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Area forecast discussion 
National Weather Service Grand Rapids Michigan
955 PM EST Wednesday Jan 28 2015

Latest update...
update

Synopsis...
issued at 328 PM EST Wednesday Jan 28 2015

Roads could be icy on Thursday morning as low pressure brings a
wintry mix of precipitation late tonight. Temperatures should rise
above freezing by late morning and conditions should improve. Some
light snow is expected during the afternoon with accumulations an
inch or less. It will turn much colder on Friday and into the
weekend.

&&

Update...
issued at 955 PM EST Wednesday Jan 28 2015

No big changes to the forecast. Still expecting a rapid increase
in precipitation coverage as the low level jet arrives along with deeper
low level moisture. This will occur between 06-09z. Precipitation type
should be mainly freezing rain and sleet along I-94. Also freezing
and sleet along I-96 which may start changing over the snow toward
daybreak. And snow mixed with some sleet toward Highway 10. The
peak of the precipitation will coincide with the morning commute and the
advisory still looks good with around a tenth of an inch of ice
expected through middle day Thursday.

&&

Short term...(this evening through Friday night)
issued at 328 PM EST Wednesday Jan 28 2015

Kept the headlines as is. Main threat appears to be light freezing
rain late tonight which will cause icy roads for the Thursday
morning commute. Warm air advection is already underway and
strengthens overnight. As the very warm air across the plains
advects east we will see 850 mb temperatures go above 0c for by 06z for
all but the far northern tier. We start off very dry so temperatures will
drop as the column saturates and we could see a quick burst of
snow at the onset before precipitation GOES over to ice pellets and freezing rain. Do not
expect much quantitative precipitation forecast so ice amounts will be limited...but enough to
cause potential travel problems beginning after midnight and
continuing through the morning commute.

Southerly flow through the morning suggests that surface temperatures should
warm as any freezing precipitation brings latent heat effects that are not
being offset by cold air advection near the surface. So expect icing issues to end
during the morning. Surface low moves east and cold air advection on
northwest flow begins after 18z with precipitation transitioning back to
snow from north to south. Snow accumulations an inch or less and
temperatures should not be cold enough to allow much accumulation on
roads...so impacts are expected to be minor.

Synoptic snows end by evening with some north to Northwest Lake
effect. Inversion heights are at or below 5kft during the evening so lake
effect should not be heavy.

Long term...(saturday through wednesday)
issued at 328 PM EST Wednesday Jan 28 2015

Overall models are trending further south with the track of the low
Saturday night through Sunday...suggesting lower Michigan will end
up with less precipitation and colder temperatures. High res Euro
suggests a dry forecast is the way to go for Sunday. Not ready to
drop probability of precipitation completely...but the pattern we are in has been a dry
one. As a result I will lower probability of precipitation on Sunday and back off on the
quantitative precipitation forecast considerably.

Looking further ahead...stronger warm air advection is noted for
Tuesday. With an Arctic airmass in place...that should support a
southwest flow event. Probability of precipitation were increased...especially west of Grand
Rapids.

I did lower temperatures especially Sunday night and Monday given
the dominance of the Arctic air. The models commonly are too warm
with the nighttime lows during these events.

&&

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 755 PM EST Wednesday Jan 28 2015

Aviation impacts developing tonight and continuing Thursday
morning. The main issue is a medium to high confidence icing event
due to sleet and freezing rain between roughly 06z and 15z. Expect
moderate icing between the surface and 3000 ft, and also between 8000
and 16000 ft, during this time. Temperatures between 3000 feet and
8000 feet should be mostly above freezing with mainly rain expected in
that layer. Lowering freezing levels after 15z-18z Thursday will
lead to precipitation changing to mostly all snow showers from north to
south in the afternoon.

Other issue is low level wind shear/turbulence between roughly 02z
and 10z tonight as winds increase to 50 knots out of the southwest in
the 2000-4000 feet above ground level layer. The surface winds during this time will be
out of the south-southeast at 12-16 kts.

Last but not least expect numerous IFR ceilings/visibilities between 12z and
18z Thursday as the surface low/trough tracks across Michigan. Ceilings/visibilities
improving after 18z Thursday with the passage of the low although
winds shifting/increasing out of the northwest to 15-25 kts with
some gusts over 30 kts possible. This will lead to more low level
turbulence developing.

The pattern for this event looks very springlike. In the warm
sector of this system... temperatures today in parts of the
Central Plains were in the 70s. This air mass... accompanied by
precipitable waters near 0... will be pushing rapidly north tonight and
interacting with a shallow cold and dry air mass over Michigan. Surface dew
points were only around 10f in Michigan at 7 PM. The contrast across the
warm front is bound to result in some interesting weather in terms
of precipitation types... although overall coverage/intensity/amount
of precipitation is still somewhat in question at this hour.

Latest short range guidance supports development of convective
precipitation between 06z and 09z over southwest lower Michigan
on the nose of the low level jet. Forecast soundings overnight support
predominately freezing rain with some sleet possibly mixed in for
the azo/btl/jxn terminals and I-94 corridor region. Meanwhile the
mkg/GRR/lan terminals are closer to the transition zone to mostly
snow which should be just north of the I-96 corridor. Suspect
these terminals will see more in the way of a snow/sleet/freezing
rain mixture... with less freezing rain than to the south.



&&

Hydrology...
issued at 328 PM EST Wednesday Jan 28 2015

Cold weather with only light precipitation should mean no
significant trends in the rivers. Ice will form over the weekend
as the cold intensifies.

&&

GRR watches/warnings/advisories...
Michigan...Winter Weather Advisory from 1 am to 4 PM EST Thursday for
miz037-043-044-050>052-056>059-064>067-071>074.

Lm...none.
&&

$$

Update...jk
synopsis...ostuno
short term...ostuno
long term...mjs
aviation...Meade
hydrology...ostuno

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