702 FXUS63 KLSX 161947 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 247 PM CDT Sun Oct 16 2022 .SHORT TERM... (Through Late Monday Night) Issued at 236 PM CDT Sun Oct 16 2022 Attention will be on the rather brief, but deep cold spill that is already underway. There is high confidence that a widespread hard freeze will occur Monday night into early Tuesday. Regional surface analysis initially showed a stationary boundary stretching from the vicinity of the TN/KY border, westward through northern AR. Thicker cloud cover remnant of active weather aligns in the general vicinity of the boundary with a few mid to high clouds extending north along I-70. A strong cold front is pushing through the forecast area from north to south, extending across the southern section of the CWA just before 20z this afternoon. Surface flow has turned out of the northwest behind the front, marking the onset of cold air advection that will continue tonight into Monday. Though today's diurnal heating potential was capped by the initial arrival of the surface front, the core of the cold air remains poised to move in on the north-to-south push within the mid-level flow late this evening into the overnight period. This will be supported by the deepening surface low over the Great Lakes Region in conjunction with a surface high building into the northern plains. Tonight's lows will be chilly with some area dropping below freezing, mainly over central and northeast Missouri. However, after collaborating with surrounding offices, it was decides to refrain from frost freeze headlines with many of these areas already hitting similar temperatures back on October 8th and multiple other nights near or just below freezing. By Monday, standardized height anomalies show height falls over the Great Lakes will peak between 3-4 standard deviations below normal, while height rises will reach 2-3 standard deviations above normal just west of the Hudson Bay during the day Monday. The anomalous tandem will act to jettison cold air southward, incorporating negative 15-20C at 850mb. Though it will moderate some by the time it reaches the mid-Mississippi Valley, it will spread negative 8-10C air across the entire forecast air with the 0C isotherm (2+ standard deviation below normal) reaching near the Gulf Coast by Tuesday morning, signaling just how strong this cold push will be. The cold air will take hold with highs struggling to reach 50 degrees and that's considering the warmest portions of the forecast area south of I-70. There is high confidence in a widespread hard freeze Monday night, strengthened by ensemble data with individual members clustering around the 50th percentile with lows in the 20s. The past couple forecast cycles had NBM/NDFD forecasts generally been plotting in the 75th-90th percentile with overnight temperatures hovering around the 90th percentile. This suggests that we may still be a few degrees too warm. Therefore, updates have been blended with 50th percentile to nudge temperatures slightly colder. Provided the high confidence forecast, the freeze watch was upgraded to a freeze warning Monday night into Tuesday morning. Maples .LONG TERM... (Tuesday through Next Sunday) Issued at 236 PM CDT Sun Oct 16 2022 Near-record cold will lead off the extended period. Temperatures begin to moderate through midweek before more substantial warmth returns later in the week. A longwave upper trough will dominate the pattern over the eastern U.S., while upper level ridging extends northward through the Intermountain West. This supports the continued northerly feed throughout the Mississippi Valley with anomalously cold air remaining in place Tuesday into Tuesday night. Surface high pressure elongates southward just west of the Mississippi River with northerly flow persisting through MO/IL. The mid-level airmass only warms by a couple of degrees with negative 5-8C being fairly representative across the forecast area. Temperatures will remain 15- 20 degrees below normal with highs largely in the 40s and lows in the 20s. A few of the normally colder locations will likely see upper teens Wednesday morning with a second straight night of widespread freezing temperatures. Though Wednesday will remain well below normal, it will mark the beginning of a moderating trend. The upper level low over the eastern U.S. begins to shift slightly east as surface high pressure shift into the southern Plains and gulf states. Surface to mid-level flow begins to turn westerly but may only do so later in the day. This allows cooler air to hang on with highs getting around a 3-5 degree boost. There is a weak upper level shortwave that quickly pushes north to south down the western side of the eastern trough late Wednesday. However, it looks to pass over unnoticed with little more than a temporary mid-level wind shift. A pattern shift occurs Thursday through the end of the period. The eastern CONUS upper low moves north and broadens over the Hudson Bay as the western ridge flattens with the arrival of another system along the coast of British Columbia. Thursday's north/northwesterly upper level flow gradually turns westerly Friday and eventually southwesterly heading into the weekend. The more sensible change will be supported by surface/mid-level ridge that builds from the northern gulf through the mid-Atlantic. Southwesterly flow strengthens around the northern periphery of this ridge Thursday through Saturday, feeding 15-20C air northeast out of the southern plains. Though there is some spread in the ensembles this far out, a majority of the member support 70s over parts of the are Friday. By Saturday and Sunday 70s are favored over much of the region with few ensemble members hinting at low-80s. Rainfall still looks to be at a premium with any potential coming late next weekend, if not early next week. An upper level trough deepens over the west and moves into the plains, potential giving rise to a surface low on the lee side of the Rockies. With plenty of time to go, far too much can change to have much confidence in how this plays out with regard to any beneficial moisture. Maples && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1240 PM CDT Sun Oct 16 2022 VFR conditions are expected to extend through the end of this TAF cycle. Thicker mid to high clouds run along a stationary boundary well to the south (AR/TN/KY) of all terminals. A few mid-level clouds over northern MO continue to erode as they encounter dry air. Provided the sunshine between the two, deeper mixing will result in an occasional afternoon gusts. Northwesterly winds will be sustained between 5 and 10 knots tonight with a better potential for gusts from mid-morning Monday through the afternoon period. Maples && .CLIMATE... Issued at 215 PM CDT Sat Oct 15 2022 MON TUE WED 17 18 19 STL-- LOW MAX 49(1976) 42(1880) 42(1989) LOW MIN 29(1943) 27(1976) 25(1972) COU-- LOW MAX 48(1976) 38(1898) 41(1930) LOW MIN 26(1976) 25(1952) 22(1972) UIN-- LOW MAX 46(1989) 45(1989) 41(1989) LOW MIN 27(1943) 24(1948) 20(1972) && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Freeze Warning from 9 PM Monday to 9 AM CDT Tuesday for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO- Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO- Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO- Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO. IL...Freeze Warning from 9 PM Monday to 9 AM CDT Tuesday for Adams IL- Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL- Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL- Montgomery IL-Pike IL-Randolph IL-Saint Clair-Washington IL. && $$ WFO LSX