Expires:No;;873147 FXUS63 KLSX 061731 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1231 PM CDT Sun Apr 6 2025 .KEY MESSAGES... - Scattered to numerous light showers will persist through the day ending gradually from northwest to southeast. Some snowflakes and sleet pellets could mix in this morning with little to no accumulation. - A freeze (<32 F) is expected tonight/Monday morning generally west of the Mississippi River, followed by a widespread freeze to hard freeze (<28 F) Monday night/Tuesday morning. Below average temperatures will moderate during mid-week. && .SHORT TERM... (Through Late Monday Afternoon) Issued at 312 AM CDT Sun Apr 6 2025 Bouts of mid-level frontogenesis associated with passing fragments of an upper-level trough across the Southern Plains "shearing out", will continue to result in scattered to numerous light showers at times this morning through afternoon. Cooling of temperatures into the mid and upper 30s F and low wetbulb zero heights could result in some snowflakes and sleet pellets mixing in across portions of central, south-central, and southeastern MO this morning, but little, if any, accumulation is forecast and impacts are unlikely. Transport of increasingly dry air upon low-level northerly flow will undercut this precipitation through the day, providing a gradual end from northwest to southeast, ending altogether this evening as large- scale forcing also shifts eastward. The cool airmass in place and clouds and light precipitation will keep temperatures once again from warming beyond the 40s to low-50s F, 10 to 20 F below average for early April. Clouds will clear tonight allowing some weak radiational cooling of the airmass with a subtle surface pressure ridge passing through the Mid-Mississippi River Valley. Accordingly, NBM probabilities of temperatures below 32 F late tonight/Monday morning are highest at 60 to 80 percent across northeastern, central, east-central, and southeastern MO, where a Freeze Warning is now in effect for impacts to sensitive spring plants. Elsewhere, temperatures are still anticipated to fall into at least the mid-30s F, but it is uncertain if winds will become light enough for widespread frost development. On Monday, upper-level northwesterly flow will ensue as today's upper-level trough migrates eastward and another, more potent trough traverses the Great Lakes. An associated cold front will pass southward through the CWA on Monday, leading to high temperatures varying from the 60s F across southeastern MO to the 50s F elsewhere, with strong low-level CAA arriving much sooner. With limited moisture and low-level moisture convergence along the front less than 20 percent of HREF membership has any precipitation along the front, suggesting dry conditions are most likely. Pfahler && .LONG TERM... (Monday Night through Saturday) Issued at 312 AM CDT Sun Apr 6 2025 Strong CAA during Monday evening and efficient radiational cooling with arrival of a surface high pressure center will be favorable for a widespread freeze across the entire CWA Monday night/Tuesday morning with 70 to 100 percent probabilities of temperatures below 32 F in the NBM. Probabilities of temperatures below 28 F, constituting a hard freeze, are also 60 to 90 percent in much of the CWA outside of urbanized locations. Therefore, sensitive plants could be killed and other seasonable plants could be damaged in these conditions with a Freeze Watch now in effect for the period. As upper-level longwave troughing shifts eastward from the Great Lakes to Northeast, northwesterly flow will persist, but migration of the surface pressure ridge to the east and a gradual northeastward lift of a warm front will result in increasing WAA and a moderation of temperatures to average or above average by Wednesday. Exact temperatures are uncertain, captured by 10 F NBM interquartile ranges, due variations in the position of the front as well as the track and amplitude of the next trough navigating northwesterly flow Wednesday through Thursday. This trough will provide the next opportunity for showers and a few thunderstorms to the Mid-Mississippi River Valley. The greatest probability of measurable rainfall (over 70 percent in 24 hours) is located generally along/east of the Mississippi River Valley late Wednesday into Thursday. However, limited moisture return and progressive nature of the trough yields ensemble model membership with rainfall less than 0.50" with most closer to 0.10". Behind the trough and associated cold front, CAA is not expected to be long-lasting, with temperatures cooling briefly on Friday and then warming again into next weekend. Pfahler && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1225 PM CDT Sun Apr 6 2025 Light precipitation continues to move southeast of the region with the departing system. Drying trends are expected to continue, favoring cloud bases remaining above MVFR despite lingering broken/overcast conditions. Skies break and clear late this evening heading into Monday. A cold front drops north to south Monday, shifting surface winds out of the north and northwest. Nocturnal periods will see winds become light and variable, while diurnal mixing supports sustained wind at 10-15 knots through the daylight hours. Maples && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Freeze Watch from late Monday night through Tuesday morning 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. Freeze Warning from 4 AM to 9 AM CDT Monday for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO- Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO- Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Francois MO-Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO. IL...Freeze Watch from late Monday night through Tuesday morning 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 IL- Washington IL. && $$ WFO LSX