Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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063 FXUS63 KLSX 130340 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1040 PM CDT Sun May 12 2024 .KEY MESSAGES... - Widespread showers and a few thunderstorms are expected tomorrow, with some breaks expected in the afternoon. A strong thunderstorm or two will be possible in the southern half of the Ozarks late in the afternoon and evening, with strong wind being the primary threat. - Lighter showers are likely to continue through Tuesday afternoon. - The next opportunity for rainfall will be Thursday and Friday. && .SHORT TERM... (Through Late Monday Night) Issued at 237 PM CDT Sun May 12 2024 Quiet weather continues this afternoon as surface high pressure remains in place, albeit temporarily. Meanwhile, temperatures have climbed into the low 80s as of 1 PM, thanks to a combination of mostly clear skies, warm southerly flow, and a passing upper level ridge. Later this afternoon and evening, patchy high level cloud cover will begin to spread into the area, the first hint of the next storm system approaching from the west. Otherwise though, weather for the remainder of the evening will remain uneventful. Changes are on the horizon, though, as a slow-moving low pressure system currently located across the Central Plains will move into the western Missouri. Ahead of this low, modest southerly low level flow will gradually advect Gulf moisture northward overnight tonight through early tomorrow morning, with PWAT values climbing to between 1.2 and 1.5 inches. This will set the stage for widespread precipitation between tomorrow morning and Tuesday afternoon. The first round of widespread rainfall is expected to move through the area between early morning and mid afternoon, as a subtle vorticity maximum pivots around the approaching trough. As this occurs, a wave of showers is expected to move from southwest to northeast, and almost all areas are expected to see at least some rainfall. Meanwhile, modest MUCAPE ranging from 100 to as much as 500 J/kg will support at least a few thunderstorms during this timeframe, although strong/severe storms are not anticipated with this initial round. Overall, rainfall rates are expected to be light to moderate outside of a few embedded convective cores, as forcing is not expected to be particularly strong. This initial wave of rain will also be progressive, and and training storms are not expected. As such, while a soaking rain can be expected for most areas, flooding is not a significant concern locally. By late afternoon, most of this rain is expected to exit the area to the northeast, with a relative lull in precipitation expected in many areas for a few hours. From here, attention turns to the possibility of redeveloping showers and thunderstorms during the mid to late afternoon, with a limited potential for a few stronger storms as well. As the first round of showers moves off to the northeast, varying levels of clearing may allow for some afternoon destabilization, particularly across central and southern Missouri. How much so will likely be limited by cloud cover and poor lapse rates, but between 1000 and 2000 J/kg of CAPE may be attainable. Meanwhile, mid level winds will increase across southern Missouri as the shortwave approaches from the west, with favorable jet dynamics underneath the left exit region of a modest 500 mb jet. With around 30-40kt of 0-6km shear to work with, it wouldn`t be out of the question to see a some more organized convection late Tuesday afternoon and evening capable of producing strong wind gusts across the southernmost parts of our area, or roughly the southern half of the Missouri Ozarks. This is highly conditional, but will be worth watching over the next 24 hours. Between Monday night and Tuesday afternoon, the low pressure system will continue its slow eastward march, and a cold front will sink into the area. Meanwhile, light showers along and behind the cold front will slowly spread into the area from the northwest, although there is some model disagreement regarding just how vigorous Tuesday`s shower activity will be. However, this activity will likely be less convective in nature save for perhaps parts of the southern Ozarks and southern Illinois, with lower rain rates and perhaps some drizzle mixed in later in the day as well. Once all is said and done late Tuesday, most areas will likely observe somewhere between .5 and 1.5 inches of rain, with forecast amounts dropping slightly from previous forecasts. Temperatures both days will also likely top out only in the low 70s, and perhaps not even out of the 60s in northern areas. BRC && .LONG TERM... (Tuesday through Next Sunday) Issued at 237 PM CDT Sun May 12 2024 A break in the rain is expected Wednesday as the cold front surges south and another transient upper ridge moves in overhead. However, this will not persist for long, as rain chances will increase yet again Thursday through Friday. Model guidance continues to suggest that a positively tilted upper trough will move through the area, providing just enough forcing to produce widespread but perhaps not particularly heavy precipitation. Moisture content will be sufficient to support this, but not anomalously high, and forcing from the upper trough and perhaps a diffuse surface cold front do not appear to be particularly noteworthy. As such, the potential for heavy rain appears to be low, but there is a consistent signal among a majority of ensemble members for at least some precipitation in most areas late in the work week. Meanwhile, seasonable, if not slightly below average temperatures are likely to persist through the end of the week. BRC && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1038 PM CDT Sun May 12 2024 A weather system will continue its eastward trek overnight and bring with it increased chances for rain showers. Expect increasing cloud cover with lowering ceilings as this system makes its way into the region by Monday morning. Rain chances will continue to increase through the day on Monday and persist through the TAF period. Confidence in embedded thunderstorms on Monday afternoon remains lower, therefore stuck with the mention of VCTS. MVFR ceilings are forecasted to accompany rain showers and impact each terminal. Confidence in IFR ceilings late Monday night remains low but cannot be completely ruled out, especially at KUIN and the St. Louis Metropolitan terminals. Visibility reductions in the heaviest rain showers are possible. MMG/Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX