Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 karx 180905 
afdarx

Area forecast discussion
National Weather Service La Crosse WI
300 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 06z tafs through 06z Monday night)
issued at 1125 PM CST sun Nov 17 2019

Still battling some IFR and LIFR along and ahead of trough axis that
is sliding through the western Great Lakes. Gradually visibilities
are clearing as gradient behind this feature mixes in. But as this
happens, starting to see IFR conditions redevelop as ceilings lower
from widespread Post-trough stratus field.

Will likely see a mix of IFR and MVFR ceilings through the
overnight, with some improvement expected on Monday as weak ridging
takes place. Confidence in any clearing is low so expect mainly MVFR
ceilings to prevail. As warm air advection returns ahead of next
feature late Monday, could see low level saturation return and
ceilings drop again.

&&

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

$$

National Weather Service Glossary of Abbreviations