Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 070800
Area Forecast Discussion
National Weather Service Marquette MI
300 AM EST Wed Dec 7 2016
.SHORT TERM...(This evening through Wednesday)
Issued at 313 PM EST TUE DEC 6 2016
Visible satellite imagery this afternoon shows the cloud layers
along the eastern half of the U.P. are less thick; however, a narrow
band of snow with a light wintry mix along the front edge was
pushing east from the Keweenaw to Iron Mtn. Hi-Res forecast guidance
indicates this band will continue to progress east with thickening
cloud cover. Within the band strong forcing was taking place, as a
result of some narrow convergence, which is producing significant
reductions to vsbys to around 1/2 mile, but not expecting this will
last for longer than a couple hours before ending. Guidance
indicates a lull in precip just prior to sunset thru 2-3z when wrap-
around moisture slides east. Pressure gradient will tighten back up
with good height falls by 3-6z, which will usher in gusty west winds
to around 30-35mph. It is possible in the higher terrain locations
gusts could approach 40 mph at times. Not expecting any wind
headlines overnight into Wed.
Main concerns heading into midday Wed, will be on the developing
lake effect snow machine for the Keweenaw. Winds will be turning
westerly to northwesterly with much colder air advecting southeast,
profiles indicate good moisture within the DGZ coupled with good
vertical lift of parcels, so expect a good band or two to develop
over the Keweenaw by Wed aftn. Coupled with the falling snow and
reduced vsby`s, mixed layer should be bringing to the surface gusts
throughout the day to around 25-30mph and with increased snow-liquid
ratio`s around 20:1, this should easily result in blowing snow and
could further reduced vsby`s in the late afternoon hours.
.LONG TERM...(Thursday through Tuesday)
Issued at 300 AM EST WED DEC 7 2016
Nam shows a 500 mb trough over the upper Great Lakes 12z Thu.
Troughing remains through 12z Sat over the area. Prolonged lake
effect scenario in NNW lake effect snow belts will continue this
forecast period. This was covered in the previous forecast and used
that as the basis for this forecast. Will have numerous advisories
up for the NNW lake effect snow belts continuing. Did not make too
many changes to the going temperatures. Snow ratios look to be
between 20 to 25 to 1 for this event.
In the extended, GFS and ECMWF show a zonal 500 mb pattern across
most of the U.S. with a broad trough across most of the country 12z
Sat. 850 mb temperatures across Lake Superior at 12z Sat are from -
17C to -19C. A shortwave digs into the upper Great Lakes 12z Sun.
Troughing continues over the area Mon into Tue with cold air
remaining over the area through then. Temperatures will continue to
be below normal and lake effect snow showers will continue through
this forecast period as well. Get system snow in for Sat night
through Sun morning and then lake effect gets going in earnest again
Sun night through Wed with even colder air arriving in. The lake
effect event will be in WNW lake effect snow belts. Could see some
below zero temperatures for lows Tue night and Wed night.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1150 PM EST TUE DEC 6 2016
As low pres moves e across northern Ontario thru today, cyclonic
flow and increasingly colder air will result in lake effect snow
developing off Lake Superior. With low-level winds from the wsw
today, developing lake effect snow will impact only KCMX thru this
aftn. MVFR conditions should prevail at KCMX overnight with
conditions then deteriorating to IFR or even LIFR at times this aftn
as intensifying lake effect snow impacts the terminal. Gusty winds
up to 35kt will create BLSN as well, further aiding the
deteriorating conditions. Sfc trof dropping across the Keweenaw this
evening is likely to bring mdt/hvy shsn and prevailing LIFR
conditions. At KIWD, MVFR conditions should prevail thru the fcst
period. Cyclonic flow around the low pres will bring ocnl -shsn, and
winds will gust to 25-30kt. Aforementioned sfc trof will reach KIWD
beyond this fcst period, bringing mdt/hvy snow and likely LIFR
conditions. At KSAW, MVFR conditions should mostly prevail, but with
a downslope component to the wind, some periods of VFR are likely.
Expect nothing more than a few flurries at times.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 313 PM EST TUE DEC 6 2016
No changes to current marine headlines. While a brief lull in gales
conditions are expected for the western portions of Lake Superior,
further west across Central Minnesota surface observations indicate
gusty winds returning to around 35kts. Expect this channel of higher
gusts to eventually return to the western portions of Superior. As a
result will leave the gales going in the western zones and including
the nearshore zones up to the western side of the Keweenaw. Along
the tip of the Keweenaw a boat earlier had reported gusts to 50kt,
but this appear to be a local enhancement due to the narrow
convergence that was taking place. Expect the convergence zone to
shift east and dissipate with a more sustained low-end gale
conditions overnight into Wed for the western half. Further east, it
is possible gales may need to be introduced; however, expect the
gradient to slacken off, so will hold off on any open water
headlines for Wed at this time.
Winds will eventually shift northwest and with much colder air
sliding across Lake Superior from Canada, this coupled with winds
mainly between 25-30kt and occasional gales to 35 kt will allow
waves to easily build later in the week.
Lake Effect Snow Advisory from 1 AM Thursday to 7 AM EST
Saturday for MIZ006.
Lake Effect Snow Advisory from 7 AM this morning to 7 PM EST
Friday for MIZ001-003.
Lake Effect Snow Watch from late tonight through Friday evening
Lake Effect Snow Advisory from 1 AM Thursday to 7 PM EST Friday
Gale Warning until 10 PM EST this evening for LSZ265-266.
Gale Warning until 10 AM EST /9 AM CST/ this morning for LSZ162.
Gale Warning until 7 PM EST /6 PM CST/ this evening for