FXUS63 KARX 281747

Area Forecast Discussion
National Weather Service La Crosse WI
1247 PM CDT Thu Sep 28 2023

.DISCUSSION...(Today through Wednesday)
Issued at 245 AM CDT Thu Sep 28 2023

Key Messages:

 - Unseasonably warm temps expected this weekend into early next

 - Although some low end (10-40%) shower/storm chances are
   expected Friday into the weekend, a predominantly dry stretch
   of weather is likely into early next week.


The stubborn slow-moving low pressure system that has impacted the
region over the past several days continues to spin across the Great
Lakes this morning. However, it will move away today as the
blocking ridge across eastern Canada finally gets kicked eastward.
GOES nighttime microphysics imagery shows plenty of stratus
across the area early today and another cloudier day with
seasonable temps is expected before higher chances of some
clearing occur into tonight with the arrival of mid-level ridging.
A few sprinkles could not be ruled beneath the stratus today,
although the moisture is shallow. Patchy fog is possible across
parts of Wisconsin early Friday where low- level wind fields will
be lightest.


An unseasonably warm late September/early October period remains on
tap as strong ridging develops across the Midwest/Great Lakes. This
pattern evolution will be underway on Friday in response to a
deepening longwave trough along the West Coast. Higher
shower/storm chances should remain farther west across Minnesota
on Friday closer to a surface front and stronger moisture
transport. That said, a low (10%) shower chance exists as mid-
level warm advection increases with some hint of a weak shortwave

There is a somewhat stronger signal on Friday night into Saturday
morning for a few showers/storms to impact areas mainly west of
the MS River and into northern WI as a weakening low-level jet
pivots eastward into the area along with the surface boundary. A
pool of instability is expected to build across the area on
Saturday but weak forcing as the mid-level ridge builds looks to
hold higher convective chances well north/west of the area later
Saturday into early next week closer to the stronger moisture
transport on the periphery of the ridge. However, the GEFS/GFS has
been more aggressive with some low end shower/storm chances at
least through Saturday night with weak perturbations/warm
advection interacting with the fairly moist, unstable environment.
With low confidence in this scenario, have continued a mainly dry
forecast during this time with only small (10-20%) shower/storm
chances north of I-90.

High temps will likely eclipse 80 degrees this weekend into early
next week with overnight lows remaining above 60 for many
locations. These highs would be well above seasonal averages,
which are in the mid 60s to near 70. The ECMWF EFI reaches 0.7 for
max temps Sunday/Monday, indicative of high confidence for
unseasonably warm temps, although the strongest signal for
anomalous warmth lies just west of the local area. Spread with
respect to both temps/rain chances increases through the middle of
next week as the ridge begins to shift east/break down, but the
next more substantive chance for rain should hold off until this
transition occurs.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1245 PM CDT Thu Sep 28 2023

Current MVFR to VFR ceilings gradually clear from west to east
over the next 12 hours, though the timing of the clearing is
somewhat uncertain--which plays into whether we will see any fog
east of the Mississippi River overnight. Similar conditions
further west yielded a narrow band of dense fog this morning, so
have maintained some mention of fog east of LSE. However, the
placement and coverage of the fog remains of lower confidence.
Winds remain from the southeast at 5-10 kts today, increasing to
10-15 kts for Friday afternoon.





NWS ARX Office Area Forecast Discussion