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Area forecast discussion
National Weather Service La Crosse WI
518 am CST Mon Nov 18 2019

Short term...(today through tuesday)
issued at 300 am CST Mon Nov 18 2019

Upper level shortwave on track to drop southeast out of western
Canada today, spinning across the upper Mississippi tonight, and
then exiting Tue morning. Not much low level thermodynamics progged
to accompany the shortwave, but a bit of upper level qg convergence
to help with the lift. Low clouds are likely to hang around through
the day, with the saturation deepening tonight as the shortwave
moves in - per soundings/relative humidity fields. However, some x-sections hint
that the moisture could shallow out enough as the shortwave exits to
lose ice in the clouds - suggesting drizzle/liquid pcpn could be
possible. Think the deeper saturation will co-exist with the better
part of the forcing, making rain/snow the main pcpn type. That said,
there is also some warming in the low levels that could act to
melt/partially melt what falls - adding the potential for some
sleet. Think sfc temps will stay too warm (above freezing on the
whole) to worry too much about an elevated warm layer, but it's just
one more forecast scenario to consider for tonight. A messy set up
for sure, and bears a close watch...but trends favor a rain/snow
outcome.

Latest short term models drag the expected band of pcpn across southeast Minnesota
this evening, shifting into western/central WI for late
evening/overnight. The GFS is fairly similar, although mostly along
the Mississippi River while the nam12 is a bit slower compared to
the other models and suggests most of the pcpn will fall across WI.
As for the ec, its quicker and even farther west - with southeast Minnesota and NE
Iowa having the higher chances. For now, siding with the short term
solutions for chances and leaning toward them for timing.

As for snow, amounts looking minimal given the forcing and
saturation with generally less than 1 inch east of the Mississippi
River.

Long term...(wednesday through sunday)
issued at 300 am CST Mon Nov 18 2019

NAM/GFS/ec in pretty good agreement with lifting an upper level
shortwave trough out of the Desert Southwest Wed, spinning it
through southern WI Thu morning. Healthy amount of low level warm
air advection leads the upper level forcing across the region Wed
night, as does low level qg convergence. The system's associated sfc
low looks to track into southwest WI by 12z Thu, quickly exiting
northeast by 18z. Sloping frontogenetic lift runs northwest of the
low and favors banding of pcpn. Meanwhile, coupled 300 mb jet looks
to enhance all the available lift Wed night. Soundings, x-sections
and relative humidity fields all suggest ample/deep saturation for the lift to work
on. All said, pcpn is likely.

As for what falls, x-sections and BUFKIT soundings also point to the
warmer-more seasonable airmass holding in place as the low pressure
system slides through. Rain is favored with the current track of the
system as it moves in. Could see some mix with and change over to
snow late Wed night as the column cools - moreso in the NAM. The GFS
is the warmer model, keeping it as rain through nearly the life of
the system with the ec leaning more toward the NAM. For now, will
ride consensus solution for the temperatures and resulting pcpn
types.

Rest of the week looking drier and fairly seasonable for
temperatures (albeit a brief cool down for friday).

&&

Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 518 am CST Mon Nov 18 2019

An extensive IFR/MVFR stratus field remains anchored over the area
early today. As a weak surface ridge axis passes through, some
improvement in ceilings is expected through the day with a period
of VFR ceilings possible for a time this afternoon. A surface
trough will slide through tonight with -ra possible, possibly
mixing with -sn at klse, although timing will likely need to be
refined in future updates. Any improvement in ceilings will give
way to IFR to MVFR ceilings as this occurs. Did not include vsby
restrictions, but rap soundings would indicate potential for
lowered vsbys later in the evening and into the overnight hours.

&&

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

$$

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