Extended Forecast Discussion NWS Weather Prediction Center College Park MD 334 PM EDT Wed Oct 09 2019 Valid 12Z Sat Oct 12 2019 - 12Z Wed Oct 16 2019 ...Pattern Overview and Guidance/Uncertainty Assessment... During the weekend into early next week the very deep upper low expected to be over northern Minnesota as of early Sat should drift slowly toward western Lake Superior and then track into Ontario, with gradual weakening after early Sun. The upper trough extending from the low will push a cold front through the East during the weekend while the southern part of the front settles near the Gulf Coast. Meanwhile shortwave energy moving into the West during the weekend will progress eastward thereafter. This energy will push another front across the lower 48 with possible anchoring low pressure crossing the Midwest/Great Lakes/southeastern Canada Mon night into Wed. Another shortwave approaching western North America around day 6 Tue should eject rapidly inland ahead of upstream amplifying trough energy (at least some of it likely associated with current Super Typhoon Hagibis). The greatest uncertainty in the forecast involves rainfall coverage and intensity across portions of the southern states including the Southwest. From the southern Plains eastward guidance diverges over how much moisture returns northward along/north of the Gulf Coast with GFS runs tending to keep moisture more suppressed than most other guidance--corresponding to that model showing lower heights aloft. By mid-late period there is also wide spread in models/ensembles for possible eastern Pacific tropical development, with influence from differing solutions for diffuse upper troughing that amplifies for a time well offshore California/Mexico as well as strength of a ridge that extends across northern Mexico. Currently the northwestward extent of GFS moisture into the Southwest U.S. is fairly extreme (or even an outlier) relative to other solutions including the 06Z GEFS mean. Aforementioned lower-confidence issues in the GFS, along with the GFS runs possibly becoming too progressive with energy reaching western Canada day 7 Wed plus progressive and amplified with the eastern U.S. upper trough late in the period, favored tilting the forecast about 70 percent toward the 00Z ECMWF/UKMET/CMC early in the period and then the ECMWF/ECMWF mean/CMC by days 6-7 Tue-Wed with the remaining 30 percent devoted to the 06Z GEFS mean at that time. The GEFS mean could still be a little fast over the East late in the period but compared well to the other means elsewhere. ...Weather Highlights/Threats... Confidence is not particularly high yet but the best potential for significant rainfall should extend from parts of the southern Plains through Lower Mississippi Valley into the Tennessee Valley. Moisture along/north of the front settling near the Gulf Coast and then eventually lifting northward, and possibly eventual input of moisture from the tropical eastern Pacific, should help to enhance rainfall totals over some locations in this area. Some of the Pacific tropical moisture could reach locations over or west of the southern High Plains. Elsewhere, moisture wrapping around the deep storm initially affecting the northern tier states will be slow to depart, leading to scattered precipitation over parts of the Upper Midwest and Great Lakes through the weekend and into early next week. The leading cold front should bring mostly light rain to portions of the East on Sat. The shortwave trough/associated cold front will bring mostly light rain/mountain snow to the Pacific Northwest and northern Rockies from the weekend into early next week. Expect the Pacific Northwest to see another episode of precipitation by next Tue-Wed. The northern Plains will continue to be the focus for coldest temperatures relative to average. Highs should be 20-30F below normal during the weekend with only gradual moderation to 5-20F below normal by the middle of next week. The Upper Midwest will be quite chilly as well with most days at least 10F below normal. The rest of the central U.S. will see a more pronounced warming trend after Sat, though another front will bring a cooling trend on Wed. The East will see above normal temperatures on Sat, while locations across the Southeast should be above normal most of the period. Warmth will extend farther west across the southern tier during the first part of next week. Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy rain across portions of the Pacific Northwest, Wed, Oct 16. - Heavy rain across portions of the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Tue-Wed, Oct 15-Oct 16. - Heavy snow across portions of the Upper Mississippi Valley and the Northern Plains, Sat-Sun, Oct 12-Oct 13. - Flooding possible across portions of the Upper/Middle Mississippi Valley, the Great Lakes, and the Northern Plains. - Flooding occurring or imminent across portions of the Northern/Central Plains, the Upper/Middle Mississippi Valley, and the Great Lakes. - Flooding likely across portions of the Northern Plains. - High winds across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Sat-Sun, Oct 12-Oct 13. - High winds across portions of the Great Lakes, Sun-Mon, Oct 13-Oct 14. - Much below normal temperatures across portions of the Northern/Central Plains, the Upper/Middle Mississippi Valley, and the Great Lakes, Sat-Tue, Oct 12-Oct 15. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml