457
FXUS63 KARX 290411
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1111 PM CDT Fri Jun 28 2024

.KEY MESSAGES...

- A few more showers/storms tonight. A conditional severe risk this
evening, moreso for northeast IA.

- Aside from spotty light showers, mostly north Sat afternoon, dry
and cool conditions expected Sat into Mon.

- More showers and storms Monday night into Tuesday. Heavy rain
threat. Conditional severe threat Tuesday into Tuesday evening.

&&

.DISCUSSION...
Issued at 245 PM CDT Fri Jun 28 2024

* REST OF THE AFTERNOON/TONIGHT: storm chances - conditional severe
  threat for northeast IA into the evening

Extensive cloud cover has persisted into the early afternoon while
the morning rains have moved east/south of the local forecast area.
The clouds are inhibiting daytime heating, thusly working against
sfc destabilization. A thin line of showers/storms has developed in
southern MN/IA on the western flanks of the cloud, on the edge of
the MLCAPE plume (100-250 J/kg), a small region of differential
heating plus what looks like a remnant MCV (per watervapor imagery).
These should continue to push east, but will quickly run out of
instability a loft.

CAMS models continue to provide a wealth of potential outcomes,
almost by the hour, lowering confidence in how the evening will
unfold. A few things to focus on though. The MCV should continue to
provide enough lift for shower/storm production into the evening as
it shifts across the area. Again, instability is limited. With
RAP/HRRR soundings holding the cap in place (thanks clouds),
effective wind shear will be mostly above 1 KM...with fairly short
hodographs. Not sure there is much there to support whatever CAPE
can be realized.

To the west a cold front is advancing east and right around the
boundary RAP/HRRR soundings show some uptick in instability
profiles, although still suggesting the CAP could hold (non sfc
based). Showers/storms should develop along the front, but likely
more favored along the southern flank - in Iowa. These would have a
bit more promise for strong/severe upscaling with a deeper
instability pool, moisture axis to work with.

In additional to all this is the potential interplay of the low
level jet. Currently the RAP has a fairly steady stream of 850 mb
moisture transport from IA into central WI, with a gradual shift
eastward ahead of the front through the evening. Not much
convergence. However, the HRRR refocuses the jet into southwest WI
by 00-02z, resulting in blossoming of convection. Instability still
limited at best and doesn`t have a lot of strong-severe support.

Overall, a few more showers and storms this evening. A conditional
severe risk continues, but more focused into IA and associated with
the cold front. Certainly a scenario to monitor.


* SAT NIGHT/MON: cooler, drier

Aside from a shortwave trough/cold air advectively driven afternoon
shower chances, mostly north of I-94 Sat, the local area is looking
at a few dry days for a change. High pressure at the sfc slides
across the region Sunday while a shortwave upper level ridge edges
over the upper mississippi river Mon morning. EPS/GEFS paint highs
for most of the area in the lower 70s - a consistent signal with
only a few degree spread in the 25/75 percentiles. Meanwhile, the
LREF suggests little chance (0 to 10%) to warm into the upper 70s
Sun/Mon. So, expect cooler, but perhaps welcomed conditions to kick
off the new week.


* MON NIGHT/TUE: more rain, storm chances - heavy rain threat

Long range guidance remains in good agreement with driving ripples
of upper level energy eastward from the PAC NW, with the progressive
zonalish flow tracking them over the upper mississippi river valley
Mon night/Tue. Broad low level thermodynamics will precede the upper
level forcing while an attendant north-south running sfc cold front
currently set to track across the region Tue afternoon/eve.
Potential 300 mb jet streak Tue could enhance lift along the front
via its right entrance region.

Broad area of rain should break out/shift in from the west late
Monday afternoon, night in response to the thermodynamics. Not much
for instability at this time but couldn`t rule out at least a few
storms thanks to the nose of a 50 kt 850 mb jet. Favoring mostly
rain though.

Moving into Tue, more bits of shortwave energy/MCV will come into
play along with the cold front. Questions on how much cloud
cover/rain early in the day will be lingering with impacts on
atmospheric recovery/destabilization. SBCAPE in the LREF currently
progged from 1-1.5+ J/kg in the afternoon with favorable deep layer
shear to support strong/severe storm development. VERY conditional
with a lot of unknowns - that may not become more clear until the
actual day.

While the severe threat is murky at this time, the potential for
heavy rain is a bit more clear. PWs in the LREF pushing near 2+"
while ECMWF and NAEFS PW anomalies creep up to 2.5. EFIs even edging
above 0.70. Add in the persistent low level jet and moisture
transport with warm cloud depths from 4 to 4.5 kft and the setup is
very favorable for heavy rain. Obviously how the system unfolds,
where the variety of forcers set up/move, and potential training are
all important factors that are much less clear. Still, as it sits,
the setup is there and will have to be watched closely - especially
given the ongoing flooding and/or high running river systems. More
water is not needed.


* THU/FRI RAIN CHANCES

The GEFS and EPS continue to trend toward rain chances for the end
of the new work as the both shift an upper level shortwave from the
PAC NW eastward across the region. However, not all their members
agree on timing/placement for the resulting QPF - a few even suggest
it could be dry, shifting the pcpn away from the area. Less
agreement compared to some previous model runs. Given the currently
progged upper level dynamics, still looks like a good shot for rain,
albeit with potential to shift in location/timing. On the plus side.
the heavy rain parameters via the GFS are shifting more south and
east of the local area. A trend the area would welcome given the
recent heavy rain and expectations as we move into the early part of
the new week.

&&

.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 425 AM CDT Fri Jun 28 2024

With three more periods of precipitation ahead - today into
tonight, Monday/Tuesday, and Thursday/Friday - area rivers will
remain swollen. Both of those first two rounds in particular
show the potential for many areas to pick up around another
1-2". Given this and the large amount of water flowing
downstream, the Mississippi River is expected remain in minor to
moderate flood through at least the next five days.

&&

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

&&

$$

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