US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 237 PM EDT Mon Jun 21 2021 Valid Thursday June 24 2021 - Monday June 28 2021 Hazards: - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Ohio Valley, Sat-Sun, Jun 26-Jun 27. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley, Thu-Fri, Jun 24-Jun 25. - Heavy rain across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Northeast, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Sat-Mon, Jun 26-Jun 28. - Flooding possible across portions of the Ohio Valley. - Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, and the Ohio Valley. - Excessive heat across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Fri-Mon, Jun 25-Jun 28. - Excessive heat across portions of the Central Great Basin, the Northern Plains, the Northern Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Sun-Mon, Jun 27-Jun 28. - Excessive heat across portions of the Central Plains and the Southern Plains, Thu-Fri, Jun 24-Jun 25. - Excessive heat across portions of the Central Plains, Thu, Jun 24. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Thu-Sat, Jun 24-Jun 26. Detailed Summary: The medium range forecast period (Thursday, June 24 to Monday, June 28) will feature a building upper-level ridge over the western U.S. and widespread shower/thunderstorm activity associated with a cold front pushing from the Midwest to the Ohio and Tennessee valleys. The aforementioned cold front is forecast to swing into a warm and moist airmass located throughout the eastern United States, sparking numerous thunderstorms and the threat of heavy rain. Rainfall amounts of over 1 inch are possible beginning on Thursday over the Midwest and Upper Great Lakes, before pushing slightly southeastward on Friday. By this weekend, showers and thunderstorm chances will increase from the Lower Mississippi Valley to interior sections of the Northeast. Much of the heavy rain is expected to come to an end by Sunday in the Lower Mississippi Valley, but as the frontal boundary stalls near the Ohio Valley and Lower Great Lakes, lingering rounds of downpours will remain a concern for the Tennessee/Ohio Valleys and Interior Northeast through at least Monday. Outside of the Lower Mississippi Valley, central Indiana, and southwest Ohio, much of the region at risk of seeing heavy rain have been relatively dry as of late. Above average and potentially record-breaking temperatures are expected to impact the Pacific Northwest beginning on Friday and last through the beginning of next week. A strengthening anomalous upper-level ridge will be the culprit for the upcoming heat wave. High temperatures are forecast to soar 20 to 30 degrees above average in Washington, Oregon, and northern Idaho. Triple digit temperatures will be easy to come by throughout the lower elevations, including east of the Cascade Mountains on Saturday. The excessive heat will likely expand south and east by Sunday and Monday, impacting sections of California, the central Great Basin, Northern Rockies, and Northern High Plains. Widespread highs into the upper-90s and triple digits are expected, with even hotter temperatures throughout the Sacramento/San Joaquin valleys and Desert Southwest. Speaking of the Southwest, current forecasts call for above average temperatures, but remain just below hazardous criteria for the region. This will be monitored during future forecast updates. Meanwhile, drought conditions remain extreme throughout the West and will undoubtedly continue or worsen over the next week. Outside of the West, excessive heat is also expected on Thursday and Friday across parts of the central and southern Plains. Heat indices over 105 degrees are possible from north-central Kansas to central Texas on Thursday, before a cold front brings relief to the region by this weekend. For Alaska, a potent low pressure system is forecast to churn over the eastern Aleutians by the end of this week and funnel moisture northward into the Alaskan Panhandle and south-central coastal regions. As a result, heavy rainfall amounts up to 2 inches are possible and could lead to isolated flooding concerns. Snell