Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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173 FXUS63 KLSX 170338 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1038 PM CDT Thu May 16 2024 .KEY MESSAGES... - Isolated to scattered showers and thunderstorms are possible across the area through the evening hours. The greatest chance for an isolated strong to severe thunderstorm is across southeast Missouri and southern Illinois with the threats being 60 mph winds and quarter sized hail. - Light winds overnight will favor the possibility of patchy fog areawide. - This weekend will be mainly dry with temperatures warming up to around 10 degrees above normal. This warming trend will continue into next week in addition to another active period. && .SHORT TERM... (Through Late Friday Night) Issued at 329 PM CDT Thu May 16 2024 Current water vapor imagery shows that there is an upper level trough north of the Mid-Mississippi River Valley that is helping keep the region in southwesterly flow aloft. Amidst this southwesterly flow is an vorticity maximum that will trek across the southern portions of the CWA through the afternoon hours. This vorticity maximum will be help support isolated showers and thunderstorms through the early evening hours. There is a marginal chance that a few of these isolated thunderstorms could become strong to severe, primarily across southeast Missouri and southern Illinois. The 19Z SPC Mesoanalysis shows that there is around 1500 J/kg of SBCAPE as well as 30-35 kts of 0-6km of shear in the aforementioned areas. Should a thunderstorm become severe, the primary threats will be gusty winds up to 60 mph and quarter sized hail. The strong to severe thunderstorm potential will decrease around sundown as daytime heating and instability becomes limited. Continued shower activity is possible through the overnight hours along and south of the I-44 corridor in Missouri and I-70 corridor in Illinois as the vorticity maximum and increased low level moisture convergence continues east/northeastwards. Southeast Missouri and southern Illinois has a greater chance (50-80%) of seeing overnight rain showers. Winds will become light and variable overnight. These light and variable winds in addition to the saturated grounds will provide the possibility for patchy fog across much of the area early Friday morning. By Friday another shortwave and associated vorticity maximum will swipe across southeastern Missouri and southern Illinois. This will provide another chance (30-50%) of showers in those areas. Persistent cloud cover across those areas will help keep daytime instability rather limited and limit the thunderstorm potential. Temperatures on Friday will be in the 70s, with the highest temperatures across the northern portions of the CWA where cloud cover will be limited. MMG/Glass && .LONG TERM... (Saturday through Next Thursday) Issued at 329 PM CDT Thu May 16 2024 An upper level trough will be exiting to the east through the day on Saturday with ridging and height rises building in behind it. At the same time near the surface, ensemble guidance is in agreement that surface high pressure will also be shifting into the Mid-Mississippi River Valley. This combined with the upper level height rises will favor dry weather and increasing temperatures into the mid to upper 80s on Saturday. The current forecast has a slight chance of showers during the day on Saturday, however we will likely end up being dry given the current forecast trends. By Sunday, NBM quartile spread has high temperatures in the upper 80s to low 90s. These high temperatures are around 10 degrees above climatological normal for mid May. A more active pattern will set up next week as an upper level low sits itself over the south-central region of Canada. Rounding this upper low will be multiple shortwave troughs and associated surface reflections swinging through the Mid-Mississippi River Valley Monday through early Wednesday. Thunderstorms are forecasted through the early week, however, the greatest chances for thunderstorms is late Tuesday into Wednesday. MMG/Glass && .AVIATION... (For the 06z TAFs through 06z Friday Night) Issued at 1029 PM CDT Thu May 16 2024 The primary concerns for the 06Z TAF period will be the potential for patchy fog and additional showers overnight tonight, followed by redeveloping scattered showers and thunderstorms tomorrow. Regarding the former, light winds and high humidity may lead to patchy fog development at many area terminals overnight tonight, with highest probabilities at UIN/COU/JEF. Visibility reductions will likely fluctuate through the night. Fog is less likely at St. Louis area terminals but can`t be ruled out, along with a few showers overnight through early morning. Wherever fog develops, visibility reductions to MVFR will be well within reason, and potentially lower for brief periods. VFR conditions are likely to redevelop by mid morning, but additional scattered thunderstorms will be possible during the afternoon. This will be most likely to impact St. Louis area terminals. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX