023
FXUS63 KARX 092316
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
616 PM CDT Thu May 9 2024

.KEY MESSAGES...

- Frost advisory for parts of north central Wisconsin

- Showers and storms will move southeast across the region
  Friday afternoon and evening. A few strong storms are possible
  with small hail and gusty winds being the primary threat.

- Periodic rain chances persist through the weekend and into
  next week. Temperatures will trend warmer than normal with
  Sunday appearing to be the warmest day with highs in the upper
  70s to lower 80s.

&&

.DISCUSSION...
Issued at 600 PM CDT Thu May 9 2024

Tonight: Cooler, Some Frost

Decaying showers and clearing skies later tonight along with
decreasing winds and temperatures dropping into the lower to mid
30s should allow areas of frost to develop, especially for
Taylor County. In coordination with neighbors, did include
Trempealeau, Jackson, Clark and Taylor Counties in a frost
advisory.

Friday Afternoon and Overnight: Showers and Storms

As we head into the afternoon and onward cloud cover will begin to
build ahead of an incoming 850mb shortwave caught in the northwest
flow regime. As the wave progresses through our area during the
afternoon and early evening, the 09.15z RAP shows a fairly robust
low-level jet behind it to 40-50 kts. This in combination with
MLCAPE of up to 1000 J/kg will help to initiate a line of showers
and storms that will quickly push southeast along with the
aforementioned low-level jet. In this case, instability appears to be
the limiting factor with strong (around 50 kts) 0-6 km bulk shear in
place. However, with fairly steep lapse rates and an inverted-v
subcloud layer, cannot rule out some gusty winds to 50 mph or some
small hail with any stronger storms when considering the freezing
levels of around 6kft. Consequently, SPC has a marginal (level 1 of
5) risk for severe storms for much of our area on Friday. Showers
and storms will quickly progress southeast through the forecast area
and will move out of the local area later into the evening.

This Weekend and Next Week: Warmer Trend with Some Shower & Storm
Chances

Northwest upper-level flow will be in place for the weekend with the
aforementioned departing shortwave trough departing leaving room for
a weak ridge to build into the region allowing for a warming trend
to take hold with surface southwesterly flow. As a result, the inter-
quartile range of for high temperatures at La Crosse on Sunday in
the 09.13z NBM is 80 to 85 degrees. Additionally, with the 09.12z
GFS/NAM showing fairly well mixed low-levels it could be a day with
overachieving warming but will feature lower dewpoints. With fairly
modest instability (1000-2000 J/kg of MUCAPE) present at peaking
heating on Sunday will have to watch for any subtle forcing
mechanisms that could set off any convection. Currently, the 09.12z
NAM/GFS shows some subtle vorticity advection associated with a weak
wave that progress through northern MN and into northwestern WI. As
this synoptic forcing pushes into the aforementioned higher
instability, a stronger 800-900mb frontogenetic signal is noted in
both the 09.12z GFS/NAM which when combined with modest precipitable
waters of around 1 inch and marginal 850mb moisture transport could
set off pulse convection across portions of the region. With any
potential convection for Sunday being outside of the range of the
short-range CAMs, hard to put confidence into localized
thermodynamics and shear profiles too much but the severe threat
with any storms appears to be minimal at this point in time with 0-
6km bulk shear values appearing very low across portions of northern
WI.

As we head into next week, northwest flow turns more quasi-zonal
with a couple of weaker short-wave troughs hinted by deterministic
guidance. However, still lots of uncertainty with how these systems
will manifest. Consequently, generally expecting a calmer period
into the first half of next week at this point in time with fairly
pleasant temperatures and occasional shower/storm chances in
accordance with the NBM. However, the EC ensemble has fairly low
probabilities for measurable precipitation (0-40% chance) early next
week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 610 PM CDT Thu May 9 2024

Predominantly VFR conditions are expected for the period as low
to mid clouds clear out this evening and clear skies ensue for
the overnight. Winds will be light from the north to northwest
overnight around 5 kts, backing to the west and increasing to 10
to 15 kts by the early afternoon. A front sweeps through Friday
afternoon, bringing scattered showers/storms and will result in
winds veering to the northwest--gusting upwards of 25+ kts
(higher in any storms). Cannot rule out localized visibility
restrictions in any stronger storms Friday afternoon.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory from 2 AM to 8 AM CDT Friday for WIZ017-029-033-
     034.
MN...None.
IA...None.

&&

$$

DISCUSSION...Naylor/Zapotocny/Skow
AVIATION...Skow