Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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689
FXUS63 KMKX 220453
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1053 PM CST Sun Jan 21 2018

.UPDATE...

A cluster of showers and storms over scntrl/cntrl IA is lifting
NNE. This is in an area of strong upper level divergence under the
right entrance region of the upper jet. Lower level convergence in
a strengthening warm air advection regime is helping the deep UVV
in this region. That will continue to lift north into southern
Wisconsin later tonight. The forecast remains on track.

&&

.AVIATION(06Z TAFS)...

IFR conditions are expected through the TAF period with LIFR
CIGS/VSBYS across the southeast through about 00z Tuesday.
Conditions will slowly improve Monday evening. Peak rainfall, with
the potential for some lightning, will roll through the area
between about 09-16z Monday. A transition over to a wintry mix and
then snow will occur Monday evening. That transition reaches
KMSN around 04z Tuesday and KMKE/KUES/KENW by 06-08z Tue. A
couple of inches of wet snow accumulation is possible across the
southeast Monday night, diminishing Tuesday morning.

&&

.PREV DISCUSSION... (Issued 858 PM CST Sun Jan 21 2018)

UPDATE...

So far this evening we`ve just had light rain and drizzle across
the area in response to persistent h8-h7 warm air advection and
ascent across the 925-850mb warm frontal zone. The big surge in
rain should arrive between 09-15z Monday as the low level jet
slams up here later tonight, bringing a strong influx of warm and
moist air north. The ground is saturated with only the top couple
of inches thawed, so we should see plenty of runoff. Thankfully,
our rivers are running low and the river models suggest only
modest rises with a few rivers touching bankfull. If we see rapid
ice breakup there is always a chance for ice jams, but right now
our guidance on that suggests a low probability of it. Overall,
the forecast is in good shape.

Our transition over to a wintry mix/snow is still looking like
Monday evening through about midnight across southern Wisconsin.

MARINE...

As strong surface low pressure lifts north into the region, look
for increasing easterly winds and building waves. A small craft
advisory is in effect from 12z Monday through 21z Tuesday. Winds
will shift to the north then northwest in the wake of the passing
low pressure.

PREV DISCUSSION... (Issued 505 PM CST Sun Jan 21 2018)

UPDATE...

No changes needed to the short range forecast. Look for the fog to
get progressively more dense, especially east. Drizzle will
eventually turn to more rain with heavier stuff arriving late
tonight.

AVIATION(00Z TAFS)...

Expect widespread IFR conditions through the TAF period.
A cold easterly flow off Lake Michigan will likely make for a
long duration LIFR situation for southeast Wisconsin.  Drizzle
this evening will turn to more steady rainfall after 09z Monday as
a strong low pressure system pushes northeast into the region.
Temps will stay above freezing through the TAF period, so wintry
precipitation is not expected. The change-over to snow will begin
to spread west to east after about 02z Tuesday, reaching KMSN
around 05z Tue and KMKE about 07z Tue.

PREV DISCUSSION... (Issued 327 PM CST Sun Jan 21 2018)

SHORT TERM...

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 Monday into Monday
night. 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
mark.

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.

AVIATION(21Z TAFS)...

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...

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.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until 6 AM CST Monday for WIZ051-052-058>060-
     064>072.

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
     LMZ643>646.

&&

$$

Update...Davis
Tonight/Monday and Aviation/Marine...SPM
Monday Night through Sunday...Gehring



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