Extended Forecast Discussion NWS Weather Prediction Center College Park MD 308 PM EDT Sat Oct 23 2021 Valid 12Z Tue Oct 26 2021 - 12Z Sat Oct 30 2021 ...A highly stormy pattern continues across our Nation next week... ...Overview and Guidance/Predictability Assessment... The weather patern will remain quite active as potent systems impact the nation next week. Guidance has trended less progressive/more amplified with these systems. An upper low developing over the lower Great Lakes Tuesday as northern and southern stream energies phase will induce a deepening cyclone with heavy wrap-around winds/rainfall and flooding threats over the Northeast U.S. Guidance is now in better agreement with this scenario and a well organized coastal storm is expected to track toward the Canadian maritimes by Thursday. Predictability with this feature is above average. Meanwhile upstream, yet another potent trough will eject out of the West/Rockies Tuesday-Wednesday. Guidance has swerved a bit and now shows more separated flow with possible development of a southern stream closed low and deeper surface low/frontal midweek that offers a slowed and southward separated track from the southern Plains to the Mid-Atlantic into next Saturday. Organized moisture and rainfall will wrap around the low and accompany a leading frontal system with rounds of heavy rainfall possible and also offers a threat for runoff issues. Predictability with this feature is less than average, but spread has decreased some in 12 UTC guidance. Well upstream, a favorable jet and onshore track of shortwaves pattern will also meanwhile fast track move into the Pacific Northwest during the period to bring more heavy rain/mountain snows to the Northwest that increasing run overtop lead/warming upper ridge development underneath over the rest of the West through late week. The WPC medium range product suite was primarily derived from a composite blend of best clustered guidance from the 06 UTC GEFS mean and 00 UTC ECMWF/ECMWF ensemble means, with emphasis attributed to the GEFS mean into days 6/7 (next Friday/Saturday). Growing forecast spread favors an ensemble mean focus and the GEFS more separated stream flow and amplitude/slowed progression with the main storms better fit latest guidance trends from recent guidance including the newer 12 UTC runs. ...Weather/Hazards Highlights... The leading closed low into the Northeast on Tuesday will allow for heavy rainfall potential to continue from the end of the short range period into much of New England early next week. Deepening coastal low development may induce pockets of enhanced rainfall on the backside of the low as it lifts northward towards the Canadian Maritimes. The cold front reaching the Plains by Tuesday and onward into the east-central U.S. Wednesday/Thursday is expected to present an emerging and expanding lead rainfall/convective focus as ample Gulf of Mexico and Atlantic moisture streams into the system. Latest guidance suggests the best potential for heavy rainfall will be across portions of the Gulf Coast states/Southeast and inland Wednesday into Thursday and then into the Ohio Valley/Appalachians/Mid-Atlantic/Northeast Thursday-Saturday with closed upper low development and a slowed frontal system progression. The Storm Prediction Center also is highlighting the potential for severe weather across parts of the central/southern Plains on Tuesday, and the central Gulf Coast on Wednesday. Meanwhile, out west, a sustained moisture plume from the short range period will continue into the Northwest U.S. on Tuesday bringing a continued threat for heavy rainfall and mountain snows to especially the Pacific Northwest/northern California but also farther inland across the northern Rockies. Another system moving towards the coast mid-later next week will continue the active weather with another round of heavy rainfall and mountain snow impacting parts of the Pacific Northwest. Schichtel/Santorelli 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, 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