Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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605
FXUS63 KMKX 191549 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
949 AM CST Thu Jan 19 2017

.UPDATE...

Dense fog continues this morning across the forecast area. Decided
to expand the advisory north based on obs and webcams. Also
extended the end time until noon based on model soundings. Will
probably see reduced visibilities into the afternoon, but likely
an improvement from dense fog by then.

Forecast highs seem to be generally on track, though may need to
lower a couple degrees based on fog and clouds into the afternoon.

Rain will arrive from the south late this afternoon into the
evening, moving through overnight into Fri morning.

&&

.AVIATION/18Z TAFS/...

Looks like dense fog will hang on through at least late morning.
Will probably see reduced visibilities into the afternoon, though
there should be some improvement by then due to daytime mixing.

Rain will arrive from the south late this afternoon into early
evening. The rain will taper off later tonight into Friday
morning.

With light winds remaining, could see more fog tonight after the
rain ends.

Low clouds are expected to hang around through Friday.

&&

.MARINE...

Light southeast winds. Fog over the waters may remain near 1 mile
this afternoon, with more fog expected by later tonight.
Generally light winds are expected into Saturday night across the
area. North to northeast winds may pick up somewhat on Sunday,
though will still be below Small Craft Advisory levels. The light
winds should linger into early next week.

&&

.PREV DISCUSSION... /Issued 323 AM CST Thu Jan 19 2017/

TODAY AND TONIGHT...Forecast Confidence Is Medium.

First issue is the persistent low stratus and fog over most of the
area. There are a few areas where the clouds have mixed out in the
south and southwest counties. However, more low stratus may move
northeast into the area from the southwest, within weak warm air
advection regime. Models have not handled these low stratus clouds
well.

The low status may linger through today, though winds at top of
inversion may try to mix out these clouds in spots. Tried to keep
things mostly cloudy for today. Fog has become dense in the far
southwest counties early this morning, and issued a Dense Fog
Advisory there until 15Z. The fog should linger across the rest of
the area this morning, improving somewhat this afternoon.

The main 500 mb low will shift from the southern Plains into
northwest Iowa today and tonight, becoming negatively tilted tonight
across the region. Initial differential cyclonic vorticity advection
by 00Z Friday should help bring leading edge of rain into the area.
Rain will continue tonight, as another shot of differential cyclonic
vorticity advection pushes northward through the region. Kept high
end PoPs for mainly tonight across the area.

It appears that most of the precipitation will remain rain across
the far northern portions of the area later today into tonight.
Surface temperatures should remain above freezing, with ice crystals
present in area forecast soundings. So, not much in the way of
freezing rain is expected in the far northern counties. Despite the
clouds, highs should reach the upper 30s to lower 40s today. Lows
tonight should be in the middle 30s in most areas.

FRIDAY...Forecast confidence is high.

Negative tilt shortwave trough lifts north through the upper
Mississippi Valley/lower Great Lakes. Dynamic support will be
present into the early afternoon, as channeled vorticity coupled
with weak jet-level divergence passes through. Rain shower chances
should persist into the afternoon before the forcing for ascent
wanes. With saturated low-level profiles on area forecast soundings,
cloudy skies will be the rule. Given 925 mb temperatures of 1 to 4
degrees Celsius and moist adiabatic lapse rates, highs should reach
the upper 30s north to the lower 40s south.

SATURDAY AND SUNDAY...Forecast confidence is medium.

Yet another upper low lifts north from the lower Missouri Valley
Saturday morning and into northern Minnesota and Wisconsin by Sunday
evening. An occluding surface low takes a similar path, skirting by
to our west, while drawing warmer air into our area on southerly
winds. While we`ll see a slight chance for rain showers in
southern Wisconsin, the better rain chances remain to our west
over Minnesota and Iowa and closer to the better dynamic and
thermodynamic support. Thermal advection boosts 925 temperatures
to around 5 to 7 degrees Celsius on Saturday, supporting very mild
highs in the upper 40s/lower 50s given moist adiabatic profiles.
Slightly cooler air will spill in behind the departing low on
Sunday, but we should still make it well into the 40s for highs.
Skies will be mostly cloudy to cloudy given plenty of low-level
moisture through the period.

MONDAY THROUGH WEDNESDAY...Forecast confidence is medium.

Most of the wave train action remains to our south into Tuesday
as a strong and expansive low pressure system tracks from the
Tennessee Valley/Gulf Coast States into New England. We could see
a few rain showers on Monday or Tuesday on the back side of this
system, with some mixed precipitation possible. Models disagree on
the strength and placement of the next upper level wave riding
southern stream energy towards the mid Mississippi Valley on
Wednesday. Temperatures will be cooling by this time, so any
precipitation, if present, could be in the form of snow.

AVIATION/12Z TAFS/...

Low stratus clouds with ceilings below alternate minimums, and
approaching airport minimums, are expected to linger across most of
the area this morning into the afternoon. There may be holes that
develop in this deck at times. Visibilities should generally remain
around 1 mile or higher this morning, improving this afternoon. An
exception will be southwest of Madison, where 1/4 mile dense fog
will occur into the middle morning hours.

Rain with more low ceilings and visibilities down to near alternate
minimums are anticipated to push north into the area later today
into tonight. Winds will remain light. Could see dense fog in spots
later tonight, though most areas should remain higher.

MARINE...

Southwest winds this morning will back to the southeast this
afternoon, and remain light. Any fog over the waters should remain
above 1 mile this morning, with more expected by later tonight.
Generally light winds are expected into Saturday night across the
area. North to northeast winds may pick up somewhat on Sunday,
though will still be below Small Craft Advisory levels. The light
winds should linger into early next week.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY until noon CST today for WIZ046-047-051-052-
     056>060-062>072.

LM...DENSE FOG ADVISORY until noon CST today for LMZ643>646.

&&

$$

UPDATE...DDV/Hentz
TODAY/TONIGHT AND AVIATION/MARINE...Wood
Friday THROUGH Wednesday...SPM



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