Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 251745 AAB
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1245 PM CDT Sat Mar 25 2017
The band of rain tracking through southern WI early this afternoon
is associated with 925-850mb frontogenesis and 500mb vorticity
advection. Persistent, light rain showers are expected in
southeast WI throughout the afternoon and early evening due to
weak vorticity advection, but inland areas of south central WI
should have quite a lull in the precip. Light drizzle and fog
will persist through the night.
The band of rain tracking north through southern WI early this
afternoon has a back edge. Expect drizzle and light fog to persist
through the night. Areas in southeast WI have a better chance of
more showers this afternoon into the early evening.
Another round of steadier rain showers is anticipated early Sunday
IFR and lower ceilings with visibility in the 1 to 3 mile range
expected through Sunday morning as low pressure tracks across
.PREV DISCUSSION... (Issued 953 AM CDT Sat Mar 25 2017)
Periods of rain will continue today on brisk east winds. This is
in response to low pressure tracking through Missouri and central
Illinois today. There is very weak instability in northern IL that
will clip southeast WI this afternoon, so kept the mention of
thunder for that area.
There should be a lull in the showers this evening, then another
round of showers is expected late tonight into Sunday morning.
Brisk northeast to east winds today, then diminishing as the
surface low approaches Sunday morning. Small Craft Advisory
in effect through tonight as waves will be slow to subside below
PREV DISCUSSION... (Issued 734 AM CDT Sat Mar 25 2017)
IFR/LIFR ceilings expected through tonight. Will probably see
some lower visibilities form as the surface boundary creeps back
north into northern Illinois later tonight into Saturday as low
pressure moves toward southeast Wisconsin from Missouri. Rain
will increase in coverage from the south into this afternoon.
PREV DISCUSSION... (Issued 302 AM CDT Sat Mar 25 2017)
TODAY and TONIGHT...Forecast Confidence...Medium
We will be on the cold side of the surface boundary with a strong
low level inversion. There is very weak elevated instability at
times, mainly 20 Joules/kg or less. As the mid/upper low moves into
the mid Mississippi River Valley. The low/mid level jet points into
northern IL, and expect most of the precipitation to fall this
afternoon. Far southeast Wisconsin will have a very small chance of
elevated thunderstorms, with CAPE reaching a minimal 20 Joules/kg.
Southeast WI will see higher amounts of rain than areas toward
central WI tonight into Saturday, ranging from around a third of an
inch northwest areas to up to an inch southeast. Rivers are forecast
to rise, with a few reaching bankfull stage, but so far we are not
forecasting rivers to reach flood stage this weekend.
SUNDAY AND MONDAY...Forecast Confidence is medium.
This period will be characterized by weak cyclonic flow throughout
the depth of the atmosphere, with abundant moisture in the low
levels. The deep, cut off low that has been spinning over the
southern plains will finally push through the upper midwest on
Sunday. The GFS brings this low the closest to southern WI, passing
just to our SE. A second, weaker trough is progged to follow the
cutoff low on Monday, through there is some disagreement on the
intensity and placement of this trof. It looks like the GFS solution
again would be the most impactful for us, with the strongest and
closest CVA, though even then, it looks pretty weak. Not a ton of
jet level divergence due to the weak flow, but generally diffluent
flow with the trough passages should provide some support for
In the lower levels, good agreement that a weak low will pass
through southeastern Wisconsin on Sunday. Plenty of moisture from
700mb on down, weak WAA at 850 and 925, and even some weak
frontogenesis to the NW of the flow and again along the trailing
trof at 925 should provide enough of lift to support likely PoPs
though Sunday. After the first low passes, another even weaker low
passes to the southeast of the area on Monday. As with the upper
levels, the GFS brings this second low is the closest to our area.
The lowest levels remain saturated though Monday, so given the weak
support for ascent, will carry slight chance PoPs through the
day. However the GFS is the only model bringing any precip to our
CWA, so this may be dropped at some point.
Given the very marginal nature of the lift on both days, am not
expecting any widespread or intense precip. It will more likely be a
spotty, light precip on both days. Additionally, with the very weak
flow and abundant low level moisture prevailing through the period,
am expecting fog for the end of the weekend and beginning of next
TUESDAY AND WEDNESDAY...confidence is low
Zonal flow aloft and high pressure in the lower levels will prevail,
so not much impactful weather expected. Looks like the lowest levels
will finally begin to dry out on Tuesday, so we`ll have our first
good chance of seeing the sun perhaps as early as Tuesday afternoon,
and likely on Wednesday.
GFS is showing much stronger CAA behind Monday`s potential low
pressure system, which is unsurprising since the GFS brings that low
so much closer to WI than the other models. Accordingly, temps
are dramatically cooler in the GFS than the Euro/Canadian.
Additionally, northerly flow on Tuesday will swing around to
easterly as the high slides over southern WI, so will have to
adjust temperatures downward along Lake Michigan, especially
WEDNESDAY NIGHT THROUGH SATURDAY...confidence is low
The consensus train falls off the tracks for the end of the week.
All guidance does show another deep closed low develop in the desert
southwest in the middle of the week, moving toward the upper
Midwest by the end of the week. However, the GFS also brings a
sharp trof down from Canada as the cut off low moves toward
Wisconsin. This northern stream trof will shunt much of the
moisture associated with the cutoff low south of the area.
Meanwhile, the Euro and Canadian show a much weaker northern
stream trof pushing well north of the area. This would allow the
cut off low and much of the associated moisture to move into the
area. Unfortunately, discrepancies in the temperature forecasts
persist into the late week. The ECMWF/Canadian solution shows
temps getting quite cool as the low moves into the area and pulls
cool air into the region. The GFS keeps the temperatures warmer
because the low never actually makes it near the state. What that
means is the blended guidance is somewhere between the two most
likely scenarios, and is therefore likely wrong. However, with no
clear signal as to which solution is correct, will continue to
split the difference and reevaluate in the coming days.
Fortunately, if precip were to happen in this period, it looks
like it will be warm enough that it would nearly all be liquid.
Showers are beginning to fill in more from the south and will
continue to do so overnight into Saturday morning. Showers will
then hang on through the day most places. Low clouds are expected
through tomorrow. Will probably see some lower visibilities form
as the front creeps back north into northern Illinois later
tonight into Saturday.
Rather brisk northeast to east winds through today, then
diminishing as the surface low approaches Sunday morning. With
persistent east winds, will extend Small Craft Advisory through
tonight as waves will be slow to subside below 4 feet.
LM...Small Craft Advisory until 7 AM CDT Sunday for LMZ643>646.
Today/Tonight and Aviation/Marine...Hentz
Sunday THROUGH Friday...BSH