Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 180920
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
320 AM CST Wed Jan 18 2017

.TODAY AND TONIGHT...Forecast Confidence Is Medium.

Areas of fog should linger into the morning hours, with light
winds and moist low levels under the inversion. Not expecting
widespread dense fog, with low stratus keeping temperatures from
falling.

Main issue during this period will be the low stratus deck trends
and its influence on temperatures. Extensive area of low stratus
exists across the region. Models are trying to shift this area to
the east this morning. However, it already appears to be too quick
with this trend. NAM forecast soundings keep this low stratus
deck around below the shallow inversion today into tonight. The
GFS soundings do show the low stratus moving out of the area this
afternoon.

Given the time of year, these low stratus decks usually linger
longer than model guidance would suggest. Thus, will keep the
cloudy skies through the morning hours, then slowly trend downward
this afternoon and evening. Would not be suprised if the low
stratus deck lingers into tonight.

There is some warm air advection today from the west, which
should bring milder temperatures into the area. If the low stratus
deck lingers this afternoon, temperatures may not rise as much.
For now, have highs in the upper 30s to lower 40s across the area.
This is quite mild for this time of year.

Lows tonight are forecast in the upper 20s, though these may need
to be adjusted higher, if the low stratus deck lingers tonight.
May see light fog later tonight, with light winds and moist low
levels.

.THURSDAY...Forecast confidence is medium.

Shortwave ridge holds court during the morning hours before being
shunted east by an upper low slowly lifting out of the central
Great Plains. Weak surface troughing will accompany the upper
wave, with pressure falls of around 3 mb per 6 hours occuring over
southern Wisconsin by afternoon. Mid to high level cloud cover
will increase through the day with cloud bases lowering by
evening. 925 mb temperatures around 5 to 7 degrees Celsius support
mild high temperatures in the 40s.

.THURSDAY NIGHT AND FRIDAY...Forecast confidence is medium.

The upper low should devolve to an open-wave trough while lifting
from the lower Missouri valley into the western Great Lakes. As
the upper wave approaches Thursday night, QG forcing for ascent
increases thanks to arriving differential cyclonic vorticity
advection, robust jet-level energy from left exit region
divergence, and some modest but focused low-level warm advection.
Strong Omega, juxtaposed with precipitable water (PWAT) values of
0.7 to 0.9 suggests decent QPF with this system. In fact, the 12z
NAEFS standardized anomalies place these PWATs around 2 to 3 sigma
above the mean for this time of year. Expect precipitation to
work in from the southwest Thursday evening, before spreading
across the area overnight and diminishing Friday morning.
Temperatures may be cold enough in our far north (Montello, Fond
du Lac, and Sheboygan areas) for a bit of freezing rain or sleet,
but this should be an all rain event for most given the forecast
thermal profiles. Highs in the 30s and 40s are expected for Friday
afternoon.

.SATURDAY INTO TUESDAY...Forecast confidence is medium.

Active flow pattern aloft continues, with shortwave energy
carving out a closed low over the central Great Plains on
Saturday. The near vertically stacked system should lift north
into the upper Mississippi valley on Sunday, bringing the chance
for a few rain showers over the weekend. Temperatures will be
quite mild with highs into the 40s to perhaps lower 50s. A potent
low pressure system passing by to our south brings a better chance
for rain on Sunday night into Monday. Temperatures will cool a
bit from the weekend, but should remain above normal.

&&

.AVIATION/12Z TAFS/...

Main issue will be how long the fog and low stratus clouds linger
across the area today. Low stratus with ceilings below alternate
minimums and approaching airport minimums should linger this
morning, and perhaps this afternoon into tonight. Some uncertainty
here with how long these low clouds will linger, but given the
time of year would not be suprised if they linger into tonight.

Fog with visibiliities below alternate minimums at times should
linger into the middle morning hours. Milwaukee may not see much
in the way of fog. Increasing south to southwest winds should then
mix out the fog later this morning into the afternoon. Winds
should become light again tonight, with light fog possible after
06Z Thursday.

&&

.MARINE...

The pressure gradient will tighten somewhat this afternoon and
early this evening across the area. This should allow for
increasing southwest winds to develop, with gusts to around 20
knots. No Small Craft Advisory is needed at this time. It appears
that winds and waves will remain below Small Craft Advisory levels
for the rest of the week and into the weekend.

&&

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

$$

TODAY/TONIGHT AND AVIATION/MARINE...Wood
Thursday THROUGH Tuesday...SPM



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