US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 419 PM EDT Fri Sep 18 2020 Valid Monday September 21 2020 - Friday September 25 2020 Hazards: - Heavy rain across portions of the Pacific Northwest and the Northern Great Basin, Wed-Thu, Sep 23-Sep 24. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, and the Southern Plains, Mon-Fri, Sep 21-Sep 25. - Flooding possible across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians. - Flooding occurring or imminent across portions of the Southeast and the Southern Appalachians. - Flooding likely across portions of the Southeast and the Southern Appalachians. - Much above normal temperatures across portions of the Central Plains, the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Thu-Fri, Sep 24-Sep 25. - Much above normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Mon-Tue, Sep 21-Sep 22. - Much below normal temperatures across portions of the Northeast, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Great Lakes, and the Ohio Valley, Mon-Tue, Sep 21-Sep 22. - Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Mon, Sep 21. - High significant wave heights for coastal portions of the Southern Plains, Mon-Thu, Sep 21-Sep 24. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Sep 21-Sep 22. - Heavy precipitation across portions of the Alaska Panhandle, Tue-Wed, Sep 22-Sep 23. - High winds across portions of the Alaska Panhandle, Tue-Wed, Sep 22-Sep 23. Detailed Summary: The medium range period (Monday, Sep 21 - Friday, Sep 25) features a pair of deep upper level troughs over the northeast Pacific and off the Northeast coast, while ridging aloft sets up over the Northern Plains. The start of the period calls for a couple more days of much below normal temperatures in parts of the Northeast and Mid-Atlantic. Daily mean temperature anomalies look to hover around 12 degrees below normal and some daily record cold lows and highs are also expected. Patchy areas of frost are also likely Monday and Tuesday morning over the interior Northeast and northern Mid-Atlantic. Temperatures will moderate to near normal levels the second half of the week as the air-mass modifies and a milder regime moves in from the Upper Midwest. While the East Coast sees the return of typical September-like temps, a more late summer-like trend develops in the Northern Plains as upper-level ridging builds in aloft. Parts of the North-Central U.S. can anticipate an abnormally warm start to the week with another round of much above normal temperatures possible late week in the northern Rockies and Plains. Precipitation-wise, the large upper trough over the northeast Pacific sends a swath of beneficial precipitation towards the drought-stricken Pacific Northwest. Several inches of rainfall are possible in the Olympics and Cascades. While much of the Lower 48 can expect drier than normal conditions overall, the water hazards of the medium range period come down to Tropical Depression Twenty-Two and Major Hurricane Teddy. The former poses the greatest threat to significant flooding stemming from Brownsville on north through the upper Texas coast and into southwest Louisiana. T.D. Twenty-Two is forecast to become a hurricane this weekend and weaken as it ingests dry air from a cold front approaching from the north. While the storm's intensity drops to a degree, the storm becomes caught between three areas of ridging: one in the tropical East Pacific, one over the north-central U.S., and another over Florida. This causes weak steering flow that forces the storm to meander near the south Texas coast. Exactly where it sets up along the coast will determine which locations receive heavy rainfall, for how long, and where the worst coastal impacts occur. Given the opportunity for multiple days of brisk onshore flow, storm surge and coastal flooding are concerns along the northwest Gulf Coast. A significant waves hazard has been drawn along the Texas coast to account for these threats. There is also the potential for tropical storm force winds, most notably on the northern and northeastern flanks of the storm. Confidence in the forecast beyond day 5 is low, but there is ensemble guidance that suggests the storm could head northeast and bring the heavy rain threat to parts of the western Louisiana and the Lower Mississippi Valley late next week. The busy weather pattern across Alaska refuses to back down through next week. A powerful storm system is forecast to pass over the Alaskan Peninsula Monday and across the Gulf of Alaska through late week. Gusty winds are possible over the Aleutians, as well as potentially across south-central Alaska, though it will depend on the exact low track. High winds are most likely for southern coastal parts of the Panhandle Tuesday into early Wednesday, but some locally high winds are also possible along the Gulf Coast and near Kodiak Island. The most widely observed hazard with this system will be heavy precipitation from the Alaska Peninsula toward the Kenai Peninsula the first half of the week, then reaching the Panhandle mid-week. Heavy snow accumulations are anticipated in the higher elevations along the coast. Precipitation should remain primarily in the form of rain throughout most of the Panhandle, and heavy rain is forecast to begin late Tuesday and persist through Thursday. There is the potential for yet another area of low pressure to usher in more rainfall to the Panhandle next Thursday and Friday, but confidence in totals meeting heavy rainfall criteria are low at this time. Mullinax