Extended Forecast Discussion NWS Weather Prediction Center College Park MD 417 PM EDT Thu Sep 12 2019 Valid 12Z Sun Sep 15 2019 - 12Z Thu Sep 19 2019 ...Heavy rain is possible over portions of the Southeast... ...Overview and Guidance Evaluation/Preferences... Two key weather features were focused on for the medium range. An amplified/slow-moving trough digging south from off the Pacific Northwest across The West and a tropical disturbance tracking from Florida. The deepening western trough will spread a cold front east across the Great Basin and Rockies Mon-Tue and possibly into the central U.S. by Wed-Thu, depending on its eastward progression which has uncertainty at this time. The tropical disturbance is now forecast to stay farther east as it moves north from Florida either into Georgia or toward the Gulf Stream Sunday into Tuesday. As a note, a northern stream shortwave over the northeastern U.S. to eastern Canada Sunday night pushes a cold front off the Eastern Seaboard that lingers over the Carolinas and may influence the track of the tropical disturbance. Recent GFS/GEFS runs have been much more anchored to the West Coast with the positively tilted trough starting on the 17th and continues to take tropical wave into the Gulf of Mexico. Meanwhile the 00Z ECMWF/UKMET/CMC are all more progressive with ejecting the trough in The West east and keep the tropical disturbance over or east of Florida. The 00Z UKMET continues its trend of having the tropical farther north. Due to uncertainty with the trough out west and the tropical, a limited model blend was chosen based on the 00Z ECMWF/00Z CMC and an increasing weight toward the 00Z ECENS and 00Z NAEFS from Days 3-7. The tropical track from FL into GA through Day 5 was coordinated with NHC. ...Weather Highlights/Threats... The tropical disturbance will bring numerous showers and thunderstorms along its track which is uncertain at this time. Non-GFS guidance keeps the system east of FL/GA/SC, so the heavy rain threat may end up being near the coast (or off the coast), but for now an inland track would create a large heavy rain threat over FL into GA and the eastern Carolinas. Widespread rains (and mountain snows) are expected across the Pacific Northwest Sunday night through Monday night as the upper trough begins to amplify. Precipitation will spread south into CA and inland across the Great Basin and northern Rockies early next week. Southerly flow east of the upper trough looks to revive monsoonal showers and storms across the Four Corners region through Days 3-7. A broad upper ridge across the central and eastern U.S. will result in above average temperatures across a wide area. Highs are forecast to be 5 to 15 F above average for many areas from the Plains to the Eastern Seaboard into next week. The upper trough reaching the western U.S. Sun-Mon will bring much cooler temperatures, with highs 10 to nearly 20 deg below average expected to overspread the Northwest, Great Basin, and eventually the northern Rockies. As mentioned above, with increasing precipitation across the Northwest, temperatures should be cold enough to support snow at the higher peaks. Jackson 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 Southeast, as well as portions of western Oregon into northern California, Sun-Mon, Sep 15-Sep 16. - Heavy rain across portions of the Carolinas, Tue-Thu, Sep 17-Sep 19. - Flooding possible across portions of the central Plains, the Great Lakes, the upper Mississippi Valley, and the northern Plains. - Flooding occurring or imminent across portions of the northern Plains. - Flooding likely across portions of the central Plains, the upper Mississippi Valley, and the northern Plains. - Much above normal temperatures across portions of the central Plains, the Great Lakes, the Upper Mississippi Valley, and the northern Plains, Mon-Wed, Sep 16-Sep 18. - Much below normal temperatures across portions of northern California, the central Great Basin, the Pacific Northwest, and the northern Great Basin, Mon-Tue, Sep 16-Sep 17. - Enhanced wildfire risk across portions of the the central Great Basin, the northern Great Basin, and the Southwest, Sun, Sep 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