US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 506 PM EDT Fri Jul 16 2021 Valid Monday July 19 2021 - Friday July 23 2021 Hazards: - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Mon, Jul 19. - Heavy rain across portions of the Southern Plains, Tue-Wed, Jul 20-Jul 21. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Tue, Jul 20. - Heavy rain across portions of the Southwest, Mon-Thu, Jul 19-Jul 22. - Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding possible across portions of the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Central Plains, the Southeast, and the Middle Mississippi Valley. - Flooding occurring or imminent across portions of the Southeast and the Middle Mississippi Valley. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains. - Excessive heat across portions of the Central Great Basin, the Northern Rockies, and the Northern Great Basin, Mon, Jul 19. - Excessive heat across portions of the Northern Plains, Mon-Thu, Jul 19-Jul 22. - Excessive heat across portions of the Upper Mississippi Valley and the Northern Plains, Wed-Fri, Jul 21-Jul 23. - Much above normal temperatures across portions of the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, the Northern Great Basin, and the Upper Mississippi Valley, Mon-Fri, Jul 19-Jul 23. - Much above normal temperatures across portions of the Central Rockies, the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Wed-Fri, Jul 21-Jul 23. - Heavy rain across portions of mainland Alaska, Mon-Wed, Jul 19-Jul 21. Detailed Summary: During the medium range forecast period (Monday, July 19th to Thursday, July 23rd), an upper-level trough settling into the Northeast will inch a slow moving cold front southward across the Mid Atlantic, Tennessee Valley, and Southern Plains. On Monday, heavy rain is possible over southern Kansas into the Ozarks as the front initiates additional rounds of storms in addition to any lingering convection from the day prior. Beginning Tuesday, the front is forecast to stall over Northeast Texas, across the South, and into the Carolinas. Model guidance continues to indicate the likelihood of moderate rainfall ahead of the stalled front but with a fair amount of uncertainty regarding if and where low pressure waves will form and develop along the front. The development of these frontal waves will be important in determining if and where heavier rainfall and thunderstorms will be triggered. The highest chance for heavy rain resides over Southeast Oklahoma, ArkLaTex, and South-Central Texas Tuesday through Wednesday. Deterministic and ensemble guidance is in reasonable agreement regarding a lobe of vorticity cutting off from the main upper-trough over the region, which combined with frontal forcing would support locally higher rainfall totals over the highlighted Heavy Rain areas. Over the southern Rockies into the Desert Southwest, monsoonal moisture will keep a good chance of showers and afternoon/early evening thunderstorms through the medium-range period. Most areas should see rainfall below hazard levels but the upslope portion west of the Mogollon Rim to the Gila Mountains in Arizona appears to be under the highest threat of heavy rain through the middle of next week when models indicate an influx of monsoonal moisture from the south. Meanwhile, the heatwave is expected to continue from the central and northern Great Basin eastward across the northern Plains and into the upper Midwest under a persistent upper ridge through much of the medium range period. The highest temperature anomalies are expected over the northern High Plains, where high temperatures into the triple digits are forecast through midweek next week. The Excessive Heat area over Montana into the Dakotas was extended until next Thursday to reflect lingering highs over 100 concurrent with very high heat risk areas per NWS HeatRisk guidance. In Idaho on Monday, the Excessive Heat was trimmed to the eastern Snake River Valley where the hottest high temperatures are expected and an Excessive Heat Watch resides. Moreover, a new Excessive Heat area was introduced beginning Wednesday across the Dakotas and West Minnesota where several days in a row of triple digit heat indices are forecast. In addition, 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 persistent heat and lack of rain. Alaska will likely enter an extended period of wet weather toward the middle of next week as a series of occluded cyclones is forecast to steadily move across the Bering Sea toward Mainland. Only a small area of heavy rain is indicated over portions of northwestern Alaska Tuesday to Wednesday ahead of the arrival of the first cyclone. However, widespread moderate rainfall can be expected to make steady progress across much of Alaska through the middle of next week. Areas toward the Kanai Peninsula could see higher rainfall amounts from the 21st-22nd, but there are discrepancies as to if the totals reach hazard values. As such, did not include a Heavy Rain area at this time. Asherman/Kong