Scientific Forecaster Discussion
fxus63 kmkx 210208
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
908 PM CDT Tue Aug 20 2019
The regional radar is quiet. It's tough to locate the surface
front given the very weak pressure/wind field across the upper
Midwest. From the dewpoint analysis, the front is likely still
over northwest Wisconsin. The h8 winds are essentially northwest
all they way into southern Wisconsin. So, we lack any decent
convergence along the weak low level boundary. Moisture remains
quite high and there is still some decent cape available, but
given the lack of forcing, it should be difficult to get any
showers to develop...especially as cin expands. The front should
exit southeast Wisconsin shortly after 12z Wednesday. Then look
for the arrival of lower dewpoints through the day on Wednesday.
The light winds and available moisture should help produce some
fog again later tonight. But, those northwest winds just off the
ground may keep enough mixing around to preclude it from getting
Light winds tonight will become northwest and increase to modest
levels Wednesday morning as a weak cold front pushes across the
lake overnight into early Wednesday morning. A large Canadian high
pressure system will build into the region Wednesday into
Wednesday night. This will result in rather persistent northeast
to east winds for Thursday into Saturday.
Previous discussion... (issued 557 PM CDT Tue Aug 20 2019)
No meaningful changes are needed to the forecast tonight. Our
focus is on the approaching cold front now located over central
Wisconsin. It may help spark off some isolated showers or a
thunderstorms later this evening and overnight. It should be
pushing southeast of Wisconsin right around 12z Wednesday. Light
winds, clear skies and the lingering high dewpoints could result
in some fog and/or stratus again later tonight, but will clear out
quickly with the frontal passage Wednesday morning. The forecast
has all this handled well.
Expect VFR conditions through the evening. A weak cold front is
approaching southern Wisconsin from the north. It may help trigger
isolated showers and storms later this evening and overnight.
Also, light winds, mostly clear skies and humid conditions ahead
of the front may result in MVFR/IFR ceilings/visibilities developing between
about 09-13z Wednesday. These lower conditions will improve to
VFR levels quickly Wednesday morning as the front pushes off to
the southeast and drier air arrives on northwest winds. Winds will
turn northeast near Lake Michigan by late Wednesday morning. This
will impact mainly kmke/kenw airports.
Previous discussion... (issued 309 PM CDT Tue Aug 20 2019)
Tonight through Wednesday night...forecast confidence is medium
The remnant mesoscale convective vortex from the morning convective system that moved
through Illinois has been slow to kick east and is now south of Kenosha
co. Light rain on the northern side of this has been moving into
the southern portions of Milwaukee co. But as we go through the
afternoon expect all of this precip to diminish as the circulation
weakens and pushes east. Outflow from an earlier line of storms is
moving into the Madison area now and although there is an increase
in surface convergence, satellite imagery, especially low-level
water vapor imagery would suggest drier air is moving in behind
the outflow boundary. This is resulted in a clearing of clouds
over the western portions of the area. It's still possible that a
few parcels could get lifted along the boundary to tap into some
modest instability of 1,000-2,000 j/kg. However, the dry air
entrainment will likely keep storms from developing. Can't rule
out an isolated storm but things are going to be hard pressed to
Overnight the cold front will be nearing the region and very
isolated showers/storms are possible along the front. With mostly
clear skies the lingering low level moisture ahead of the boundary
should allow for fog formation again tonight for a period. The
winds picks up as the front moves through and this should help to
mix the fog out closer to sunrise.
Cold air advection will be taking place for Wednesday and highs will stay in the
70s. The drier air and slight breezes behind the front will make
for a nice day. Lows Wednesday night into Thursday bottom out in
the lower 50s.
Thursday through Sunday...forecast confidence is high:
High pressure will keep it dry across southern Wisconsin through
the remainder of the work week and into the weekend. There should
be plenty of sunshine during this period, with temps a few degrees
below normal Thu/Fri warming back to around normal by Sunday.
Monday and Tuesday...forecast confidence is medium to high:
Southerly low level flow between departing high pressure and an
approaching low will bring warmer and more moist conditions to
southern Wisconsin early next week. A chance for showers and
storms is likely to return as well, with some uncertainty as to
the timing of the better forcing and storm chances this far out.
Lingering light rain and isolated thunderstorms are possible until
00z for locations near the WI/Illinois border. Drier air in the low/mid
levels will clear any low level cloud cover still hanging around.
Fog is expected to develop tonight after midnight but winds begin
to shift to the north/northwest closer to 12z. Gusty northerly winds are
expected for Wednesday behind the cold front.
An isolated shower or storm is possible as a front moves across
the area overnight. Ahead of the front though, lingering low level
moisture could result in some fog in the nearshore waters tonight.
Winds and waves increase behind the front on Wednesday with gusts
to 20 knots at times and waves between 1 to 3 feet in the
nearshore and 4 to 6 feet in the open waters. High pressure builds
in on Thursday resulting in lighter winds and lower waves for the
rest of the week.