Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 212317

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
617 PM CDT Wed Mar 21 2018

.UPDATE...A shortwave trough over ern IA will continue sewd
reaching the IL/IN border around 06z. A narrow cloud deck around
6 kft over far sw WI is associated with the trough and will move
into south central WI this evening. The cloud deck is expected to
thin with time or clear after the passage of the trough. With a
polar sfc ridge finally moving overhead tnt, chilly temps expected
for the morning.


.AVIATION(00Z TAFS)...VFR conditions tonight and Thursday. A
narrow cloud deck around 6 kft over far sw WI will move into south
central WI this evening, but will thin out with time.


.PREV DISCUSSION... (Issued 321 PM CDT Wed Mar 21 2018)

Tonight into Friday - Confidence...High
High pressure will dominate this period. Conditions for lake
induced clouds have eased. Cirrus is gradually moving out as well.
Watching a pocket of AC across se MN but will plan on this
largely breaking up before arriving into our area. So trended
towards some of the colder guidance numbers overnight. Looking at
low/mid 40s for Thursday with a lighter onshore flow expected with
the more slack gradient expected.

Friday night into Saturday - Confidence...Medium
Focus is on the shot for snow over this period, both on how much
and how far northeast the snow will make it. Currently, the
system that will be responsible for bringing this snow in is off
of the southern California coast and will propagate across the
central plains over the next couple days.

21.12z guidance is coming into agreement on having an elongated
band of precipitation developing from the Dakotas down to the mid-
Mississippi River Valley region on Friday ahead of the mid level
trough and along the thermal gradient in the low levels where
warmer air rides up over the boundary. As the system pushes
eastward into Friday evening, the snow will develop/push into
southwestern Wisconsin. There are some differences between the
21.12z GFS/ECMWF/NAM but they all at least show southwest WI
getting hit with some decent QPF of around a half inch. The drop
off to the northeast of the band will be rather sharp, so have
tried to show that detail in the QPF/snow amount forecast for
today. The GFS was the favored model with the ECMWF only pushing
the higher QPF a tier of counties northwest. The NAM still appears
to be an outlier with it having a secondary band developing much
further northeast of where the rest of the guidance has it. This
will be a moderate to heavy wet (8-10:1 snow to liquid ratio)
snow at times though the axis for that heavy snow appears to be
just off to the southwest of WI into IA/IL. The main period for
this snow has been pretty consistent with it starting Friday
evening and ending Saturday morning. However, the ECMWF does
linger the snow a bit longer along the inverted surface trough
into Saturday afternoon, so that trend will have to be monitored
as well.

Saturday night into Wednesday - Confidence...Medium
Whatever snow does fall into Saturday will melt away quickly as
southerly low level winds bring warmer air back into the region
for early next week.

The next system of note comes in on late Monday night into early
Tuesday and potentially lingers into Wednesday. This one looks to
be mainly rain for much of the region, which is really needed due
to how dry the conditions have been lately.

AVIATION(18Z TAFS)...VFR this period with high pressure in
control. Any lingering gusty northeast winds near the lake will
ease this evening with pressure gradient become more slack. Quiet
into Thursday with a lighter onshore wind.

MARINE...Small craft advisory remains in effect until 5 PM to
account for lingering onshore flow and higher waves.


LM...Small Craft Advisory until 6 PM CDT this evening for LMZ643>646.



Tonight/Thursday and Aviation/Marine...Collar
Thursday Night through Wednesday...Halbach is the U.S. government's official web portal to all federal, state and local government web resources and services.