this coming
in the Tuesday system. Rivers will be monitored through the next
several days in that case that any variability is sensed.


GRR watches/warnings/advisories...


short term...wdm
long term...njj

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