527
FXUS63 KARX 131152
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
652 AM CDT Mon May 13 2024

.KEY MESSAGES...

- Wildfire smoke impacts continue this morning, with hazy/milky
skies persisting into Tue

- Rain chances across the far south today, but most locations will
stay dry

- Next rain chances move in Wed night/Thu with unsettled pattern
into the weekend

&&

.DISCUSSION...
Issued at 220 AM CDT Mon May 13 2024

* SMOKE: improving this morning, more milky skies possible Tue

The HRRR and RAP show improvement through the morning in near sfc
concentrations. Vsbys per latest sfc obs are mostly very good with
6+ miles with just some spotty 3-5SM. Air Quality Alerts continue
for MN and much of WI this morning.

The RAP sinks more smoke from Canadian forest fires southward across
the region tonight/Tue, but holds most of this a loft (above 8 kft).
Near sfc smoke impacts are favored to hold well west. This suggests a
milky sky for Tue but likely less impacts in sfc air quality.


* RAIN CHANCES TODAY? Trending southward...

Churning upper level trough/low was trekking slowly east across the
southern plains early this morning. Spiraling bands rotating
counterclockwise around the trough were interacting with a west-east
running cold front that was easing southward across the local area
(extending from the MN/IA border into northeast WI at early
morning). Areas of showers and a few storms was the result, the bulk
of which were located over IA. Track of the upper level trough,
coupled with where the moisture transport/instability pool is progged
to layout, suggests the bulk of the continued rain chances will hold
across IA and northern IL, but northern fringes could spread into
farther southern WI. There has been a trend pulling the rain chances
farther south over the past couple days, and meso models continue
this.


* WED NIGHT/THU: rain chances, but how widespread?

The long range guidance continues to suggest a shortwave trough in
the northern portion of the flow will shift across the northern
plains eastward over the upper mississippi river valley Wed night into
Thu. Meanwhile, a piece of the energy in the southern portion of the
flow looks to kick out of the southern plains and across the mid
mississippi river valley during this time. Do these shortwaves merge
in this split flow scenario? Stay separate? The GEFS members favor
keeping them separate. Rain chances would then have to rely heavily
on moisture transport, instability ahead of an associated sfc front.
The EPS, on the otherhand, is a bit more stout with the northern
stream shortwave, dropping it farther south...thus producing a bit
more QPF and higher probabilities to get wet regionwide. Not clear on
how this will shake out, but the models have been consistent in
producing at least scattered showers/storms for this period...and
model blend continues to produce chance to low end likelies (30-60%)
for rain potential. Will stick with that for now.


* END OF THE WORK WEEK/WEEKEND: more rain chances, uncertainties on
  when/where

Progressive upper level flow persists for the end of the week with
the GEFS and EPS promising quick moving shortwave ridges/troughs.
Timing, location differences crop up (not unexpected), lowering
confidence considerably on the resulting sensible weather
outcomes. As it has the past few days, the differences in the
ensemble members of each model suite cause the NBM (model blend) to
spread out rain chances over several days - which in reality would
likely be focused to smaller periods. Will hold with the blend which
has low end pops (20-30%) through the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 626 AM CDT Mon May 13 2024

MVFR visibilities from haze and associated wildfire smoke
extends in an east-west line from the Iowa-Minnesota border
through western Wisconsin and north into central Wisconsin.
Remains a challenging detail as a weak low pressure sags
southeast through northern Wisconsin at 13.12Z TAF issuance. The
associated weak cold front aligns with the aforementioned MVFR
visibilities. Given a lack of sinking air (subsidence--high
pressure) as well as daytime heating expected to push this
colder air back north, expect VFR to return at both TAF sites
(KLSE & KRST) through the early morning hours. The smoke gets
pulled apart along this boundary from southeast Minnesota into
western Wisconsin into the early afternoon, decreasing total
particulates throughout the atmosphere and overall coverage.

High pressure eventually exerts influence later today into
tonight, turning winds clockwise (anticyclonically) out of
east-northeast overnight. Therefore, given ongoing upstream
wildfires, smoke and haze are expected to be more widespread.
Have increased ceilings as model consensus suspected to not be
picking up on upper level smoke. Haven`t introduced visibility
restrictions as most likely after this TAF (13.12Z) period. Will
be an important forecast detail.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Air Quality Alert until noon CDT today for MNZ079-086>088-
     094>096.
IA...None.

&&

$$

DISCUSSION...Rieck
AVIATION...JAR