166
FXUS63 KARX 172352
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
652 PM CDT Wed Jul 17 2024

.KEY MESSAGES...

- Quiet and comfortable weather for the next week with slowly
  rising temperatures to near normal /80-85F/ by the weekend
  into next week.

- Rivers will get some much needed time to fall areawide with
  little rainfall runoff expected through the middle of next
  week.

&&

.DISCUSSION...
Issued at 118 PM CDT Wed Jul 17 2024

The large scale pattern over North America will stay nearly
steady over the next week under an Omega block over the eastern
Pacific and North America per Grand Ensemble forecasts. The
area will remain under north-northwest flow which will keep
temperatures below or near normal. With some cool air aloft and
mild instability, chances of afternoon showers or a storm begin
Saturday.

GOES water vapor imagery is showing shortwave trough energy
rotating through the U.P. of Michigan and northern WI as of 18Z,
bringing broken skies and cooler than forecast temperatures in
north central WI. Ridging will build in overnight and dominate
Thursday and Friday. Some fog is possible tonight along the WI
river and possibly into northcentral WI with cooler highs
observed today and clearing expected.

Another weak weather impulse in the northwest flow "generally"
phases with the remnants of the low currently over the Pacific
NW for late week. GOES water vapor has an impressive low lifting
north through OR/WA at this time...which has a well-agreed on
guidance track over the ridge position and into the northcentral
U.S. This carves out a weak, broad trough position over WI into
the deeper low center over western IA/swrn MN. This will
promote afternoon showers centered on that trough axis beginning
Saturday as the surface ridge weakens and shifts east, lasting
through Wednesday. Instability is modest with MLCAPE of 300-750
J/Kg. Would expect much of the area to remain dry in the
afternoons with clouds increasing with heating. Precipitable
water values are about normal for mid-July at 1.25" suggesting
normal rainfall intensity. Runoff should be minimal over the
week allowing rivers to fall.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 640 PM CDT Wed Jul 17 2024

Surface high pressure builds in tonight with diminishing winds.
850mb moisture is in place, but clouds should continue to
decrease diurnally tonight and increase with heating Thursday.
Some mixed signals for fog with the GFSlamp data showing patchy
fog around RST and some low dewpoint depressions at KLSE per NAM
forecast soundings with the RAP/HRRR forecast soundings still a
bit dry. The NBH guidance trend has been stable over the last
several runs with low; <5% for IFR conditions at KLSE. Could be
some patchy fog in the river valleys with the light winds, but
confidence too low to mention in TAFs at this time. Winds will
remain light from the north or northwest.

&&

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

&&

$$

DISCUSSION...Baumgardt
AVIATION...Zapotocny