Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 190800
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
300 AM CDT Wed Apr 19 2017

.TODAY AND TONIGHT...Forecast confidence is medium.

There is a lot going on over the next 24 hours. A cold front that
moved through southern Wisconsin overnight will stall from
southern Lake Michigan to southern Iowa by sunrise this morning.
That surface front will likely remain stalled through late
afternoon as we wait for surface low pressure moving into western
Iowa to give it a goose north this evening. We could see some
elevated convection north of the surface front, closer to the
850mb frontal boundary, move into far southern Wisconsin later
this morning and afternoon. But, this activity will be challenged
due to capping issues and it`s elevated nature. This stuff should
be pretty weak.

The Storm Prediction Center has increased the risk for severe
thunderstorms across southern Wisconsin tonight. Please refer to
their outlook for details and discussion. A slight risk for
severe storms now covers a decent part of southwest Wisconsin,
including the Madison metro area. An enhanced risk covers much of
eastern Iowa and a part of Grant county in far southwest
Wisconsin.

The surface low is projected to move from western Iowa to
southeast Minnesota to the Fox Valley in east central Wisconsin
from tonight through mid morning on Thursday. A strong low level
jet of 50-55kts develops ahead of the low this evening, pushing
through eastern Iowa into western Wisconsin. The deep layer shear
increases to around 50kts. This will push a warm front quickly
north into southern Wisconsin. The warm front, along with the
cold front right on its heels, will be the focus for the storms,
some of which could be severe. The genesis for the convection will
be across Iowa later today, eventually moving into Wisconsin
later in the evening and overnight hours. As is typical, they will
likely be discrete supercells upstream, evolving into more
multicellular, larger complexes, lines, etc by the time they move
into Wisconsin. Large hail, strong winds and isolated tornadoes
are possible, especially west and south of Madison.

The heaviest rainfall should be located along and north of low
pressure track where the deeper forcing is expected. This would
put the heavier rain north of the forecast area. In our forecast
area, we are looking at rainfall totals ranging from around 0.75
inch around the Wisconsin Dells to 0.25 in the southeast.
Stronger convection would likely bring isolated higher totals.
Look for things to begin quieting down quickly by sunrise on
Thursday.

.THURSDAY - Confidence...Medium
500 millibar low will be moving across the Lake Superior region
keeping srn WI within a cyclonic mid level flow regime. 850 temps
show lingering influence of warm sector at the outset with low
level cold advection kicking in. In fact 925 temps will be in the
teens celsius in the morning though a shift to west winds will
usher in the colder 925 temps. Have kept a chance of showers and
even some thunder in the southeast in the forecast along and ahead
of the cold front. LLVL RH progs/MOS shows plenty of potential
for stratus/stratocu within the amplifying low level thermal
trough. Highs may end up being in the morning with the milder
airmass within the warm sector.

.THURSDAY NIGHT THROUGH SUNDAY NIGHT - Confidence...Medium
This is shaping up to be a dry period. Broad cyclonic flow
lingers into Thursday night before a positive tilt mid level
trough passes through Friday night into Saturday morning. Then mid
level ridging takes hold through Sunday night. The NAM and GFS
reinforce the low level thermal trough into Saturday as low level
winds turn northeast. This modifies briefly Saturday with progs
hinting at another back door cold front on Sunday.

.MONDAY AND TUESDAY - Confidence...Medium
While there are some timing differences this period the models are
all showing a 500 millibar vort max/shortwave affecting the area,
most likely Monday night. Surface/850 low tracks to our north and
sets up a southerly flow. A fairly potent 850 jet max is noted
Monday night. All in all best forcing parameters are focusing on
Monday night. Will use Superblend guidance for this period.

&&

.AVIATION(06Z TAFS)...Patchy MVFR sct-bkn developing vicinity of
cold front over western CWA. Will carry a brief period of lower
clouds at most TAF sites early this morning. Otherwise, more
extensive low cloud cover over MN and northwest WI making steady
eastward progress but not much shift to the south. Hence wl lean
toward mostly VFR conditions during the after 12z with lower
clouds returning in increasing easterly flow during the afternoon.

&&

.MARINE...Will hoist a small craft advisory for strong westerly
winds expected in the wake of a passing cold front. Breezy
conditions are expected from late tonight through late Thursday
night.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory from 5 AM Thursday to 4 AM CDT Friday for
     LMZ645-646.

     Small Craft Advisory from 11 AM Thursday to 4 AM CDT Friday for
     LMZ643-644.

&&

$$
Today/Tonight and Aviation/Marine...Davis
Thursday through Tuesday...Collar



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