Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 230310
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
910 PM CST Sun Jan 22 2017
.UPDATE...Several webcams northwest of Madison in Sauk and
Columbia counties showing visibilities less than one mile. KDLL
was down to one half mile earlier this evening but has since
increased to over a mile. Despite high low level moisture, expect
slightly better boundary level mixing to prevent more widespread
dense fog from developing overnight. Weak cold air advection and
mid- level troffing may generate some patchy drizzle overnight.
.AVIATION/06Z TAFS/...Expect cigs to remain mostly IFR overnight
with visibilities in fog likely dropping to 1 to 3 miles with a
few spots of 1/4 to 1/2 miles. Some drizzle possible as well.
.MARINE...With surface temperatures and dewpoints remaining close
the the lake surface temperature along with better low level
mixing, leaning toward dense fog remaining patchy over the near
shore waters overnight. Currently visibility from lakeshore
webcams looking good. Small patch of fog that affect the Racine
lakeshore area earlier appears to have thinned.
.PREV DISCUSSION... /Issued 224 PM CST Sun Jan 22 2017/
TONIGHT - Confidence...Medium
Cloud cover looks to remain stubborn this period. Not an appreciable
airmass change. Weak cold advection kicks in due to slight
tightening pressure gradient on far nw periphery with the SE US low.
925 winds become northerly and increase a bit. Still potential for
more fog tonight due to relatively light winds at the surface. Does
not appear to be as prime of a setup as the last couple of nights
but potential for fog still there. Seeing a dropoff in SREF vsby
percentages though highest probs are in the northern CWA. MOS also
showing some vsbys dropping under a mile but at this time not seeing
the signals for widespread dense so will hold off on any headlines
but still have fog in the forecast.
MONDAY - Confidence...Medium
Surface ridging amplifies into wrn WI during the afternoon. LLVL RH
remains high and expect a fairly solid cloud deck to remain in
place. SREF cig prog shows high confidence in this scenario as does
MOS cig prog. A nnw 925 wind flow however not much going on with
thermal advection so expect temps to still be mild in the upper
30s to mid 40s.
Monday Night through Wednesday...Forecast confidence is medium.
An upper ridge across southern Wisconsin gives way to an
approaching trough and upper low that pushes into the central
plains Tuesday that fills as it reaches Wisconsin Tuesday night. A
lingering trough extends across southern Wisconsin Wednesday
The precipitation is expected to arrive Tuesday afternoon as low
pressure tracks across Iowa and towards the Wisconsin/Illinois
border area. The ECMWF and GFS have trended a bit farther north of
their prior track, with the GFS the farthest north. The ECMWF now
brings the low over far southern Wisconsin, with the NAM tracking
it across far northern Illinois.
Precip will begin as mainly rain, but change over to a mix of snow
later Tuesday night as the mid levels cool. Boundary layer
temperatures will dictate the precip type and forecast soundings
show a rather warm low layer, since there is no cold air source.
Models are showing between 0.25 and 0.60 inch. Because of the
mild temperatures, not all the snow that falls will stick to
pavement, but snowfall totals could be in the 1 to 4 inch range
over a 24-hour period, with the higher totals toward central
Thursday through Sunday...Forecast confidence is medium.
The upper trough still extends across southern Wisconsin Thursday
before extending across the eastern great lakes Friday. Another
shortwave drops southeast into southern Wisconsin in the northwest
This will keep clouds in place and the chance for light snow
showers and flurries across southern Wisconsin.
Temperature`s will drop to seasonal normals.
SREF suggests better redevelopment for dense
fog tonight would be north of TAF sites but all will hinge on how
much wind can be maintained overnight into Monday morning. Upstream
airmass modification is more subtle than pronounced. However 925
winds are expected to increase from the north tonight so that may
help to keep widespread dense fog at bay with enough mixing and at
least a slightly drier airmass push.
MARINE...Have areas of fog mentioned for tonight. At this time
it looks patchy though. Will hold off on headline issuance for now.
Otherwise offshore winds will continue into Tuesday with no
other impacts expected at this time.
TONIGHT/Monday AND AVIATION/MARINE...Collar
Monday NIGHT THROUGH Sunday...Hentz