Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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143
FXUS63 KMKX 171129
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
629 AM CDT Tue Apr 17 2018

.UPDATE...

No changes to the going short term forecast at this time.

&&

.AVIATION(12Z TAFS)...

VFR conditions are expected early this morning. Late morning into
this afternoon, a stratocu deck is expected to develop across much
of the area, with ceilings bouncing between VFR and MVFR. Winds
today will initially be from the northwest, but will become
northerly this afternoon and then northeasterly by this evening.

Winds will then become easterly tonight, ahead of the next storm
system. Mid level cloud cover will increase from the southwest,
with ceilings lowering with time. Precipitation should hold off
until after 12Z, but once it does start, IFR to LIFR vis is likely
with areas of moderate to perhaps heavy snow.

&&

.PREV DISCUSSION... (Issued 333 AM CDT Tue Apr 17 2018)

SHORT TERM...

Today...Forecast Confidence High...

Surface ridging will build into the area from the west, as the
storm system that has been affecting the area since last week
finally starts to pull to the east. A few outer vort lobes will
still be rotating around the main upper level low, which will
result in a decent amount of cloud cover. Clouds should be most
widespread across the northeastern part of the forecast area, with
lesser amounts further south and west.

Temperatures today will remain on the cool side, with highs in the
mid to upper 30s. A few spots across southwestern Wisconsin may
touch the 40 degree mark.

Tonight through Wednesday night... Forecast confidence is medium
to high.

A fast moving system will track through the Midwest tomorrow and
bring a swath of snow to southern Wisconsin, mainly from from
late morning through late evening. This system will drop a quick 4
to 7 inches on portions of south central Wisconsin that will
impact the afternoon commute due to the high snowfall rates. A
Winter Storm Watch is in effect for this area. We will re-evaluate
the snow forecast before deciding which of these counties needs a
Warning and which need an Advisory. Elsewhere, snow will also
impact the afternoon commute, but snowfall amounts are expected to
be a little lower since the system should be weakening a little.
A Winter Weather Advisory is in effect. If it looks like our snow
amounts or snowfall rates will be higher as current trends
suggest, some of this area could get bumped up to a warning.

The uncertainties with this system are definitely snowfall
amounts and perhaps precip type. The latest forecast temperature
profiles support more snow than previous forecasts, thus the ramp
up in snowfall amounts and headlines. I think we might still be
underdone with snowfall amounts. The thing that would limit the
snow amount is our surface temperatures. The snow will be
occuring mainly during the day which would a suggest warmer
boundary layer, but the snowfall rates will be high, so that would
counteract that effect, and also dynamic cooling (cooling from the
top down due to snow) will help.

Precip type is still a little uncertain since we could get some
mixy stuff during the onset, but this latest set of models
suggests we`ll change over to snow quite quickly. The catch is
that moisture will need to be deep enough to get ice crystals and
the NAM has a little more shallow moisture than the GFS which is
skewing our forecast to a little lower snowfall amounts. The
immediate lakeshore might be more of a rain/snow mix due to a
stiff northeast wind off the mild lake, but just inland will see
snow.

LONG TERM...

Thursday through Tuesday... Forecast confidence is high.

Any lingering precip will exit southeast WI by Thursday morning.
Dry air spreading into the Upper Midwest will allow for sunshine
and warming temperatures. High pressure will hang around the
region through the weekend so we will finally have a stretch of
dry and mild weather. Highs will gradually warm into the 50s this
weekend. Cyclonic flow aloft and also a closed upper low drifting
through the center of the country will contribute clouds over
southern WI on Saturday. Sunday and Monday will bring southerly
winds and sunshine back to southern WI. Our next chance for precip
should hold off until Tuesday.

AVIATION(09Z TAFS)...

VFR should generally prevail today, though periods of MVFR
ceilings are possible.  Winds will be a bit gusty from the west-
northwest early, but should decrease as the day goes on. Winds
will be northerly this afternoon and evening, then become
increasingly easterly as low pressure develops well to our
southwest.

MARINE...

Winds and waves have decreased this morning, and have gone ahead
and cancelled the Small Craft Advisory. Winds will be westerly to
northwesterly early today, becoming northerly later this
afternoon. Heading into tonight, developing low pressure well to
our southwest will result in increasing easterly winds. This
onshore flow will also result in building waves over time.

Gusty north winds are expected late Wednesday into Thursday
morning.  Another Small Craft Advisory will likely be needed
by this time.

After this system passes through, a period quiet
weather is in store of the region, with no significant storm
systems expected through the weekend.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 10 AM Wednesday to 7 AM CDT
     Thursday for WIZ051-052-058>060-064>066-068>072.

     Winter Storm Watch from Wednesday morning through late Wednesday
     night for WIZ046-047-056-057-062-063-067.

LM...None.
&&

$$

Update...Boxell
Today/Tonight and Aviation/Marine...Boxell
Wednesday THROUGH Monday...99



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