006
FXUS63 KARX 071940
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
240 PM CDT Fri Jun 7 2024

.KEY MESSAGES...

- Rain likely across much of the area (50-90% chance) overnight
  and into Saturday morning. Rain chances (50-70%) have
  increased across portions of northeast IA and southwestern WI.

- Below normal temperatures expected this weekend and early next
  week. An isolated shower or two are possible late Saturday and
  Sunday (10-20% chance).

- Warming trend is expected with temperatures trending above
  normal by the second half of next week. Highs will reach well
  into the 80s for much of the local area.

&&

.DISCUSSION...
Issued at 240 PM CDT Fri Jun 7 2024

Tonight - Saturday: Rain Likely Overnight, Isolated Thunder Possible

Current surface analysis shows low pressure centered over the pan
handle of Nebraska with southerly flow advecting moisture north in a
somewhat narrow ribbon 3/4ers the width of the state. The 60F
dewpoint line has rapidly shot north to near I-80 with radar showing
elevated /10ft/ showers and storms across SD into nwrn IA early this
afternoon. This area is associated with a strong area of 600-700mb
frontogenesis within the MuCAPE gradient of 250-750 J/Kg per SPC,
with the heart of the MUCAPE pool further southwest over wrn NE/CO.
Per latest RAP guidance, this elevated forcing /fgen/ translates
east today in swift zonal flow, grazing northeast IA closer to I-35
early this evening, however without the elevated instability /which
spreads in late tonight/. With the low-level ridging and dry air
mass holding firm across the Upper Miss Valley, would think this
will translate into thick clouds at 10kft and scattered very light
showers or sprinkles.

GOES water vapor showing a well-formed shortwave trough in northwest
flow dropping southeast through srn Saska/Alberta at 18Z. Short term
model consensus has moderate 300-500mb QVector convergence along and
north of I-90 Saturday morning with moderate isentropic lift through
the low-levels as well with this wave. As the low-level southwest
flow increases late tonight as the ridge axis pushes east, low
MUCAPE instability /100-300 J/Kg/ does shift in near and south of I-
90, and is speed convergent, isentropically upgliding. Have a hard
time believing showers would not be present south of I-90 with
isolated thunder too after about 3 am. At that same time, a cold
front with the northwest flow trough is heading through MN, moving
through the area Saturday morning into very early Saturday
afternoon. This will act to prolong the period of showers Saturday
and there is some timing spread among the CAMS. So, forecast will
paint a little bit bigger window than may actually occur and
hopefully timing can be refined in the next 12 hours. So, continued
very high rain chances near and I-90 and north late tonight into
Saturday, and increased them southward into northeast IA and
southwest WI /60%/...with clearing trying to work in post-frontal in
the afternoon from NW->SE.

Saturday Night - Monday: Cool, Slight Shower Chances

Heading through the rest of the weekend, temperatures will continue
to remain on the cooler side of average with highs consistently
shown in guidance to remain in the upper 60s and lower 70s areawide,
roughly around 5-10 degrees below normal. Monday will likely be
the coolest day with the 07.00z grand ensemble (GEFS/EC
ens/Canadian ens) showing an inter-quartile range of 66 to 72
degrees for highs at La Crosse with a median of 70 degrees. A
few showers and storms are possible late Saturday and Sunday
with continued cyclonic flow in place allowing for cooler air
aloft enabling some diurnal instability. However, this is fairly
inconsistent between different CAMs runs so will hold with
lower precipitation chances (10-20%) for now.

Tuesday - Friday: Warming Trend, Shower/Storm Chances

As we approach the middle of next week, deterministic guidance shows
a weak shortwave trough progressing towards our region. While
deterministic guidance has come into some more agreement on how this
trough will manifest, still lots of questions with available
moisture and any instability associated with it. Consequently,
confidence still remains not the highest with the 07.06z GEFS
showing around 50-70% chance for measurable precipitation with this
wave. As a result, have some increase in precipitation chances
(20-40% chance) with the recent NBM for Tuesday but will still
need to assess, either way would likely be very light amounts
and have minimal thunder chances.

Otherwise, the other story for next week, mainly into Wednesday is
an upper-level ridge will progress east and flatten as it inches its
way into our region. While this will help warm temperatures some,
northwest flow appears to maintain through the period which should
keep temperatures from trending well above normal when also
considering the 07.00z EFI shows minimal signal for
significantly above normal temperatures. Consequently, expecting
highs to get as warm as the middle to upper 80s, perhaps a 90
in a few spots. Thursday currently appears to be the warmest day
next work week with the NBM percentiles showing an inter-
quartile range of 84 to 91 degrees with a median of 87 degrees.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 100 PM CDT Fri Jun 7 2024

Moisture will be on the increase overnight with probabilities
will increase toward sunrise for some flight restrictions. A
weather system moving in from the northwest will provide
widespread rain showers later tonight and Saturday morning. It
looks like visibilities should remain VFR except small periods
of time where more intense rainfall cores may hit the airfields.
However, the ceiling probabilities increase rapidly for either
MVFR or IFR ceilings after 11Z. NBM guidance suggests IFR would
be reached at RST by 14Z, with MVFR guaranteed. Probabilities
are more favorable for lower MVFR at LSE after 11Z per the NBM
guidance.

For this TAF cycle, have decided to play a bit more conservative
with MVFR ceilings at both sites during the morning. Probabilities
for IFR will be monitored in future forecasts as there is some
chance of that occurring /25%/ at KRST. Moisture is increasing
across the area versus the dry air in place, however confidence
is a bit lower on the degree and depth to the saturation.

&&

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

&&

$$

DISCUSSION...Baumgardt/Naylor
AVIATION...Baumgardt