Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 336 AM EDT Sat Jun 26 2021 Valid 12Z Sat Jun 26 2021 - 12Z Mon Jun 28 2021 ...A long duration and extreme heat wave is set to grip the Pacific Northwest and Northern Great Basin... ...Continued rounds of showers and potentially severe thunderstorms anticipated between the Southern Plains and Great Lakes, generating a significant risk for flash flooding this weekend... Oppressive and unprecedented heat will be felt throughout the Pacific Northwest and Northern Great Basin today, with record-breaking temperatures lasting through at least the beginning of next week. The weather pattern responsible is highlighted by a strong and highly anomalous upper-level ridge located over far southwestern Canada. This upper-level ridge is forecast to very slowly meander eastward along the U.S.-Canada border. Easterly flow underneath the upper-level high will allow for coastal regions to experience record-breaking temperatures over the next few days as well. Starting today, high temperatures will soar 20 to 30 degrees above average throughout Washington and Oregon, extending into northern Idaho by Sunday. For the Northwest, this equates to widespread high temperatures in the upper 90s and triple digits, with highs into the 110s possible over the Columbia Basin. Dozens of daily record high temperatures will undoubtedly be set, with monthly and even all-time records in jeopardy of falling. In short, heat of this magnitude has very rarely (if ever) been felt throughout this region, especially this early into the summer season. Seattle, WA and Portland, OR are just a few examples of places currently forecast to break all-time high temperature records during this heat wave. Oppressive heat will also be found throughout portions of northern California and western Nevada, where triple digit temperatures are expected. Excessive Heat Warnings/Watches and Heat Advisories have been issued for nearly the entire Pacific Northwest and northern Great Basin, as well as parts of California and Nevada. Nighttime temperatures will remain quite warm and only dip into the 70s throughout lower elevations of the Northwest, which could exacerbate the threat of heat related illnesses. Residents are urged to avoid extended periods of time outdoors, stay hydrated, and check on vulnerable family members/neighbors. With severe and extreme drought conditions found throughout much of the West, elevated fire concerns exist. Hazardous weather is also likely to impact parts of the central United States this weekend, in the form of severe thunderstorms and flash flooding. A slow-moving cold front is expected to become stationary at times between the Southern Plains and Great Lakes through Monday morning. Heavy rain and thunderstorms are expected to focus along this frontal boundary and repeat over similar areas, which will likely lead to compromised soils and an increased flash flood threat. A Moderate Risk (level 3/4) of Excessive Rainfall has been issued for today between northern Texas and southwest Missouri. Widespread rainfall totals over 1 inch, with local amounts up to 5 inches can be expected here. The heavy rain threat should slowly dissipate by the end of the weekend, but scattered downpours and instances of flash flooding will remain a concern on Sunday from the Southern High Plains to the Middle Mississippi Valley. Flash Flood Watches currently remain in effect between Lower Michigan and north-central Texas. Severe weather is also possible today, particularly throughout the Southern Plains and central/lower Michigan. The Storm Prediction Center has issued a Slight Risk (level 2/5) of severe thunderstorms for these regions. Damaging wind gusts, large hail, and isolated tornadoes are possible. Elsewhere, below average temperatures are forecast throughout the central and southern High Plains behind a cold front, while warmer temperatures and increasing humidity returns to the East Coast. In fact, above average temperatures and highs into the 90s are forecast throughout the Northeast by Sunday. Isolated and slow-moving thunderstorms are also expected to impact areas along the Gulf Coast this weekend. Snell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php