Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 191216
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
716 AM CDT Fri May 19 2017

.UPDATE...

Light rain has pushed into far southwest areas southwest of
madison. This area will move slowly northeast but diminish
somewhat as it encounters drier air.

&&

.AVIATION(12Z TAFS)...

MVFR gigs due to northeast winds off Lake michigan. These may
break up a little today.  Expect them to spread back in overnight
with MVFR ceilings in rain..

Look for light rain to initially spread into southern Wisconsin
this morning and tend to dry up as it pushes northeast. The main
rain area will move in tonight. Some thunder possible toward
sunrise Saturday.

&&

.PREV DISCUSSION... (Issued 230 AM CDT Fri May 19 2017)

DISCUSSION...

Today and Tonight...Forecast Confidence is Medium...

The upper ridge over Wisconsin will weaken, as a subtle lead
short wave moves into southern Wisconsin later this morning.
Meanwhile a strong upstream trough will begin to exit the Colorado
Rockies area tonight, as the upper levels across southern
Wisconsin become diffluent, ahead of the approaching jet lifting
north on the leading side of the trough. The resultant upper
divergence and 700 mb upward motion then increases later tonight.

Mid levels saturate today ahead of the initial short wave, and
should produce some light rain, which would likely initially be
Virga, or light sprinkles due to the initial dry air.

Looks like plenty of lift and moisture for showers tonight as the
850 mb front reaches southern Wisconsin late tonight. GFS
soundings do have around 250 Joules/kg of elevated CAPE around
sunrise Saturday, so some thunder possible toward morning.

It will be a cool day across southern Wisconsin between the
cooler airmass, clouds, and east to northeast winds off Lake
Michigan.

Saturday and Saturday Night - Confidence...Medium to High
A wet and unsettled period as low pressure is still on track to
draw a warm/moist airmass northward into the area. Fairly dynamic
system with 500 low taking on a negative tilt as it tracks of west
and northwest of srn WI this period. Cloud cover and extent of
rainfall will likely limit instability. Will keep thunder mention
in place as there is some limited elevated CAPE. However by and
large appears better instability will set up to our south as progs
suggest deeper convective initiation will take 0place just to our
south or southeast and this is highlighted by SWODY2 risk layout.
As low lifts to our north a bit later Saturday night drier air
wraps in and brings an end to precip chances. 925 millibar cold
air advection kicks in after 06z with temps in the teens celsius
dropping into the single digits celsius.

Sunday - Confidence...Medium
Nearly stacked system will be near Lake Superior. The 500
millibar low will keep our area within the cyclonic flow while the
low level flow will be ushering in the dry airmass along with the
low level thermal trough. At this time the progs keep any of this
showery precip across northern WI so will hang onto the going dry
forecast.

Monday through Wednesday - Confidence...Medium
Models continue to show the evolution of a closed off low across
the Great Lakes or Ohio Valley as energy rides southeast on
western periphery of the the Canadian vortex and forms a new
circulation. Low level cyclogenesis occurs across WI Monday night
with the low tracking to our east on Tuesday tapping cooler air on
north or northeast winds. Progs are showing quite a bit of rain
with this system, warm showers ahead of the low Monday into Monday
night with much cooler def zone type rain Tuesday and Wednesday.
The GEM is the slowest solution and keeps this rain lingering well
into Wednesday night.

Thursday - Confidence...Low to Medium
The GFS shows a vigorous shortwave dropping southeast while the
ECMWF is more sheared with this. The 12z ECMWF had been dry and
now is showing precip with its 00z run as is the 00z GFS. The GEM
just lingers the prior system across the Ohio Valley and we would
still be under the throes of this. Will go with the Superblend
guidance for now which has slgt to chc pops which looks reasonable
given the above potential scenarios.

AVIATION(06Z TAFS)...Tricky forecast for sky cover and ceiling
height tonight. It looks like low clouds are clearing out across
south central WI late this evening. Expect them to spread back in
overnight with ceilings in the 2000 to 3000 ft range.

Look for light rain to spread into southern WI later this morning
and dry up toward the afternoon.

MARINE...Small craft advisory in effect through Saturday afternoon
for brisk northeast to east winds and high waves due to low pressure
approaching from the Plains. The headline may need to be extended
into Saturday night for lingering high waves.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 7 PM CDT Saturday for LMZ643>646.

&&

$$

Update...Hentz
Today/Tonight and Aviation/Marine...Hentz
Saturday THROUGH Thursday...Collar



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