US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 515 PM EDT Tue Jul 20 2021 Valid Friday July 23 2021 - Tuesday July 27 2021 Hazards: - Heavy rain across portions of the Southern Rockies, the Central Great Basin, and the Southwest, Fri-Tue, Jul 23-Jul 27. - Heavy rain across portions of the Great Lakes, Sat, Jul 24. - Flooding occurring or imminent across portions of the Central Plains, the Middle Mississippi Valley, the Southern Plains, and the Ohio Valley. - Flooding occurring or imminent across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains. - Flooding likely across portions of the Central Plains and the Middle Mississippi Valley. - Excessive heat across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, the Ohio Valley, and the Tennessee Valley, Sun-Tue, Jul 25-Jul 27. - Excessive heat across portions of the Northern Plains, Thu, Jul 23 and Mon, Jul, 26. - Excessive heat across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Fri, Jul 23 and Mon, Jul26. - Excessive heat across portions of the Central Plains and the Middle Mississippi Valley, Mon-Tue, Jul 26-Jul 27. - Much above normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Sat-Mon, Jul 24-Jul 26. - Much above normal temperatures across portions of the Central Plains, the Northern Plains, the Great Lakes, the Northern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Fri-Mon, Jul 23-Jul 26. Detailed Summary: Heavy rain associated with the Monsoon in the Southwest as well as hot weather across the Central/West U.S. remain the primary headlines for the medium-range hazards forecast period (Friday, July 23 - Tuesday, July 27). Additional moderate to heavy rain is expected to spread from Northern Tier into the Northeast this weekend into next week ahead of a frontal system. Over the Desert Southwest, daily heavy rain associated with the Southwestern Monsoon is expected to continue through the entirety of the forecast period, with a steady influx of moisture progressing slowly northward. Locally enhanced rainfall is possible over the region ahead of a weak upper-level low retrograding westward, with the usual caveat of uncertainty regarding the timing and placement of weak features at the medium range. Regardless of shortwave influences, the persistence of deep moisture over the region through the next week supports a broad heavy rain footprint over the area. Moreover, areas containing inundated soils from previous rain or burn scars will be especially sensitive to heavy rainfall. Accordingly, the Heavy Rain area was expanded over much of Arizona into South Utah to address this possibility. More excessive heat and above average temperatures are on the way for the interior Pacific Northwest and Central U.S. as a high pressure center migrates into the Central Plains from the Gulf of Mexico later this weekend. Meanwhile, an upper ridge will take shape over the Great Basin in the wake of a closed low over Central Canada. High temperatures are forecast to remain 5-10 degrees above average throughout the Much Above Normal Temperatures areas, generally in the mid-upper 90's. Excessive Heat is likely over the Dakotas on Friday as maximum heat indices approach 110 degrees. Heat indices abate somewhat over the Northern Plains as a cold front ushers in dry continental air this weekend, but high temperatures will generally remain above average in the 90's. One more round of Excessive Heat is possible over the Northern Plains on the 26th as Gulf moisture returns north and heat indices hit 100-105. Further south in the Central/Southern Plains, the persistent high pressure center overhead combined with the tropical airmass will make for unpleasant heat to begin next week. In the Central Plains, several days in a row of heat indices hitting 105 combined with appreciable ensemble probabilities of low temperatures exceeding 80 degrees prompted the addition of Excessive Heat in the area through the 27th. Over the Ozarks, the Excessive Heat area was expanded until the 27th to correspond with the forecast 110 degree heat index area. Ahead of the aforementioned front in the Great Lakes, thunderstorms producing moderate to locally heavy rainfall are possible on Saturday before the front pushes east by Sunday. Some higher rain amounts are possible over the Northeast/New England early next week, but uncertainty regarding the timing and placement of the front and associated frontal waves precludes a Heavy Rain area at this time. For Alaska, rain showers are expected for the eastern Kenai Peninsula on Saturday and east into the Panhandle on Saturday and Sunday ahead of a storm system over the Gulf of Alaska. There is reasonable convergence between guidance for marginally hazardous rainfall totals, in the area, but dry antecedent conditions will limit any impact from the rain. Additionally, generally below normal temperatures are expected across the mainland through the period, particularly in the Far North. These temperatures are not expected to be hazardous at this time. Asherman