US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 513 PM EDT Wed Jul 21 2021 Valid Saturday July 24 2021 - Wednesday July 28 2021 Hazards: - Heavy rain across portions of the Southern Rockies, the Central Great Basin, and the Southwest, Sat-Tue, Jul 24-Jul 27. - 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 occurring or imminent across portions of the Southeast and the Middle Mississippi Valley. - 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-Wed, Jul 25-Jul 28. - Excessive heat across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Mon-Wed, Jul 26-Jul 28. - 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 Southern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Great Lakes, Sun-Wed, Jul 25-Jul 28. Detailed Summary: Heavy rain associated with the Southwest Monsoon and hot weather across the Central/West U.S. remain the primary headlines for the medium-range hazards forecast period (Saturday, July 24 - Wednesday, July 28). Moderate to locally heavy rain chances will extend across the Plains into the Northeast early next week, before the focus shifts to the Great Lakes by Wednesday. No changes have occurred regarding the Heavy Rain area over the Desert Southwest. The beginning of the forecast period (Saturday) falls in the middle of an active Southwest Monsoon, with daily heavy rain expected through Tuesday along the envelope of slow moving deep Pacific moisture. Local enhancement of rainfall is possible over the region ahead of an upper-level low retrograding westward, with the usual caveat of uncertainty regarding the timing and placement of shortwave features at the medium range. Areas containing inundated soils rainfall this week or burn scars will be especially sensitive to heavy rainfall. Otherwise, clouds and rain will provide relief from the usual desert heat, with afternoon temperatures 10-15 degrees below average possible through Wednesday over the Southwest and South-Central Great Basin. Rainfall also should assist with the prolonged drought conditions that blanket the majority of the region. North of the monsoon activity, hot weather will linger over the interior Northwest until Monday as a high pressure center parks over the Great Basin on Saturday, with high temperatures anomalies greater than 10 degrees forecast. Since yesterday, the north portion of the Much Above Normal Temperatures area was trimmed to better align with the anomalous high temperature forecast. Beginning Monday, temperatures in the lee of the Cascades will moderate to around seasonal as the aforementioned high pressure strengthens over the Central Plains. Showers are possible over the North Great Basin into Southwest Montana as remnant monsoon moisture wraps around the newly located high pressure, which would provide some much needed drought relief there. As temperatures abate in the west, the consolidating upper-high over the Plains will pull Excessive Heat east of the Rockies beginning Monday. Triple digit high temperatures resume within the Excessive Heat over eastern Montana into the Dakotas through Wednesday. A weak frontal system is forecast to pass through on Tuesday, but will do little to quell the heat overall. Given the recent impacts from extreme heat in the region, synoptic footprint of a strengthening upper ridge, and supporting ensemble probabilities of exceeding 100 degrees, the Excessive Heat area was extended until the 28th. Over the Central Plains the Excessive Heat area was left largely the same, as anomalous triple-digit highs collocated with lows exceeding 80 degrees remain a possibility. Thunderstorms initiating along a front in the Northeast Missouri Valley could throw a wrench in the the heat that materializes, but specifics are unclear at the medium range. Elsewhere, the Excessive Heat area in the Ozarks/Southern Plains was extended until the 28th, where sweltering maximum heat indices of 110 are possible. Similar to the Central Plains, thunderstorm development may impact the heat that materializes but confidence in specifics is low. Summer heat aside, multiple rounds of thunderstorms are expected throughout the medium range. Moderate to locally heavy rain is possible from the Great Lakes into the Northeast later this weekend ahead of a cold front. As the front slides east on Monday, rain chances will expand from New England into the Plains. Some deterministic guidance depicts some higher totals around the front Monday and Tuesday, but overall a fair amount of uncertainty still exists regarding the timing and placement of heavier amounts that limits confidence in a Heavy Rain area. Another round of thunderstorms is expected over the upper Midwest on Wednesday as another cold front pushes through the Great Lakes, but totals remain below hazard levels as of now. 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 system over the Gulf of Alaska. Additionally, generally below normal temperatures are expected across the western mainland through the period. These temperatures are not expected to be hazardous at this time. Some higher amounts are possible along the West Coast of Alaska as a system approaches from the Aleutians toward the later half of the forecast period, but confidence is too low to introduce a Heavy Rain area. Asherman