Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Sat Sep 21 2024 Valid 12Z Tue Sep 24 2024 - 12Z Sat Sep 28 2024 ...Eyes to the Carribean for next week... ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of the 18 UTC GEFS mean, the 12 UTC ECMWF mean and WPC continuity. These guidance solutions are reasonably well clustered and compatible through medium range time scales and best fits latest NHC guidance on a possible formation and northward track of a tropical system into the Gulf of Mexico late next week to monitor. Recent model runs suffer from greater than normal cycle to cycle continuity, both with interacting flow evolution over the lower 48 and with any tropical development. However, it should be noted that latest NHC system evolution is now on the slower side of newer 18 UTC and 00 UTC model solutions, pending potential formation and impacts for the western Carribean earlier next week. ...Weather/Hazards Highlights... Energy digging southward over the Rockies/High Plains in uncertain separating flow may offer a period favorable for enhanced rainfall over the southern High Plains under upper diffluent flow and with frontal proximity. A WPC Marginal Risk area remains in place on the WPC Day 4/Tuesday Excessive Rainfall Outlook (ERO). Meanwhile, upper trough energy and wavy frontal systems will be kicked slowly into the Midwest/East early next week along with an associated threat of showers/thunderstorms with some local runoff issues given motion. WPC (ERO) Marginal Risk areas are depicted to shift eastward Day4/Tuesday and Day/5 Wednesday across the Upper Ohio Valley and northern Mid-Atlantic. Upper trough reinforcement may support additional rainfall potential to monitor over the East-Central U.S. mid-later next week in amplified but uncertain flow. The eastward progression occuring remains contingent of far upstream development of a potent and slowly progressive upper trough from the northeast Pacific early next week that provokes downstream upper ridge amplification, with possible shift of the warming ridge from the West Coast to mid-continent over next week. Meanwhile NHC and WPC will continue to monitor possible tropical development in the Caribbean that may slowly lift northward into the Gulf of Mexico to threaten the Gulf Coast late next week. The ultimate position and southward breath of the upper trough over the lower 48 will determine extent of northward lifting. Given some of the latest guidance trends, there is potential that heavy rainfall may begin impacting parts of the Gulf Coast by late next week. The timing and exact location of impacts is uncertain at this time. Out West, most areas should stay dry. The Washington coastal ranges/Cascades will be an exception with growing daily enhanced rain potential with Pacific system energy and moisture approaches. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw