####018009524#### FXUS61 KCLE 181837 AFDCLE Area Forecast Discussion National Weather Service Cleveland OH 237 PM EDT Sat Jul 18 2026 .WHAT HAS CHANGED... A Severe Thunderstorm Watch has been issued for all of northern Ohio and Northwest PA until 9 PM. && .KEY MESSAGES... 1) A line of severe thunderstorms will move across the area this evening, with most of the storms in the 4 to 9 PM window. A few scattered storms are possible this afternoon ahead of the line. Main hazard is damaging winds and heavy rainfall, but isolated tornadoes and hail up to quarter size are possible. 2) Additional showers and thunderstorms are likely Monday night and Tuesday. Storms may be strong to severe, primarily on Tuesday. 3) Cooler and less humid Sunday and Monday, brief return to heat and humidity Tuesday, then more significant cooling the rest of the week. && .DISCUSSION... KEY MESSAGE 1... A very active summer evening is on tap as a strong cold front crosses the region and interacts with a hot, moist, and unstable airmass to bring widespread strong to severe thunderstorms. Early afternoon satellite and water vapor loops show a significant mid/upper shortwave trough digging into the southern Great Lakes with an associated 1000 mb surface low NE of Georgian Bay. This shortwave will swing through the eastern Great Lakes this evening, with the left exit of a 90+ knot H3 jet streak and somewhat negatively tilting trough deepening the low to 990 mb by tonight as it lifts toward the Canadian Maritimes. The trailing cold front looks to progress southeastward across Lake Erie, northern Ohio, and Northwest PA between 21 and 03Z this evening. Forecast soundings have shown little to no capping in the warm sector today, and convective temperatures have already been reached with air temps in the upper 80s to around 90 and dew points in the low to mid 70s. Heating of this very moist low-level airmass is resulting in MLCAPE values pushing 3000 J/Kg and surface based CAPE as high as 5000 J/Kg. This has already initiated convection in NW PA and along and south of the U.S. 30 corridor where a weak surface boundary has locally enhanced convergence. This convection is primarily a locally heavy rain risk, but an occasional downburst is possible given steep low-level lapse rates of 7.5 to 8 C/Km. The main show will come immediately along and ahead of the cold front where strong forcing for ascent will trigger a QLCS in southern Lower Michigan and Ontario Province. This line will propagate southeastward across Lake Erie and much of northern Ohio and NW PA this evening, with the greatest risk for severe weather in the 20 to 01Z (4 to 9 PM window). Mid-level flow will strengthen as the front approaches, with deep layer (0-6 Km) bulk shear increasing to around 35 knots. This combined with the impressive aforementioned thermodynamics will be more than sufficient for organized, sustained updrafts. The orientation of the deep layer shear vector is somewhat parallel to the expected orientation of the line overall. This may cause parts of the line to sag across the area and backbuild a bit, leading to a sneaky heavy rain risk since PWATs will be nearing 2 inches, but the overall threat remains damaging winds. Any parts of the line that can orient more N to S will be more normal to the deep layer and 0-3 Km shear vectors, and this will cause those portions of the line to surge out and bow. Where these surges occur will have the most widespread damaging winds, with pockets of 70+ mph possible. Mid-level dry air (DCAPE around 1200 J/Kg) will further air in downdraft strength and associated wind risk. The surges/bows combined with low-level (0-1 Km) shear marginally favorable at 15-20 knots could support a couple of brief QLCS tornadoes. Finally, any embedded areas of rotation will help to sustain taller updrafts for pockets of hail, but high freezing levels should keep the largest stones around quarter size. The convection will quickly exit the area by Midnight tonight, with dry conditions the rest of the night through Monday as Canadian high pressure builds across the Great Lakes. KEY MESSAGE 2... After a quick shot of Canadian high pressure Monday, another strong mid/upper shortwave will dive from the Upper Midwest Monday night through the southern and eastern Great Lakes Tuesday as a longwave trough and associated closed low deepen across the Great Lakes and Northeast CONUS. This continues to look like another dynamic system for mid summer with the potential for severe weather Tuesday ahead of the strong cold front as a deepening surface low lifts up toward Hudson Bay. However, the timing, location, and evolution of the Tuesday storms remain uncertain because a low-level jet Monday night will probably initiate convection (possibly an MCS) upstream along a retreating warm front. This activity could linger Tuesday morning and disrupt the heating, as well as put down outflow boundaries that could cause new convection to initiate southeast of our area. Maintained high POPS for showers and thunderstorms