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Area forecast discussion 
National Weather Service Grand Rapids Michigan
719 PM EST sun Feb 7 2016

Latest update...
aviation

Synopsis...
issued at 243 PM EST sun Feb 7 2016

A low pressure system over the upper plains this evening will
slow down as it tracks into the Great Lakes region Monday into
Tuesday. Snow showers will be on the increase during this period
as a colder airmass accompanies the arrival of this system. The
combination of falling temperatures and accumulating snow will
support impacts Tuesday into Wednesday across the region.

&&

Short term...(this evening through Tuesday night)
issued at 243 PM EST sun Feb 7 2016

The main challenge in the short term deals with the impacts
associated with the low pressure system that tracks through the
region through Tuesday.

To start...models are trending warmer for Monday. With forecasted
highs already above freezing...it looks likely that any impacts
from falling snow will be minimal. Toward the end of the evening
commute...it may get close to freezing...but that will more likely
happen after 00z Tuesday. Going through Monday night...temperatures
will fall below freezing...and the snow showers will become better
organized...especially later at night.

It looks like by the time the morning commute begins for
Tuesday...we will be seeing impacts. The north northwest flow
favors the area west of Highway 131. Low level convergence
supports the region south of Holland for the heaviest snow
showers. Once they develop...the snow showers will persist through
Tuesday night. Lift in the dgz actually increases along the
Lakeshore later Tuesday night. It appears we will likely need
some headlines to account for the potential for moderate impacts
much of the region Tuesday into Tuesday night...with a low end
risk for high impacts...mostly the Holland to South Haven region.

Long term...(wednesday through sunday)
issued at 243 PM EST sun Feb 7 2016

The main theme of the long term continues to be the expected pattern
change of much colder air affecting the area along with lake effect
snow. There has not been much change in the thinking with regards to
the long term.

The Arctic air mass and lake effect will be pretty much established
over the area by the beginning of the long term. Much of the eastern
U.S. Will be encompassed by a large amplitude trough. This pattern
will be favorable for lake effect with a parade of short waves
expected to move through the area on northwest flow aloft. The northern branch
of the jet will be south of the area...allowing for cyclonic flow
and deep cold air to be overhead. This will provide for higher
inversion heights with moderate to extreme instability coming over
the lakes. There look to be some strong areas of enhanced low level
convergence. The areas that will be more prone to the heavier lake
effect will be the northwest and SW corners of the County warning forecast area with low level northwest
flow expected.

Some reprieve can be expected by Thursday night into Friday with regards to
the intensity of the lake effect. The upper low will briefly lift
out and allow inversion heights to come down a bit as a result.
Instability will remain...so snow showers should not totally
dissipate.

We will see a reinforcing shot of colder air come in then for next
weekend. This surge will bring even colder air than middle week with
h850 temperatures dropping into the negative middle 20s c. We will likely not
see as much lake effect over the weekend with the upper pattern set
up a bit different. Due to the position of the upper ridge across
Canada...surface ridging will situate itself such that we will see a north-
NE flow. This will focus lake effect west of lakes Michigan and
Huron. We will just see Arctic air with some potential sunshine for
next weekend.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 718 PM EST sun Feb 7 2016

Confidence is high that VFR conditions will continue through 06z
but confidence is low regarding ceilings/visibilities during the late night
and early morning hours.

Guidance and low level relative humidity forecasts indicate the possibility of low
stratus and fog developing after about 09z as winds diminish and
temperatures fall to near freezing. This may lead to some IFR or
lower conditions developing and possibly even some light
drizzle/freezing drizzle... but again confidence is on the low
side.

Conditions should trend to mostly MVFR category for Monday
afternoon with scattered light snow or mixed rain and snow
showers.

&&

Marine...
issued at 243 PM EST sun Feb 7 2016

The wind will decrease this evening as the pressure gradient
weakens. Will allow the Small Craft Advisory to expire at 7 PM
this evening. After a lull in the winds tonight...they will start
to increase Monday into Tuesday. With cold air advection
developing...we will likely see building waves. We may need
headlines to account for this trend.



&&

Hydrology...
issued at 1216 PM EST sun Feb 7 2016

The river at Maple Rapids is expected to fall below bankfull by
late Tuesday or early Wednesday. Cold temperatures this week will
cause ice to redevelop... so we will have to watch for river
level fluctuations if freeze up ice jams occur. With many rivers
currently running higher than seasonal normals... a few rivers
could rise out of their banks again.

&&

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

$$

Synopsis...mjs
short term...mjs
long term...njj
aviation...Meade
hydrology...cas
marine...mjs

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