Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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290 FXUS63 KLSX 282331 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 631 PM CDT Fri Jun 28 2024 .KEY MESSAGES... - Storms are likely this evening through the overnight hours. A few of these storms could be strong to severe with damaging winds and large hail the main threats, especially over central and northeast Missouri. - Saturday afternoon into evening storms could be strong to severe, mainly along and south of I-70. The primary threats are damaging winds and large hail. - With temperatures in the low to mid 90s on Saturday, expect heat index values near 105 over portions of southeast Missouri. Therefore, a heat advisory has been issued from Noon to 7 pm. && .SHORT TERM... (Through Late Saturday Night) Issued at 257 PM CDT Fri Jun 28 2024 As the next system continues to slide east along the U.S./Canadian border, the upper level ridge has begun to flatten overhead. A cold front associated with the system will approach the region, moving into northwestern Missouri this evening. On the western periphery of the upper ridge, moisture continues to stream northward into Kansas and western Missouri with the latest deterministic as well as ensembles indicating an axis of high MU CAPES 3000-4000 J/kg. This combined with 0-6km bulk shear of 25-35 kts, increasing LLJ (35- 45kts) and shortwave sliding along the cold front, will see storms develop and eventually congeal into an MCS over western Missouri. Then as the LLJ veers with time, the complex will slide east into the forecast area late this evening and through the overnight hours. Initially they are likely to be severe in this area, then as they move into our area, CAPE as well as shear values quickly drop off, so will see a weakening trend. However, could see a few strong to severe storms with the main threats being damaging winds up to 60 mph and large hail up to an inch in diameter, especially over portions of central and northeast Missouri. The storms will diminish by mid morning on Saturday. Then focus shifts back to the cold front. Still some uncertainty on exactly where the boundary will be. The majority of the deterministic as well as ensembles have the front just north of the I-70 corridor by midday. Depending on how quickly areas along and south of the cold front recover from the morning activity, will determine where and when another round of storms develops. Guidance suggests surface instability could recover rather quickly with MUCAPE of 3000-4000 J/kg, per the latest forecast soundings, so this combined with better mid-level lapse rates near 8C, strong to severe storms are possible Saturday afternoon into evening. The main threats would be large hail and damaging winds. As for precipitation amounts, with PWATs of around 2 inches, could see fairly efficient rainfall, so locally heavy rainfall possible at times. One other concern on Saturday is the return of heat and humidity for a brief period, south of the cold front. With highs in the low to mid 90s and dewpoints in the mid to upper 70s, could see heat index values near 105, especially for portions of southeast Missouri. So issued a Heat advisory for this area from Noon to 7 pm on Saturday. As the cold front exits the region Saturday night, the precipitation will taper off from north to south. Byrd && .LONG TERM... (Sunday through Next Friday) Issued at 257 PM CDT Fri Jun 28 2024 By Sunday morning the front will be south of the forecast area. Showers and a few storms will taper off by mid morning. Then as surface high pressure builds into the region, much drier and cooler air will filter in for Sunday and Monday. The cool down will be fairly brief as the surface ridge slides off to the east early next week and upper ridging over the western CONUS moves in. Surface flow will veer to the south once again with well above normal temperatures returning by Tuesday. The latest deterministic and ensembles have some differences in timing, location and strength with a system that slides east out of the Pacific Northwest. This system will usher in another cold front by midweek, introducing additional chances for showers and thunderstorms, some of which could affect the July 4th holiday. Confidence is low on timing, location, etc. thus stuck with the latest NBM solution with chance POPs through the period. Byrd && .AVIATION... (For the 00z TAFs through 00z Saturday Evening) Issued at 618 PM CDT Fri Jun 28 2024 Southerly winds will slacken off this evening and attention will turn to the northwest. Thunderstorms are expected to expand in coverage into parts of northwest Missouri over the next few hours. These storms will then move generally eastward, first reaching KUIN around 0400 UTC and then central Missouri terminals closer to 0600-0700 UTC. For metro St. Louis, arrival time is likely to be closer to 0900-1000 UTC. Storms should be a bit stronger further west, so have a TEMPO for IFR visibilities in heavier downpours at KCOU/KJEF. Further east/southeast, there is more uncertainty in strength and coverage of storms. The threat for showers and thunderstorms should depart from west to east late tonight into early Saturday morning, with a lull into mid-late afternoon. That is when additional thunderstorms are expected to form along the cold front. The central Missouri and KUIN terminals should stay dry as the front will move through earlier in the day (KUIN near 1500 UTC and KCOU/KJEF just after midday). However, the metro terminals will likely be near the northern edge of this development so have a 3-hour VCTS group from late afternoon into the early evening hours. Winds behind the front are expected to veer to the northwest. Outside of any thunderstorms, VFR conditions are expected. Any downpour could reduce visibilities to IFR and cannot rule out some gusty winds at KCOU/KJEF. There is also a chance of MVFR ceilings (bases around 2500 feet AGL) behind the front in northeast Missouri and west-central Illinois mid-late Saturday morning. Better chances are west of KUIN so held off for now, but did add a SCT025 mention from 1500-1800 UTC. Gosselin && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Heat Advisory from noon to 7 PM CDT Saturday for Crawford MO- Iron MO-Madison MO-Reynolds MO-Saint Francois MO-Sainte Genevieve MO-Washington MO. IL...None. && $$ WFO LSX