Monday night and Tuesday afternoon, but details will need to be worked out. Rapid drying is expected Tuesday night in most areas, although showers could linger in NE Ohio and NW PA into Wednesday due to the deepening mid/upper trough and associated cool air aloft/cyclonic flow across the warm lakes. KEY MESSAGE 3... Mid/upper troughing across the Great Lakes and Northeast CONUS Sunday and Monday combined with Canadian high pressure at the surface will bring cooler, less humid air, with highs in the mid 70s to around 80 Sunday and low to mid 80s Monday. This will set up a refreshingly cool night Sunday night, with lows in the mid 50s to around 60. A brief surge of heat and humidity will return ahead of the significant shortwave Tuesday, as a warm front lifting across the area Monday night and Tuesday morning brings 70+ F dew points back into the area. However, the cooling behind the cold front Tuesday night looks even more significant as the deep trough/upper low takes up residence over the Great Lakes. This will drop highs into mainly the 70s Wednesday through the end of the week, with lows in the 50s. && .AVIATION /18Z Saturday THROUGH Thursday/... Warm front has swept to the northeast. Only residual wildfire haze was affecting KTOL. Otherwise, smoke and low ceilings have eroded this morning. Visible Satellite displayed a cu field over NC/NE OH and W PA with isolated sh over central Ohio. This afternoon and evening showers and thunderstorms develop ahead of a cold front, potentially impacting all TAF sites with a brief window of lower vsbys and gusty to strong winds. Highest confidence in thunderstorm coverage and the potential for wind gusts to exceed 40 knots. Have inserted gusts up to 35 to 40 knots in the window from 19z to 01z in a tempo group for all taf sites this afternoon. Additional scattered showers and perhaps a thunderstorm or two are possible with the cold front later in the evening as it sweeps south through the area. Gusty southwest winds of 15 knots with gusts up to 25 knots will continue through 22z for most sites outside of convection. Winds will abruptly shift towards the north behind the cold front later this evening and overnight, around 10 knots. Outlook...Non-VFR possible with haze/smoke on Sunday and Monday. Non- VFR becoming more likely in showers and thunderstorms Monday night through Tuesday. Some thunderstorms Tuesday afternoon and evening may contain strong wind gusts. Residual non-VFR possible on Wednesday on rain showers across the eastern half of the area. && .MARINE... Rough marine conditions will arrive across Lake Erie today as southwest winds of 15 to 25 knots develop ahead of a cold front. Winds will shift towards the north behind the front later this evening and overnight, 15 to 20 knots, before diminishing to less than 10 knots by Sunday afternoon. In this package, have extended the Small Craft and Beach Hazards for the central basin, and added a couple of zones west towards the Islands, mainly for the onshore flow later this evening and overnight. Another period for rough marine conditions will arrive on Tuesday as southwest winds of 15 to 25 knots develop ahead of a cold front. Will likely need another round of marine headlines Tuesday through Wednesday as winds shift towards the northwest behind the cold front, around 20 knots. Strong thunderstorm wind gusts are expected across Lake Erie this afternoon and evening ahead of a cold front. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...Beach Hazards Statement from 10 PM EDT this evening through Sunday morning for OHZ009-010. Beach Hazards Statement through Sunday morning for OHZ011-012- 089. PA...Beach Hazards Statement until 10 PM EDT this evening for PAZ001. MARINE...Small Craft Advisory from 10 PM this evening to 8 AM EDT Sunday for LEZ144-145. Small Craft Advisory until 8 AM EDT Sunday for LEZ146>148. Small Craft Advisory until 10 PM EDT this evening for LEZ149. && $$ DISCUSSION...Garuckas AVIATION...FZ MARINE...FZ ####018006420#### FXUS63 KLSX 181839 AFDLSX Area Forecast Discussion National Weather Service St Louis MO 139 PM CDT Sat Jul 18 2026 .KEY MESSAGES... - A cold front stalls near the Mississippi River on Sunday. To the west, hot and humid conditions continue. To the east, a little cooler conditions are expected with some smoke. Along the front, afternoon showers are likely. - Heat and humidity spread area wide on Monday, but a cold front Tuesday will bring substantial heat relief for the rest of the week. && .SHORT TERM /THROUGH SUNDAY/... Issued at 135 PM CDT Sat Jul 18 2026 Regional satellite imagery shows surface high pressure over Louisiana with a westerly flow to the north of it across Missouri and Illinois. Although cumulus has formed, showers have been hard to come by so far. One pocket of convection over southwest Missouri will continue to push eastward this afternoon and likely affect our southern forecast area. Otherwise only isolated showers with occasional embedded lightning are expected. To the north a cold front is pushing south