Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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986 FXUS63 KLSX 081932 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 232 PM CDT Sat Jun 8 2024 .KEY MESSAGES... -Thunderstorms will move into the forecast area this evening, capable mainly of damaging winds, large hail, and heavy rainfall. The best location for severe thunderstorms is across southeast Missouri. -Additional thunderstorms will form overnight across southeast Missouri and locally heavy rainfall of up to 3-5" is possible. The Flood Watch remains in effect for this area. && .SHORT TERM... (Through Late Sunday Night) Issued at 228 PM CDT Sat Jun 8 2024 This morning`s MCS pushed convection and the associated outflow into central Arkansas this afternoon, and is no longer the focus for thunderstorm development across our CWA today. The focus for convection will be a warm front that is currently developing across central Kansas into western Missouri near Kansas City, while a cold front is draped from roughly northeastern Iowa into southeast Nebraska. Across the warm sector dewpoints are surging into the 70s and MLCAPE has built to 1000-2500 J/kg, with 0-6 km shear around 40kts. The warm front will continue to extend eastward through the day as warm, moist air is advection northeastward into central and eastern Missouri. Isolated warm air advection showers have formed near the warm front in western Missouri and tracked eastward into the western CWA. So far convection has struggled to grow upscale due to the weak forcing and weak, mid-level height rises. Warm air advection may be strong enough across central Missouri to form more isolated showers and thunderstorms this afternoon. The better chances for severe thunderstorms continues to be this evening as a subtle mid-level shortwave passes over the area and interacts with the better surface convergence in southwestern Missouri. The thunderstorms will track southeastward along the deep layer shear vectors into south central and southeast Missouri this evening. Recent runs of hi res guidance have continued to shift this area of thunderstorms further south, and the best location for these storms continues to be across southern and southeast Missouri. Overnight, a WSW to ENE oriented LLJ will ramp up across southwest Missouri, enhancing thunderstorm development across the southern portion of the state and into southern Illinois. Thunderstorms that form during the afternoon and early evening will be a mixture of discrete and multi-cell clusters. These storms will become more linear with time as the LLJ kicks up overnight and generates more convection. With initially discrete/multi-cell clusters, damaging winds, large hail, and heavy rainfall are the main concerns. There is a low threat for a tornado with a discrete storm that forms along the front in the afternoon to early evening where the weak 0-1 km shear and helicity could be locally enhanced. As storms become more linear the threat will transition to mainly damaging winds and heavy rainfall. Additional shower and thunderstorm development is possible across west-central Illinois along the weak cold front as it slides southeastward through the forecast area overnight, but confidence in development is low given the uncertainty in strength of low-level convergence. As the WSW to ENE LLJ kicks up overnight convection will become more widespread in southern Missouri, increasing the risk for flash flooding particularly in areas that already saw rainfall from thunderstorms during the early evening. There has been a southward shift in convection within the last several runs of the CAMs, which would result in a southward shift of the heaviest axis of precipitation. So while confidence is high a narrow band of heavy rainfall will occur in southern Missouri, where exactly it occurs remains uncertain. HREF LPMM continues to indicate areas of 3-5 inches of rain are possible across portions of southern and southeast Missouri, with locally higher amounts up to 7 inches possible across portions of southern Missouri. These highest amounts would occur with training convection and will be highly isolated. Showers and thunderstorms will diminish as the LLJ weakens Sunday during the day. Most of the forecast area will be largely dry Sunday, except for portions of far southeast Missouri where rain could linger into the afternoon. A surface high will slide into the area during the evening to help shunt any lingering precipitation south of the forecast area. MRM && .LONG TERM... (Monday through Next Saturday) Issued at 228 PM CDT Sat Jun 8 2024 The surface high will remain the dominate feature across the mid- Mississippi Valley for the first half of the work week while a mid- level shortwave ridge pushes through the region. Northwesterly low- level flow will keep temperatures below normal while the surface high and mid-level height rises will keep the area dry. A weak mid- level trough axis will pass through the region mid-week as the mid- level trough slides through the Great Lakes region. The associated surface low will likewise track through the Great Lakes region, and the attendant cold front will be weak as it moves through the mid- Mississippi River Valley. Differences remain in timing and strength of the front which results in uncertainty in mid-week precipitation chances. Southwesterly low-level flow will become established behind the surface high and cold front, warming temperatures for the end of the work week and start of the weekend. 850 mb temperatures will climb into the upper teens to low 20s, which will push high temperatures above normal during this period. How far above normal will depend on cloud cover and precipitation chances which will come into focus in coming days. MRM && .AVIATION... (For the 18z TAFs through 18z Sunday Afternoon) Issued at 1211 PM CDT Sat Jun 8 2024 Broken MVFR ceilings have moved into the area behind this morning`s precipitation, but are expected to improve to VFR this afternoon with deeper mixing. VFR conditions are expected to prevail through the remainder of the TAF period. Previously another round of showers and thunderstorms was expected overnight into Sunday morning, but the threat for this precipitation has shifted southward. The mid-Missouri terminals have the best chance of seeing a shower or thunderstorm in the early morning hours (10-13Z), but confidence in the northern extent of the precipitation is low, so have changed the mention to VCSH. While I can`t rule out a brief period of showers and/or thunderstorms at the other terminals (KUIN, KSTL, KSUS, KCPS), I have removed the mention of precipitation all together, as confidence is even lower in the occurrence of precipitation at this time. Through the course of the TAF period winds will become westerly and then northerly as a largely dry cold front pushes through the region. MRM && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flood Watch from 7 PM CDT this evening through Sunday afternoon for Cole MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO- Madison MO-Moniteau MO-Osage MO-Reynolds MO-Saint Francois MO-Washington MO. IL...None. && $$ WFO LSX