Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 140252
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
852 PM CST Mon Nov 13 2017

.UPDATE...Area of low clouds slowly moving north and east across
southern WI since late afternoon as low level south winds
increase. Fog has remained light so far with visibilities of 3 to
5 miles most areas due to the low clouds and areas of high clouds
as well, and low level mixing. However back edge of low clouds
also moving steadily northward and will be crossing IL border
shortly into southern WI. Southwest areas will be the first to
clear out and clearing may make it far east as Jefferson and into
the Dells/Reedsburg areas during the night. However the moist low
levels and boundary layer mixing favors additional stratus
development during the night. Also, another back of widespread
stratus over central IA moving steadily eastward as well.

Will hit fog a little harder in the susceptible southwest areas
overnight.

&&

.MARINE...Small Craft Advisory will likely be needed for Tuesday
night into Thursday. Gusts may reach small craft levels (GTE
22kts) as early as 18Z Tuesday, but may hold off until 00Z
Wednesday. Hence due to a lack of confidence wrt start time, will
hold off on issuing Small Craft Advisory until later tonight.

&&

.PREV DISCUSSION... (Issued 559 PM CST Mon Nov 13 2017)

UPDATE...Increasing low level southerly winds should carry
widespread stratus across far southern WI and adjoing portions of
IL/IA across the rest of southern WI during the night. Low
temperature/dew point spread will result in areas of fog
overnight, which may turn dense in areas. However just enough
increase in low level winds may keep visibilities in fog above
dense levels.

AVIATION(00Z TAFS)...Expect low MVFR and IFR ceilings to
overspread much of southern WI during the night. Fog is expected
as well, and may turn dense for a time. However increasing low
level winds may help to keep the fog above dense levels.

PREV DISCUSSION... (Issued 246 PM CST Mon Nov 13 2017)

SHORT TERM...

Tonight and Tuesday - Confidence...Medium

Surface ridge axis across WI will shift east this period with
increasing southerly flow setting up. Large area of cloudiness
across IL into far srn WI not much northward progress and showing
some signs of erosion on northern edge with a more cellular
appearance. May see some more fog set up but increasing winds
within the column should prevent things from getting too much out
of hand like last night. But still some fog in the grids with some
lingering lighter winds and somewhat higher dew points creeping
northward. Models still showing some very light qpf on Tuesday
with the warm advection/moisture return so have some light rain
chances in grids esp in central/western cwa.

Tuesday night and Wednesday...Forecast Confidence Is High.

An upper level shortwave moves across the Lake Superior region.

Models then are in agreement with bringing warm air and moisture
advection into the region Tuesday night. Moderate upper
divergence and 700 mb upward motion Tuesday night into Wednesday
morning. The upward motion becomes stronger, just to the east over
lake michigan around sunrise. This should bring a period of rain
to the area. Likely PoPs for late Tuesday night, that quickly end
late Wednesday morning with downward motion and drier air behind
the shortwave.

Fairly strong cold air advection Wednesday afternoon with falling
temperatures as a mid level shortwave moves across the northern
great lakes.

LONG TERM...

Wednesday Night and Thursday...Forecast Confidence is High.

the southern edge of the stratocumulus should reach into at least
northern area Wednesday night.

A mid/upper level ridge should bring brief quiet weather
Wednesday night into Thursday, with another high pressure system
moving across Wisconsin. Upward motion begins west areas late
Thursday afternoon.

Friday Through Sunday...Forecast Confidence Is Medium...

A strong trough moves across the plains and becomes negatively
tilted , especially on the faster GFS. The ECMWF is a little
slower and weaker with the trough.

A surface low will intensify across the Upper Great Lakes during
this period.

Models are more in line, but the ECMWF is a little more south and
a little slower in the cyclogenesis. The GFS has backed off the
the intense low a little, but the canadian continues to develop a
974 mb low near Lake Huron.

Warm air advection develops Thursday night and brings more
moisture into the region. Little if any precipitation is on the
slower ECMWF, with mainly rain developing late on the faster GFS.

It will be windy, with wind advisories possible and Gales likely.

For now, will continue with the blended model PoPs and
temperatures for Thursday night into Saturday. Possibility of
snow accumulations in our area is low, as by the time the cold air
moves in behind the low, the precipitation is diminishing.

By Sunday all models have a surface high across the Upper
Mississippi River region.

Monday...Forecast Confidence Is Medium...

The high hangs on over the Upper Mississippi valley, but a south
flow begins on the ECMWF.

AVIATION(21Z TAFS)...

Lower cloud deck (IFR/LIFR cigs) trying to
lift northward to I-94 though erosion on the edges has slowed the
progression. Models not handling this large area very well. In
fact LLVL RH progs are showing much of this area with very little
RH. Meanwhile cirrus cruising well overhead. As surface ridge axis
shifts east of WI tonight expect a return flow to set up but
overall low level winds look light. Some increase though off the
deck which may help inhibit the fog from getting to out of hand
like last night. Will still mention some fog though. SOme light
rain potential on Tuesday afternoon with moisture advection. MVFR
stratus potential greatest in western cwa.

MARINE...

Expect southerly winds and waves to increase through the day
Tuesday into Tuesday night. A Small Craft Advisory may be needed
later Tuesday into Wednesday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...MBK
Tonight/Tuesday and Aviation/Marine...Collar
Tuesday Night through Monday...Hentz



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