Extended Forecast Discussion NWS Weather Prediction Center College Park MD 205 AM EDT Thu Sep 12 2019 Valid 12Z Sun Sep 15 2019 - 12Z Thu Sep 19 2019 ...Heavy rain possible across portions of the Southeast... ...Overview and Guidance Evaluation/Preferences... An amplified upper-level pattern is expected to develop across the CONUS during the medium range, with an expanding and broad ridge across the eastern third of the nation, and an amplified/slow-moving trough digging into the West. A northern stream shortwave is forecast to skirt the northeastern U.S. through Canada Sun-Mon, pushing a cold front off the Eastern Seaboard. The deepening western trough will also spread a cold front east across the Great Basin and Rockies Mon-Tue and into the central U.S. by Wed-Thu. Meanwhile, a tropical disturbance is forecast to move northwestward across Florida and the eastern Gulf of Mexico and into the southeastern U.S. Sun-Tue. A blend of the 12Z ECMWF/CMC/18Z GFS (with more emphasis place toward the ECMWF/CMC) was used as a basis for the forecast through much of the medium range. The ECMWF/CMC showed relatively good consensus on the track of the tropical disturbance affecting Florida and the Southeast days 3-5 (Sun-Tue). The GFS was eventually much farther west with this system, showing an interaction between it and an upper low farther west across the Gulf. Elsewhere, models showed relatively good consensus with the northern stream shortwave crossing eastern Canada days 3-4, and differences with the amplifying western trough were much less than in recent days, primarily confined to relatively small timing and amplitude differences (especially days 3-5). By days 6-7 (Wed-Thu) as the western trough begins to emerge into the central U.S. timing differences increased a bit with the GFS now among the slower solutions and the ECMWF/CMC deeper but a bit quicker. Given increased spread days 6-7, significantly boosted weight of ECENS/NAEFS means during that time period to account for the spread/uncertainty. ...Weather Highlights/Threats... Numerous showers and thunderstorms are expected across Florida and the Gulf Coast states this weekend into early next week in association with the aforementioned tropical disturbance. Several pieces of guidance suggest the potential for multi-inch rainfall totals across several days over portions of Florida and southern Alabama/Georgia from Sun through the first part of next week. Widespread rains (and perhaps some snow at the highest elevations) are expected across the Pacific Northwest by Sun as the upper trough begins to amplify. Precipitation should spread inland across the Great Basin and northern Rockies early next week. Southerly flow east of the upper trough may revive monsoonal showers and storms across the Four Corners region, with coverage of precipitation increasing through early next week. The 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 deg 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. Ryan 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 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