785
FXUS63 KARX 270916
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
416 AM CDT Thu Jun 27 2024

.KEY MESSAGES...

- Storm Chances Return Tonight, Lingering Through Friday. A
  Widespread 0.5" to 1.0" of Rainfall Is Expected.

- Slightly Below Normal Temperatures This Weekend.

- Subsequent Storm Chances Monday, Lasting Into Tuesday.

&&

.DISCUSSION...
Issued at 325 AM CDT Thu Jun 27 2024

Rain & Storm Chances:

Initial precipitation chances reach our western peripheral
counties in southeast Minnesota and northeast Iowa tonight ahead
an upper level trough seen over the northwest CONUS on GOES
water vapor imagery early this morning. These initial
precipitation chances are expected to remain along our west
though as the ridge lingers locally. Eventually, the
progressive pattern and veering of the moist low level jet
increases precipitation chances through the overnight hours
locally. As a result of these passing moisture lobes, have
quickened initial onset near 27.21Z only in these western
counties. As the synoptic low wobbles and phases east,
precipitation and storm potential persists through Friday into
early Saturday morning.

Rainfall Amounts Through Friday:

Higher rainfall amounts overnight are expected to remain along
our northwestern periphery aligned with the nose of the
heightened low level moisture gradient, northerly lifting low
level trough, and associated frontogenetical bands. HREF
confidence suggests a mean of 0.25" to 0.5" to a maximum near 1"
along our periphery during this time. Through Friday, as a low
level trough advects southwest-northeast oriented frontogenesis
bands within the heightened low level moisture transport, narrow
corridors of ~0.75" mean rainfall amounts spread east through
the forecast area. In summary, highest confidence for a
widespread 0.5" to 1.0" across the forecast area by Saturday
morning.

Local Severe Threat:

Quite a conditional severe storm threat at the current forecast
hour as the main wave passage is expected to remain outside of
peak diurnal heating and associated building instability.
Therefore, current confidence places heavy rain as the primary
hazard. With a quick storm motion, ~30kts, the threat for
damaging winds also cannot be ruled out in this scenario.

However, quickening of the synoptic pattern would present more
of a severe storm threat scenario locally. As a result, the
quickest high resolution model solutions show a line of storms
building Friday evening and progressing through the forecast
area. Given the ongoing precipitation and small storm potential,
building sufficient instability remains questionable.

Temperatures This Weekend:

Slightly below normal temperatures on tap for the week as a cold
frontal boundary shifts east across the Upper Mississippi River
Valley Saturday morning. An amplified upper level ridge in its
wake sustains these slightly below normal temperatures through
Sunday. Long term global ensemble confidence suggests
temperatures approximately 10 degrees below normal for the
weekend.

Subsequent Storm Chances Next Week:

Long term global ensemble confidence suggests the amplified ridge
exiting east into Monday, returning storm activity from west to
east Monday into Tuesday. Similar to Friday, separate upper
level synoptic troughs are resulting in main impacts remaining
to the north and south of the local forecast area. The initial
wave is expected to lift north through the Northern PLains
through Monday, leaving an increased low level theta e axis
draped across the local forecast area. Subsequent perturbations
and low level troughs may perpetuate precipitation and storm
potential through Tuesday. Spread in individual ensemble
(EPS/GEFS) member low locations extends from the Southern Plains
into central Saskatchewan and Manitoba.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1037 PM CDT Wed Jun 26 2024

Main taf concerns is development of fog in low lying areas and river
valleys overnight. High pressure builds into the region overnight
and provides mostly clear skies/light winds overnight. With drier
airmass over the area and light north wind aloft near the surface.
This will inhibit widespread Mississippi River Valley fog. With
confidence low on widespread valley fog development...have continued
patchy fog...BCFG...at the LSE taf site. Wind direction switch
around to a southerly direction Thursday afternoon...as high
pressure moves east of the region. Wind speeds increase to around 10
knots Thursday afternoon/evening.

&&

.HYDROLOGY...
Issued at 401 AM CDT Thu Jun 27 2024

While rivers continue to fall below flood stage, most of this
water is still on route to the Mississippi River. As a result,
the Mississippi River is expected to keep rising through the
next 3 to 5 days depending on location and routing of tributary
rivers. While official forecasts from the River Forecast Center
do take into consideration all of the water that has already
fallen and is on its way into the Mississippi River, it only
takes the next 24-48 hours of forecast precipitation.

The next chance of precipitation returns late tonight lasting
through Friday. While widespread amounts of 0.5" to 1.0" are
not expected to immediately or substantially affect ongoing
flooding concerns, an additional widespread 1" to 2" of rainfall
upstream will prolong residence of elevated river
levels. As a result, the Mississippi River levels may initially
slightly decrease before increasing again as the additional
rainfall flows downstream this weekend into next week.

Elevated rivers with ongoing minor to moderate flood stages
from Lake City through Guttenberg are expected to persist beyond
the next 7 to 10 days.

&&

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

&&

$$

DISCUSSION...JAR
AVIATION...DTJ
HYDROLOGY...Zapotocny