720
FXUS63 KARX 290952
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
452 AM CDT Sat Jun 29 2024

.KEY MESSAGES...

- A few sprinkles are possible Saturday followed by cooler, drier
conditions into Monday.

- More rounds of showers/storms are expected Monday night into Tuesday
  which bring a threat for heavy rain. Should details come
  together, some severe storms could occur Tuesday afternoon and
  evening.

- Additional rainfall could occur Thursday and Friday but, at
  this time, heavy rain and severe chances appear to be lower
  during this period.

&&

.DISCUSSION...
Issued at 402 AM CDT Sat Jun 29 2024

* TODAY INTO MONDAY: Sprinkles, then Cooler and Drier

Today, a few sprinkles may occur as an upper shortwave dives
southeastward out of ND. While the overall pattern is reminiscent of
a setup where scattered thunderstorms may occur despite a recent
cold frontal passage, progged soundings from most guidance show warm
temperatures at 700mb keeping a lid on things. Therefore, while have
kept sprinkle mentions in the forecast, have opted to limit mentions
of thunder this afternoon.

Tonight and Sunday night, as surface high pressure builds eastward,
light winds and mostly clear skies should result in efficient
radiational cooling. Have therefore moved forecast lows toward the
cool side of consensus blends, with the Black River Falls/Tomah area
favored to see temperatures below 45 Sunday night.

* MONDAY NIGHT INTO TUESDAY: Heavy Rain Threat, Potential Severe

Monday, as the aforementioned surface high shifts eastward, next
upper trough advances over the central/northern Rockies. Expect
850mb moist fetch from the Gulf of Mexico to resume in earnest as a
result. With plenty of moisture returning to the CWA, as lead
shortwaves eject downstream Monday night into Tuesday and the main
body of the upper trough arrives Tuesday evening, expect multiple
rounds of convection to develop.

The primary threat during this period will be heavy rain. Both NAEFS
and ENS PWATs approach and even exceed 2", approaching the 99.5
percentile of their respective model climatologies. NBM
probabilities indicate most areas will receive around 0.5" to 2" of
rain from Monday night through Tuesday night but with a long tail on
the high side of the distribution, suggesting the potential for
localized areas to receive higher amounts around 4". Needless to
say, given the high amount of antecedent rainfall, flash flooding
and additional river flooding look to be possible given this setup.

As for severe thunderstorm potential, focus is largely on Tuesday as
winds aloft increase ahead of the main upper trough. Accordingly,
progged hodographs should a good deal of wind shear with plenty of
turning in both the low and mid levels. With potential instability
building as heights aloft fall and low level moist advection
continues in earnest, severe storms capable of all hazards would be
possible if sufficient destabilization occurs. Given the likelihood
of abundant cloud cover following Monday night`s round of
convection, it remains far too early to lock this one in.

* THURSDAY/FRIDAY: Next Chance for Rain

The wave train rolls on Thursday into Friday when guidance is in
good agreement that an upper low will bring potential for additional
precipitation. While ensembles continue to differ in details,
resulting in an extended time period with precipitation mentions,
good news is that best moisture transport is still largely displaced
to our south across much of the 29.00z guidance suite.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1103 PM CDT Fri Jun 28 2024

Current convection is expected to exit the TAF sites by the
start of the 06Z TAF period. Signals are increasing for low
stratus and some fog developing early Saturday morning. Have
gone with IFR to LIFR ceilings and IFR visibility, with
conditions likely to be worst for a few hours just before dawn.
Should see pretty quick improvement to VFR after sunrise as
clouds scatter out.

Winds will swing around to the northwest Saturday morning,
becoming breezy with gusts to 20-25 knots through the afternoon.
Winds will diminish after 00Z Sunday. VFR stratocumulus likely
to develop in the cold air advection pattern.

&&

.HYDROLOGY...
Issued at 452 AM CDT Sat Jun 29 2024

While additional rain should take a break through at least
Monday morning, expect continued minor to moderate flooding at
most locations along the Mississippi River in our CWA as large
amounts of water continue to flow downstream from the Minnesota
River into the Upper Mississippi. Latest HEFS guidance suggests
all sites except Alma will very likely (95%) remain in at least
minor flood for the next 7 days.

Monday night into Tuesday night continue to remain of high
interest as most areas look to receive around 0.5" to 2" of
rainfall with the potential for localized amounts to around 4".
Smaller basins may return to flood as a result, with flashier
basins showing a good deal of variation in HEFS projections due
to the expected localized nature of those higher end amounts.
Thus, interests along all water courses in the CWA will need to
remain vigilant as Monday night approaches.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Kurz
HYDROLOGY...Ferguson