Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 211825
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1225 PM CST Sun Jan 21 2018

.UPDATE...

Visibility has improved markedly as clouds arrive and ceilings
gradually lower. The exception is in the far northeast, where
visibility remains low. Extended the Dense Fog Advisory for
Sheboygan and Fond du Lac counties for a few more hours as a
result. Feel that visibility may improve before the expiration
time as the clouds move in, and may be able to cancel early
depending upon trends.

Areas of drizzle are developing within a low-level warm advection
regime from central Iowa into northern/central Illinois and far
southern Wisconsin. Expect the drizzle to continue pushing north
into our area, and to be with us for the remainder of the
afternoon. The steadier rainfall is not expected to arrive until
later tonight.

Concern for freezing rain and/or drizzle in the far north has
decreased for tonight, as it appears that warm advection will be
strong enough to warm temperatures before the steady precipitation
arrives. There could be a short window for some freezing drizzle
and/or freezing fog in far north Marquette/Green Lake counties,
but right now the threat appears minimal. Will keep an eye on this
as additional model data arrives however.

&&

.AVIATION(18Z TAFS)...

Ceilings will lower from MVFR to IFR into this evening with areas
of drizzle possible. Conditions should further deteriorate
tonight, with rain and drizzle becoming more widespread. The rain
will continue into Monday morning. Fog is also a concern,
especially for areas within several miles of Lake Michigan where
dense fog may move inland from the Lake this evening into tonight.
Expect IFR to LIFR flight conditions for tonight into tomorrow
morning. There is also a slight chance for lightning/thunder after
midnight tonight, but not enough confidence to include this in
the TAFs.

&&

.PREV DISCUSSION... (Issued 955 AM CST Sun Jan 21 2018)

UPDATE...

Greatest concern for this morning remains areas of dense fog and
freezing fog. Expanded the dense fog advisory into Sheboygan
county where the visibility has dropped over the past few hours.
The lowest visibilities remain generally north of the I-94
corridor at this time, but kept the counties farther south in the
advisory for now, due to patchy low visibilities. The greatest
concern for freezing fog and slick spots remains across our north
(generally north of I-94), so motorists should exercise caution
in these areas.

MARINE...

Issued a dense fog advisory for the nearshore waters into
tomorrow morning. Visibilities of 1 mile or less are expected, so
mariners should exercise caution. Otherwise, a Small Craft
Advisorywill likely be needed for a time on Monday into
Wednesday.

PREV DISCUSSION... (Issued 653 AM CST Sun Jan 21 2018)

UPDATE...

Fog has become dense and widespread enough for an advisory across
the central portion of the CWA. For now, took the expiration time
to 18Z, but it`s possible that it may need to be extended with
time, as it`s not clear what will cause conditions to improve
later this morning.

Also of note is the continued potential for slick spots on area
roadways where fog is dense and temperatures are below freezing.

AVIATION(12Z TAFS)...

Flight conditions have fallen into the IFR range in most
locations, and should remain there today. Dips into LIFR are
probable at times.

Later tonight, rain and drizzle will become more widespread, and
fog will continue. Most model guidance takes the region well into
LIFR range, but confidence is low on how things will unfold. For
now, generally kept sites in the lower ranges of IFR, but further
updates to take things into LIFR are possible.

The one exception at this point is KMKE, with vis dropping to 1/2
SM this evening and tonight. The main concern at KMKE will be fog
moving in off the lake as winds turn easterly. This could
potentially result in even lower flight conditions, so updates are
likely as the day goes on.

Winds will remain light and variable into this afternoon, before
becoming easterly this evening and through the day Monday.

PREV DISCUSSION... (Issued 307 AM CST Sun Jan 21 2018)

SHORT TERM...

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

Challenging short term forecast at this hour, with the initial
focus being on fog/freezing fog potential this morning. Stratus
has been slow to make its way north into the forecast area, and we
have seen some radiation fog develop where skies have remained
clear. As more abundant cloud cover moves in, fog may briefly
lift, but visibility is likely to eventually come back down as
stratus build-down takes place.

Short term temperatures are also a challenge, with the freezing
line currently situated from roughly Mineral Point to Whitewater
to Waukesha, and then on north to the Port Washington area. North
of this line, and dense fog that develops would have the
potential of depositing a thin layer of ice on untreated road
surfaces, leading to the potential for a few slick spots. Thus
far, most of the denser fog has been confined to areas above
freezing, but it`s certainly plausible that we see some areas of
freezing fog develop before sunrise.

Temperatures will slowly rise through the day today, reaching the
mid 30s by this afternoon as better warm air advection takes hold.
This WAA will be associated with considerable low level moisture
advection as well, with stratus, fog and drizzle becoming more
widespread this morning and early afternoon, before eventually
transitioning to light rain showers late this afternoon into this
evening. By the time the more substantial precipitation moves in,
temperatures should generally be above freezing.

Rain will then become rather widespread and somewhat heavier
overnight tonight, and with model guidance suggesting several
hundred J/KG of elevated CAPE, a few thunderstorms are possible
south of I-94/US 18.

LONG TERM...

Monday through Tuesday... Forecast confidence is Medium.

The center of the occluded surface low will track into southern WI
by late Monday afternoon. Widespread showers (and perhaps some
thunder from I-94 south) are expected through most of the day. As
the low moves into far south and southeast WI, expect showers to
diminish with the dry slot. More showers and storms are possible
along the occluded front in far southeast WI Monday evening. Total
rainfall with this system should be around an inch. Rivers are
low, but many are frozen, so this rain could help thaw them a
little. We will need to be on the lookout for ice jams.

Toward the Dells, the temperature gradient and rain/snow line
will be rather tight. I expect the snow to hold off for the MKX
forecast area until early evening.

Dry air wrapping into the mid levels of the system on the
northwest side of the low could cause a loss of ice crystals and
therefore a period of freezing drizzle (northwest of Madison and
Fond du Lac) Monday night. We will change back over to snow as the
system slides east of the area. Snowfall amounts will still be
light with around an inch accumulation, perhaps up to 3 at the
most by Tuesday morning. That could lead to a slippery commute.

We could see some lingering flurries or light snow showers into
late Tue morning, but overall it looks like we`ll dry out fairly
quickly on the back side of this system. Temps will dip into the
teens Tue night.

Wednesday through Friday... Forecast confidence is high.

There is a weak signal for a shortwave to bring some light snow to
portions of WI on Wed, but no mention of it in the forecast yet.
Wed highs will only be in the 20s, but warmer air will spread back
in for later in the week. Highs by Friday should be in the 40s.

Next Weekend... Forecast confidence is Medium.

Another amplified upper trough crossing the country could bring
rain or perhaps a rain/snow mix to southern WI Friday night into
Saturday. There may be light snow/flurries on the back side that
could get us on Sunday. There is good agreement between the GFS,
ECMWF, and even the Canadian models at this time.

MARINE...

Reduced visibilities are expected across the nearshore waters
through tonight, and it`s possible that a Dense Fog Advisory may
eventually be needed.

Light winds today will become easterly tonight, with waves
building into Monday morning. Small Craft Advisory is likely to be
needed from Monday into Wednesday, with initial high waves
associated with easterly winds tonight and Monday giving way to
gusty northwest winds early Tuesday morning. Gusts may approach
gale-force early Tuesday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until 3 PM CST this afternoon for WIZ051-052.

LM...Dense Fog Advisory until 6 AM CST Monday for LMZ643>646.

&&

$$

Update...SPM
Today/Tonight and Aviation/Marine...Cronce
Monday THROUGH Saturday...Boxell


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