Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 111453
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
853 AM CST Mon Dec 11 2017

.UPDATE...We decided to go with an impact based Winter Weather
Advisory (rather than based on amounts alone) to enhance the
concern of this band moving through at a time that will be
affecting the afternoon rush period. Also, meso models are showing
that the heaviest band could set up right along the I-94 corridor.
So timing and location are key with pulling the trigger. Could see
some pretty hefty snowfall rates with lapse rate considerations as
well. Going forecast amounts look ok for now but will continue to
evaluate to see if any further tweaks are needed.

PC

&&

.MARINE...Gale Warning looks good starting tonight and into the
morning hours on Tuesday as gusty north/northwest winds prevail in
the wake of the low pressure trough the area today.

PC

&&

.PREV DISCUSSION... (Issued 545 AM CST Mon Dec 11 2017)

UPDATE...The first round of light snow is decreasing over south
central WI and should end in far ern WI around 14z. The afternoon
round of snow is currently approaching the Twin Cities. A w-e
swath of 2-3 inches of snow could occur with this round mainly
from Madison to Milwaukee with lesser amounts to the north and
south.

AVIATION(12Z TAFS)...Cigs of 1-3 kft and vsbys of 1-3SM is expected
with the light snow early this morning. The snow will end around
14z with good vsbys and higher cigs expected afterward.
However another round of snow will lower the cigs and vsbys for
the afternoon, especially from Madison to Milwaukee. The bkn-ovc
stratus will then scatter out after midnight, as brisk nly winds
bring much colder and drier air into the region.

PREV DISCUSSION... (Issued 342 AM CST Mon Dec 11 2017)

SHORT TERM...

Today And Tonight...Forecast Confidence Is Medium.

Snow is beginning to reach the ground over sw WI and expect this
to continue ewd this morning. A round of PVA and 850-700 mb warm
advection and frontogenesis is the catalyst for the light snow
this morning. Snow accums will remain under 1/2 inch this morning.
The longevity of the snow this morning will only be 1-3 hours at
any one location followed by more development this afternoon.

The strong shortwave trough currently over ern ND and nw MN will
track to north central IL by 00Z. PVA and mid level frontogenesis
associated with the upper wave will likely produce a narrow w-e
band of moderate snow for the afternoon. The consensus of the
models focuses this band from Madison to Milwaukee. 2-3 inch
accums are forecast with this band. A Winter Wx Advisory may be
needed if primary highways become snow covered for the afternoon
rush hour. This is uncertain given high temps in the lower to
middle 30s today and expected treatment of the roads.

For tnt, brisk and gusty nnwly winds and strong cold advection
will prevail with temps falling into the teens and below zero wind
chills for sunrise on Tue.

Tuesday Through Wednesday Night...Forecast Confidence Is Medium.

Models are in decent agreement with showing a tight pressure
gradient remaining over the area Tuesday, with gusty northwest
winds. This will bring a raw, cold day to the area. Clouds should
gradually move out of the area as well. Tuesday night looks to be
a very cold night, as winds become light with mostly clear skies
and a snow covered ground. Adjusted temperatures downward a bit
Tuesday into Tuesday night, to account for the warm bias with
the blended model temperatures.

Models then start to differ with trends Wednesday into Wednesday
night. The ECMWF/Canadian models show weak low pressure sliding
southeast across Iowa into central Illinois during this period.
The NAM is much further north, with the GFS in between. They all
have a potent 500 mb shortwave trough sliding southeast from the
northern Plains into northern Missouri Wednesday, then southeast
of there Wednesday night.

The GFS/ECMWF are relatively dry Wednesday night, with the
NAM/Canadian bringing some QPF through the area. They all show
some type of 500 mb shortwave trough moving southeast through the
region. There is some timing differences with this feature. The
upward vertical motion is not very strong, and there are
differences with moisture profiles within the ice crystal growth
region aloft.

For now, went with consensus model blended PoPs for Wednesday
into Wednesday night, which give generally lower end PoPs. There
is a mention of light freezing rain for a time Wednesday evening
in southern and western parts of the area. However, there is
uncertainty with this occurring, given the dry look on some
models. Temperatures should moderate a bit, but remain below
normal.

LONG TERM...

Thursday Through Sunday...Forecast Confidence Is Medium.

Models are showing several 500 mb vorticity maxima shifting
southeast through the area Thursday into Friday morning. Held onto
lower end PoPs for Thursday, as low level moisture lingers within
steep low level lapse rates per GFS forecast soundings. May need
higher PoPs in later forecasts, if this trend holds. Things then
look dry Thursday night into Friday. Below normal temperatures
look to linger Thursday into Thursday night, before moderating on
Friday.

Models are generally trending toward a more zonal flow pattern at
500 mb over the weekend. They are trying to bring a developing
trough through the region Sunday, with some timing differences.
The ECMWF/Canadian models try to bring low pressure northeast
through or south of the area Saturday night into Sunday. The GFS
keeps any low track well north of the area. There is uncertainty
here with these features. For now, kept consensus model blended
PoPs and temperatures for the weekend. Temperatures may moderate
to near or even above normal over the weekend, depending on how
things develop.

AVIATION(09Z TAFS)...

Cigs of 1-3 kft and vsbys of 1-3SM is expected with the light
snow this morning. The snow will end later this morning with good
vsbys and higher cigs expected, however another round of snow
will lower the cigs and vsbys for the afternoon, especially from
Madison to Milwaukee. The bkn-ovc stratus will then scatter out on
midnight, as brisk nly winds bring much colder and drier air into
the region.

MARINE...

A Gale Warning is in effect tonight into Tue for nly winds around
25 kts and gusts around 35 kts. The nly winds will begin after
the passage of a strong cold front. A Small Craft Advisory will
likely be needed after the gales cease from late Tue morning into
Tue eve.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST this evening for
     WIZ058>060-063>066-070>072.

LM...Gale Warning from 8 PM this evening to 10 AM CST Tuesday for
     LMZ643>646.

&&

$$
Today/Tonight and Aviation/Marine...Gehring
Tuesday THROUGH Sunday...Wood



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