Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Fri Sep 20 2019 Valid 12Z Mon Sep 23 2019 - 12Z Fri Sep 27 2019 ...Heavy rainfall threats in the Southwest early in the week and Midwest/parts of the Plains during portions of next week... ...Overview... An amplified pattern this weekend will briefly transition to flatter flow during the early/middle part of next week. Then toward next Fri most guidance begins to re-establish an amplified western trough/eastern ridge regime that will likely extend for a while beyond the medium range period. Early in the week, upper shortwave energy (probable closed low) may interact with East Pacific tropical moisture to bring significant rainfall to parts of the Southwest. Some of this energy/moisture extending northeastward as well as a couple fronts (the latter potentially stalling over the Midwest late in the week) will also provide support for areas of heavy rainfall over portions of the central U.S. ...Guidance Evaluation/Preferences... For the first few days of the forecast period (Mon-Wed) a blend of the 06Z GFS and 00Z ECMWF/Canadian offered a reasonably well-clustered starting point. Differences in timing of the western trough/closed low became evident by the early Tue forecast time with the 00Z GFS/UKMET quicker/farther east than the larger ensemble consensus (including the 06Z GFS and 00Z ECMWF/Canadian) that aligned with continuity and was the continued preferred evolution. For next Thu/Fri, uncertainty increases in fairly typical fashion with timing/track differences of the weakening Southwest upper low as well as the incoming/reinforcing troughing along the British Columbia coast. However, by the end of the period into next weekend (days 8-9), the ensembles show better than average agreement on a deepening western trough and increased heights in the east (see the Climate Prediction Center's forecast for days 6-10 and 8-14 for more details). ...Weather Highlights/Threats... The primary areas of emphasis for heavy rainfall potential will be over the Southwest early in the week and over parts of the Plains/Midwest. Over the Southwest (and favored terrain over central Arizona in particular) rainfall should be enhanced by the combination of the upper trough/low dropping southeast toward and into the region as well as leading flow of moisture originating from tropical systems Lorena and Mario. Some of the moisture/energy aloft may eventually reach into the central U.S. Beyond those ingredients, an initial southern Plains front should return toward the northeast as a warm front Mon-Wed ahead of a cold front approaching from the northern Plains. The northern part of the cold front will continue eastward but stall over the Midwest/central Plains, leading to a more persistent focus for rainfall during the latter half of the week. The Northwest may see a couple episodes of mostly light precipitation, though this may trend heavier and more widespread at the end of the week as the next upper trough digs southward. This trough will likely support some high elevation snow over the northern Rockies/Pacific Northwest by late in the week. Meanwhile rainfall along the front reaching the East early in the week should be trending somewhat lighter and less broad compared to the short range time frame. Areas of rain could linger for a time over New England depending on specifics of the upper trough/low affecting the region. Expect the Southeast to see consistently well above normal high temperatures with coverage of plus 10F and greater anomalies expanding northward by Thu-Fri as an upper ridge strengthens over the region. Potential for some record highs will also increase in that time frame with an unusually strong signal continuing into next weekend. On the other hand the West and northern Plains should be on the cool side of normal for highs during the majority of the period. Coolest days should be Mon over parts of the Interior West with the initial trough/upper low over the region and then Thu-Fri over the Northwest as deeper upper troughing digs along the West Coast. Some highs may be 10-20F below normal on Fri with many valley locations only in the 50s/60s. Morning lows will likely be near to above normal over much of the lower 48 during the week. Warmest anomalies for mins should be over parts of the Plains/Mississippi Valley Tue-Fri and in parts of the East by Thu-Fri (5-15F above normal). Fracasso/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 precipitation across portions of the Northern Rockies, Fri, Sep 27. - Heavy rain across portions of the Central Plains and the Middle Mississippi Valley, Tue-Thu, Sep 24-Sep 26. - Heavy rain across portions of the Southwest, Mon-Tue, Sep 23-Sep 24. - Flooding possible across portions of the Plains and Mississippi Valley. - Flooding occurring or imminent across portions of the Plains and the Upper Midwest. - Flooding likely across portions of the Middle Mississippi Valley. - Much above normal temperatures across portions of the Southeast and Southern Appalachians, Thu-Fri, Sep 26-Sep 27. 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