Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 210317
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
917 PM CST Fri Jan 20 2017
.UPDATE...Light onshore winds, high humidity and cold surface
temperatures continue to generate areas of dense fog across
southern WI. Visibilities have been bouncing a bit across inland
areas where patchy light rain and drizzle have helped scour the
fog a bit. However expect dense fog to redevelop in these areas as
even warmer air advances slowly northward into southern WI from
the south. Status quo on Dense Fog Advisory.
Still expect patchy light rain and a few showers to affect
the area overnight as upstream short wave over eastern Kansas
.AVIATION/06Z TAFS/...Visibilities have come up briefly over some
inland areas including KMSN this evening as patchy drizzle and
light rain help cleanse some of the thicker fog from the area.
However with moist east winds persisting, and even warmer, more
humid air pushing northward from northern Illinois, would expect
fog to become dense at times most inland areas as well. Scattered
light showers and rain may help briefly improve visibilities over
inland areas once again overnight. Still expect an improvement
later on Saturday once warm front pushes through most of southern
.MARINE...Dense fog advisory will remain in effect through
Saturday morning. Occasional drizzle and light rain helping to
improve visibilities at times, but light onshore flow and even
warmer and more humid air moving northward across southern Lake
Michigan will continue to generate dense fog. Some improvement is
possible once low level winds switch to the south to southwest
later on Saturday and increase.
.PREV DISCUSSION... /Issued 307 PM CST Fri Jan 20 2017/
TONIGHT - Confidence...Medium
With a favorable setup for further fog growth just went ahead and
put out an area wide DFA to cover this through Saturday morning.
Guidance all suggesting this whether looking at the MOS or SREF vsby
progs. Potent negative tilt shortwave will ride northeast from the
southern Plains. DCVA maximizes between 6-12z. Sfc low pressure will
lift into Iowa with a warm frontal boundary extending west/east
towards nrn IL. Meso models all show an uptick in shra activity
later in the night as the wave and low level frontal boundary
approach. May bump pops up a smidge in some areas.
SATURDAY - Confidence...Medium
The sfc low lifts nwd towards KMPX vcnty which pulls low level
forcing nwd as day wears on. In addition the 500 millibar vort max
lifts newd so mid level forcing should be winding down. So any shra
beyond mid morning likely to be quite isolated. The low level flow
looks quite weak but from a moist southerly direction so stratus to
remain and fog, possibly dense, to persist for at least the morning
hours. So headline in place through 18z. Lowest vsbys likely to be
early ahead of the low level boundary. No sunshine expected though
low level thermal ridge pokes into se WI through early afternoon so
some temps may still take a run at 50 in the far south or southeast.
Saturday night through Monday night...Forecast confidence high.
Srn WI will be on the far north to northwestern periphery of a
large low pressure area that will track from the srn Great Plains
to VA for this time period. Cloudy skies and above normal temps will
continue while nly winds will begin to limit the extent of fog by
late Sun and Mon. There will be only slight chances of rain in far
ern WI for Sun night through Mon night.
LONG TERM...Tuesday through Friday...Forecast confidence medium.
A shortwave trough and low pressure area will track from the Great
Plains across Srn WI for Tue night and Wed. This will put the rain
snow line across the region. Highest probabilities for a few
inches of snow would be toward central WI. Afterward nwly flow
will gradually cool the temps through the week. 1000-500 mb
thicknesses of 540-546 DM early in the week will fall to 522 DM by
later in the week.
AVIATION/00Z TAFS/...Stratus and fog will be widespread this
period. Dense Fog Advisory in place area wide through 18z. LIFR and
VLIFR conditions should be fairly prevalent in this moist regime
with light winds. Some improvement expected Saturday mid
day/afternoon boundary shifting north. Shortwave should bring a
round of shra back into the area esp between 06-12z. Some
improvement in cig heights/vsbys expected Saturday afternoon.
MARINE...Fog expected to persist over the waters through at
least Saturday. Have extended the Dense Fog Advisory through 6 PM
Saturday. 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.
WI...DENSE FOG ADVISORY until noon CST Saturday for WIZ046-047-051-
LM...DENSE FOG ADVISORY until 6 PM CST Saturday for LMZ643>646.
TONIGHT/Saturday AND AVIATION/MARINE...Collar
Saturday NIGHT THROUGH Friday...Gehring