436
FXUS63 KARX 131905
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
205 PM CDT Thu Jun 13 2024

.KEY MESSAGES...

- Lingering showers will diminish by late this afternoon with a
  dry, seasonable end to the work week.

- Trending hotter and humid late this weekend into next week
  with high temps near or above 90F for some areas Sunday into
  early next week.

- Intermittent showers/storms possible Saturday into next week.
  Confidence in coverage/timing is lower, but heavy
  rain/stronger storms would be possible. Right now the highest
  rain chances look to be later Saturday/Saturday night.

&&

.DISCUSSION...
Issued at 205 PM CDT Thu Jun 13 2024

This evening-Friday:

A cold front continues to sweep south of the area this afternoon.
Mid-level frontogenesis on the cool side of the surface boundary has
been aiding in a band of showers across the region today with gusty
winds of 40 to 55 mph, given dry low-level profiles, but these
will diminish through late afternoon as drier air works in. The
severe weather threat still looks to hold farther south across
southeast Iowa and Illinois late today closer to the surface
front and greater instability. As of 2 pm, SPC mesoanalysis
indicated the surface-based CAPE gradient had already shifted
south of the area. Canadian high pressure will build across the
Great Lakes Friday into Friday night providing a seasonable, dry
mid-June airmass with some diurnal cumulus development through
the day.

Saturday-Thursday:

A pattern change will occur over the weekend into next week as ridge
building occurs across the central US, eventually amplifying over
the Great Lakes into the Northeast next week. This will usher in a
hotter, more humid airmass.

More unsettled weather is expected to start the weekend as a few
shortwaves eject from the plains and broad warm advection/moisture
transport increases. The thunder threat looks low during the day on
Saturday with the higher instability out to the west. A more humid,
unstable airmass moves in by Sunday, but deep layer shear looks
modest, so confidence in organized severe weather is low. However,
increasing precipitable water values and deepening warm cloud depths
could result in localized heavy rain potential, especially by
Saturday night as instability advects eastward and interacts with
the passing shortwave and stronger moisture transport. The higher
rain chances (70-80%) currently extend from southeast Minnesota
through north-central Wisconsin later Saturday/Saturday, and WPC has
included a level 2 of 4 risk for excessive rainfall for this area
during this time. A noticeable airmass change is expected heading
from Saturday into Sunday as dew points climb and temps likely rise
to near 90 in some areas by Sunday, pending coverage of
showers/storms.

Heading into next week, the ridge will amplify across the Great
Lakes with the Upper Mississippi Valley residing on the western
periphery of the ridge in a very warm/hot, humid southwest flow.
NAEFS 850 mb temp and precipitable water values exceed the 90%
percentile relative to climo during this stretch. The stronger mid-
level southwest flow is expected to be oriented across the northern
plains, which may keep the greatest focus for severe weather to the
west. However, there is some uncertainty in the amplitude in the
amplitude/position of the ridge. A flatter/eastward displaced ridge
orientation (~40% of EC/GEFS/CPC members) would support increased
chances for intermittent showers/storms (including strong/severe
storms and heavy rains) as embedded shortwave troughs progress
through the flow while a more amplified ridge would likely
result in drier conditions with the higher shower/storm
potential farther northwest. Broad NBM rain chances in the
20-40% range seem reasonable at this time Sunday into next week
given the uncertainty. Likewise, temps could be impacted by
clouds/rain, dependent on ridge position, with spread increasing
by later in the week due to uncertainty in the longwave
evolution.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1235 PM CDT Thu Jun 13 2024

VFR conditions expected through the TAF period. A band of rain
is currently moving southeast across the local area. An isolated
thunderstorm is possible as these showers shift southward.
Gusty northwest winds will continue to be possible these
showers, mainly gusting up to 35kts. Clear skies and light
northwest winds are expected overnight.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Cecava