Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Thu Jun 20 2024 Valid 12Z Thu Jun 20 2024 - 12Z Sat Jun 22 2024 ...Heavy rain/flooding threats and gusty winds over South Texas gradually decrease today as Tropical Storm Alberto makes landfall in Mexico and dissipates... ...Heavy rain and flash flooding concerns increase across the northern Plains to the upper Midwest later Thursday into Friday as scattered thunderstorms could result in localized flooding issues from the southern High Plains to the Four Corners... ...A heat wave will persist over the Great Lakes, Ohio Valley, and portions of the Northeast into the weekend as heat intensifies in the western U.S.... Tropical Storm Alberto centered over the southwestern Gulf of Mexico has begun heading west toward northern Mexico early this morning. Organized bands of heavy rain extending north from the center have already brought close to 10 inches of rain locally near the mid-Texas coast. As the heavy rain bands continue to steadily move west through the Rio Grande Valley into northern Mexico today, the heavy rain and flooding threats will gradually decrease across South Texas. Strong and gusty winds will also gradually weaken with time. Some of the tropical moisture from Alberto will be drawn northward and energize the scattered showers and thunderstorms from the southern High Plains to the Four Corners heading into the weekend. These showers/storms will be more numerous during the late afternoon to early evening hours in these areas. Meanwhile, the National Hurricane Center continues to monitor the potential of tropical cyclone formation over the western Atlantic as a tropical wave moves west-northwest in the general direction of northeastern Florida and Georgia. Some enhanced rainfall with gusty winds can be expected to reach these areas Thursday night and will likely linger through much of Friday. Across the northern tier states, relatively less active weather is expected today as a high pressure system brings cooler and more stable air from Canada. However, the next piece of energy exiting the central Rockies will set up the next episode of heavy rain and strong to severe storms across the northern Plains to the upper Midwest beginning tonight. A couple rounds of heavy rain focusing just north of a nearly stationary front across the region will result in slight to moderate risks of excessive rainfall from eastern South Dakota, across southern Minnesota into western Wisconsin through Saturday morning. Farther east, scattered thunderstorms are likely across the Great Lakes region and the Northeast near and north of the stationary front. Marginal to slight risks of severe storms are delineated each day from the Storm Prediction Center (mainly for the threat of severe wind but with some low chances for hail), and marginal risks of excessive rainfall are in place as well. All these rain and thunderstorm areas are taking place along the periphery of an upper ridge/heat dome that edges from the Mid-Atlantic into the Mid-South over the next couple of days and sustains a heat wave across the Great Lakes, Northeast, and Mid-Atlantic. Afternoon high temperatures and warm overnight lows will challenge daily records and even some monthly and all-time records. Heat index readings are expected to peak from 100 to 105 degrees in many locations. Those without access to reliable air conditioning are urged to find a way to cool down. Record warm overnight temperatures will prevent natural cooling and allow the heat danger to build over time indoors without air conditioning. Temperatures may be lower and less hazardous closer to the coast if/where sea breezes form. By Friday, conditions should improve over New England as cooler air dips a bit farther south into the area behind a front, but temperatures well into the 90s and higher heat indices are forecast to continue across the Ohio Valley to Mid-Atlantic. Meanwhile, cooler than average highs are likely into the southern High Plains with the clouds and rain forecast, but temperatures over the West will gradually rise above normal Thursday and Friday. In the western U.S., it appears that the heat will increase by Saturday as triple-digit high temperatures are forecast for the Central Valley of California and the Great Basin. Kong/Tate Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php