Scientific Forecaster Discussion
fxus63 karx 182103
Area forecast discussion
National Weather Service La Crosse WI
303 PM CST Mon Nov 18 2019
Short term...(this evening through tuesday)
issued at 303 PM CST Mon Nov 18 2019
Early afternoon water vapor imagery showed a shortwave moving
through the Dakotas and into Minnesota, with an associated surface
warm front and precipitation draped from north to south across
the Dakotas. Behind the front and precip, clear skies and strong
westerly winds allowed temperatures to climb into the upper 50s
and lower 60s. The strong warm air advection and shortwave will
serve as the primary forcing for continued precipitation in our
forecast area tonight, though models do hint at a little low level
frontogenesis developing. Overall trends in guidance have been
slower with onset of precipitation in the forecast area, so may
need to further adjust forecast timing as we go through the
afternoon, but at this point it looks like it will move into
western portions of the forecast area a little before midnight.
While clouds have kept temperatures a bit cooler today, the
aforementioned strong warm air advection along with the persistent
cloud cover tonight should keep temperatures relatively "warm"
tonight, with lows in the upper 20s across central Wisconsin to
the upper 30s in northeast Iowa and southeast Minnesota.
Therefore, expecting mainly rain west of the Mississippi River,
and more of a rain/snow mix to the east. The coldest areas
(generally along I-94) could also see some freezing rain/drizzle
along with their half inch or so of snow, but not expecting much
more than a trace of icing. That said, will need to watch surface
temperatures (and Road temperatures) closely tonight. After the
main band of precip exits the area, model soundings do show a
pretty good drizzle signal with loss of in cloud ice on Tuesday
morning. Will need to continue to watch surface temperatures
through the morning, but with the continued strong westerly winds,
we should warm above freezing relatively quickly.
Long term...(tuesday night through monday)
issued at 303 PM CST Mon Nov 18 2019
Main concern for the long term will be the system moving in
Wednesday night/Thursday. The region will be in southerly return
flow Wednesday night as surface ridging slides east and low pressure
races northeast toward the upper Midwest from the Southern Plains.
Plentiful moisture will surge northward with this system, with
precipitable water approaching 1" across much of the area (2
Standard anomalies above normal for this time of year). Needless to
say, this system looks wet, with quantitative precipitation forecast around 0.5 to 0.75". The big
question will be temperatures over our area as this will determine
rain/snow potential. Models are in fairly good agreement on taking
the low through Iowa into southwest Wisconsin Thursday morning, and
into the Great Lakes by Thursday evening. As it stands now, it looks
like the area will be under enough warm air to keep most
precipitation as rain, with perhaps some snow mixing in on the back
side of the system late Thursday morning as colder air works into
the area. Better chances of accumulating snow look north and west of
our area at this time. However, this system will definitely have to
be watched as we get closer in time.
High pressure then nudges into the area for Friday into the weekend,
with drier weather expected. After a brief cool down Friday, the
weekend looks to rebound to near normal again, with highs near 40
into early next week. Precipitation chances start to increase again
by early next week, but at this time there is a lot of model spread
and thus confidence is low.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1133 am CST Mon Nov 18 2019
A pesky IFR/MVFR deck remains in place across the area and given
time of year, not seeing much of a chance for improvement through
the afternoon. Satellite imagery does show some breaks up stream,
but it looks like they wouldn't get to the taf sites until late
afternoon or early evening, when they're expected to start filling
back in with loss of daytime heating. Bottom line, there's an
outside shot at a very brief period of VFR, but it's not looking
very likely at this time.
Will then be watching a band of precipitation moving through the
area late this evening into Tuesday. Guidance has trended toward
both taf sites being impacted now, so have introduced -ra mention
at rst. In addition, guidance is in pretty good agreement of some
drizzle lingering behind the main band of precip. Temperatures
should stay warm enough to preclude much freezing precip at both
taf sites, though a few snowflakes could mix in at times.
Otherwise, winds will become westerly as the rain moves through.
The two main things that will likely need refinement in later taf
issuances are arrival and end timing of the precip (trend has been
later), along with visibility with any drizzle, though ceilings
look to remain IFR.