Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 170456
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1056 PM CST Sun Feb 16 2020

.UPDATE...No changes to ongoing forecast at this point.

&&

.AVIATION(06Z TAFS)...Mostly VFR conditions are expected the rest
of the night with falling ceilings and visibilities later Monday
morning into the afternoon as snow and a wintry mix spreads across
southern WI. Still possibly increasing onshore winds and low level
convergence may cause some lower ceilings to develop along the
lakeshore and spread inland, but not seeing any signs of this yet.

&&

.PREV DISCUSSION... (Issued 909 PM CST Sun Feb 16 2020)

UPDATE...Will postpone start time of Winter Weather Advisory for
northwest CWA several hours until 15Z Monday. Dry air intially
across the area early Monday holds back start time of snow and/or
wintry mix until later in the morning.

Few reports of flurries getting shaken out of the mid-clouds from
weak passing short wave. Flurries still possible across eastern
and northern CWA next several hours.

MARINE...High pressure ridge passing across the western Great
Lakes will result in variable winds, eventually turning to the
east to southeast later tonight as ridge axis moves off to the
east. Tightening pressure gradient will result in gusty east to
southeast winds developing later Monday morning. Small Craft
Advisory remains in effect for near shore waters, beginning at
15Z Monday.

PREV DISCUSSION... (Issued 549 PM CST Sun Feb 16 2020)

UPDATE...Few flurries being reported at KLNR in the last hour and
likely a few flurries getting shaken out of mid-level clouds
farther east around Madison. However best lift associated with
warm air advection enhanced by mid-level short wave shifts off to
the northeast this evening. Some weak advection lingers through
the night helping to produce considerable mid-high level clouds.
Also, with low level winds becoming more ESE and Delta-T around 5
to 8 degrees, may see some lower clouds develop by Lake Michigan
overnight due to enhanced convergence. No changes to ongoing
headlines at this point. Too much uncertainty as to low level
thermal structure and precipitation types at this point.

AVIATION(00Z TAFS)...Mostly VFR ceilings expected much of the
night, however a period of MVFR ceilings may affect northern areas
this evening. Also, low level winds turning to the ESE may allow
some lower clouds to develop by the lakeshore overnight. Not
enough confidence to introduce any lower ceilings at this point,
but wl introduce a SCT lower layer in 00Z TAFs. Isolated to
scattered flurries this evening should diminish overnight. Snow
should spread into southern WI later Monday morning and afternoon,
becoming mixed with or changing to rain in some areas.

PREV DISCUSSION... (Issued 348 PM CST Sun Feb 16 2020)

SHORT TERM...

Tonight through Monday Night...Forecast Confidence is Low to
Medium...

High pressure across Lake Superior pushed in some much drier air
than forecast with dewpoints falling into the single digits in
central and eastern WI this afternoon. A weak upper wave moving
across the region coupled with some weak frontogenesis is
producing light snow across IA/western WI this afternoon. However,
the drier air than forecast from the high is helping to erode the
snow as it moves east. Expecting only some flurries or very light
snow with no accumulations this afternoon/evening. The weak
forcing from these two features pushes off to the N/NE this
evening ending any lingering snow chances.

Attention quickly turns to a stronger system that is taking shape
over the central plains. Latest GFS/CMC/ECMWF suggest that the
surface low may not deepen as quickly and fast as previous
guidance was suggesting. They all had the system strengthening as
it was entering southern WI and was the reason for the more
northern track. This shift to a more delayed strengthening of the
system has pulled the track of the surface low southward. Previous
low track was from Madison to Green Bay and now it`s from
Dubuque, Rockford, to Milwaukee. With this late shift in models
and ensemble members still advertising a decent spread and
confidence in track and QPF/Snow amounts is low. This forecast
acknowledged the southward trend but still kept some influence of
past guidance in there, thus brought the higher QPF a bit further
south compared to the previous forecast. This change puts snow
amounts closer to the 75 percentile of guidance but as discussed
above there is plenty of uncertainty and is evident in the 25th
percentile having only 2-3 inches in the NW portion of the area
and little to no snow elsewhere. Felt that even with any
additional changes/jogs there is enough confidence to issue a
Winter Weather Advisory for the far NW portion of the area for
snow amounts ranging from 2-5 inches.

There is plenty of WAA in the lower levels to allow for rain and
rain/snow mix for much of southern WI but the line to all snow
remains in question. Expect the mix to begin Monday afternoon and
continue into the early evening hours before quickly tapering off.
This will likely impact the evening commute for much of central
and southern Wisconsin. Some freezing drizzle on the backside of
the system is possible late Monday evening but with drier air
rushing in any drizzle won`t last long.

LONG TERM...

Tuesday through Sunday...Forecast confidence is medium to high:

Strong arctic high pressure is progged to build into the region
Tuesday behind the departing low pressure system. This high will
bring dry weather and below normal temperatures for Tuesday
through Thursday, with temps possibly near or below zero Tue
night and Wed night.

A weak shortwave is expected to move through by Friday night or
early Saturday as the high moves on, with a weaker high then
building in for the remainder of the weekend. Kept the forecast
dry for the trough passage given limited moisture and forcing.
Should see temps back around normal for Friday, warming a few more
degrees into the weekend.

AVIATION(21Z TAFS)...

High pressure passing to the north should keep the VFR conditions
going overnight. Then as a system approaches from the SW moisture
builds back into the area and cigs gradually drop Monday morning
into the afternoon hours. MVFR to IFR cigs and vsbys are forecast
for much of Monday afternoon and evening as a wintry mix of rain
and snow move through the area. Increase southeasterly winds are
expected ahead of the system with gusts to 25 knots possible in
the afternoon. Winds then shift to the NW as the low passes to the
east and gusts on the backside of the low could be up to 20 knots.

There is lower confidence in the wintry mix as it`s possible there
is enough warm air to all for mostly rain.

MARINE...

Light northerly winds continue into the overnight hours before
shifting to the E/SE and increasing Monday morning. A low pressure
system will track across the southern portions of Lake Michigan
Monday into Tuesday and brings higher winds and waves for much of
the lake. A Small Craft Advisory has been issued for Monday
through Tuesday. A few gusts could approach gale force over the
open waters on Monday afternoon. Winds shift to the NW behind the
low and remain gusty until Tuesday evening. An Arctic high spreads
into the Great Lakes Wednesday and lingers through Thursday. The
colder airmass could result in some freezing spray in the open
waters.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 9 AM to 9 PM CST Monday for WIZ046-
     047-056-057.

LM...Small Craft Advisory from 9 AM Monday to noon CST Tuesday for
     LMZ643>646.

&&

$$

Update...MBK
Tonight/Monday and Aviation/Marine...MBK
Monday Night through Sunday...Stumpf



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