677 FXUS63 KSGF 242254 AAA AFDSGF Area Forecast Discussion...UPDATED National Weather Service Springfield MO 554 PM CDT Thu Aug 24 2023 Key Messages: 1. Dangerous heat continues through Friday with afternoon heat index values of 104 to 114 degrees. 2. 10-20% chance for isolated thunderstorms late this afternoon and early this evening across the eastern Ozarks and south- central Missouri. 3. Widely scattered thunderstorms Friday afternoon across the eastern Ozarks with a Marginal Risk for severe storms. 4. 30-50% chance for thunderstorms this weekend with temperatures beginning to cool. 5. Much cooler and dry next week. .SHORT TERM...(This evening through Friday) Issued at 243 PM CDT Thu Aug 24 2023 Synoptic Scale Pattern and Current Conditions: Water vapor imagery indicates that an upper level ridge remains entrenched across the central CONUS. 12Z upper air analysis does indicate that the center of this ridge has continued to shift southwest of the Missouri Ozarks. The center of the 500 mb high is now analyzed across southeastern Oklahoma. The retrogression of this ridge has resulted in slightly higher amounts of mid-level moisture and less in the way of large scale subsidence. We are therefore seeing more in the way of a cumulus field this afternoon, especially across the eastern Ozarks and central Missouri. Isolated thunderstorms have actually developed in the higher terrain of northern Arkansas with a few updrafts also noted around Stockton. Otherwise, hot and humid conditions are again being observed across the region. Temperatures are generally in the middle to upper 90s with dew points in the lower to middle 70s. There are pockets of upper 70s dew points along the Highway 54 corridor. As of 3 PM, heat indices are in the 104-114 range. The going Excessive Heat Warning covers this well. Thunderstorm Potential into this Evening: Low and mid-level water vapor imagery indicates that moisture quality will continue to gradually improve across the eastern Ozarks into this evening. Ascending mixed-layer parcels will encounter little in the way of inhibition, especially east of Highway 65 and up closer to the Highway 54 corridor. We therefore think that there is low-end potential (10-20%) for isolated thunderstorms to continue into early this evening. If any storms are able to become more robust in nature, a new and experimental Ozarks Pulse Severe Thunderstorm Index (OPSTI) does show several mesoscale parameters in place to support downburst potential. We will continue to advertise a conditional risk for wind gusts up to 50 mph. The reason for not going with even higher wind gust potential is the presence of weak lapse rates in the 700-500 mb layer. These lapse rates may tend to somewhat inhibit stronger updrafts. Otherwise, another very warm and muggy night is in store for the region. NBM data is strongly clustered around lows in the middle to upper 70s. Given the muggy conditions in place, these anomalously warm low temperatures will continue to present a risk for heat stress to vulnerable populations. Heat and Thunderstorm Potential Friday: The upper level ridge will continue to slowly migrate west and will put the Missouri Ozarks in a weak northwesterly flow aloft. Meanwhile, a short wave trough progressing east across the northern Great Lakes will begin to drive a cold front south through the Corn Belt. Another hot and humid day is in store for the area with highs once again topping out in the upper 90s to around 100 degrees. The NBM gives us high confidence in these temperatures given only 2-3 degree spreads between the 25th and 75th percentile data. Dew points on Friday may come down 1-2 degrees which would result in slightly less oppressive heat indices. Nevertheless, we are still looking at values in the 105-110 range from mid to late afternoon. Thunderstorm potential looks slightly better Friday afternoon, especially across the eastern Ozarks. Mid-level moisture will continue to increase which will make the environment less hostile to developing updrafts. The OPSTI indicates an even more favorable environment for pulse severe across the eastern Ozarks as we see slightly better mid-level lapse rates advect into the region. We are therefore advertising localized wind gusts up to 60 mph. This jives well with the SPC Marginal Risk. .LONG TERM...(Friday Night through Thursday) Issued at 243 PM CDT Thu Aug 24 2023 Big Pattern Change Starting this Weekend: That upper level ridge will continue to retrograde with ensemble means showing the 500 mb ridge axis centered from the central Rockies into the Four Corners region by Sunday morning. This will firmly entrench the Missouri Ozarks in a northwest flow aloft. Shorter term ensembles do indicate the potential for multiple weak short wave troughs to be embedded within the northwest flow across the central Plains and into our general vicinity throughout the weekend. At the surface, a cold front will slowly move south across the region from Friday night into Saturday. Given the front and the aforementioned weak short wave energy, we have increased PoPs into the 30-50% range this weekend. We are not looking at all-day washouts by any means, but those with outdoor plans should remain weather aware. The threat for any severe storms remains unclear. High temperatures on Saturday could either be in the upper 80s or middle 90s, all depending on the amount of cloud cover and precipitation. This leads to uncertainty in heat index values. The NBM does indicate that dewpoints will remain in the 70s during the day therefore we will need to monitor for the potential of 100 degree heat index values with the highest chances south of Springfield. Given this uncertainty we will not be extending the Excessive Heat Warning into Saturday. Much Cooler Next Week: WPC cluster scenarios indicate strong consensus that the upper level ridge will remain across the western U.S through midweek before beginning to slowly build back east late in the week. Below normal temperatures and much lower dew points will therefore occur for the first half of next week. Overnight lows dipping into the middle and upper 50s appear increasingly likely for both Tuesday and Wednesday nights. NBM statistical data then shows a slow warming trend starting late next week. This is believable given the building heights advertised by ensemble systems. While we may see some lingering showers and thunderstorms across southern Missouri early Monday (NBM 10-20% chances), the remainder of the week looks dry with PoPs remaining below 5%. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 547 PM CDT Thu Aug 24 2023 Confidence is high that VFR conditions will persist through the TAF period with passing high clouds. Winds will remain out of the south to southwest. There is a 10 to 20 percent chance of a thunderstorm Friday, mainly east of the TAF sites. && .SGF WATCHES/WARNINGS/ADVISORIES... MO...Excessive Heat Warning until 10 PM CDT Friday for MOZ055>058- 066>071-077>083-088>098-101>106. KS...Excessive Heat Warning until 10 PM CDT Friday for KSZ073-097-101. && $$ SHORT TERM...Schaumann LONG TERM...Schaumann AVIATION...Burchfield