US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 405 PM EDT Thu Apr 01 2021 Valid Sunday April 04 2021 - Thursday April 08 2021 Hazards: - Flooding possible across portions of the Southeast and the Tennessee Valley. - Flooding occurring or imminent across portions of the Middle/Lower Mississippi Valley, the Ohio Valley, and the Tennessee Valley. - Much above normal temperatures across portions of California and the Southwest, Sun-Mon, Apr 4-Apr 5. - Heavy rain across portions of the Central/Southern Appalachians, the Ohio Valley, and the Tennessee Valley, Thu, Apr 8. - Heavy snow across portions of mainland Alaska, Sun, Apr 4. - Much below normal temperatures across portions of mainland Alaska, Tue-Thu, Apr 6-Apr 8. Detailed Summary: During the medium range period (Sunday, April 4th - Thursday, April 8th), persistent ridging aloft at the start of the week will keep the weather relatively quiet precipitation-wise while simultaneously opening the door for temperatures to soar well above normal for a significant portion of the CONUS. From the Desert Southwest to the Upper Midwest temperature departures ranging from 15 to 25 degrees above average are expected Sunday and Monday, potentially breaking numerous daily high temperature records throughout the affected regions. Though the greatest temperature anomalies are forecast for the Central and Northern Great Plains they are not anticipated to be hazardous, as highs will only reach into the 70s and 80s. Conversely, in the Desert Southwest highs are expected to reach the mid to high 90s and may hit triple digits in some areas. According to NWS Phoenix, if Phoenix were to hit 100 degrees on either Sunday or Monday, it would be "the third earliest arrival time for the triple digits." Residents of southwestern Arizona and southeastern California should exercise caution when outside to prevent dehydration and heat stroke. High temperatures will begin to moderate over the southwest and north-central CONUS on Tuesday as the upper-level ridge progresses eastward, giving the South and East their own taste of warm weather for a few days, and cold fronts pass through the Plains and the Southwest. With the arrival of an upper-level trough over the Pacific Northwest comes the return of wet weather over the lower 48 after a short reprieve. To the south and east of this trough multiple low pressure/frontal systems are expected to pass through the West and Northern Tier, bringing with them a mix of light to moderate rain and high elevation snow through Wednesday. Though current model guidance suggests the rain could be heavy at times, their deterministic and ensemble solutions are in stark disagreement with regards to the timing and location of the heaviest rainfall due to differing evolutions of the upper-level trough. This high degree of uncertainty precludes the inclusion of a heavy rain area at this time. Despite the disparity in the models through Wednesday, it does appear some degree of consensus is reached come Thursday. Though the deterministic solutions are somewhat spread, the ensembles appear to cluster around a heavy rain signal in the Ohio and Tennessee Valleys. As such, a heavy rain area has been drawn for that region for Thursday and will be adjusted in the coming days as predictability increases and the guidance comes into focus. Elsewhere on Thursday, a cold front moving onshore into the Pacific Northwest will likely bring moderate coastal rain and high elevation snow to the region. In Alaska, a cold front is expected to pass through the mainland on Sunday bringing heavy snow to portions of the Southwest. Throughout the rest of the period high pressure at the surface is forecast to build to the north and west of the state, driving cold, arctic air into the Interior and portions of the Far North, causing temperatures to plummet 20 to 30 degrees below normal. With lows sitting at or well below zero, residents are urged to take caution when outside, keeping skin covered to prevent frostbite and dressing warm to stave off hypothermia. Zavadoff