204
FXUS63 KARX 152308
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
608 PM CDT Sun Sep 15 2024

.KEY MESSAGES...

- Summer warmth through much of the new week with highs in the 80s.

- Dry start to the week with increasing rain chances from west to
east moving into the weekend.

&&

.DISCUSSION...
Issued at 110 PM CDT Sun Sep 15 2024

OVERVIEW: models remain steadfast with reestablishing the upper
level ridge axis across the region as we kick off the new week.
There have been various interpretations of what will happen to the
ridge as west coast troughs dig and spin shortwaves into the ridge`s
western flanks and/or across its "top". While there have been some
differences in the GEFS and EPS, one trend has been standing out -
holding the ridge influence longer into the week, and keeping rain
chances at bay (to the west). Comparing previous runs of the WPC
cluster analysis of the 500 mb pattern show this trend with all
clusters favoring it. Somewhat subtle, but definite impacts on the
local forecast area`s sensible weather. Looking at the EPS and GEFS
suites of members also portrays this, keeping the area essentially
"dry" until the weekend. Further, the grand ensemble doesn`t start
to press in small measurable rain chances (10-30%) until early Fri
morning. The NBM has pushed back rain chances to Thu night, through
the weekend. This looks more reasonable, although still might be a
bit early depending on ridge strength. Meanwhile, there are some
hints in the GEFS and EPS that the ridge could hold even longer
through the weekend. A Canadian trough that looked to drop southeast
for the weekend, kicking the ridge east and/or taking the top off of
it, could hold across southern Canada - essentially skirting north
of the ridge axis. Whether that shortwave would interact with others
originating from the CONUS west coast and give that ridge a firm
push is uncertain - lowering confidence in how the weekend will
shape up. That said, confidence is high on the summer warmth through
the work week and moderate/high that the local area will stay dry
through mid week.


PCPN: as mentioned in the overview section above, pcpn chances this
week are going to hinge on the stoutness of the upper level ridge
and the ability of west coast troughs/shortwaves to work into it.
Recent model trends have the ridge winning out for most of the work
week, spreading pcpn chances in from west to east for the weekend.
This looks reasonable given some of the model uncertainties. And
again, there is the possiblity the ridge influence wins out over the
weekend - although these chances are likely less than 30%.

Will continue to hold with the NBM for rain chances.


TEMPS: no change in the summery forecast with the long range
guidance holding fast to an upper level ridge and the pooling of
warm air under it. The grand ensemble continues to paint 80-100%
chances for 80+ degree highs Mon-Wed, trending a bit lower moving
into the latter half of the week due to model uncertainties with
ridge/shortwave placement (rain or no rain). GEFS and EPS ensembles
also continue to show very little variance between its 10-90%,
generally under 10 degrees with 75% of their members lying in the
80s. Dewpoints will be dropping as the ridge works in however, so
humidity will be a bit more comfortable compared to this weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 608 PM CDT Sun Sep 15 2024

VFR conditions are expected with persistent S/SE winds 10 kts or
less and some increase in mid/high clouds overnight and
scattered afternoon cumulus on Monday. Sufficient flow aloft and
some increase in clouds likely will limit fog development
tonight at KLSE, but some fog is possible in valley locations
early Monday, particularly the Wisconsin River Valley.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...JM