Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Thu Jul 15 2021 Valid 12Z Thu Jul 15 2021 - 12Z Sat Jul 17 2021 ...Heavy rain and potential flooding for parts of the Central U.S. and the Desert Southwest... ...Heat wave across the western U.S. abates through the end of the week; some additional hot temperatures possible beginning this weekend... ...Severe weather possible across the Upper Mississippi Valley and Upper Midwest... Intense afternoon and evening thunderstorms with heavy downpours will continue across the Upper Mississippi Valley, Upper Midwest the Desert Southwest. Over the next few days a sprawling, slow-moving cold front over the central/north-central U.S. will be the focus for scattered to widespread thunderstorm development. The environment over these regions will be conducive for high rainfall rates. SPC is expected these storms to be strong/severe over the Upper Mississippi Valley and has this area under an Enhanced Risk. Damaging winds are anticipated to be the primary threat over this area, although large hail and tornadoes are also possible. WPC has much of this same area, including portions of the Central Plains and Midwest, in a Slight Risk for excessive rainfall through Friday morning. As the front slowly shifts eastward, so will the precipitation footprint. The highest amounts are expected across northern Illinois to Ohio Friday and over the Mid-Atlantic and southern portions of the Northeast on Saturday. Monsoon season is in full swing in the Desert Southwest. Moderate to heavy rainfall has been observed this past week and more is on the way. Diurnal heating combined with the deep moisture pooled over the area will trigger afternoon and evening showers, especially near the Four Corners region. Given relatively weak steering winds aloft, many of these storms will likely be slow moving and result in flash floods for canyons, burn scars, and other vulnerable areas. A Slight Risk for excessive rainfall is in effect over Central Arizona and far western New Mexico today and a Marginal Risk area is in effect for eastern Arizona/western New Mexico Friday and Saturday. The ongoing heat wave across much of the western U.S. will relax across the Southwest as monsoonal moisture increases, but noteworthy positive anomalies will still exist across interior portions of the Pacific Northwest and Great Basin through today. Overnight low temperatures are expected to be above normal as well and across a greater portion of the western U.S. compared to the daytime highs. Daily maximums may return to the 100s this weekend for portions of central Montana before spreading westward into Idaho as high pressure builds. An Excessive Heat Watch is in effect beginning from Saturday through Wednesday evening. Elsewhere, warm and humid conditions will persist across much of the Eastern U.S. through the end of the week before cooler weather arrives in time by Saturday. Campbell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php