Scientific Forecaster Discussion
fxus63 kmkx 181924
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
224 PM CDT Wed Oct 18 2017
Tonight and Thursday - confidence...high
Gusty south-southwest winds maintaining low level thermal ridging ahead of
approaching trough. Only high level moisture associated with this
per visible/infrared satellite imagery. Winds shift to the west-northwest as this
trough passes overnight. A bubble of high pressure passes through
Thursday with a lighter return southerly flow setting up in the
afternoon. After brief visit of weak low level cool advection the
925 temps rebound to warm levels in the teens celsius by
afternoon, so expect another warm day well into the 60s with some
spots topping 70 degrees.
Thursday night through Friday night...forecast confidence is high.
A big upper ridge will slide east Thursday night, quickly putting
US under a dry and very warm southwesterly flow for Friday. Look
for high temps to push into the mid 70s most places. Any lake
breeze off Lake Michigan should stick very close to shore, pushing
a bit more inland over Sheboygan County as usual. High
temperature records for Friday are in the lower to mid 80s, so
those should be safe. The dry/mild pattern will continue into
Saturday and Sunday...forecast confidence is medium.
Mid level short wave energy will ride that southwest flow into the
Great Lakes Saturday night with a sharper trough axis sliding
across the area later Sunday afternoon and evening. At the
surface, a trough/cold front will reach our western forecast area
after midnight Saturday night, exiting to the east Sunday
afternoon. Timing of precip has been a bit of a challenge with
this system, but it is coming into better focus. The front looks
to be slowing down some, therefore, most of Saturday will be dry.
There was concern that some of the leading short wave energy
could fire off some pre-frontal showers, but that is looking less
and less likely. Any showers should be late in the day, but
probably not until Saturday evening. The warm southerly flow
ahead of the front will push temps into the 70s once again. So,
overall, a nice day on tap for Saturday.
Showers are likely with the frontal passage. There is just enough
cape, though elevated, to justify a small chance of thunderstorms
Saturday night, but that threat should be over by the early
morning hours on Sunday. Showers chances will linger into Sunday,
but diminish from west to east by afternoon. Cooler Sunday as
Monday through Wednesday...forecast confidence is medium.
The GFS and the European model (ecmwf) are in close agreement for the Post frontal
evolution of the overall pattern. The Canadian is much more of an
outlier. We see a very large mid level trough centered over Canada
begin to dig deep across the Great Lakes into the Ohio Valley.
This deep cyclonic flow will likely keep things on the cloudy side
with temps trending more towards seasonal normals. This pattern
can also give US some showers from time to time.
Aviation(18z tafs)...VFR mostly sky clear this period. Low level wind shear setup time
with some stronger winds remaining aloft associated with a wind
Max ahead of and slightly behind a trough. Winds shift to the west-northwest
for a time after trough passage. Then a bubble of high pressure
settles in for Thursday morning which slowly shifts off to the
east Thursday afternoon.
Marine...a Small Craft Advisory is in effect through tonight for
breezy sswly winds and higher waves. Waves of 3-6 feet forecast
north of Port Washington with 2-4 feet from Port Washington to
Winthrop Harbor Illinois.
Lm...Small Craft Advisory until 4 am CDT Thursday for lmz643>646.