Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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954 FXUS63 KLSX 131638 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1138 AM CDT Thu Jun 13 2024 .KEY MESSAGES... - There is a threat of severe thunderstorms this evening, mainly over northeast Missouri and west-central Illinois. The primary threats are large hail and damaging winds. There there is a low threat for tornadoes. - Temperatures will run 5-15 degrees above normal through at least the middle of next week. The hottest days (today, Sunday, and Monday) will have highs at least in the mid 90s and nighttime lows no cooler than 70 degrees. && .SHORT TERM... (Through Late Friday Afternoon) Issued at 322 AM CDT Thu Jun 13 2024 A few storms have developed over north central/northeast Missouri as of 0730z and will continue to move southeast early this morning. It should diminish by daybreak. Otherwise, the main issue in the near term will be the temperatures for today. As the upper level ridge builds in and the surface ridge continues to slide off the southeast, surface flow will pickup from the south to southwest. This will usher in plenty of moisture with dewpoints rising into the upper 60s to low 70s by this afternoon. In the meantime 850mb temperatures will rise to between 22 and 25C with surface temperatures topping out in the low to mid 90s, though could see mid to upper 90s in the urban heat islands. With such hot temperatures and high dewpoints, will see afternoon heat index values 100-104. As for storm chances later today, a majority of the latest CAMs are in good agreement that storms will fire up along the cold front that will stretch east to west across far southern Iowa between 20z and 22z as the cap eventually breaks. Then as the front slowly sinks south through the forecast area, this activity will move into northeast Missouri and west central Illinois. As for what type of convective mode initially, still feel confident that it will be supercellular as the latest forecast soundings have MU CAPEs in excess of 3000 J/kg, 0-6km bulk shear 30-40kts, and ML LR 7.5-8C/km. So the main threats will be large hail and damaging winds initially. Then with mean mid-level flow running parallel to the front, this would suggest that the discrete development will become linear with the primary threat transitioning to mainly damaging winds. Even though low-level shear (0 to 1km shear around 10kts) will not be particularly strong, a couple of tornadoes will also be possible, given the potential for a few intense supercells within a strongly unstable environment. As the cold front and associated activity pushes south through the evening, the instability and shear lessen considerably. Thus there is still some uncertainty on exactly how far south strong to severe storms will make it before waning. For now, best chances will be along and north of I-70 between 23z-04z. Still some uncertainty on exactly how far south the cold front will move before stalling out. The majority of the latest deterministic models have the front stall out just south of the forecast area between 12z and 18z Friday. With moisture pooling along the boundary and moderate instability with MU CAPEs between 2000 and 3000 J/kg, could see some isolated activity flare up during the afternoon hours, so added slight chance POPs in portions of southeast Missouri between 18z Friday and 00z Saturday. As for temperatures on Friday it will be a bit cooler, but still above normal in the upper 80s to low 90s. Byrd && .LONG TERM... (Friday Night through Wednesday) Issued at 322 AM CDT Thu Jun 13 2024 As the upper level ridge slowly slides to the east Friday night into Saturday, the next system over the Central Plains will begin to lift northeast towards the Great Lakes region. As it does so, the stalled front to our south will begin to lift northward as a warm front on Saturday. A majority of the latest deterministic and ensembles keep the best chances of showers and storms just off to the west and northwest of the forecast area at this time where the main upper support is. However, there is a chance for isolated showers/thunderstorms Saturday as the front moves northward, so have added slight chance POPs over portions of central Missouri. Otherwise, the warmup begins in earnest as hot and humid weather returns for the rest of the weekend and into next week. So with dewpoints in the 60s to low 70s and temperatures in the 90s, could see heat index values between 100 and 105, especially Sunday and Monday. However, some of the latest deterministic models and ensemble runs are indicating that the upper ridge may weaken and move a bit further to the east by Sunday with shortwave energy sliding along the western and northern periphery of the ridge. This would increase chances of showers and storms over the region during this period, which could affect the warmup. But confidence is low at this time for this solution. Byrd && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1130 AM CDT Thu Jun 13 2024 The primary concern during the 18Z TAF cycle is the potential for thunderstorms late this afternoon through the overnight hours. A cold front will move through the area, triggering thunderstorms that will move from northwest to southeast. These storms are likely to diminish as they move south, and UIN is the most likely local terminal to be impacted directly. For the remainder of local terminals, there is some potential for storms to reach these areas, including STL, but confidence is low that they will maintain strength this far south. At UIN, heavy rain with visibility reductions, large hail and strong wind will be possible with storms, and these threats will likely diminish as storms move farther southeast. Otherwise, a ceilings may briefly dip to MVFR levels, but confidence is lower regarding this potential and VFR categories are likely to prevail. Showers are likely to clear prior to daybreak. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX