Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 421 AM EDT Mon Aug 17 2020 Valid 12Z Mon Aug 17 2020 - 12Z Wed Aug 19 2020 ...Record heat wave across the western U.S. will culminate today before gradually becoming less intense as fire weather risk persists... ...Relatively cool conditions will prevail from the Plains to the East Coast with occasional showers and storms from the Mississippi Valley to the East Coast... A strong ridge of high pressure aloft is forecast to reach peak intensity today with more record heat for many locations across the western U.S. Excessive Heat Warnings and Heat Advisories engulf much of the western third of the Lower 48 except the Sierra Nevada. Actual high temperatures are forecast to soar well pass the century mark for the hottest locations in the interior Pacific Northwest, while temperatures at some locations in the Desert Southwest will exceed 120 degrees. The persistent heat and dry conditions coupled with spotty thunderstorms could produce dry lightning that would lead to the development of wildfires especially across the interior Northwest. The strong upper ridge is forecast to begin weakening slowly by Tuesday, bringing very slow moderation of temperatures into much of the region. However, temperatures are still expected to reach record levels over much of the Southwest for the next few days. Meanwhile, the southern Plains will see a break in the stifling heat today as a welcomed surge of cooler air behind a cold front drops temperatures by about 10 degrees or so. The eastern half of the country can also expect cooler temperatures and more comfortable conditions than our western neighbors thanks to upper level troughing aloft. This is due to a series of cold fronts sweeping across the Plains and exiting off the East Coast. Some thunderstorms are expected along the Eastern Seaboard today ahead of the lead cold front. Farther west, a weak low pressure system forming on a reinforcing cold front is expected to bring some thunderstorms across the Midwest and Ohio Valley today followed by the interior eastern U.S. on Tuesday. Lingering thunderstorms are expected across the Southeast as well as southern Texas where tropical moisture remains entrenched. Triple-digit high temperatures will be confined to southern Texas for the next couple of days. Kong/Mullinax Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php