Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 290257 AAB
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
957 PM CDT Fri Apr 28 2017

.UPDATE...

A little light rain or drizzle will hang around in spots late
evening into early tonight, but otherwise expect mainly dry
weather through the remainder of the night. Skies should remain
mostly cloudy overnight given latest satellite trends. Lows seem
to be on track, so no major are changes expected there.

&&

.MARINE...

Northeast winds will pick up later tonight into Saturday, with
gusty winds and high waves persisting through the weekend. A Small
Craft Advisory goes into effect later tonight.

&&

.PREV DISCUSSION... (Issued 643 PM CDT Fri Apr 28 2017)

UPDATE...

Rain across most of the area will wind down by mid to late
evening. May not see much at all in the far southeast forecast
area. Dry weather is then expected overnight.

AVIATION(00Z TAFS)...

Should see rain wind down by the middle of this evening, with a
few showers possibly hanging on into late evening. Dry weather is
then expected overnight, with more rain moving in later Sat
morning into the afternoon.

Some lower ceilings continue to push in from the south. These are
expected to hang on across mainly the southern half of the
forecast area through at least midnight, with ceilings returning
to VFR by early morning. More low clouds are likely to return
from the south by later Sat afternoon with the next batch of
rainfall.

PREV DISCUSSION... (Issued 335 PM CDT FRI APR 28 2017)

TONIGHT AND SATURDAY - Forecast Confidence...Medium.

An amplified upper trough is currently situated over the western
CONUS while low pressure develops at the surface over the far
Southern Plains.

A shortwave well ahead of the western CONUS trof and an associated
mid-level baroclinic zone are currently passing over the CWA. These
features are resulting in widespread, light radar echos. However,
dry air at the surface is resulting in a fair amount of evaporation,
and only some of the rain from these echoes is making it to the
ground. The low levels will gradually saturate this afternoon, and
by the early evening, much of the widespread virga will transition
to rain. Further complicating the picture, current radar trends show
a distinct back edge to the precip stretching from north central IL
into SE IA, slowly sliding to the northeast. This may result in much
of our far southeast missing out on much of this evening`s rain. The
upper and mid-level forcing will move north out of the area tonight,
bringing an end to this fist round of precip.

The western CONUS trough will continue to deepen tonight and into
tomorrow, setting up strong flow with ample divergence over the
Upper Midwest, while ejecting another shortwave toward the region.
Meanwhile, the surface low will strengthen and move to the
northeast. By tomorrow afternoon, the 700mb warm front will reach
into southern Wisconsin, bringing in more moisture and ample low
level lift to compliment the upper level forcing. This will kick off
an extended period of rainfall as the low slowly tracks through the
region.

SATURDAY NIGHT THROUGH MONDAY - Forecast Confidence...Medium.

Periods of rain and a few embedded thunderstorms are likely through
this period.  Precipitable water values will have increased to
around 1 inch tonight into Saturday.  An additional surge in column
moisture is expected later Saturday into Saturday evening when
precipitable water further increases to around 1.25 to 1.75 inches
across most of CWA by Sunday afternoon.  This is about 200-250
percent of normal for late April in southeast WI.

Second surge of moisture advection later Saturday into Saturday
evening and northward moving elevated warm front should bring a
round of showers to southern WI.  Elevated instability looks minimal
so wl hold off on introducing any thunder.  Best chance for thunder
looks to be Sunday aftn and night when main short wave trof gets
nudged northeast from the southern Plains toward WI.  Heaviest
rainfall could occur at this point when strongest synoptic lift
moves through.  However some concern about heavy rainfall also
occurring Saturday aftn and evening during push of deeper column
moisture.  Mean steering winds not very strong Saturday night,
mostly less than 10 knots.  With saturated ground and unseasonably
high column moisture likely, QPF may be higher than currently
expected, leading toward more standing water and rapidly rising
rivers in some areas.  For now, not planning on issuing a Areal
Flood Watch but wl need to reevaluate later Sat night into early
Sunday before second round of heavier QPF were to occur later Sunday
into Sunday night.

Drier air wrapping into occluding system will diminish showers later
Sunday night into Monday, but more showers will return to portions
of southern CWA later Monday.

EXTENDED PERIOD...

MONDAY NIGHT THROUGH FRIDAY - Forecast Confidence...Medium.

Precipitation intensity from passing low pressure and occlusion will
begin to wind down on Monday, but may pick up again later Monday
into Monday night for a time as mid-level trof associated with low
passes slowly through Wisconsin Monday night into Tuesday.  Colder
air associated with occlusion will overspread southern WI during
this period with 925H temps falling to 0-2C by 12Z/Tuesday.  Hence
possible a little snow may mix with the occasional -ra Monday night
into early Tuesday.  Otherwise, the chance for -ra wl linger into
Tuesday as upper low slowly pulls away from the western Great Lakes.

Weak short wave rotating around departing low may bring a few rain
or snow showers to the area Wed into Wed ngt. Temps look to remain
below normal through Wednesday with a warming trend to finish off
the work week as the upper level steering winds begin to slowly back
across the Upper Midwest.  Potential for low chance of showers
returning late in the period but too much uncertainty to include at
this point.

GFS 500MB standardized anomalies shows large negative anomoly of
over 100 meters centered on the midwest at 00Z/Wednesday.  This
large negative anomoly shifts off to the east by the weekend.

With the cooler weather expected next week, any tender vegetation
planting should hold off until next weekend at the earliest.
Nighttime temperatures likely to be in the 30s much of next week.

MARINE...

Low pressure will move through the region this weekend, setting the
stage for a prolonged period of strong, onshore winds. Winds will
ramp up to Small Craft Advisory criteria beginning early Saturday
morning, and remain elevated into late Sunday night. Given the
onshore flow, waves will also be quite vigorous, reaching as high as
7 feet at times.

HYDROLOGY...

Two bouts of heavier rainfall expected across southern Wisconsin
over the weekend.  First will be Saturday afternoon into Saturday
night and second Sunday afternoon into Sunday night.  Between two
events, expected rainfall between 1.5 and 3 inches with the heaviest
in the southeast CWA.  This will likely push several rivers in the
southeast to at least Minor Flood Stage, with moderate flood stage
possible on the Fox River.  With saturated ground already in place,
possible a Areal Flood Watch may be needed but want to wait until
after first bout of heavier rain occurs later Saturday into Sat
night before making decision.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory from 4 AM Saturday to 7 PM CDT Sunday for
     LMZ646.

     Small Craft Advisory from 4 AM Saturday to 5 AM CDT Monday for
     LMZ643>645.

&&

$$

Update...DDV
Tonight/Saturday and Marine...BSH
Saturday Night through Friday and Hydrology...MBK


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