Scientific Forecaster Discussion
fxus63 kmkx 160753
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
255 am CDT Monday Sep 16 2019
Today - confidence...medium.
Widespread dense fog the main story at the outset here. Areas of
stratus that lingered over the southeast though has shifted east
which should allow the fog to fill in more across the southeast
where fog has been slower to evolve. This evolution shows up well on
the nighttime microphysics and night fog GOES-16 loops. So going
dense fog advisory looks good so no changes planned. Surface high
dominates today with winds eventually becoming onshore. Once fog
Burns off mid morning or so would expect any lingering stratus to
mix out with model soundings showing appreciable depth to the dry
air. Warmer guid temps look good inland with cooler readings likely
closer to the lake given the onshore component.
Tonight - confidence...medium.
Surface high will be off to the east though we will still be well
within the influence of the anticyclonic flow. The return flow
suggests winds off the deck may be a bit higher which may limit the
extent of dense fog but with an overall light surface wind would
still expect areas of fog to take shape with some possible dense fog
Tuesday through Wednesday - confidence...medium to high.
Quiet conditions will continue but a bit more cloudiness can be
expected at times. Long wave ridging and drier mid-levels over the
area will keep any precipitation at Bay and result in continued dry
conditions for this period. Periods of high clouds will likely
affect the area due to occasional upstream convection across the
northern plains and parts of the upper Midwest. Boundary layer
mixing and mid-high level clouds should prevent widespread fog
Tuesday night, however mixing will be less in the east closer to low
level ridge axis and low level moisture feed off of Lake Michigan.
Hence wl introduce patchy fog over eastern areas later Tuesday night
into Wednesday morning. Expect the fog and any low stratus to thin
Wednesday morning with at least partly sunny skies for the aftn most
areas. Warm temps well above normal will continue, with slightly
cooler conditions by Lake Michigan.
Wednesday night through Sunday - forecast confidence...medium.
Protective long wave ridging finally shifts slowly eastward on
Wednesday and Wednesday night as upstream long-wave low pressure
trof spreads into the Pacific northwest. A piece of short wave
energy will be moving northeast across the northern plains into
southern Canada during this time ahead of the main trof. This will
usher a weakening cold front into southern and eastern WI Wednesday
night and Thursday. "Humberto" will also be moving farther east into
the Atlantic resulting in the shifting upper level pattern.
Increasing south winds will result in a significant increase in
moisture to warrant continuing shower and T-storm chances as medium
range guidance in general agreement on weak short wave trof moving
through the area on Thursday. Precipitable water increases to over
1.5 inches, which is above the 90th percentile for mid-September.
High pressure ridging briefly re-exerts its influence on the area
Thursday night and Friday lowering the precipitation threat. We may
be able to drop the precipitation mention completely from some of
these periods in later forecasts.
Upstream long-wave trof begins to shift eastward over the weekend
into the northern plains and south central Canada. This system will
drag a more significant cold front across Wisconsin later Saturday
into Sunday morning, returning shower and T-storm chances to the
area. Cooler, more seasonal temperatures will then settle into the
upper Midwest for the start of the new week. Until then, expect
above normal temps for mid-September to continue.
Aviation(09z taf update)...widespread LIFR conditions expected to
continue early this morning. Light winds, abundant low level
moisture and clear skies have led to ideal conditions for fog.
Improvement will be noted towards mid/late morning as fog lifts to a
likely IFR stratus deck for a time before mixing out. Much of the
afternoon likely to be VFR with plenty of dry air in the column. The
influence of high pressure will likely lead to more fog development
tonight, possibly dense in spots.
Marine...high pressure will be across the area today, which will
bring lighter winds to the region. Have issued a dense fog advisory
for the northern nearshore zone based on obs and webcam vicinity
Sheboygan Lakeshore area. Some patchy or areas of fog elsewhere is
plausible, especially across the nearshore waters.
High pressure will slowly push east into the eastern Great Lakes and
New England over the next few days. Winds will remain fairly light,
and eventually become more southerly by Tuesday and Wednesday.
WI...dense fog advisory until 10 am CDT this morning for
Lm...dense fog advisory until 10 am CDT this morning for lmz643.