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953
FXUS63 KARX 120726
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
225 AM CDT Sun May 12 2024

.KEY MESSAGES...

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- Warm today! Highs could top out in the mid 80s in warmer valley
locations.

- Scattered late afternoon showers/storms today into the evening (20-
40%) with pcpn chances shifting south of I-90 Monday.

- Seasonable temps for the new work week with the next, better shot
for widespread rain chances coming Thu.
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&&

.DISCUSSION...
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Issued at 225 AM CDT Sun May 12 2024

* OVERVIEW:

Upper level flow remains fairly progressive as we move through the
weekend and next week. Various shortwave troughs/ridging could/will
shift west to east across the Upper Mississippi River valley,
although long range guidance has been at odds at how this will shake
out. The model blend suffers as a result, "smearing" the pcpn
chances over a longer period than is likely - while also lowering
them. That said, the EPS and GEFS are showing some signs of coming
together - at least for pcpn chances Thu. Meanwhile for temps, after
a warm one today, trends continue to favor highs topping around
around the seasonable norms through the work week.


* TODAY/SUNDAY: very warm today, cooler (seasonable) Monday.
  Scattering of late afternoon/evening showers-storms today (20-40%)
  with shift in chances to south of I-90 Monday.

Southwest-northeast running sfc cold front still set to sink
southward across the region, tied to an upper level shortwave trough
just north of the great lakes. Weakly convergent in the near sfc
layer without much low level thermodynamics to air the lift ahead of
it. No help in the upper levels either. GFS and NAM builds 1500+
J/kg of SBCAPE by late afternoon in the warm sector ahead of the
front. However, soundings continue to show deep mixing (upwards 7
kft) - which will promote drying along with gusty winds. Thus, GFS
and NAM overshooting sfc Td (GFS into the low 60s!) and SBCAPEs are
overdone. HRRR more reasonable in the 500 to 750 J/kg range. No wind
shear. CAMS models spark scattered showers/storms along and ahead of
the front by mid afternoon, persisting into early evening. Again,
due to over forecasting moisture concerns, coverage in some of these
short term models is likely over done. Still, should be enough to
spark a few showers/storms of the pulse variety (20-40% chances).
Any storm will produce enhanced wind gusts. Severe storms not
anticipated.

The front is set to lay up across central IA into southern/northern
IL for Monday...a bit more southern compared to some previous model
runs. A shortwave trough in the southern portion of the upper level
flow will track across the mid mississippi river valley on Monday,
while a piece of energy drops southeast from the northern plains.
Both will work on the sfc boundary, helping force  deformation band
of pcpn across IA into southern WI. Shear remains uninteresting
while the bulk of the instability shifts south/southeast. Mostly
rain with perhaps a clap or two of thunder is the likely
outcome...and generally south of I-90 (locally).

Still looking like a warm end to the weekend. 850 mb temps on track
to warm from around +9 C at 00z last night to +13 C by 21z today.
Deep mixing upwards of 700 mb will work to bring that warmer air to
the sfc. Latest HREF paints a 70-90% to reach or exceed 80 degrees
for highs (lower north of I-94). Valley locations likely the warmest
and look to peak in the mid 80s. A taste of summer but minus the
humidity. It will cool back to the early May normals Monday with the
passage of the cold front.


* THURSDAY: next shot for rain

Long range guidance is in a bit better agreement with trying to
refine timing/placement of the potential pcpn makers for the new
work week. Latest EPS and GEFS runs have the preponderance of their
ensemble members bringing at least some light QPF across the upper
mississippi with an upper level shortwave trough Thu (perhaps as
early as the the overnight Wed). Not looking very dynamic at the
moment, but should have some fetch to southerly moisture. Latest GFS
doesn`t show much for instability nor wind shear. Still way too
early to ferret out any stronger storm risk.
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&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
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Issued at 1033 PM CDT Sat May 11 2024

VFR conditions expected through the TAF period. South winds will
transition to southwest winds during the morning on Sunday.
Through the day, wind gusts up to 25mph will be possible. Some mid
and high level clouds will continue to move through the region
overnight. Scattered showers and potentially some thunderstorms (20
to 30%) will be possible beginning in the late afternoon and
continue to be possible through the evening.
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&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...Cecava