US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 437 PM EDT Tue Jul 13 2021 Valid Friday July 16 2021 - Tuesday July 20 2021 Hazards: - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Sun-Tue, Jul 18-Jul 20. - Heavy rain across portions of the Central Plains, the Northeast, the Central Appalachians, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Fri-Sat, Jul 16-Jul 17. - Flooding possible across portions of the Southeast, the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding possible across portions of the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Southeast, the Middle Mississippi Valley, and the Southern Plains. - Flooding occurring or imminent across portions of the Southeast, the Middle Mississippi Valley, and the Southern Plains. - Flooding likely across portions of the Middle Mississippi Valley. - Excessive heat across portions of the Northern Rockies and the Northern Great Basin, Sun-Tue, Jul 18-Jul 20. - Excessive heat across portions of the Northern Plains, Fri-Tue, Jul 16-Jul 20. Detailed Summary: The medium range forecast period (Friday, July 16th to Tuesday, July 20th) will feature a rather stagnant synoptic pattern, including a stationary closed low off the coast of British Columbia, an amplifying ridge over the Four Corners, and a weak trough propagating through the Great Lakes and Northeast by early next week. This weather pattern is expected to lead to numerous chances for thunderstorms and heavy rain to the Central Plains, East Coast, and South. With the eastward progression of the upper trough Friday morning, an associated cold front and low pressure wave is forecast to traverse the Great Lakes before swinging south through the Central Plains, Middle Mississippi Valley, and Northeast through the weekend. Downpours will quickly exit Michigan by Friday, with lingering thunderstorms capable of producing higher rainfall rates from the Northeast into the Central Plains through Sunday. As the aforementioned frontal boundary slowly stalls throughout the Middle Mississippi Valley beginning Monday, continued reforming rounds of convection can be expected to spark and track southeastward into portions of northern Arkansas and western Tennessee. By Tuesday, the front is forecast to sag further south toward the Lower Mississippi Valley and further serve as a catalyst for thunderstorm development over the area. A broad Heavy Rain area was added over much of the South and Mid Atlantic toward the end of the forecast period based on the ensemble signal for heavy rain in the region, although uncertainty with the event precludes a more focused Heavy Rain area. Elsewhere, before the upper-level ridge strengthens over the Rockies late this weekend/early next week, additional monsoonal moisture is expected to reach parts of the Southwest. Scattered shower activity is forecast, but rainfall amounts below an inch will keep any rain below hazard levels at this time. Heat is also expected to remain a concern throughout parts of the West and north-central United States during the medium range period. The highest temperature anomalies are currently expected over the Northern High Plains, where high temperatures could enter the triple digits for several consecutive days beginning on Friday. Hot weather and above average highs into the mid-90s are forecast across North Dakota and into northern Minnesota as well, but these values currently don't reach hazardous criteria. Nonetheless, much of the Dakotas, northeast Wyoming, and the western half of Minnesota are experiencing severe to exceptional drought that will likely worsen due to the upcoming heat and lack of rain. Most of the Northern Rockies and Great Basin won't get a break from the ongoing oppressively hot summer. Above average temperatures are forecast through early next week, with highs into the upper-90s and low triple digits across lower elevations. For Alaska, a general increase in precipitation is expected to enter western portions of the state by Saturday. Some isolated heavy rains atop above average streamflows in Northwest Alaska on the 18th-20th will be monitored for a potential Heavy Rain area in future updates. Asherman/Snell