US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 321 PM EDT Tue Sep 17 2019 Valid Friday September 20 2019 - Tuesday September 24 2019 Hazards: - Heavy rain across portions of the Central Plains to the Midwest, Sat-Sun, Sep 21-Sep 22. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Fri, Sep 20. - Heavy rain across portions of the Upper Mississippi Valley and the Northern Plains, Fri-Sat, Sep 20-Sep 21. - Severe weather across portions of the Northern Plains and Upper Mississippi Valley, Fri, Sep 20. - Flooding possible across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains. - Flooding occurring or imminent across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains. - Much below normal temperatures across portions of the Great Basin and Northern Rockies, Fri-Sat, Sep 20-Sep 21. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Fri-Sat, Sep 20-Sep 21 and Mon-Tue, Sep 23-Sep 24. Detailed Summary: The medium range period (Friday to Tuesday) should be pretty active in terms of hazardous weather threats. Tropical Storm Imelda made landfall this afternoon along the Texas Gulf coast, and will spread heavy rainfall inland across Eastern Texas during the short range period. Though most of this is forecast to fall during the short range, lingering moisture with whatever is left of the circulation may extend into the very beginning of the medium range period and a small heavy rainfall area was included on today's hazards chart from northeast Texas into far southeast Oklahoma. To the north, upper level troughing will push a cold front eastward across the northern Plains into the Upper Midwest Thursday - Friday. The threat for heavy rainfall and severe weather appear possible to likely along and ahead of this boundary. This boundary sinks into the Midwest this weekend, with models indicating it may stall across the region. Tropical moisture streaming northward will interact with this front to produce heavy rainfall from eastern portions of the Central Plains to much of the Midwestern states Saturday and Sunday (the 21st-22nd). Rainfall across this region may linger past this weekend, though models remain uncertain on whether it will meet heavy rainfall criteria. Across the Southwest, there are some indications that tropical moisture from the eastern Pacific may reach portions of the area and interact with a potential closed upper level low across southern California by the early to middle part of next week. There remains significant uncertainty with how much rainfall and whether or not this will meet heavy rainfall criteria for the hazards chart. For this reason, opted to leave out a heavy rain area for today. Deep upper level troughing initially across the Western U.S. on Friday, will result in below to much below normal temperatures across parts of the Central Great Basin into the Northern Rockies. Minimum temperature anomalies in these areas are forecast to be near 5 to 10 degrees below average, which would normally not be enough to include on the medium range hazards chart. However, due to frost/freeze concerns this late in the season the area from yesterday's chart was continued into today. To the east, upper level ridging sliding from the northern Plains to the Northeast will bring much above normal temperatures (with anomalies 10 to 15 degrees above normal), but daily max temps are only forecast to be in the low to mid 80s which is likely not necessarily hazardous for this time of the year, so no area was included. An active pattern is expected in Alaska during the medium range period too as a pair of deep surface lows drifts from the Aleutians into the Gulf. This will likely bring a couple of rounds of potentially heavy rainfall to parts of the southeast Coast/mainland and much of the Alaskan Panhandle Friday-Saturday, and again Monday-Tuesday. There is model signal for 5-day rainfall totals (so a combination of the two events) in excess of 5 inches, with several inches of snow also possible in the highest elevations. The second system may also bring a round of enhanced precipitation to parts of the eastern Aleutians, though amounts appear to be marginal at best and doesn't warrant a heavy rain area at this time for the Aleutians. Santorelli