US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 356 PM EDT Wed Jun 23 2021 Valid Saturday June 26 2021 - Wednesday June 30 2021 Hazards: - Heavy rain across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, the Great Lakes, and the Ohio Valley, Sat, Jun 26. - Heavy rain across portions of the Middle/Lower Mississippi Valley, the Great Lakes, the Ohio Valley, and the Tennessee Valley, Sat-Tue, Jun 26-Jun 29. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Sat-Sun, Jun 26-Jun 27. - Heavy rain across portions of Florida, Tue-Wed, Jun 29-Jun 30. - Flooding possible across portions of the Middle/Upper Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley. - Excessive heat across portions of the Pacific Northwest, California, the Northern Great Basin, and the Northern Rockies, Sat-Wed, Jun 26-Jun 30. - Excessive heat across portions of the Pacific Northwest and the Northern Great Basin, Sat-Mon, Jun 26-Jun 28. - Excessive heat across portions of the Pacific Northwest, California, the Northern/Central Great Basin, the Northern Rockies, and the Southwest, Sun-Wed, Jun 27-Jun 30. - Excessive heat across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin, Tue-Wed, Jun 29-Jun 30. Detailed Summary: The medium range forecast period (Saturday, June 26 to Wednesday, June 30) will feature a persistent and strong upper-level high initially centered over southwestern Canada and moving into the northwestern U.S., while upper-level troughing will be centered over the Midwest. The anomalous upper high is expected to cause much above average and likely widespread record-breaking temperatures this weekend into the first half of next week in the West. Temperatures should warm to 20 to 30 degrees above average beginning Saturday across Washington and Oregon. Seattle, for example, can expect several days in a row in the 90s and nearing 100 degrees, while Portland should see temperatures over 100. The hot temperatures are also forecast to expand eastward early next week into Idaho and Montana, as well as southward into interior portions of California and the Intermountain West, with highs nearing or exceeding 100, depending on the region and elevation. Temperatures in the Pacific Northwest are forecast to gradually moderate on Tuesday into Wednesday as the upper high pivots a bit east, but will remain persistently hot through midweek in the Great Basin. Temperatures in the Desert Southwest are forecast to be in the low 110s--but this would only be a few degrees above normal, and not quite meeting hazardous criteria. Meanwhile, drought conditions remain extreme throughout the West and will undoubtedly continue or worsen over the next week in the Northwest given the heat and no expected rainfall in the medium range period. However, some welcomed moisture is likely to impact New Mexico next week, and some showers may occur in Arizona and Colorado by around midweek as well. Elsewhere, the upper-level trough is expected to slowly push a couple of fronts across the central U.S. late this week into early next week. Abundant moisture streaming into the vicinity should cause numerous showers and thunderstorms, while gusty winds are also possible with the fronts. Rainfall will begin during the short range period across the Middle Mississippi Valley and Midwest, and the slow initial frontal push will spread rainfall into the Ohio Valley as well by Saturday. Rounds of rain are expected to remain across the Ohio Valley back into portions of Missouri, Arkansas, and Tennessee as another frontal boundary catches up to the initial front, providing areas for the moisture to focus and produce storms and possibly flooding, as multi-day rainfall totals of several inches are likely. Heavy rain is also possible in the Southern Plains into New Mexico this weekend near the southwestern portion of the cold front. Fortunately, much of the Middle Mississippi Valley has been relatively dry over the last month or so, but areas from northern Texas into the Lower Mississippi Valley and portions of the Ohio Valley have seen wetter conditions. There is potential for scattered thunderstorms all the way to the Eastern Seaboard, but heavy rainfall is not currently expected to be too widespread there. The main exception could be in the Florida Peninsula, which could see tropical moisture causing rain amounts of an inch or two there around midweek. Also, some areas in the northeastern U.S. could see localized heavy rain, so this area will continue to be monitored, as frontal and upper trough timing become more clear. In Alaska, a surface low is forecast to approach and cross the Aleutians by next Monday into Wednesday, setting up a moist flow pattern into the Alaska Peninsula. This should lead to at least moderate rainfall there, but whether or not rainfall amounts will be heavy or hazardous is still uncertain. Gusty winds are also possible with that low pressure system. Additionally, farther north, cool temperatures return to the Brooks Range by around Tuesday next week, and some precipitation there could be in the form of light snow. Tate