Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 300420
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1120 PM CDT Wed Mar 29 2017

.UPDATE...
Forecast is on track. A bit of a lull in the showers here in the
late evening, but a stronger surge of rain is headed northeast out
of Illinois and Iowa. There`s thunder in that activity, but
stability indices suggest it would struggle to get this far north.
We do have a slight chance of thunder in the forecast across the
south, so that`s still looks good. Little in the way of snow is
expected north of Milwaukee and Madison.

&&

.AVIATION(06Z TAFS)...
Not much change to the TAF forecast. Look for CIGS to gradually
lower to MVFR overnight, then to IFR conditions after 12z
Thursday continuing through the remainder of the TAF period. A
windy and wet day is expected Thursday. Winds will be easterly at
15 to 30kts. Look for the rain to diminish toward late afternoon
on Thursday.

&&

.PREV DISCUSSION... (Issued 831 PM CDT Wed Mar 29 2017)

UPDATE...
Strong and deep warm air advection is in progress across southern
Wisconsin - most of it going up and over the cold boundary layer.
The first wave of rain has rolled into southern Wisconsin this
evening, struggling against a dry and cold northeast wind. But,
the precip is finally overwhelming that dry air and the radar
coverage is filling in. The HRRR model suggests this first band
should diminish through the evening, with the next more
substantial wave of rain coming after about 3 am tonight and
continuing through much of Thursday. I`ve been updating hourly
temps and dewpoints using short range blended guidance and it`s
looking a few degrees warmer overnight than previously thought.
Not surprising with all the clouds and rain saturating things up.
This is enough to probably keep the snow threat pretty low across
that Sheboygan to Marquette area. We could still see some mix up
there late tonight through about 9 am, but with air temps staying
around 36-37F and enough of a warm layer aloft, it will be hard to
get any accumulation that would be problematic. Adjusted accums
to 1/2 inch or less.

MARINE...

Northeast winds are gusting to small craft advisory levels south
of Milwaukee now. Have started the small craft advisory a few
hours early there and will start it by midnight north of
Milwaukee. Brisk northeast to north winds will continue through
Friday night as low pressure passes by slowly to the south of
Wisconsin.

PREV DISCUSSION... (Issued 624 PM CDT Wed Mar 29 2017)

UPDATE...
Rain is spreading in, but based on radar trends it is clear there
is a battle with dry air going on. Eventually, the column will
saturate and the rain will make better progress north. This first
band may erode by mid evening with the next, main area of rain
arriving shortly after midnight. These details are tough to
resolve with good temporal fineness, so expect the initial period
of this wet forecast to be on and off with the rain, then more
steady late tonight through Thursday. With regard to the snow
threat to the north, temps and dewpoints are still on the mild
side for it to become much of a problem. Lows tonight shouldn`t
drop much below 37F, so whatever falls will have a hard time
sticking.

AVIATION(00Z TAFS)...

Look for CIGS to gradually lower to MVFR levels later this evening
with IFR CIGS/VSBYS pushing in around sunrise on Thursday as rain
becomes steady across all of southern Wisconsin. No ice or snow is
expected with this entire system over the TAF sites. We may see
some snow mix in around Sheboygan and Fond du Lac, but little in
the way of accumulation. Look for northeast winds to steadily
increase overnight into Thursday morning.

PREV DISCUSSION... (Issued 320 PM CDT Wed Mar 29 2017)

SHORT TERM...

TONIGHT AND THURSDAY - Confidence...Medium

An unsettled period with widespread rain gradually overtaking the
area tonight. The primary mid level circulation will stay to our
south as will the surface and 850 lows. 850 waa/moist advection
takes place tonight and lifts the 850 baroclinic zone northward. The
far northern cwa still looks thermally vulnerable for at least a
brief period of a snow or a mix. Amounts have continued a downward
trend with the 12z run and this has been reflected in the forecast
snow amounts with highest amounts of around an inch in the far
northern reaches of our northern tier of counties. Some decent lift
noted with one 250 millibar jet max providing right rear lift
tonight then a renewed southerly upper jet pivots northward around
low with left front positioning on Thursday. Even a hint of some
coupling at times between these 2 features. Throughout the event
both the RAP and NAM Bufkit soundings show enough elevated CAPE to
warrant at least a small chance of thunder in the southern cwa so
have included that potential.

Thursday night through Saturday...Forecast confidence medium.

The weakening low pressure area and upper low will track from wrn
IL to Lake Erie from Thu nt into Fri eve. The upper trough axis
extending north of the upper low will pass Thu nt into Fri AM.
Low to mid level frontogenesis may linger during this time. Thus
rain will continue to be likely over ern WI for Thu nt with areas
of light rain or drizzle elsewhere including on Fri. Gradual cold
and dry air advection Fri aft-eve will eventually lead to
clearing skies. High pressure will then prevail late Fri nt and
Sat. The cool temps on Fri will return to seasonal values on Sat.

LONG TERM...Sunday through Wednesday...Forecast confidence low to
medium.

The passage of a weak shortwave trough and round of warm advection
will bring chances of light rain for late Sat nt-Sun nt. Chances
of rain will then continue for Mon-Wed. Low pressure over the
Lower MS River Valley will move newd into the Ohio River Valley
for Mon-Tue followed by another low moving from the central Great
Plains into possibly the Great Lakes for Wed-Thu.

AVIATION(UPDATE)...VFR ceilings will progressively lower this
period as rain overspreads TAF sites. Bufkit is showing the
process may take a while, with initially deep dry layer. Seeing
the upstream IFR conditions across IA and western IL. Will
gradually head this way especially after 06z. Increasing forcing
will lead to rain development. Already seeing some of this across
eastern Iowa with mid level returns into western WI. This precip
fighting off some dry air in the low levels. As low pressure
approaches tonight into Thursday morning we will see IFR ceilings
and vsbys develop. May even have an isolated thunderstorm or two
as soundings are implying some elevated instability. With low
pressure passing to our south later tonight into Thursday a
tightening pressure gradient will set up rather gusty east winds.

MARINE...Main focus shifts to increasing onshore and long duration
wind regime tonight which gets underway tonight. This will build
high waves near the shore and remain in place through late Friday
night.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 AM CDT Saturday for LMZ645-646.

     Small Craft Advisory until 4 AM CDT Saturday for LMZ643-644.

&&

$$

Update...Davis
Tonight/Thursday and Aviation/Marine...Collar
Thursday Night through Wednesday...Gehring


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