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Area forecast discussion 
National Weather Service Grand Rapids Michigan
639 am EST Tuesday Jan 27 2015

Latest update...
aviation

Synopsis...
issued at 322 am EST Tuesday Jan 27 2015

It will remain quiet and cool today through Wednesday. Highs will
be in the 20s today...then warm to around 30 on Wednesday. Lows
tonight will range from the single digits above zero for inland
areas...to the teens along the Lakeshore.

Snow is expected to move into the region late Wednesday night
through Thursday morning. Most areas should pick an inch or two of
snow accumulation. However some areas south of I-96 could see a
wintry mix of rain... snow...freezing rain and sleet.

The rest of the week and into the weekend looks rather quiet again.
It should remain cold...with highs mainly in the 20s...although
Monday could cool further...with highs only in the teens.

&&

Short term...(today through thursday)
issued at 322 am EST Tuesday Jan 27 2015

Mainly focus was on the clipper system for Wednesday night and
Thursday. This should give most of the County Warning Area snow...but precipitation type
issues arise mainly south of I-96.

The clipper remains an open wave as it crosses our region....so the
precipitation will not linger...therefore significant accumulations are not
expected. Much of the precipitation will occur from midnight Wednesday night
through about noon on Thursday. However the main issue is how much
warm air aloft moves in ahead of the system...possibly producing a
wintry mix.

Decent agreement in the models now showing around +2c 800 mb air moving
into areas south of I-96 Wednesday night. This gradually gets
pinched off Thursday morning as the system occludes. So will
introduce more of a mix for this area. Should be enough shallow
cold air near the surface to support mostly freezing rain Wednesday
night...then switching to and rain/snow mix Thursday morning...
before going back to snow Thursday afternoon as the system exits.
For areas along and north of I-96 it looks like mostly snow with 1
to 2 inches of accumulation. We will need to watch trends for
possible adjustment to precipitation type across the County Warning Area as the system was
only just coming onto the British Colombian coast early this
morning.

Prior to Wednesday night it will remain quiet and cool. We will see
increasing amounts of sunshine by late this morning as the system
to our west continues to shear out. Clear skies and light winds
will produce some single digits readings tonight. Wednesday will
see more middle/hi clouds...but some sun should come through and with
winds turning to the south it will be a bit warmer.

Long term...(thursday night through monday)
issued at 322 am EST Tuesday Jan 27 2015

Main impact weather in the long term centers on chances for snow
Saturday night and Sunday...with colder air in store for Monday...
albeit nothing excessive for this time of year. No significant
snowfall is expected in the extended period at this time
although a few inches are possible late in the weekend.

00z GFS and European model (ecmwf) are in decent agreement regarding arrival of a
vorticity maximum by Sunday night along an approaching longwave trough as
seen at h500. Ahead of this feature...a baroclinic zone is forecast
to move through the Great Lakes as a weak low eventually develops
along the Ohio Valley. Being on the northern periphery of this
feature would yield light snow for the region...perhaps a few inches
on Sunday. Will have to watch model trends with this system as a
weaker low/baroclinic zone would tend to keep more precipitation south of
our area whereas a sharper h500 trough would help deepen the low a
bit more...and bring it further northwest. For now we have generally 40-50%
probability of precipitation across the area for Sunday with light accums possible.

Behind this system...h850 cold air advection is shown by the GFS and European model (ecmwf) as both
models seem to be converging on a quick arrival and departure to
Arctic air. Could see h850 readings between -20c and -24c for Monday
which would yield highs generally in the teens to near 20...cold for
sure but nothing remarkable. There is at least a chance for lake
effect snow showers Monday and Tuesday.

Outside of these systems...there is a decent chance for northwest flow
light lake effect snow showers Friday in spite of a very shallow
inversion of around 4k feet. The dgz is shown to be saturated at mkg
and ldm along with some marginal lift. Accums would be minor.

&&

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 627 am EST Tuesday Jan 27 2015

Main thing to watch today will be stratocumulus development off
Central Lake Huron and Saginaw Bay that will move SW toward lan
and GRR this afternoon. This is mostly shown by the rap13 model
but also to some extent the GFS and NAM as well. As a
result...will feature bkn020 at lan and sct020. It is possible GRR
could go broken by 18z but not totally confident at this time.



&&

Hydrology...
issued at 302 PM EST Monday Jan 26 2015

General steady or slowly dropping river levels across the area with
a few rivers showing bigger fluctuations over the past day... but
none are currently threatening to reach bankfull. Cold temperatures
for the coming week will keep the ice locked up. Currently no
suspected ice jams in the area... but will continue monitoring for
any that might develop. Serious ice jams and flooding concerns are
unlikely until a significant warm up and rainfall.

&&

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

$$

Synopsis...jk
short term...jk
long term...Hoving
aviation...Hoving
hydrology...cas

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