Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 449 PM EDT Sat Aug 19 2023 Valid 00Z Sun Aug 20 2023 - 00Z Tue Aug 22 2023 ...There is a Slight to High Risk of excessive rainfall over parts of Southern California and the Great Basin... ...There are Air Quality Warnings over the parts of the Pacific Northwest and Northern Rockies... ...Excessive Heat Warnings and Advisories from parts of the Plains, the Mississippi Valley, and Central/Western Gulf Coast... Hurricane Hilary is forecast to move northward over the Eastern Pacific on Saturday and make landfall over Baja California Peninsula on Sunday. Hilary is then forecast to continue to move northward into Southern California by Sunday evening and then into central Nevada before dissipating on Monday. Hilary will also produce potentially historic rainfall amounts expected to cause flash, urban, and steep-sided gully flooding, including landslides, mudslides, and debris flows. Dangerous to locally catastrophic flooding impacts are expected late tonight through early Monday. Therefore, the WPC has issued a High Risk of excessive rainfall over Southern/Central California from Sunday into Monday. Severe, widespread flash flooding is expected. Areas that normally do not experience flash flooding will flood. Lives and property are in great danger from Sunday into Monday. As the moisture from Hilary flows northward, heavy rain will develop over parts of Nevada, eastern Oregon, Idaho, and northwestern Montana. Therefore, the WPC has issued a Slight Risk of excessive rainfall from Monday into Tuesday morning. The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable. In addition, showers and thunderstorms will develop over most of the West Coast inland to the Great Basin, Southwest, Northern Intermountain Region, and Northern Rockies through Monday evening. Furthermore, wildfire smoke over Northern California and the Pacific Northwest has prompted Air Quality Alerts over parts of the Pacific Northwest, Northern Intermountain Region, and Northern Rockies. Meanwhile, a front crossing the Great Lakes will produce scattered showers and thunderstorms over parts of the Upper Great Lakes/Ohio Valley from Saturday evening into Sunday morning. Moreover, the same front will produce showers and thunderstorms over parts of the Northeast Monday into Tuesday. In addition, upper-level energy and tropical moisture will produce showers and thunderstorms over parts of Florida through Sunday night. Further, onshore flow off the Atlantic will continue to produce showers and thunderstorms over the southern tip of Florida through Monday. Furthermore, an upper-level high over the Central Plains/Middle Mississippi Valley will create oppressive daytime heat, limited overnight cooling, which will also contribute to the effects of heat, prompting Excessive Heat Warnings and Heat Advisories over portions of the Central/Southern Plains and a small sliver of the Northern Plains, the Upper/Middle/Lower Mississippi Valley, Central/Western Gulf Coast. In addition, dangerous heat will continue to intensify and expand into the Plains states, with numerous daily high-temperature records expected, especially in the Central Plains and Texas. The heat wave will then expand on Sunday and early next week to include much of the Central and Southeast U.S. Some locations in the Midwest may see their hottest day of the year so far this weekend. Portions of the South Central U.S. and Gulf Coast may further extend their record number of hours with a heat index reading of at least 110ĀF. Moreover, the prolonged nature of the heat wave, combined with very warm overnight temperatures, will limit the relief from the oppressive daytime heat and compound overall heat impacts. Further, excessive heat is anticipated to focus over the southeastern quadrant of the country next week. The greatest risk of excessive heat is for eastern Texas and parts of the Gulf Coast States. Ziegenfelder Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php