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000
FXUS63 KARX 150823
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
325 AM CDT Mon Apr 15 2024

.KEY MESSAGES...

- Another dry day with some concerns for elevated fire weather
conditions. However, winds will be much diminished compared to
previous days, helping to lower the risk for quick moving fires.

- Punchy spring storm promises a wet day Tue with 1+" amounts (60-
90% chance) along with strong easterly winds (gusts upwards of 40
mph).

- Some severe risk Tue...although uncertainty on storm track lowers
confidence in extent of the threat.

- Colder end to the week. Could see some freezing temps for the
weekend.

&&

.DISCUSSION...
Issued at 325 AM CDT Mon Apr 15 2024

* OVERVIEW:

Upper level shortwave trough spins out of the desert southwest
today, developing a negative tilt/closed low as it drives over the
plains. Associated sfc low set to track across central IA by 06z
Wed, then slide over/near the local forecast area overnight. The
storm starts to weaken as it exits east/northeast of the region Wed.

Ample low level thermodynamics, coupled with a strong fetch of 850
mb moisture transport/nose of LLJ will power-fuel expansive area of
showers and a few storms Tue, trending northeast of the local area
by mid evening. Further convection could/will pop southwest of this
rain region - more attendant to the sfc low. Pcpn chances will
linger into Wed.

* SEVERE RISK? much depends on positioning of sfc low/warm front

Mixed signals in the models over the past few days on how to move
this system...with a significant bearing on how much of a severe
risk the local area will be under. Farther north with the low -
higher threat for severe weather. Conversely, if it tracks father
south, the risk lowers.

Timing plays a role too. With rain moving in by early Tue morning,
how quickly it can shift northeast could allow for instability to
rebuild behind it...or keep the area "mucked over" for most of the
day, inhibiting the atmosphere`s ability to rebuild CAPE (locally).

Positioning/track also factors in how wind shear will be utilized.
30+ kts of 0-1km progged with a lot of turning would not be realized
as you move north of the warm sector...but 1-7km shear 30-40 kts
would aid convective development.

All said, it`s still unclear how the severe risk will shake out
locally. Expect refinement to the forecast over the next 24
hours...and keep a keen eye on Tue afternoon/evening when the risk
looks highest.

* RAINFALL: how much?

While there remains a fairly large spread in potential outcomes, the
GEFS and EPS tell similar stories with approx 1 to 2" Tue through
Wed night. Latest operational runs of both models are running on the
higher end of their members, leaning more into the 2+ inch range.
The ensemble guidance suggests there is a smaller threat for that to
occur, with approx a 30% shot for that much - and mostly confined to
northeast IA/southwest WI.

The bulk of the rainfall looks to fall in the warm air advective
band Tue afternoon/night, coincident with the PWs of 1 1/4+" and
strong push of low level moisture transport.

* WINDY! Strongest Tuesday

Pressure gradient tightens ahead of the deepening low pressure
system as it shifts northeast out of the southern plains Tue. Strong
signal in all the guidance for strong/gusty winds kicking in Tue
morning, with these strong easterlies persisting into the evening
before shifting northeast of the local area with the approach of the
sfc low. The GEFS is the stronger of the models, the EPS members and
then the NAM bringing up the rear. They all suggest 40+ mph wind
gusts are not only possible/probable - peaking late morning through
the afternoon. Wind Advisory is a possibility if these trends
continue.

Winds subside for later Tue night into Wed morning as the low tracks
across the area, but pick back up from the northwest for the
afternoon as the low exits. Wind fields Wed not as robust as Tue and
shouldn`t be nearly as strong/gusty. Guidance tempers expectations
by 10 to 15 mph off of what they paint for Tue. Not looking like an
Advisory kind of day at this time, but still windy none-the-less.


* REST OF WEEK OUTLOOK: trending cooler (freeze for weekend?), drier

Upper level flow swings a bit more northwest but remain fairly
progressive for the the latter half of the work week, into the
weekend. A few bits of upper level energy could rotate across/near
the region, but no clear-cut signals from the long term guidance
(nor agreement) on timing/positioning. Will let the model blend
dictate any pcpn chances for now (generally 20% or less).

For temps, much cooler air flows in from Canada post the early week
storm system. 850 mb temps peak around +10 C Tue, tumbling to sub
zero by Thu night. Over 75% of both the EPS and GEFS members hold
highs in the 50s from Wed through the weekend. Some potential for
frost/freeze temps by the weekend too. Early season planters should
pay close attention to forecasts - some action may be needed to
protect tender vegetation.


&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1045 PM CDT Sun Apr 14 2024

VFR conditions are expected to continue through the TAF period, with
some mid to high level clouds moving over parts of the area. Light
and variable winds will gradually shift more northeast/east into the
morning. Otherwise, east winds will be on the increase late in the
TAF period and into the day on Tuesday with much gustier conditions
forecast into Tuesday ahead of an incoming low pressure system.

&&

.FIRE WEATHER...
Issued at 325 AM CDT Mon Apr 15 2024

Another relatively dry day with afternoon humidities expected to
bottom out in the lower 20 percents. Winds will be lighter than
previous days though, easterly from 10 to 20 mph with a few higher
gusts into the lower 20s. The higher winds will be across the open
and unsheltered areas west of the Mississippi River. The recent
relatively warm and windy conditions have worked to dry fuels with
FFMCs now in the lower 90s. The diminished wind speeds will help
lower the threat for quick spreading fires, but fuels are conducive
and care should be taken with any outdoor burning.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION.....EMS
FIRE WEATHER...Rieck