Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 300810
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
310 AM CDT Sun Apr 30 2017
.TODAY AND TONIGHT...Forecast Confidence Is High.
An additional 1 to 2 inches of rain is expected, with the most
over the far southeast. This will continue to cause area rivers
to rise, with several expected to reach flood stage. Also the far
south is now in a marginal risk of severe, mainly early evening.
The upper trough will continue to deepen, as it takes on a
slightly negative tilt and progresses northeastward. The upper
trough develops a closed low as it tracks across central Kansas
The strong southern stream jet of 120 knots will develop on the
eastern flank of the trough by afternoon, setting up a coupled jet
situation over southern Wisconsin. Meanwhile, the surface and mid
level low will continue to deepen and move to the northeast. The
elevated warm front above 850 mb will push to the north, remaining
over southern Wisconsin through afternoon.
Strong moisture advection will take place as the upper levels of
the warm front gradually push north of the area, with PWATS
reaching as high as 1.50" by this afternoon. Meanwhile, the 850
mb warm front is closer to the Illinois border through the
afternoon, with the core of a 60 knot low level jet pushing
across Indiana toward evening, and over the eastern Great Lakes
overnight. The convection allowing models have been showing a
consistent signal of a lull in the precipitation into mid morning,
which is occurring.
Precipitation will push back in later this morning, as the
surface front approaches the southern Wisconsin. Most of the
guidance is showing at least some MUCAPE by late afternoon,
especially far south, so left the chance mention of thunder in the
forecast for the afternoon.
Expect showers and a few embedded thunderstorms to be occuring
during the evening. Low pressure moving along occluding front will
have considerable synoptic lift as it passes across northern IL
and southern WI this evening. Models now have more elevated
instability, and due to strength of lift, will raise the chance of
tstorms during the evening, as low level jet pivots across
southern WI where low level thermal ribbon will be draped.
Expect showers to diminish in areal coverage behind the occluded
front overnight as mid-level drier air wraps northward around
parent low circulation in the central Plains. This will end the
thunder threat by late evening or shortly after midnight.
.MONDAY THROUGH TUESDAY NIGHT...Forecast Confidence Is High.
Occluded surface low, along with associated cutoff 500 mb low,
will shift slowly northeastward across Wisconsin on Monday, then
to the northeast Monday night and Tuesday. Differential cyclonic
vorticity advection, with several vorticity maxima within the 500
mb low, will likely bring light rain showers Monday.
Area forecast soundings from NAM/GFS support the shower activity,
with very weak low level instability and saturated moisture
profiles. Kept likely PoPs for Monday, and may need higher values
if forecast remains consistent.
These showers should slowly taper off Monday night into Tuesday
morning, as drier air starts to move into the area. Low clouds are
likely to linger Monday into Tuesday, before some breaks occur
Tuesday night. Gusty southwest winds will bring cold air advection
into the area Monday, with winds veering west by Tuesday and
Highs should remain in the upper 40s to lower 50s Monday and
Tuesday, with lows in the upper 30s Monday night. If skies clear
out enough Tuesday night, lows may drop into the middle 30s
inland, and allow for frost to form.
.WEDNESDAY THROUGH SATURDAY...Forecast Confidence Is Medium.
Models in this period are showing a fairly dry pattern setting up,
with northwest to northerly flow at 500 mb across the area. There
is a 500 mb shortwave trough that moves eastward across the area
late Wednesday night into Thursday, which may bring a shower.
However, there is some uncertainty with how this feature will
evolve. Kept most of the area dry during this time.
Low pressure remains well to the southeast of the area later in
the week, with weak high pressure over most of the region. Thus,
kept the dry forecast going for Friday into Saturday. Temperatures
should gradually warm closer to seasonal normals by later in the
week or during the weekend.
Another round of rain is moving through most places right now and
will wind down from south to north 06-08Z. Looks like a little
break in the precip then until around daybreak Sunday when yet
another slug of rainfall is anticipated to move through. Expecting
locations east of Madison will see the most with this round.
Widespread showers will then likely develop from the south by late
afternoon and continue into the evening. Kept chance for thunder
going with this batch of showers.
Ceilings will continue to lower tonight from south to north, with
low ceilings expected through the day Sunday. Some lower
visibilities of 2-4 miles are possible at times with the moderate
The gale warning will expire at 4 AM CDT. A Small Craft Advisory
will then be in effect into Tuesday afternoon. The strong surface
low will track across Wisconsin Monday. The northeast to east
winds will become lighter as the low approaches, but then pick up
behind an occluded front tonight. Brisk southwest to west winds
are then expected, with a few gale gusts possible later Monday
and Monday night. Waves will eventually ease a bit by
Monday/Tuesday, as winds become offshore.
Another 1.00 to 2.00 inches of rainfall is forecast across the
area for today into Monday night, with most of it falling today
into this evening. The lowest amounts would be in the western
counties, with the highest over far southeast Wisconsin, toward
the Racine and Kenosha areas.
This will continue to result in rising river stages across the
area for the next several days, with some reaching minor to
possibly moderate flood stage. The main concern will be across the
southern Fox and Root River basins, which are expected to receive
the heaviest rainfall. There are several Flood Warnings and
Watches in effect for area rivers in these basins, as well as for
parts of the Rock River basin.
There may be some minor street and lowland flooding that occurs
as well. Did not see much impact from the first round of rain from
overnight, so did not issue an Areal Flood Watch for today into
tonight at this time.
LM...Small Craft Advisory until 5 PM CDT Tuesday for LMZ643>646.
Gale Warning until 4 AM CDT early this morning for LMZ643>646.
Today/Tonight and Aviation/Marine...Hentz
Monday through Saturday...Wood