Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Thu Jun 17 2021 Valid 12Z Thu Jun 17 2021 - 12Z Sat Jun 19 2021 ...Dangerous and record-breaking heat will continue across portions of the West and Central Plains, along with fire danger... ...Severe thunderstorms and heavy rainfall causing flash flooding are possible throughout the Midwest on Thursday and Ohio Valley on Friday... ...Tropical rains and potential for flash flooding are expected to approach the central Gulf Coast beginning Friday... The persistent and extreme heat wave being felt across the western U.S. is set to continue and even expand over the next couple of days. A strong upper-level ridge over the Southwest is expected to remain in place through the end of the week, while only slightly weakening. High temperatures 10 to 25 degrees above average will spread into central and northern California today, before reaching portions of the Northern Great Basin by Friday. Dangerous and potentially deadly heat will continue throughout the Southwest and Intermountain West during this time period as well--highs into the 110s and even 120s are likely throughout the Desert Southwest. Meanwhile, widespread triple digits will be felt throughout California and lower elevations of the Central Great Basin and Central Rockies. A brief period of sweltering heat should also impact areas farther east across the Central Plains and Middle Mississippi Valley to end the workweek, with highs in the upper 90s and low 100s stretching from eastern Colorado to southern Illinois. Much of the aforementioned regions from the West to Midwest could see dozens of daily record high temperatures set. A few monthly and even all-time records have already been tied/broken this week associated with the current stretch of heat. Widespread Excessive Heat Warnings and Heat Advisories are in effect for the southwestern quadrant of the country as well as the Central Plains/Middle Mississippi Valley today. Residents enduring the abnormal heat are urged to stay hydrated and avoid extended periods of time outdoors if possible. With warm temperatures and dry soil in place, fire danger is another threat. A Critical Risk of fire weather is in place today for southern Wyoming, while Elevated Risks stretch across much of the Great Basin to Rockies and Northern Plains. Dry thunderstorms (containing lightning that could start fires with no rain reaching the surface) are also a concern across portions of California, Nevada, and the Four Corners states through at least Friday. A weak area of low pressure and associated frontal boundaries will fuel scattered showers and thunderstorms over the Midwest today into tonight. An Enhanced Risk of severe weather and a Slight Risk of excessive rainfall are in place there today, as these storms are capable of producing damaging wind gusts, large hail, tornadoes, and flash flooding. Then on Friday, storms are forecast to shift into the Ohio Valley. Slight to Enhanced Risks of severe weather are in place for Illinois to western Pennsylvania, with scattered flash floods possible for that region as well. Farther south, an area of low pressure in the Bay of Campeche is likely to develop into a tropical cyclone over the next 48 hours per the National Hurricane Center. Regardless of tropical cyclone status, however, the low is expected to drift northward across the Gulf of Mexico and spread abundant tropical moisture into the central Gulf Coast beginning Friday, causing heavy rainfall. Much of southern Louisiana has received double their normal rainfall over the last month; therefore, tropical moisture entering the region would exacerbate flooding concerns. A Slight Risk of excessive rainfall is currently in place for the central Gulf Coast for Friday into Friday night, with a Moderate Risk beginning Saturday. Tate/Snell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php