Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/15/23

Area Forecast Discussion

National Weather Service La Crosse WI

 955 PM CDT Fri Jul 14 2023

.DISCUSSION...(This evening through Friday)
Issued at 234 PM CDT Fri Jul 14 2023

Key Messages:

 - Wildfire smoke returns to the area.

 - More storm chances into the evening.

 - Periodic rain chances to continue well into next week.

Weekend Smoke and Air Quality:

GOES East Visible satellite imagery shows broad area of thick,
gray particulate matter (i.e., smoke) from southeast Minnesota and
western Wisconsin to smoke sources in western Canada. Upper level
water vapor imagery exhibits an upstream upper level ridge,
subsiding the thick smoke towards the surface. Resultant surface
observations from the Northern Plains into Montana exhibit
reduction in visibilities to 1-5 SM and haze/smoke in weather
sensor. Therefore, Air Quality Advisories have been issued for
Wisconsin and Minnesota from respective state`s DNRs where higher
confidence for advection from northwest to southeast through
Saturday. The respective Advisories highlight impacts to sensitive
groups in the "orange" category. Therefore, have continued
mention in weather grids through much of the weekend. While both
high resolution smoke models show reduction in surface PM 2.5
concentrations (~35 ug/m3) early Saturday morning, another
upstream punch above 60 ug/m3 possible through Saturday afternoon.
Something to keep an eye on if concentrations that increased do
make it to the surface.

Storm Chances and Setup For This Afternoon:

Similar mesoscale setup today as yesterday with moist low level
air mass in place with slightly drier air off the deck. Today`s
result has been decreased coverage in storms, comparatively, as
the drier air has reduced surface dewpoint temperatures from low
70s to mid to low 60s. The decrease in instability and increase in
inhibition evident in ACARS aircraft soundings at Minneapolis St
Paul Int`l Airport (KMSP) this morning into the early afternoon
with 200-400 J/kg MLCIN and only 25-75 J/kg SBCIN. Similar to
yesterday, minimal, nebulous surface convergence limiting any
forcing mechanism. With any auto convection extremely hampered by
the aforementioned drier air.

Initial showers along the Iowa/Minnesota border advecting from
west to east through the early afternoon initialized near
northwest Iowa in better convergence. As previously mentioned,
limited confidence for isolated to scattered storm potential early
this afternoon. Later this afternoon, better forcing, from a
perturbation evident in water vapor imagery reaching west central
Minnesota this afternoon, expected to advect through southeast
Minnesota into northeast Iowa and western Wisconsin.

Storm Chances Increasing This Evening, Cooler For Saturday:

Timing of forcing, reaching convective temperatures to overcome
aforementioned dry air & low level warm nose inversion, and
stabilizing of mid level lapse rates decrease strength of storms
as they advect in the area. While the plume of higher instability
(2000 J/kg) pushes into central Wisconsin, loss of diurnal heating
decreases instability along frontal forcing, 500-1000 J/kg, as it
reaches our northwestern periphery in southeast Minnesota. Not
expected to access the 0-1km shear of 20 knots, which is the same
as 0-3km shear, given elevated nature of storms. Given the low
level dry air, strong wind gusts most possible hazard, but again,
limited chances for stronger storms. Given low shear, single cells
bunching along the frontal boundary and dissipating strength with
southeasterly advection, initially around near 7pm along our
northwestern periphery of Dodge to Buffalo counties.

Slightly cooler temperatures expected for Saturday as the low
level cold front and upper level trough axis passes over the
forecast area. Other than the increased Haze and Smoke
probabilities, have continued slight storm and rain chances with
minute low to mid level instability and daytime mixing.

Saturday night through Monday...

The upper level currently near Hudsons Bay is forecast to sink
south toward the northern Great Lakes over the weekend with the
14.00Z ECMWF suggesting it could sink a little farther south
across the Upper Midwest. Either way, short wave troughs will
continue to rotate around the upper level low and swing over the
region to provide some forcing for additional shower and storm
development. The most widespread coverage continues to look to be
off the east of the local area with the main baroclinic zone
extending from the Eastern Great Lakes south through the Ohio
River Valley. Without a discernible boundary to help focus
development over the local region, expect any showers and storms
that develop to remain scattered in coverage. The exception to
this may be on Sunday if the farther south solution of the ECMWF
comes to fruition there could be more widespread coverage of
showers and storms. In this overall pattern, the instability looks
to be pretty minimal leading to an overall very low severe
weather threat.

Tuesday into Thursday...

Weak upper level ridging is still expected to be over the Midwest
Tuesday between the departing upper level low over the Great
Lakes and the next incoming system across southern Canada. With
the ridge look fairly flat, this next system will not take long to
bring the rain chances back to the area. Short wave troughs from
this low look to start bringing in some forcing Tuesday night with
the upper level low itself then tracking across the Upper Midwest
Wednesday into Thursday, although in a weakening trend as it
becomes an open wave. Again, not a lot of instability is expected
to be in place with just enough to support general thunder at
times.

Temperatures through next week look to remain seasonable with
highs in the 70s and 80s. No heat waves are suggested with
extremely low probabilities of reaching 90 degrees from the Grand
Ensemble data.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 955 PM CDT Fri Jul 14 2023

VFR conditions are expected through mid-morning with sct high clouds
and light winds expected. Both the HRRR and RAP vertically
integrated smoke fields have a signal for increased surface smoke
coming in during the mid-morning which given 5-6SM visibilities in
the Dakotas seen from this airmass today, will possibly see MVFR
visibilities throughout much of the day Saturday. Winds will
increase slightly from the west/northwest at RST to 10-15 knots with
gusts to as much as 20 knots. Some short-range guidance wants to
have some slight indication for a couple showers and storms tomorrow
afternoon associated with a weak shortwave but confidence is low as
to if this will occur. Visibilities should improve to VFR as surface
smoke concentrations improve late tomorrow.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

DISCUSSION...04/JAR
AVIATION.....Naylor