US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 412 PM EDT Mon Apr 19 2021 Valid Thursday April 22 2021 - Monday April 26 2021 Hazards: - Heavy precipitation across portions of the Northeast, Thu, Apr 22. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Fri, Apr 23. - Heavy rain across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sat, Apr 24. - Heavy snow across portions of the Northern Rockies, Thu, Apr 22. - Severe weather across portions of the Southern Plains, Fri, Apr 23. - Flooding occurring or imminent across portions of the Lower Mississippi Valley. - High winds across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Thu-Fri, Apr 22-Apr 23. - High winds across portions of the Northeast, Mon, Apr 26. - Much below normal temperatures across portions of the Central Plains, the Middle/Lower Mississippi Valley, the Tennessee Valley, the Southern Plains, and the Ohio Valley, Thu, Apr 22. - Much above normal temperatures across portions of mainland Alaska, Thu-Mon, Apr 22-Apr 26. Detailed Summary: In the medium-range forecast period, the Hazards Chart has an area of heavy rain near the Gulf Coast States, heavy precipitation over parts of the Northeast, heavy snow over parts of the Northern Rockies, and high wind along with parts of the Northeast and New England Coast, and much below normal temperatures over parts of the Central/Southern Plains, and parts of the Middle/Lower Mississippi Valley and Tennessee Valley. A front along the Montana to Washington State/Canadian border will move southward into the Northern Rockies/Northern High Plains by Friday. The boundary will produce heavy snow over parts of the Northern Rockies on Thursday. Meanwhile, low pressure over parts of the Northeast/Canadian border will produce heavy precipitation over parts of Northern Maine on Thursday. The tight pressure gradient associated with the low will produce high wind over parts of the Northeast on Thursday into Friday. Additionally, high pressure over the Middle Mississippi Valley will allow temperatures to become 12 degrees or lower below average on Thursday morning that will moderate by Friday. These cold temperatures have led to the placement of much below normal temperatures over parts of the Middle/Lower Mississippi Valley and the Central/Southern Plains for Thursday morning. Furthermore, a front and a wave of low pressure over the Southern High Plains/Southern Plains will move eastward to the Lower Mississippi Valley on Saturday and advance northeastward to the Mid-Atlantic Coast by Sunday and to the Gulf of Maine by Monday. Moisture moving northward out of the Gulf of Mexico will interact with the front to produce an area of heavy rain over parts of the Southern Plains to the Tennessee Valley on Friday. The front and moisture will make the atmosphere unstable over parts of the Southern Plains on Friday. Due to the unstable air, an area of severe weather has been depicted on the Hazards Chart of Friday. The area of heavy rain will move eastward with the system to the Southeast and southern Mid-Atlantic by Saturday. The low over the Gulf of Maine will deepen by Monday, with the pressure gradient becoming strong enough to produce an area of high winds over the Northeast Coast on Monday. For Alaska, an upper-level ridging over the southern mainland to the Far North will remain in place from Thursday into Monday when upper-level troughing will move in from the east. The upper-level ridging will allow temperatures to become above freezing for a good portion of the day through Monday. A low just south of the Aleutians/Alaska Peninsula will produce precipitation but will not reach our criteria for a hazard. However, another low will move near the Aleutians/Alaska Peninsula Saturday through Monday. This system will have strong low-level flow pulling moisture off the Gulf of Alaska for a short time on Sunday afternoon. Yet again, the precipitation will be close or may even begin to exceed the criteria for a hazard, but at this time, WPC will leave this hazard off the chart. The hazard may be introduced over the next several days if the models suggest it. Ziegenfelder