Scientific Forecaster Discussion
fxus63 kmkx 160256
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
956 PM CDT sun Sep 15 2019
Update...fog has quickly been developing in clear areas so issued
a dense fog advisory for south central and se WI until 15z.
Believe enough clearing will occur over ern WI for some dense fog
to develop there during the early morning hours. Fog and low
stratus will then burn off by late Mon am followed by a warm day.
Marine...light winds will prevail over Lake Michigan through at least
Tue as high pressure builds into the region. Areas of dense fog
may develop tnt-Mon am due to a humid airmass over the region.
Previous discussion... (issued 657 PM CDT sun Sep 15 2019)
Update...areas of light drizzle over far ern WI will move over
Lake Michigan by 01z. The stratus field is currently decreasing from
west to east across south central WI but there is uncertainty
whether this will continue into the evening. Where clear areas do
exist, expect areas of dense fog to form late this evening into
the overnight. Dense fog advisories may eventually be needed later
tnt especially over south central WI.
Aviation(00z tafs)...areas of light drizzle with MVFR vsbys over
far ern WI will move over Lake Michigan by 01z. The stratus field with
cigs of 1000-1900 feet is decreasing from west to east over SW and
south central WI. There is uncertainty whether the clearing trend
will continue ewd across all of srn WI this evening. Will maintain
broken stratus over ern WI for now. For the overnight hours, areas
of 1/2-1/4sm fog will form in the clear sky areas with lighter fog
where the stratus holds. The fog and stratus will burn off by late
morning on Monday with mostly sunny conditions for the afternoon.
Previous discussion... (issued 242 PM CDT sun Sep 15 2019)
Rest of this afternoon through Monday afternoon...forecast
confidence is moderate.
Stratus is holding strong across the area this afternoon, though
despite the cloud cover, temperatures have managed to warm into
the low to mid 70s. A weak surface front is advancing toward the
region from the northwest, and will move into southeastern
Wisconsin through this evening before essentially washing out over
the area. Some clearing has been taking place behind the front,
though it's not entirely clear just how far that clearing line
will make this evening.
With high pressure building in and large scale subsidence aloft,
moisture should get trapped below the inversion layer as we head
into tonight. Suspect that this will initially manifest itself as
a regeneration of stratus this evening, but with calm winds and
very moist ground over much of the area, we should see stratus
build down overnight, setting the stage for fairly widespread fog
by morning. Given uncertainties with stratus vs. Fog and just how
dense any fog will be, will hold off on a dense fog advisory for
now. Wouldn't at all be surprised to see one be needed by late
tonight/early Monday, however.
Clouds and fog will likely be slow to clear Monday morning.
Looking at upstream obs from Minnesota today, it was 10-11 am
before fog and low clouds started to clear in earnest, and would
expect similar timing across the area tomorrow morning. This will
likely keep temperatures a few degrees lower than they otherwise
would be. Highs should top out in the low to mid 70s to upper 70s
west, where clearing may take place a bit earlier.
Monday night through Tuesday night...forecast confidence is
Models continue to show high pressure lingering to the east of the
region Monday night into early Tuesday. Light winds are expected,
with low level moisture lingering. Thus, more fog may occur during
this time, with dense fog not out of the questions. Some low
stratus clouds may also develop with the fog. It may linger into
Tuesday, before gradually mixing out.
The 500 mb ridge axis is expected to remain just to the east of
the area Monday night into Tuesday night. The influence of high
pressure to the east of the region should continue to bring quiet
weather. Temperatures are expected to remain warm for middle
Wednesday through Friday...forecast confidence is moderate.
Models are in general agreement with the 500 mb ridge axis
remaining east of the region during this time, with a trough
moving from the northwestern Continental U.S. Across the Great Basin and
into the central rockies. South winds during this period should
maintain the warm and humid conditions across the area. A weak
cold front may push east into the area by 12z Thursday and
stalling out into Friday. There is enough moisture and instability
for keeping the decent chances for showers and storms Wednesday
night, with low pops lingering into Friday.
Friday night through Sunday...forecast confidence is moderate.
Some disagreement with timing and placement of features in this
period. However, southwest flow at 500 mb should continue. The
cold frontal passage may occur as early as Saturday or as late as
Sunday. Will maintain pops through this period for now. Mild
temperatures should continue during this time.
Aviation(21z taf updates)...
MVFR stratus will continue through at least late afternoon. A few
scattered showers will be possible late this afternoon and early
this evening as a weak cold front moves in, but coverage/intensity
appears to be too low to include in the tafs at this time.
Some partial clearing is possible this evening, especially at
Madison, before stratus builds back in overnight. This will build
down to the surface with time, with IFR to LIFR conditions
expected by Monday morning due to low stratus and fog.
A weak trough of low pressure will push through the lake through
this afternoon. Winds across the southern half of the lake will
remain from the south and southwest, with easterly flow over the
northern reaches of the lake.
High pressure builds into the area tonight, which will bring
lighter winds to the region. Some patchy fog isn't out of the
question, 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
WI...dense fog advisory until 10 am CDT Monday for wiz051-052-058>060-
Dense fog advisory until 10 am CDT Monday for wiz046-047-056-057-