Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 352 AM EDT Mon Jul 23 2018 Valid 12Z Mon Jul 23 2018 - 12Z Wed Jul 25 2018 ...Moderate risk of flash flooding possible across the Mid-Atlantic and Northeast today and Tuesday... ...Dangerous heat to continue across the southern central and portions of the western U.S... An upper low will bring copious amounts of moisture across the East Coast--and combining this with a frontal boundary draped across the Carolinas and into the Mid-Atlantic will bring unsettled weather the next few days. Showers and thunderstorms will give way to heavy rainfall throughout the short term period. Because of the recent heavy rainfall activity, any more activity will exacerbate conditions. Thus, a moderate risk of flash flooding will be possible across the Mid-Atlantic and the Northeast today and Tuesday. Dangerous heat remains in place across the southern Plains, lower Mississippi Valley, and much of the Southwest and far western United States. This heat is expected to remain in place today across the southern Plains and lower Mississippi Valley--with temperatures dipping into the mid to low 90s by Tuesday. However, the Rio Grande Valley will continue to be very warm with high temperatures in the mid to upper 100s. The western U.S. will experience the oppressive heat through at least the short term period. Excessive heat watches, warnings and heat advisories are currently in place across these regions. By Tuesday, the Desert Southwest will see temperatures climb well above 110 degrees--with places like Phoenix, AZ forecast to reach 117 degrees, Las Vegas, NV forecast to reach 114 degrees. A frontal system will sweep across the Mississippi Valley and central Plains today and bring showers and thunderstorms along its boundary. Meanwhile, a plume of deep moisture will extend from the western Gulf of Mexico into Colorado and New Mexico. Thunderstorms are expected throughout the short term period--with highest coverage in the late afternoon/early evening. A slight risk of flash flooding is possible particularly in favorable terrain. In addition, the Sierra Nevada mountains can also expect diurnally driven thunderstorms--where a marginal risk of flash flooding is possible. Elsewhere, showers and thunderstorms in northwest Florida will be possible today and Tuesday. Some of these thunderstorms could move quite slowly and produce heavy downpours--leading to a marginal risk of flash flooding for today. Reinhart Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php