Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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058
FXUS63 KMKX 220302
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
902 PM CST Wed Feb 21 2018

.UPDATE...

Temps have been a little slow to fall this evening given high
cloud cover, but should slowly settle into the teens overnight.
Other than adjustments to hourly temp trends, no other changes
needed.

&&

.MARINE...

North winds tonight will become easterly and increase on Thursday.
Waves will increase as well, with 3-5 ft waves Thursday afternoon
building to 4-7 feet Thursday night. Winds will increase as well
during this period, with a few gust near 30 kt. A Small Craft
Advisory is in effect.

Winds will become westerly behind this system Friday, before
becoming easterly to southeasterly once again late Saturday into
Sunday. There are indications that strong low pressure may move
through the Great Lakes region Sunday, with increasing winds and
waves in response.

&&

.PREV DISCUSSION... (Issued 522 PM CST Wed Feb 21 2018)

UPDATE...

No changes to the going forecast at this point. High pressure will
push into the area tonight, with just some passing high clouds
aloft.

AVIATION(00Z TAFS)...

VFR will prevail tonight and tomorrow, with light winds and
passing high cloud cover is expected overnight tonight into
Thursday morning. Moisture will start to increase Thursday, with
ceilings gradually lowering through the day. However, they should
remain well into VFR territory through 00Z.

PREV DISCUSSION... (Issued 225 PM CDT WED FEB 21 2018)

TONIGHT...Forecast Confidence - High.

Quiet conditions will continue tonight, however temperatures to
remain below freezing resulting in icy spots of lingering water and
puddles on roadways. Snow cover in most areas has been reduced to
piles and shaded areas, however a few 1-2" spots remain in the
southwest CWA. Persistent high clouds likely to continue across the
area at least through the evening as right entrance region
of upper jet remains nearby.

THURSDAY and THURSDAY NIGHT...Forecast Confidence - Medium.

Protective high pressure ridges shifts northeast into southern
Canada, away from the western Great Lakes on Thursday.  However
most, if not all of Thursday looking dry across southern WI as dry
easterly flow persists through the day.  Deeper moisture from the
Gulf will be pushing northward on Thursday as southerly winds
increase ahead of strengthening low pressure in the central Plains.
Strong warm air advection developing along a tightening baroclinic
zone will produce areas of snow and sleet across IA/MN on Thursday,
and some of the precip may graze the western CWA in the afternoon.
The low level warm air advection and elevated warm front will
advance northward across southern WI Thursday night as a weak mid-
level wave grazes the area. The better lift associated with this
feature remains to the northwest but enough broad scale lift and
layer q-vector convergence to bring a period of light precipitation
to the area overnight.  Forecast soundings are not showing much ice
crystal initiation falling into the low level cloud layer overnight
as temperatures hover in the low 30s.  Hence expecting a period of
light freezing rain most areas with the potential for light snow and
sleet in the northern and western CWA.  Expect glazing of 0.01 to
0.10 inch and may affect the Friday morning early morning commute. A
Winter Weather Advisory may be issued this evening or overnight for
Thursday night.

FRIDAY AND SATURDAY...Forecast Confidence...Medium.

Any lingering light wintery mix should exit southern WI quickly
Friday morning.  A brief period of quiet weather is expected Friday
afternoon and night.  However more precipitation may return by
Saturday afternoon as another low pressure system organizes in the
central Plains. Further discussion about uncertainties in next
section.

EXTENDED PERIOD...

SATURDAY NIGHT THROUGH WEDNESDAY - Forecast Confidence...Low to
Medium.

Computer issues at NMC so not all Medium range guidance available
for this forecast period. Latest available guidance does continue
to show unsettled weather returning across the Upper midwest for
the weekend, possibly followed by a quieter stretch early next
week. GFS most aggressive on bringing deepening low pressure
across IA into northern WI Sat night with southern WI receiving a
period of liquid precipitation and possibly an isolated storm.
However new Canadian and latest ECMWF show much weaker low
pressure trof moving across WI Saturday night. While stronger GFS
shows a greater punch of warmer air into southern WI Sat and Sat
night, ECMWF and CMC show a greater potential for a wintery mix
and greater impacts for Sunday morning. GFS ensembles show a large
variability in low pressure track across WI Saturday night.

A quieter period is looking more likely from Sunday through Tuesday
as several slow moving high pressure systems move through the
region.  Temperatures look to remain near or slightly above seasonal
normal as we move through the last week of the month.  Strengthening
warm front across the central CONUS may eventually return
liquid precipitation to the area by Wednesday night/Thursday.

AVIATION(21Z TAFS)...

VFR conditions likely to persist into Thursday evening before MVFR
and possibly IFR ceilings spread into the area along with a light
wintery mix of precipitation.  Light fog will accompany the wintery
mix.

MARINE..

Northwest winds will continue to weaken and veer to the east to
northeast tonight as high pressure approaches and passes to the
north.  Strengthening low pressure in the plains will cause a
tightening pressure gradient and increasing onshore winds Thursday
afternoon and night.  Wind gusts are looking more likely to reach 25
knots for a time Thursday night and wave heights may reach 5 feet as
soon as Thursday afternoon across the southern zones.  Hence a
staggered Small Craft Advisory has been issued, beginning Thursday
afternoon in the south, and in the evening north, lasting into
Friday morning.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory from 3 PM Thursday to 8 AM CST Friday for
     LMZ645-646.

     Small Craft Advisory from 6 PM Thursday to 8 AM CST Friday for
     LMZ643-644.

&&

$$

Update...Boxell
Tonight/Thursday and Aviation/Marine...Boxell
Thursday Night through Wednesday...99



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