Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Rapids Michigan
1159 PM EST sun Mar 1 2015
issued at 320 PM EST sun Mar 1 2015
The snow showers from the system passing south of Michigan this
evening will come to an end however lake effect snow showers will
continue in areas within two rows of counties from Lake Michigan
into early Monday morning as a cold front moving through the area
brings a reinforcing push of cold air to the area.
High pressure moves across lower Michigan Monday bringing partly
cloudy skies and afternoon temperatures mostly in the middle 20s.
Meanwhile a storm system currently over the southwest United
States will track northeast toward the central Great Lakes for
Tuesday. This will bring snow by middle morning Tuesday that will mix
with and change to rain and freezing rain in the afternoon. That
will change back to snow showers Tuesday night as another Arctic
front comes through the area. Lake effect snow showers and cold
temperatures will prevail Wednesday into Thursday.
A warm up starts Friday with afternoon temperatures in the 30s
over the next weekend.
Short term...(this evening through Tuesday night)
issued at 320 PM EST sun Mar 1 2015
The primary issue with this forecast is the threat for wintry mix
of precipitation Tuesday. There is some question as to just how
far north the warmer air will really get. This event may well
lead to advisory headlines once the models come to a better
consensus of what will really happen with the warm air surge.
Currently we are watching the system that was forecast to pass off
to our south do just that. We did however get a little More Lake
enhanced snowfall than we were originally thinking. In any
event...as the colder air comes back in behind the departing
system to our South...Lake enhanced snow showers will continue for
the first two rows of counties east of the Lake Michigan shore
into the early morning hours of Monday. Till then we have decent
lift...convergence and moisture in the 950 to 850 layer and it is
cold enough too. Also while there is lake ice out there it is
clear there is enough open water yet to keep the lake effect snow
showers going. Accumulations will be limited since most of the lift
is not in the dgz.
Quiet weather returns for Monday as high pressure moves across the
area. That does not last for long however. The system is currently
rounding the base of the upper trough over California into Nevada
and Arizona. An upstream kicker off the coast of British Columbia
pushes this system eastward into the Central Plains Monday. As the
upper wave moves into the mean upper trough over the eastern
United States the upper level strengthens to around 190 knots by
early Wednesday over central lower Michigan. Clearly all that
dynamical forcing will demand a low level response. Unlike the
current system...where the core of the jet streak was south of
Michigan this time the jet core will be near htl. That makes all
the difference for our surface weather. The strong fgen related to
that jet core result in a 60 knot low level jet aimed at lower
Michigan Tuesday morning. The convergence of the 1000/850 moisture
transport vectors is near I-94 during the day time hours of Tuesday.
The precipitable water return reaches 2 Standard deviations from
normal by 18z Tuesday (naefs mean standardized anomalies).
So here is my problem with this system.... with the jet axis north
of here...the surface low should track north of here and with that
we should be getting into the warm air. In fact the cips analogs
show a 40 to 50 percent chance of temperatures reaching the 40s south
of Interstate 96 Tuesday. The models are not nearly that warm and
I am thinking the problem is the extensive snow cover south of
here. The models typically have problem with warming the air going
over a large area of snow cover.... I wonder if the models are
under doing the warming at the surface tuesday? Also the cips
analogs show a 50 percent probability of at least 1 hour of freezing
rain over most of the County Warning Area... however there is a near zero
probability of 3 hours or more of freezing rain. That also agrees
with the Storm Prediction Center sref output curiously. So I am fairly skeptical about
just how much frozen precipitation we will really get from this
event. We will have to watch this closely as there is a strong
warm advection moisture burst so precipitation amounts should be
over a half inch in most places. One other issue is strong winds
Tuesday...winds could gust to over 40 knots along the Lake Shore
we will have to watch this too.
Tuesday night the cold air comes back in and the dgz GOES into the
ground by Wednesday morning. As typical the models are not strong
enough of lake effect snow so I pushed probability of precipitation to likely but I could
just a well go categorical as it will snow west of US-131 as the
cold air comes back in Tuesday night. While there is some lake ice
to cut back on this today's event shows there is still enough open
water for lake effect to occur and all the wind on Tuesday may
well open up more of Lake Michigan anyway. So the deep freeze and
snow showers come back Tuesday night.
Long term...(wednesday through sunday)
issued at 320 PM EST sun Mar 1 2015
Another surge of Arctic air will move in Wednesday through Thursday
when maximum temperatures will only reach the teens. Scattered lake effect snow
showers are also anticipated as 800 mb temperatures fall to -22 to -24 c.
However any accumulations should be quite light given the dry
airmass in place and extensive ice cover over Lake Michigan and
cellular nature of the scattered snow showers during the daytime as
is typically the case during this time of year.
Temperatures will undergo a gradual moderating trend Friday through the
weekend as the upper level pattern becomes more zonal. This will
also be a period of tranquil weather.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1158 PM EST sun Mar 1 2015
MVFR conditions expected to persist a few hours overnight with
ceilings in the 1500 to 2500 foot range along with some very light
snow through about 08z. Then VFR expected after that. Winds will
start out west and go northwest around 10 to 15 knots overnight.
Winds will go west to southwest by Monday afternoon around 10
issued at 1140 am EST sun Mar 1 2015
The forecast gets a little tricky in the upcoming week with the
approaching system going into Tuesday. Temperatures could vary
quite a bit right along with expected precipitation totals and
precipitation type. The current guidance suggests we could get a
bit further into milder air (near normal) and add more liquid
precipitation as opposed to snow. Overall....it is not a drastic
warm up and amounts may remain around or below half an inch. This
could mostly be soaked up by current snow pack. With low river
levels and given situation...this should not raise any immediate
concern but will be added liquid to be considered in forecasts
down the Road.
The good news is that the system last night into today was quite
lackluster in regards to totals. Therefore...what we missed last
night will just subtract from the overall weekly amounts we were
looking at yesterday. Though it was not anything too heavy to
begin with it just raises confidence that any upward trends in
temperatures will not have as much of a negative impact.
Conditions are expected to remain stable for now and in the near