508 
FXUS63 KARX 170904
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
404 AM CDT Thu Aug 17 2023

.DISCUSSION...(Today through Wednesday)
Issued at 342 AM CDT Thu Aug 17 2023

Key Messages:

 - Air Quality Advisories for Counties in Minnesota and Wisconsin
   from Canadian Wildfire Smoke Resulting in Increased 
   Particulate Matter.

 - Departing Trough Results in Cooler, Breezy Conditions with
   Chances for Sprinkles.

 - Warming Through the Weekend and Into the New Week.

Smoke/Particulate Matter & Air Quality Advisories:

Smoke/PM 2.5 expected to return primarily west of the Mississippi
River from southeast Minnesota into northeast Iowa and western 
Wisconsin this afternoon, according to high resolution smoke 
models (HRRR 17.06Z; RAP 17.03Z). Overnight observations keep 
visibility reductions and increased impacts well to the northwest 
near the Rocky Mountain west. But as the trough exits this 
morning, with strong cold air advecting northwesterly flow increasing
winds, smoke expected to quickly dive through Minnesota today. 
Accordingly, state agencies in Minnesota and Wisconsin have issued
Air Quality Advisories for decreased Air Quality.

Lingering Trough Impacts Today:

As the upper level trough exits over the Great Lakes early this 
morning on Water Vapor imagery, upstream surface observations depict 
a large area of anticyclonic flow from the Central Plains into the 
Rocky Mountain West. But, before we can fully bid adieu to said 
departing trough, lingering impacts are expected through tonight. 
Firstly, maximum daytime temperatures are expected to be a few 
degrees below normal from the low level cold air advection. Cold 
air advection will also steepen low level lapse rates, resulting 
in increased winds gusting near 30 mph at times. Thirdly, 
finally, sprinkles will possible with CAA saturating lower levels 
according to high resolution guidance (ARW 17.00Z; RAP 17.03Z; 
HRRR 17.05Z). 

Tonight into Friday morning, lower level winds expected to wane
within the River Valleys. This, combined with aforementioned cooler
temperatures, will likely result in fog formation. Have continued
valley fog for Mississippi River Valley, its associated 
tributaries, and Wisconsin River Valley. Increased low level wind 
profile expected to sustain further east into central Wisconsin 
and therefore have not introduced fog. Although, overnight 
temperatures in this classically cold spot expected to drop into 
the 40s.

Warming Up This Weekend & Next Week:

Reminiscent of the early summer pattern, long term ensembles 
agree on the aforementioned anticyclonic flow returning this 
weekend and mid level heights building into next week. Local 
impacts will be reminiscent of aforementioned early summer 
weather: hotter and drier. Cluster analysis (17.00Z) contains 
unanimous agreement for synoptic higher heights closed over 
Central Plains near 600 dam at times. Ensembles (EPS 17.00Z; CMCE 
17.00Z; GEFS 17.00Z) do disagree on impacts, bifurcating the 
forecast area with quite bullish probabilities (80-100%) for 90+ 
temperatures this weekend into the mid next week.

In one camp are the CMCE and GEFS, exhibiting high (70-100%) 
confidence for maximum daytime temperatures in the 90s as early as
Saturday, primarily west of the Mississippi River. dProg/dT of 
these models contain consistency for higher confidence regarding
the weekend, degrading into the new week. Wavering of the highest
(70-100%) probabilities farther northeast and southwest places 
the local forecast area along the periphery in these select 
ensemble runs. Whereas, the EPS contains meager (10-40%) 
confidence for the 90 degree isotherm reaching the local forecast 
through the new week. However, dProg/dT for the EPS has been
increasing confidence over a larger area over the last 4 runs,
closer and closer to the local area. Have continued with National
Blend with the current forecast, exhibiting anomalous maximum 
daytime temperatures for Sunday and Monday, 90th percentile 
according to Model Certainty, although remains consistent with 
previous forecasts.

All in all, anomalously warm temperatures expected through the new 
week. EC Shift of Tails suggests a "unusual event" is likely from 
Sunday through Wednesday. Shift of Tails values greater than zero 
during that time are evidence of at least 10% of the EPS members lie
above the 99th percentile of the model climate. NAEFS/EPS 
standardized anomalies 2-3.3 standardized anomalies above model 
climate are in the maximum percentile for the same time period. In
other words, high confidence for an anomalously warm period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1052 PM CDT Wed Aug 16 2023

A shower/storm may impact KLSE near the beginning of the TAF
period, but coverage this evening has been quite scattered, so
confidence in thunder is low (20%). Otherwise, winds will shift 
NW and gust up to 25 kts on Thursday. A SCT/BKN cumulus field will
rotate across the region on Thursday, mostly VFR, but MVFR 
conditions could not be ruled out briefly for a time on Thursday 
morning. Winds will subside Thursday evening. Wildfire smoke is 
expected to impact the area by later afternoon. Did introduce 
smoke at KRST, but confidence in visibility is lower at this time.


&&

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

$$

DISCUSSION...JAR
AVIATION...JM