140
FXUS63 KARX 191946
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
246 PM CDT Wed Jun 19 2024

.KEY MESSAGES...

- Cooler through Thursday with scattered showers/storms, but
  organized severe weather/heavy rain threats are unlikely.

- Increasing risk of heavy rain from multiple rounds of
  showers/storms Friday/Saturday, with the axis of highest
  amounts favoring areas north of I-90. Stronger storms are
  also possible, but confidence is low.

- Periodic shower/storm chances are expected next week.

&&

.DISCUSSION...
Issued at 245 PM CDT Wed Jun 19 2024

This Evening-Thursday: Cooler, areas of showers/storms

A drier, cooler airmass has advected into the area with widespread
clouds and scattered showers so far today. Deeper moisture
persists into southwest Wisconsin and northeast Iowa closer to
the surface boundary. This will be the focus for scattered
showers into tonight with modest moisture transport along the
front. Any thunder threat will be mostly confined to far
northeast Iowa/southwest Wisconsin near/south of the slowly
southward- moving boundary.

The region looks to remain north of the boundary on Thursday with
perhaps modest destabilization occurring across northeast
Iowa/southwest Wisconsin. Broad warm advection within southwest flow
could result in scattered showers/isolated storms, but overall, with
the limited instability, widespread heavier rains are not likely.
The severe storm risk also looks low, especially if the
boundary remains south of the area.


Friday-Saturday: Unsettled, heavy rain possible

Will have to keep a close eye on this time period as a surface warm
front tries to lift northward ahead of a stronger trough ejects
eastward along the US/Canadian border. Eventually a cold front will
swing through late Saturday/Saturday night as the wave passes east.
Multiple waves of showers and storms will be possible
Friday/Saturday within southwest flow and periods of stronger warm
advection/moisture transport. NAEFS precipitable water values
increase to above the 99th percentile relative to climo late
Friday/Saturday with increasing instability and deep warm cloud
layers. This environment would be very favorable for heavier rain
amounts. Global ensembles already indicate 60-90% probabilities for
at least 2" of rain north of I-90 and 20-40% probabilities for at
least 3" through Saturday night, and the convective nature of the
rainfall would suggest potential for corridors of higher amounts
locally. Although mesoscale factors/boundary placement will impact
the area of favored higher rain amounts, the highest chances right
now are within the region that has seen the higher rain amounts
through the week, so flood concerns could ramp up if these
trends hold. Some strong/severe storms could occur in this
regime as well, especially as the stronger trough approaches,
but confidence is quite low in how the environment evolves.


Sunday-Wednesday:

The pesky front draped near the area may finally be pushed south and
east Sunday into Monday as Canadian high pressure builds over the
area within northwest flow aloft. Some showers are possible
Sunday, though, as a shortwave trough swings southeast.
Otherwise, a tendency towards a fairly active zonal flow
pattern is expected through the coming work week with lower
predictability rain/storm chances and temps near to above
average favored.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1251 PM CDT Wed Jun 19 2024

MVFR cigs and showers will be the main TAF concerns through 18z
Thursday. Currently, MVFR bkn to ovc cigs can be noted across much
of the local area with coverage slowly beginning to transition more
to sct as some subtle dry air aloft works its way in. This is
starting to be noted at KRST where increasing wind gusts indicating
diurnal mixing has led to a decrease in low-level sky cover. This
trend is expected to continue over the next few hours with sky cover
clearing. VFR conditions will then persist into the evening and
overnight hours with MVFR cigs and shower potential returning by the
morning hours on Thursday. Winds will remain fairly light through
much of the period at around 5-10 kts.

&&

.HYDROLOGY...
Issued at 400 AM CDT Wed Jun 19 2024

There will be a break from the heavy rain through Thursday, but
another round of heavy rainfall (2-5 inches) looms for Friday
and Saturday across central Minnesota into central Wisconsin.
This heavy rain across already saturated soils will result in
continued rises along the Mississippi and any tributaries
affected by this heavy rain. Many locations along the
Mississippi River will approach flood stage towards next weekend
(50-70% chance) if rainfall unfolds as forecast.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Naylor
HYDROLOGY...Skow