Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 308 AM EDT Wed Sep 04 2024 Valid 12Z Wed Sep 04 2024 - 12Z Fri Sep 06 2024 ...Heat wave builds over the Southwest and the West Coast this week... ...Heavy rain and flash flood potential continues for the Gulf Coast states the next couple of days... An upper-level ridge building northward over the West Coast will help to expand and intensify a heat wave over the region through the next few days. Forecast highs today (Wednesday) range from the upper 100s to mid-110s in the Desert Southwest, the mid-90s to low 100s for southern and central California, and the mid-90s to low 100s for portions of the Pacific Northwest. Temperatures soar even higher on Thursday, with highs into the 110s for the Desert Southwest, the 100s to near 110 in southern California, the mid-100s for the central California Valleys, and the low 100s for portions of the Pacific Northwest. Widespread heat-related warnings and advisories are in place as the threat for heat-related illness and impacts will increase today and especially on Thursday. This heat will be dangerous to anyone without effective air conditioning or sufficient hydration. While not quite as hot, temperatures will also be well above average along the immediate Pacific Coast, with highs into the 80s for many locations. Heavy rain and the threat for flash flooding will remain in the forecast for the Gulf Coast states this week as a stationary front and coastal low drive multiple days of widespread showers and thunderstorms across the region. The placement of the elongated area of low pressure in the western Gulf will keep the focus for the most widespread rainfall over portions of the central and upper Texas Gulf Coasts, and possibly a bit further north into the Lower Mississippi Valley. Extremely moist Gulf air will lead to very heavy downpours (upwards of 2-3" per hours rates) with continued rounds of storms moving onshore. Forecast areal average rainfall totals are in the 3-5" range, with locally higher amounts of 7"+ possible, most likely near the immediate coast. A Slight Risk of Excessive Rainfall (level 2/4) is in place for the region both today and tomorrow given the threat for scattered instances of flash flooding. Storms will also increase along the southeastern Atlantic Coast today and Thursday, and daily thunderstorm chances will continue for the Florida Peninsula. The passage of the frontal boundary to the coast and widespread storms and clouds will keep temperatures down across Texas and the Southeast the next couple of days, with highs generally in the 80s. Conditions will be hotter south of the boundary in Florida with temperatures into the 90s. A Heat Advisory is in place for South Florida today as the combination of highs into the 90s and high humidity will lead to heat indices in the 105-110 degree range. Elsewhere, much of the eastern U.S. outside of the the South will be dry with generally mild temperatures. Early Fall-like highs in the 70s are expected throughout New England, the Mid-Atlantic, and Carolinas through Thursday. An upper-level ridge passing over the Midwest will bring temperatures back up into the mid- to upper 80s over the next couple of days. An approaching upper-level trough/surface frontal system will bring shower and thunderstorm chances to portions of the Central/Northern Plains and Upper Midwest today, with the greatest storm coverage and chance for some more moderate rainfall in the Upper Midwest and the central High Plains/adjacent Rockies. The frontal system will push further southeastward on Thursday, bringing storm chances to the Great Lakes, Central Plains, and central/southern High Plains/adjacent Rockies. Once again, the greatest storm coverage and heavier rainfall will be focused to the north over the Great Lakes and to the southwest over the central/southern High Plains and adjacent Rockies. Some isolated flash flooding will be possible over the southern Rockies given more sensitive soils from recent rainfall and over any burn scars. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php