Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 221622

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1022 AM CST Mon Jan 22 2018


Surface low pressure was located over south central Iowa this
morning, with the surface warm front extending eastward into
northern Illinois. Precipitation located within the warm advection
regime is currently pushing through northern portions of our area,
with a lull before more showers push in from the south this

Our first concern is with convective potential for this afternoon
into early evening. As the day progresses, the surface warm front
will near the Wisconsin/Illinois border, with surface based
instability developing along and south of it. Convective allowing
mesoscale models show convective development across our south
central this afternoon, with cells tracking north across portions
of the southern Wisconsin into this evening. Will need to keep an
eye on these, as cold temperatures aloft and deep layer shear
exceeding 60 knots point towards some hail possibility. At this
point it appears that any appreciable surface based instability
will remain to our south, but we`ll need to keep an eye on this as

Turning our attention towards tonight, we`ll be on the backside of
the low pressure system with cooling temperatures aloft, steep
lapse rates, and a strong TROWL. Model guidance shows a
frontogenesis band traversing our area, with good agreement on a
bulls-eye of heavier precipitation in the general vicinity of
southeast Wisconsin. Model forecast soundings suggest 50 units of
omega located within the saturated dendrite growth region during
this time. Our concern remains for a heavy, wet snow during this
period later tonight towards tomorrow morning, with some high
snowfall rates possible within the frontogenesis band. Will
evaluate model guidance this morning, with some possibility that
a headline may be needed giving potential impacts to the morning



Poor visibility at times and high winds/waves are expected for the
nearshore waters for tonight into Tuesday. Mariners should
exercise caution.


.PREV DISCUSSION... (Issued 628 AM CST Mon Jan 22 2018)


The next slug of rain is spreading into southern WI early this
morning. This is associated with the nose of a low level jet and
moisture convergence. There are a few lightning strikes over the
Chicago area and southern Lake Michigan that could brush southeast
WI with this round.

The fog is diminishing with the rain. It has a good chance of re-
developing this afternoon along the lake once the rain ends, but
it`s not widespread enough to keep the dense fog advisory going
for right now, so I cancelled it.


Rain is overspreading southern WI from the south early this
morning. This is helping to scour out the dense fog, but ceilings
remain low. A few lightning strikes are possible in southeast WI
this morning, and there`s another chance early this evening.

A brief period of low level wind shear is expected today over far
southeast WI. We will have light winds at the surface and an
abrupt shift to 35 knot southwest winds at around 2000 feet as the
low level jet brushes the area.

Once this main area of rain clears by late morning, visibilities
should drop below a mile. It`s likely we could see more dense fog
near the lakeshore (MKE) once again.

Look for rain to change over to wet snow overnight. Timing looks
like around 10 or 11 pm in Madison and 2 to 3 am near the
lakeshore. 1 to 2 inches accumulation is possibly through 9 am
Tue morning.

PREV DISCUSSION... (Issued 338 AM CST Mon Jan 22 2018)


Today and Tonight...Forecast Confidence is Medium.

We are getting our first round of steady rain early this morning
with a wave of 850mb warm air advection and frontogenesis. I
haven`t seen any lightning with it, but it`s not out of the
question. This will continue to lift north. The next wave of
precip is focused on the nose of the low level jet. That will
reach southern WI by 6 am this morning and could also have a few
rumbles of thunder. Persistent 925-850mb frontogenesis will lead
to steadier rain across northern portions of the MKX forecast area
(Dells to Sheboygan) today.

Look for a diminishing trend to rain from south to north midday.
Drier air working its way into the system will lead to more fog
and drizzle across southern WI this afternoon. I extended the
dense fog advisory until 9 am for the areas where it`s currently
in effect, but we will need to re-evaluate this. It`s possible
that the eastern forecast area could need one into this evening.
Visibilities are improving within the rain, but drop down once it

The dry line may trigger a few more showers and thunderstorms
across southeast WI early this evening. Cold air will be sliding
southeast into southern WI this evening as well. Look for rain to
transition over to snow near Madison around 10 pm and in the
Milwaukee area 1 to 2 am. We could see a wet 1 to 2 inches of snow
by morning. The Tuesday morning commute could be slippery.

Tuesday - Confidence...Medium
Lingering mid level cyclonic flow and lower level troughing will
keep precip chances going the morning hours, esp in the early/mid
morning time frame in the eastern cwa. Have noticed some loss of
saturation within the dendritic growth zone which suggests some
spotty FZDZ potential. Have boosted pops above the blended
guidance esp in the east during the 12-15z time frame.

Wednesday and Thursday - Confidence...Medium
Quiet period. Mid level flow becomes increasingly anticyclonic
with ridging amplifying a bit more into Thursday. With surface/850
high shifting east a return flow sets up with 850 temps rising
well above zero C later Thursday through Thursday night.

Friday and Friday night - Confidence...Medium
Temps likely to be quite mild ahead of surface/850 front. 925
temps reach the 4-6c range. GFS and GEM generate some light rain
with the front as it passes later Friday into Friday night. Enough
colder air working in behind the front brings at least a chance
for a quick changeover before precip departs.

Saturday and Sunday - Confidence...Medium
Mid level flow becomes more energized with colder air working in.
For now the blended guidance is favoring the drier look of the
ECMWF. The GFS does show very light qpf Saturday night with the
leading edge of the colder air. the ECMWF does have this but it is
slower to arrive and further north. So for now will leave the
quiet pops in place for this.

AVIATION(06Z TAFS)...There is very little change to the forecast.
We are seeing brief periods of improved visibilities within the rain.

IFR conditions are expected through the TAF period with LIFR
CIGS/VSBYS across the southeast through about 00z Tuesday.
Conditions will slowly improve this evening. Peak rainfall, with
the potential for some lightning, will roll through the area
between about 12-16z this morning. A transition over to a wintry
mix and then snow will occur this 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 tonight, diminishing Tuesday morning.

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

The Marine Dense Fog Advisory was extended through early evening.


LM...Dense Fog Advisory until 9 PM CST this evening for LMZ643>646.

     Small Craft Advisory until 3 PM CST Tuesday for LMZ643>646.



Today/Tonight and Aviation/Marine...Cronce
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