Scientific Forecaster Discussion
fxus63 karx 171555
Area forecast discussion
National Weather Service La Crosse WI
1055 am CDT Thu Oct 17 2019
Short term...(today and tonight)
issued at 207 am CDT Thu Oct 17 2019
Surface analysis early this morning has a ridge of high pressure
overhead. Stubborn low and mid cloud hung up under subsidence
inversion but expect these to diminish from west to east today as
the ridge axis moves into eastern WI, setting up southeasterly
flow and mixing of drier air through the column. Otherwise,
looking at a splendid mid-October day with increasing sunshine and
highs topping off in the 50s.
That ridge moves into the Great Lakes region tonight as a low and
cold front move into the northern/Central Plains. Increasing
pressure gradient between these two systems will set up increasing
southerly flow overnight along with some increase in cirrus cloud
ahead of that low/cold front. Look for overnight lows in the mid
30s to lower 40s, coldest in the sand/bog country of central WI.
Long term...(friday through wednesday)
issued at 207 am CDT Thu Oct 17 2019
This has the potential to be damp period across the region. The
upper level ridge that will be over the region to close out the
work week will get shoved east into the eastern part of the
country as a trough moves out of The Rockies toward the Midwest.
This trough looks move across the area Friday night and Saturday.
While the main short wave trough looks to pass north of the area,
there should be several other weaker short wave troughs that will
help to produce some weak to moderate pv advection in the 500-300
mb layer. The low level moisture transport does increase ahead of
the trough, but does not look to be overly strong. The local area
will be under this transport axis as it will be focus farther to
the north ahead of the main short wave trough. As the cold front
with this system comes through, there will be a weak band of
frontogenesis in the 1000-700 mb layer with it. All this looks to
be enough forcing to produce a band of scattered showers along
the front with the best chance for rain looking to be across the
eastern sections Saturday morning.
A brief break in the rain chances will then occur Saturday night
through Sunday before a stronger system looks to impact the upper
Midwest for the start of the new work week. The 17.00z models are
indicating some differences on the path and speed of this system,
but these do not look to have much of an impact on the sensible
weather. A short wave trough is expected to come out of The
Rockies Sunday with an upper level low forming and quickly
becoming a closed low as it travels northeast across the plains
into the upper Midwest through Monday. The GFS is quicker to take
the low across the region and has it reaching southern Canada
Monday night while the European model (ecmwf) is slower and a bit farther north
with the track. Both models are very similar with spreading
precipitation over the area Sunday night but some differences on
how long it may stick around. With the quicker movement of the
GFS, it would suggest most of the precipitation should end Monday
night while the European model (ecmwf) would linger the precipitation into Tuesday
before lifting it out Tuesday night. The 17.00z gefs looks to be
pretty much split 50/50 on the timing, so with no clear cut signal
at this point, will carry some small chances through Tuesday for
most of the area.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1055 am CDT Thu Oct 17 2019
Cigs: generally skc to a few high clouds through Fri afternoon. Look
for increasing clouds from the west Friday night, with a lowering of
the deck overnight/Sat morning. Some MVFR possible/probable.
Weather/vsby: no impacts expected through the period. Increasing threat
for -shra overnight Fri/Sat morning.
Winds: light winds will be on the increase overnight tonight, then
become breezy/gusty by Fri morning as pressure gradient tightens.
South/southeast sustained at 20 with gusts to 30 kts likely at krst.