426 FXUS63 KLSX 302350 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 650 PM CDT Wed Oct 30 2019 .SHORT TERM... (Through Late Thursday Night) Issued at 336 PM CDT Wed Oct 30 2019 This is a complex forecast over the next 12 -18 hours across the area. The expectation is for light rain to breakout by early this evening as a midlevel disturbance ejects eastward out of the lee of the Rockies. The precipitation will eventually changeover to snow from northwest to southeast overnight into early Thursday morning as the temperature profile rapidly cools in the 700-800 hPa layer. However, there likely will be at least a brief period of time where there is a lack of cloud ice nuclei aloft and surface temperatures drop below freezing. This situation would produce light freezing rain, with a light glaze expected. This is most likely this evening across portions of northeast Missouri where upstream infrared satellite imagery depicts cloud top temperatures mostly in the -5 to -10C range. These cloud top temperatures likely will not be cold enough to support the introduction of ice. The light snow should wind down late tonight and into the early morning hours with lingering flurries possible for several hours. Snowfall accumulations will take place mostly across the northwestern third of the CWA with the heaviest accumulations (1-3") from near Kirksville ENE toward Canton. Have issued a winter weather advisory for these locations as there is expected to be several hours of light snow falling with temperatures falling through the upper 20s. Therefore, travel conditions may deteriorate as road temperatures fall toward the freezing mark. The other story is the anomalously cold conditions. Widespread near or below freezing temperatures are expected tonight so no changes made to tonight's freeze warning. Temperatures through midday will likely remain steady, with only a slight rebound in the afternoon. Highs should only be in the mid to upper 30s, which is about 25-30 degrees below normal! In fact, all three of our climate sites are likely to break daily record low maximum temperatures for Halloween. Please see the CLIMATE section for more details. A clearing sky will greet the region late Thursday afternoon into the evening hours from west to east. A surface ridge will quickly slide southeastward across the area into the mid south and Ohio Valley. Southwesterly return flow around this surface ridge will act to help keep temperatures up a bit, with steadying or even slowly rising temperatures late Friday night for parts of the area. Consequently, raised low temperatures a few degrees for northwestern sections of the forecast area. That being said, very cold temperatures are still forecast areawide. Lows should range from the mid to upper 20s across the bi-state area. Gosselin .LONG TERM... (Friday through Next Wednesday) Issued at 336 PM CDT Wed Oct 30 2019 A broad long wave trof will dominate much of NOAM during this period. Short waves of varying intensity translating across the region within the mean long wave trof will be responsible for several frontal passages and any precipitation threat along with helping modulate temperatures. We are in between short waves on Friday in the wake of Thursday's departing trof and just in advance of the next prominent trof. Low level WAA will be in full force in the wake of the retreating surface high pressure system and this along with an initial lack of clouds should allow for much warmer temperatures than Thursday's chill. Still highs will remain below normal for the beginning of November. This upstream short wave trof will then amplify and dig into the Mississippi Valley Friday night into early Saturday driving a cold front through the region. The cold front itself will bring a reinforcing shot of cold air and keep temperatures well below normal. Any real question with this system is the potential for any post-frontal precipitation. The NAM is the sole model showing any potential into our CWA with the southern edge of a post-frontal band clipping northeast MO and west central IL between 06-12z Saturday. This band would be the result of low-mid level frontogenetic forcing and weak large scale forcing associated with the digging upper trof, and thermal profiles on the NAM would suggest largely snow. If this occurs it looks like a quick round with very minor accumulations less than an inch. The good news is that all of the other deterministic guidance and SREF and GEFS suggest this precipitation will remain north of the CWA, and that is the course of the current forecast. Otherwise brisk northwest winds and typical post-frontal stratus/stratocu is expected to accompany the front. Fast cyclonic upper flow accompanying the broad long wave trof will keep things zipping along and the surface high that moves into the region in the wake of the cold front moves quickly to the east on Sunday. This results in the return of low level WAA and moderating temperatures again Sunday-Monday, with highs approaching normal on Monday. Like yesterday we begin to see some differences with the deterministic model solutions and within members of the GEFS late Monday into midweek with the handling of short waves moving within the mean long wave trof. It still appears we will see a cold front move through the area Monday night into Tuesday. Whether or not it is accompanied by any precipitation depends on the amplitude of these aforementioned short waves and the resulting low level forcing. The ECMWF and GEFS mean are beginning to support a precipitation threat Tuesday into Tuesday night which should largely be rain at this point. Glass && .AVIATION... (For the 00z TAFs through 00z Thursday Evening) Issued at 650 PM CDT Wed Oct 30 2019 Band of wintry precipitation extending from eastern IA into eastern KS through northern MO, will gradually translate eastward tonight and Thursday morning, affecting all of the TAF sites with wintry precipitation types at some point as colder air spills in. This is expected to occur at KUIN around 02z and KCOU around 05z and involve a brief period of FZRA before becoming all SN. For the STL metro sites, this is expected to occur around 09z and should involve precipitation going straight to SN. This will intersect with the SN then tapering to flurries and ending during Thursday morning. The biggest runway impacts will likely be at KUIN where wintry precipitation will occur the longest but could also impact all the other TAF sites as well, becoming less likely towards the STL metro sites. Otherwise, look for IFR CIGs to persist for all TAF sites tonight and then clear out late Thursday morning or in the afternoon. N surface winds will back to NW and become gusty to 25-30kts later tonight and continue for much of Thursday. SPECIFICS FOR KSTL: Rain or drizzle will be the main precipitation-type until around 09z with a few hour window of potentially accumulating snow before it backs off to flurries by around 12z. FZRA probs during the transition looks too low to mention at this time. Otherwise, IFR conditions to prevail until Thursday morning with improvement to VFR and clearing during the afternoon. TES && .CLIMATE... Issued at 326 PM CDT Tue Oct 29 2019 Record low max temperatures for Thursday October 31st St. Louis 41 (1993) Columbia 39 (1993) Quincy 36 (1951) Record low temperatures on Friday November 1st St. Louis 26 (1954) Columbia 16 (1895) Quincy 23 (2014) && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Freeze Warning from 1 AM to 10 AM CDT Thursday 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-Shelby MO-Warren MO-Washington MO. Freeze Watch from Thursday evening through Friday morning for Sainte Genevieve MO. Winter Weather Advisory until 10 AM CDT Thursday for Knox MO- Lewis MO-Shelby MO. Winter Weather Advisory from 10 PM this evening to 10 AM CDT Thursday for Marion MO. IL...Freeze Warning from 1 AM to 10 AM CDT Thursday for Adams IL- Brown IL-Calhoun IL-Greene IL-Jersey IL-Macoupin IL-Madison IL-Monroe IL-Montgomery IL-Pike IL-Saint Clair IL. Freeze Watch from Thursday evening through Friday morning for Bond IL-Clinton IL-Fayette IL-Marion IL-Randolph IL- Washington IL. Winter Weather Advisory from 10 PM this evening to 10 AM CDT Thursday for Adams IL-Brown IL. && $$ WFO LSX