Scientific Forecaster Discussion
fxus63 kmkx 181736
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1136 am CST Mon Dec 18 2017
Update...the increasing swly winds and breaks in the clouds over
far srn WI should contribute to decreasing stratus through the
afternoon. Brisk swly winds and warm advection will continue tnt
with a weak cold frontal passage to shift the winds to wly on Tue,
although sunshine and a drier airmass will make for mild temps.
A sfc ridge and cooler temps will then return Tue nt.
Aviation(18z tafs)...cigs of 600-1500 feet and MVFR vsbys will
gradually improve through the afternoon as the stratus scatters
out and vsbys rise to p6sm. Afterward VFR conditions are expected
tnt-Tue however low level wind shear on wly wind shear is expected tnt.
Previous discussion... (issued 532 am CST Mon Dec 18 2017)
Widespread low clouds and fog continue at this hour, with
visibilities generally between 1 and 2 miles. Light precipitation
is pushing east through the Milwaukee Metro, and should move east
of the region by sunrise. For the most part, the precipitation is
limited to areas where the surface temperature is just above
freezing, limiting impacts. A few slick spots are still possible
on bridges and overpasses, as well as any untreated surfaces where
temperatures are below freezing.
LIFR conditions with low cigs and vis will persist for a few more
hours this morning, before a gradual improvement to IFR by mid
morning, followed by ceilings lifting and scattering out by this
afternoon. Winds will increase this afternoon as well, with
gustiness persisting into the nighttime hours. Low level wind shear is expected
tonight at all terminals.
Previous discussion... (issued 218 am CST Mon Dec 18 2017)
Rest of this morning through tonight...forecast confidence is
Light precipitation continues across the region early this
morning, mostly in the form of drizzle or freezing drizzle, though
a few snowflakes have been mixing in on occasion. Temperatures
south of I-94 are generally above freezing, with readings at or a
degree or so below freezing north. Thus far, impacts from any
freezing precipitation have been little to none, with pavement
temps seemingly a couple of degrees warmer than ambient air
temps, and thus just above freezing. We'll continue to closely
watch any travel impacts as we head toward the Monday morning rush
Most precip should be done by daybreak, with clouds sticking
around through most of the morning. Clearing should begin to take
place by afternoon, though the exact timing of that clearing
remains in question.
Temperatures today should range from the upper 30s north to low to
mid 40s south, where sunshine should be more widespread.
Temperatures tonight are expected to fall back into the low to mid
Tuesday through Wednesday night - confidence...medium
strong northwest mid level flow becomes broadly anticyclonic this
period with low level surface ridging being dominant. There is a
hint of a return flow setting up later Wednesday with some of this
possibly reaching our far north or northwest. The Gem and European model (ecmwf)
keep this out of our area while the GFS brings it in. Will ride
with the superblend pops for now which keep our area dry. A little
surprised the superblend isn't giving US at least some small pops
Wednesday night as that isentropically induced band skims our
northern cwa. Will leave dry forecast for now.
Thursday through Friday night - confidence...medium
main focus of the forecast centers on a potent storm system
lifting northeast from the central/Southern Plains. The progs
continue to show surface/850 tracks and baroclinic zone placement
that favors the better snow potential across the northern and
northwest cwa. The consensus of the GFS and European model (ecmwf) surface tracks
brings it either into extreme southeast WI or extreme northeast
Illinois. The 850 low tracks are across central WI with the European model (ecmwf) quite
broad with this feature. The cold air doesn't really get pulled
into the southeast until later Friday or Friday night. The European model (ecmwf)
is slower in this regard. So still potential for a potpourri
across our forecast area with the southeast looking more rain than
snow at this time and the north seeing a longer window within a
more thermally favorable environment for snow production. So at
this time the thinking is our northern County Warning Area will be more under the
gun for the most impactful conditions. Both the GFS and European model (ecmwf) pull
some fairly warm 850 temps into the southeast cwa Thursday night
and Friday morning so have adjusted the blended numbers a bit
warmer to account for this consensus.
Saturday and Sunday - confidence...medium
colder air arrives with still some timing differences on how
quick the bitter air arrives. The GFS is overall quicker and
colder bringing 925 temps of GOES down to the minus teens celsius
for Saturday and into the -20s celsius for Sunday along with a
gusty WNW wind regime. Meanwhile the European model (ecmwf) develops some light
snow Saturday night into Sunday along the slower arriving Arctic
front. Will stick with the superblend numbers this far out. Bottom
line looking like a bitterly cold Christmas eve and some
locations may need some temp reduction due to the potentially
fresh snow cover in place.
Aviation(09z tafs)...mix of light rain and drizzle continues to
affect the terminals this morning. At sites appear to be at or
just above freezing, limiting impacts from any freezing
In general, IFR conditions will continue through mid morning,
before ceilings begin to lift and gradually scatter out.
Winds will pick up from the southwest today as well, with a few
gusts possible by afternoon.
Marine...winds will increase from the southwest today and
tonight, and a Small Craft Advisory will go into effect this
evening through tomorrow evening, with gusts between 25 and 30
Winds will decrease for a time Wednesday, before the next storm
system begins to impact the region Thursday and Friday.
Lm...Small Craft Advisory from 6 PM this evening to 6 PM CST Tuesday