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Area forecast discussion
National Weather Service La Crosse WI
652 PM CDT sun Oct 20 2019

Short term...(tonight through tuesday)
issued at 220 PM CDT sun Oct 20 2019

Models have remained consistent and in lockstep with the storm
system to impact the region from late tonight through Tue. Upper
level shortwave trough pushing out of the southern rockies,
strengthening as it drives east/northeast to across the upper
Mississippi River valley by 00z Tue. The system becomes vertically
stacked as it does, with the sfc low staying west/north of the local
forecast area. Low level warm air advection will lead the system in
later tonight, just ahead of a cold/occluded front that looks to
slide to the northeast around 21z Mon. Some low level moisture
transport along with a 40 kt 850 mb jet will help fuel showers along
and ahead of the front. Weak instability could spark a
isolated/scattered storms.

Post the front, into Mon afternoon the southern half of the forecast
area could get a break from the rain as a mid level dry punch wraps
into the low. Showers will return for Monday night though as the
stacked low moves northeast, with bits of upper level energy and
plenty of saturation continuing to spark some precipitation. Higher
threat continues mostly along and north of I-90.

Tue looks to stay showery and cloudy for the northern half as the
storm system takes it's time working into southeast Canada. Could
see some late afternoon sun across the far south.

In addition to the rain will come some wind. Pressure gradient
tightens as the stacked low approaches. Strongest winds will come on
the backside of the low, kicking up later Monday night, persisting
through much of Tue. Gusts upwards of 35 to 40 mph look probable at
this time, mostly for southeast Minnesota. Don't think an advisory will be
needed, but it's a time period to watch.

Long term...(wednesday through sunday)
issued at 220 PM CDT sun Oct 20 2019

Colder air starts to push in from Canada Post the Mon/Tue low
pressure system, with a stronger punch of cold air for Thu/Fri as
another shortwave trough drops southeast from the north. Highs will
probably struggle to get out of the 40s through Friday. Could see a
bit of a rebound for the weekend as models continue to suggest
shortwave ridging will work in - although it looks short lived as
the GFS and ec point to a long wave trough and colder air returning
for the early part of the following week.

As for pcpn chances, another piece of shortwave energy is progged to
slide from the pac NW across the Dakotas and through the upper-mid
Mississippi River valley. Good shot of showers will this scenario,
although where the higher chances lie will be tied to the shortwave,
and some uncertainty on where it will move. Will stick with
consensus for chances. After that, the forecast continues to trend
dry.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 652 PM CDT sun Oct 20 2019

VFR criteria expected area wide through this evening. Conditions
change overnight as the next system approaches, bringing rain and
possibly a few storms along its cold front. Ceilings should drop
to MVFR, perhaps IFR at krst, with the arrival of precip, with
some restrictions to visibility possible. Winds look to increase
overnight into Monday morning as the low strengthens. This will
create wind shear concerns, with 2k ft winds around 45 kts, mainly
at klse. Some model differences with wind speeds aloft further
west, but wind shear cannot be completely ruled out at krst. Did
not mention in this period, but will be monitored and adjusted if
needed during the next issuance. There should be a break in rain
during the afternoon hours of Monday as drier air spreads
northward. This should result in a brief period of VFR ceilings
before the next wave of rain moves in Monday night. Winds will
shift from southeast to southwest by late morning/early afternoon
with the frontal passage.

&&

Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&

$$

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