####018006815#### FXUS63 KLSX 091945 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 145 PM CST Tue Dec 9 2025 .KEY MESSAGES... - Very windy conditions are expected behind a cold front late tonight through Wednesday morning. Sustained northwest winds of 20- 30 mph with gusts of 35-50 mph are forecast. - Gradually colder and colder temperatures are expected through the weekend, with the coldest period expected Saturday night/Sunday. && .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 145 PM CST Tue Dec 9 2025 A clipper is currently across southeast North Dakota and will progress quickly into the Great Lakes overnight tonight. A cold front draped to its southwest will progress eastward across the mid- Mississippi Valley late tonight/early Wednesday morning. Behind the front, winds will swing to the northwest and increase in speed. Sustained wind speeds of 20-30 mph with gusts in the 35-50 mph range are expected. The highest winds/gusts should be between 0900 and 1800 UTC across eastern Missouri over into Illinois. The 12Z HREF shows 50-70% probabilities for 45+ mph wind gusts (advisory criteria) in this time period, and given the tight pressure gradient and near 50 knots of flow at the top of the mixed layer, went ahead and issued a wind advisory for much of eastern Missouri and our Illinois counties. The pressure gradient relaxes fairly quickly from northwest to southeast during the morning hours on Wednesday, so while it still will be a bit breezy during the afternoon, gusts should drop well below the 45 mph advisory threshold. Strong low-level cold air advection will also lead to colder temperatures on Wednesday compared to today. Temperatures should cool for most locations through much of the morning hours, before leveling off for the most part in the afternoon. Readings in the 30s to low 40s are expected from late morning through the afternoon. Given the strong northwesterly winds, it will feel quite a bit colder than that though. Gosselin && .LONG TERM... (Wednesday Night through Next Tuesday) Issued at 145 PM CST Tue Dec 9 2025 (Wednesday Night - Friday Night) Seasonably cold temperatures and dry weather is forecast Wednesday night and Thursday as a surface ridge of high pressure progresses across the Mississippi Valley. Yet another clipper is expected to move from northwest to southeast Thursday night into early Friday. This system will be further south/southwest, with the track of the low potentially across northern sections of the area. There remains some uncertainty with the track of this system, but most ensembles from the LREF argue for little/no impacts from this clipper in our area like its predecessors this December. Climatology also strongly argues for impacts (i.e., accumulating snow) to stay to our northeast more across north-central Illinois into Indiana. Temperatures will be closely tied to the track/timing of this clipper, but warmer (upper 20s - mid 30s) lows are expected Thursday night ahead of this system, with colder temperatures building back southward behind it. By Friday night, lows in the teens/twenties are expected. (Saturday - Sunday Night) Confidence is increasing in a short, but intense period of anomalous cold for this upcoming weekend. The coldest 24-36 hour period is expected between Saturday night and Sunday night. This is when lows in the single digits/teens are forecast, with highs Sunday only in the teens/twenties. These readings would be about 15-25 degrees below normal for mid December. There is still some uncertainty on exactly HOW cold, as our CWA will be more toward the southwestern edge of the most extreme portion of this air mass. The spread on the inter-quartile range for temperatures from the NBM this weekend is still almost 10 degrees. The deterministic forecast mentioned detailed above though generally sits near the 75th percentile, and I would not be surprised to see both Saturday night's lows and Sunday's highs trend at least toward the 50th percentile of the NBM. This would be potentially knock those values down about 3-5 degrees. If this occurs, we may be looking at our first extreme cold/wind chill products of the season. Probabilities on the LREF for wind chills at or below -10F are in the 30-60% range along/north of I-70 and 10-40% for -15F or colder. Dry weather is favored this weekend. The only chance of snow looks to come Saturday/Saturday night behind the main push of arctic air. Deterministic model guidance depicts some low/mid level frontogenesis combined with a midlevel shortwave trough moving across the Upper Mississippi Valley. Like a broken record, this axis of snow is very likely to setup northeast of our region. The highest probabilities for measurable snow stretch from central Iowa east/southeast across north-central Illinois into Indiana. Probabilities drop further southwest, with only a 20-40% chance for any measurable snow in northeast Missouri and west-central Illinois at this time. (Monday - Next Tuesday) Ensemble guidance is in very good agreement that a quick moderation in temperatures will occur early next week. Mid/upper level heights rise with strong low-level warm air advection commencing in the wake of the departing surface high. Temperatures are forecast to warm back closer to seasonal normals by Tuesday along with dry weather also being favored. Gosselin && .AVIATION... (For the 18z TAFs through 18z Wednesday Afternoon) Issued at 1111 AM CST Tue Dec 9 2025 South/southwest winds will veer more to the west ahead of an approaching cold front. Behind the front, winds swing to the northwest and increase in speed/gusts. Highest gusts of near 40 knots are forecast Wednesday morning at KUIN and the metro terminals. There may be a period of MVFR stratus at well impacting KUIN, but chances are higher further to the north/northeast so left mention out for now. Gosselin && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Wind Advisory from 3 AM to noon CST Wednesday for Franklin MO- Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Marion MO-Monroe MO-Pike MO-Ralls MO-Saint Charles MO-Saint Louis City MO- Saint Louis MO-Shelby MO-Warren MO. IL...Wind Advisory from 3 AM to noon CST Wednesday for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL- Jersey IL-Macoupin IL-Madison IL-Monroe IL-Montgomery IL- Pike IL-Saint Clair IL. && $$ WFO LSX