821
FXUS63 KARX 132342
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
642 PM CDT Fri Sep 13 2024

.KEY MESSAGES...

- Summer warmth will persist this weekend through much of next week
with highs in the low to mid 80s for most. Higher humidity for the
weekend.

- Showers press in overnight, persisting Saturday. Higher chances
(60-70%) over southeast MN tonight, then more favored north of I-90
Sat. Isolated thunder possible. Smattering of showers (20%) could
linger into Sun/Mon.

&&

.DISCUSSION...
Issued at 145 PM CDT Fri Sep 13 2024

OVERVIEW: models remain in good agreement with a break down/nudge
east of the upper level ridge axis this weekend, allowing remnants
of Francine to spin northward. Bits of shortwave energy could also
be felt by features pushing into the ridge from the west. But long
range guidance has also been in very good agreement with reasserting
the ridge over the great lakes/upper mississippi river valley for
the new work week while digging a sharper long wave trough into the
west coast. The ridge would get a shove east by the trough moving
into next weekend in this favored scenario.


PCPN CHANCES: short/medium range guidance all in good agreement with
a bit of what is left of Francine breaking northward, spinning
across the local area overnight. These bits of energy progged to
take a more north-south orientation over the region Sat. In
addition, moisture from Francine is also on its way northward. PWs
climb to 1.5+" late tonight, lingering into Sunday. Sfc dewpoints
climb back into the mid 60s for most while 850 mb moisture transport
noses into southeast MN overnight, with a ribbon following along the
upper level forcing Sat into Sun. The mix of upper level forcing
(some 600:700 mb Fgen evident too) and increasing/deepening
saturating should lead to scattered/widespread shower activity
overnight through Saturday. Instability relatively weak with longish
but skinny profiles in bufkit soundings. Should be enough for
isolated storms but not severe. While the source of the moisture is
tropical in nature, NAEFS and GEFS PWs anomalies only inch toward
+1. Also, forcing isn`t strong. So, rainfall amounts don`t look to
be overly robust. The grand ensemble only paints a 10-30% chance to
drop more than 1/4" later tonight/Sat - mostly for southeast MN.

The model blend (NBM) remains a bit low for probabilities and will
continue to push higher chances/low end likely (40-70%) for the
forecast area.

For Sun/Mon, with the the decaying tropical system meandering over
the tenn river valley/southeastern states, cut off from the mean
flow, a few models rotate lingering bits of shortwave energy
northwest into the local area. A smattering of showers could/would
be the result. Not a lot of consensus in the models, but warrants at
least low end chances for now (20%).

With the reassertion of the ridge for the new work week, rain
chances should be held to the west for at least a few days. The
model blend starts to push chances into the west by Wed however,
heavily flavored by the more aggressive/eastward pushing EC. Not a
lot of clarity here and current model blend could be too high with
rain chances in the west/too quick. Will let the NBM tell the story
for now.


TEMPS: the mild to warm temps look to hold fast for the weekend and
likely through next week as an upper level ridge remains the main
weather influence for the region. Not unduly warm with 850 mb temp
anomalies in the NAEFS and ECMWF only flirting with +1. However, the
grand ensemble of models continues to push 50-80% probabilities for
80 or warmer days for the forecast area into next Friday. Meanwhile,
the EPS and GEFS also continue to depict only a few degree spread in
their 25-75% for likely temps while keeping the upper 75% of
outcomes in the upper 70s to mid 80s. A lot of agreement between and
with the model ensembles, holding confidence high for more of same -
above normal temps (but not crazy warm).

The weekend will be more humid with a northward push of Francine air
- a definite summery feel to the air. Drier dewpoints (lower
humidities) should return for at least the start of the new week as
the ridge works back in.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 641 PM CDT Fri Sep 13 2024

Scattered showers will be possible, especially west of the
Mississippi River, overnight and through Saturday morning. By
Saturday afternoon, these showers will move into western and central
Wisconsin. While instability is not too high, there remains a
small chance (20 to 30%) of thunder occurring with these
showers. CIGS are expected to drop to around 5kft, with a 20 to
40% chance of MVFR CIGS possible. Predominant light southeast
winds through the TAF period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...Baumgardt
AVIATION...Cecava