Area Forecast Discussion
Issued by NWS St. Louis, MO

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845 FXUS63 KLSX 182352 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 652 PM CDT Sun Apr 18 2021 .SHORT TERM...
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(Through Late Monday Afternoon) Issued at 304 PM CDT Sun Apr 18 2021 Early this afternoon, an upper longwave TROF was over central and eastern North America with several shortwave disturbances of note embedded within. The first was crossing through southern Missouri currently and was helping to instigate showers and a few thunderstorms across our region. The second disturbance was located in western Alberta province while another was over the Northwestern Territories in Canada. Scattered showers and a few storms dotted our area this afternoon with temperatures from the mid 50s to mid 60s. The first disturbance will exit our area early this evening and with loss of diurnal heating, should result in dissipation of clouds and showers/storms. Min temps are expected to drop into the upper 30s and lower 40s. A cold front will begin to drop into our region on Monday and while there has been better convergence on the speed of this front through our area, there remains some differences in guidance on this feature. That said, there is good confidence on the front not making it south of I-70 until after sunset Monday evening, leaving a mostly sunny day with W-SW winds to drive temps well into the 60s, topping out in the low 70s in spots. Cooler air will filter into northern MO and central IL from a likely cold FROPA, resulting in temps topping out around 60 there and falling through the 50s Monday afternoon. Used the highest MOS for a starting point for max temps most areas Monday and increasing a degree or two further, which has verified well the past few "warm" day scenarios. TES .LONG TERM... (Monday Night through Next Sunday) Issued at 304 PM CDT Sun Apr 18 2021 Key messages in the extended period: 1) Widespread precipitation is a near certainty between early Tuesday morning and early Tuesday evening, on the leading edge of a significant push of unusually cold air for this time of year. 2) Accumulating snow looks increasingly likely for areas near Quincy, IL to Columbia, MO and areas northwest from there, with up to 2" of snow possible mainly on grassy surfaces. Temps look to be above freezing throughout the event. Snow may even be seen for areas farther southeast, including the STL metro area, but accumulating snow chances look very low there. 3) Unseasonably cold air is expected to follow the rain/snow event on Tuesday with record cold likely on Wednesday morning and a widespread freeze. A Freeze Watch has been issued for Wednesday morning. We have not seen temperatures this cold this late in April in the Saint Louis area (32F or lower) since 1986 and in the Columbia area (28F or lower) since 1967. Another round of record cold is possible again on Thursday morning. See the CLIMATE section for details. The rest of the forecast supports a trend back to above normal temps by late this week with another round of rain looking more likely. TES
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&& .AVIATION...
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(For the 00z TAFs through 00z Monday Evening) Issued at 640 PM CDT Sun Apr 18 2021 The scattered showers and isolated thunderstorms that dot the area will diminish over the next 2-3 hours and should be gone by 03z. Similarly the associated cloud deck from 5000-7000 feet will diminish and shift eastward. Outside of a direct terminal impact of a shower, VFR flight conditions will be the rule tonight. A cold front will move south through the region from late Monday morning through the afternoon. Occasionally gusty west winds are expected ahead of the front with gusty northwest winds in its wake. Most of the region can expect to see a continuation of VFR flight conditions on Monday, but KUIN is the exception which will see MVFR ceilings develop post-frontal on Monday afternoon. Glass
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&& .CLIMATE... Issued at 1137 AM CDT Sun Apr 18 2021 An unusually chilly airmass is expected to affect our area for the middle of the week. Here is a look at record min temps and record low max temps during that time. TUE 4/20 WED 4/21 THU 4/22 RECORD MIN TEMPERATURES St. Louis (KSTL) 28/1904 32/1904 31/1936 Columbia (KCOU) 28/1953 29/1907 29/1986 Quincy (KUIN) 27/2013 26/1904 27/1986 RECORD LOW MAX TEMPERATURES St. Louis (KSTL) 42/1918 46/1893 43/1884 Columbia (KCOU) 38/1918 42/1992 48/1893 Quincy (KUIN) 39/1918 37/1918 44/1927 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Freeze Watch from late Tuesday night through Wednesday 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. IL...Freeze Watch from late Tuesday night through Wednesday 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- Washington IL. && $$ WFO LSX

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