Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 212127

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
327 PM CST Sun Jan 21 2018


Tonight and Monday...Forecast Confidence is medium...

A closed mid/upper level cyclone will progress from the central
High Plains into the western Great Lakes through Monday. Surface
low pressure will accompany the upper wave, with the occluded low
pressure system crossing southern Wisconsin later tonight. Warm
advection will stream out ahead of the system this evening, with
weak lift producing areas of drizzle. Fog development is also
likely, given the weak low-level winds, and easterly wind
component. There is concern, backed up by probabilistic model
guidance, that dense fog may advect several miles inland from Lake
Michigan given this setup. Decided to take a proactive approach
and expand the Dense Fog Advisory across our eastern and southern
areas into early tomorrow morning. The advisory may need to be
expanded farther northwest overnight if conditions warrant.

Deep layer moisture and synoptic lift increases tonight as the
system draws closer. Southwesterly moisture transport will
increase precipitable water values up over 0.75 inches, which is
near the 99th percentile climatologically for this time of year,
with a NAEFS standardized anomaly of 3, which has a 1 to 5 year
return period for our area. Sources for ascent include strong
jet-level warm advection and divergence, increasing cyclonic
vorticity advection, and plenty of low-level warm advection. Look
for light to moderate rain to break out as this better forcing
arrives, generally after midnight tonight and lasting into Monday
AM. This will be a decent rainfall area-wide, with over 1 inch
possible. Kept a slight chance for thunder in, given some
elevated CAPE present on area forecast soundings.

The rain will persist into at least tomorrow morning, with some
potential for fog and drizzle to return in the afternoon. High
temperatures will range from the upper 30s in the north, with
areas near the Illinois border possibly cracking the 50 degree

Monday night through Wednesday...Forecast confidence medium.

A low level TROWAL and sfc trough will hang back from the center
of the low bringing rain changing to snow for Mon nt. 1 to 3
inches of snow accum is forecast Mon nt over se WI. The rain to
snow changeover will occur from late evening over south central WI into
the early morning hours over se WI. Wet snow will freeze for the
Tue AM commute as temps fall into the 20s.

Brisk nwly winds and cold advection will continue to bring polar
air into the region on Tue, but polar high pressure will settle
over the area for late Tue nt-Wed. Aloft, a shortwave trough will
pass, bringing some clouds for this period.

.LONG TERM...Thursday through Sunday...Forecast confidence medium.

Upper ridging will then develop for Thu-Fri as a longwave trough
moves from the wrn USA into the Great Plains. The longwave trough
and a cold front will then bring chances of rain/snow for Fri nt-Sat.
Above normal temps will return with the approach of the longwave
trough for Thu-Sat AM. Nly winds and a polar airmass will return
for Sun.



Ceilings will lower from MVFR to IFR early this evening with
areas of drizzle. Conditions should further deteriorate tonight,
with rain and drizzle becoming more widespread. The rain will
continue into Monday morning. Fog is also a concern, especially
for areas within several miles of Lake Michigan where dense fog
may move inland from the Lake this evening into tonight. Expect
IFR to LIFR flight conditions for tonight into tomorrow morning.
There is also a slight chance for lightning/thunder after midnight
tonight, but not enough confidence to include this in the TAFs.



Marine dense fog will continue into at least tomorrow morning with
visibilities of 1 mile or less. Winds and waves will increase on
Monday morning into Tuesday afternoon, and a Small Craft Advisory
is now in effect during this time. Mariners should exercise
caution from Today into Tuesday given the multiple marine hazards
outlined above.


WI...Dense Fog Advisory until 6 AM CST Monday for WIZ051-052-058>060-

LM...Dense Fog Advisory until 6 AM CST Monday for LMZ643>646.

     Small Craft Advisory from 6 AM Monday to 3 PM CST Tuesday for



Tonight/Monday and Aviation/Marine...SPM
Monday Night through Sunday...Gehring is the U.S. government's official web portal to all federal, state and local government web resources and services.