through Iowa and northern Illinois. Scattered storms are expected to form in the vicinity of this boundary this evening. Considering a hot and humid low levels, any stronger cores could produce locally gusty or damaging winds. However, storms are expected to decrease in coverage and intensity as the front pushes southward into our area this evening. This front is being driven by a trough moving through the Great Lakes into New England. As this trough moves east, the front loses its push southward, resulting in a stalling boundary in our area tomorrow. The front is likely to stall just west of the Mississippi River in a roughly northwest to southeast orientation. To the east of the front, it will be a little cooler with highs only in the 80s. With this air mass coming out of the Great Lakes and southern Canada, there's some potential for smoke as well. See the latest Air Quality Alert for portions of Illinois. Along and to the west of the front, temperatures rise into the 90s again with humidity even a bit worse than it is today as moisture pools near the front. So we'll see another day of 100 to 105 heat index values. However, the front will also serve as a focus for afternoon thunderstorms which will provide brief local heat relief in spots. With little wind shear available, these storms will be primarily capable of gusty winds and heavy local downpours. Latest guidance has been a little more aggressive in pushing the front westward, so it's possible the St Louis area may get a better break from the heat than initially expected. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Issued at 135 PM CDT Sat Jul 18 2026 The front lifts back northeast Sunday night into Monday putting the entire area back into the hot and humid air mass again for Monday. For many locations this will be the hottest day of the week with highs in the low to mid 90s and heat index values peaking near 105. But the next trough will be dipping down into the Northern Plains bringing with it our next more substantial cold front. This front pushes north to south across our area during the day on Tuesday. For more southerly areas that remain ahead of the front for a good portion of the day, it'll be another hot and humid day, potentially even hotter than Monday. But to the north the heat relief begins. We'll have to watch this day for the potential for thunderstorms. Although current NBM POP remains fairly low as guidance does favor areas further east along the front, there's still 40 to 60 percent of low resolution ensemble guidance that produces rain in our area in the 24 hours ending Tuesday night. With better wind flow aloft, the potential for more organized thunderstorms with primarily a wind threat will be higher here than with any of the other convection expected in this 7-day forecast. Although the core of the coolest air with this air mass will be aimed more to the east across the Ohio Valley and Northeast, we'll still feel the cool down. For the middle of next week we're looking at highs in the low to mid 80s with a substantial drop in humidity. Dewpoints fall into the 50s. It's hard to get much drier this time of year in the absence of a drought as local evaporation and transpiration tend to modify dry air masses quickly. Either way, it'll be a noticeable break from the humidity. Although the front makes it all the way to the Gulf coast of Florida, it does get hung up across the Southern Plains. Here continued humidity along with shortwave troughs dropping through the northwest flow will produce a few rounds of showers and storms. Our area may be peripherally impacted by this as early as Thursday night. Our air mass largely moderates in place over the coming days with temperatures drifting closer to normal with continued modest humidity. But by this weekend we start to see the moisture creeping back toward our area with the upper ridge expanding its influence into the center of the country leading to another potential period of hot weather. && .AVIATION /18Z TAFS THROUGH 00Z MONDAY/... Issued at 1216 PM CDT Sat Jul 18 2026 VFR expected today with a light WSW wind. A few pop up showers are possible, but should be few and far between. A front drops in from the north tonight with thunderstorms possible along it. These should be dissipating as they arrive. They'll have the best chance of affecting UIN, but confidence remains low that they'll even survive that far. The front gets stalled near or just west of the Mississippi River on Sunday, with a very light NNE wind east of the front. More widespread showers and storms are likely in the vicinity of the front Sunday afternoon, most likely affecting the St Louis metro area. && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Heat Advisory until 7 PM CDT Tuesday for MOZ041-047>051- 059>065-072>075-084-085-099. IL...Air Quality Alert from 4 AM Sunday to midnight CDT Sunday night for ILZ058>060-065-095>097. Heat Advisory until 7 PM CDT Tuesday for ILZ069-074-079- 100>102. && $$ SHORT TERM...Kimble LONG TERM...Kimble AVIATION...Kimble