Extended Forecast Discussion NWS Weather Prediction Center College Park MD 308 AM EDT Wed Oct 26 2022 Valid 12Z Sat Oct 29 2022 - 12Z Wed Nov 02 2022 ...Heavy rain/snow threat for the Northwest/Rockies Sunday through early next week... ...Weekend closed low heavy rain threat from the Lower Mississippi Valley through the Southern Appalachians... ...Guidance and Predictability Assessment... The WPC medium range product suite was primarily derived from a composite of reasonably well clustered guidance from the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian for this weekend along with compatible input from the 01 UTC National Blend of Models (NBM) and WPC continuity. Latest 00 UTC model and ensemble guidance still seems broadly in line during this period forecast in a pattern with seemingly above normal predictability. As has been the case recently, forecast spread grows steadily by later day 4/day 5, about a day earlier than the norm. Accordingly, prefer a solution closest to the compatible GEFS/ECMWF ensemble means that provide decent product continuity into next week versus chasing run to run flow varied systems in the deterministic model guidance. ...Pattern Overview and Weather/Hazard Highlights... The details with a potent series of Pacific systems to work into the West/Northwest this weekend and through early-mid next week remains more run to run varied than normal in recent model guidance, but the compatible GEFS/ECMWF ensemble means offer a increasingly strong signal for a pattern with long fetch moisture to fuel periodic moderate to locally enhanced precipitation from northern California and the Pacific Northwest inland across the north-central Great Basin/Rockies. This will offer heaviest rainfall potential for the coastal ranges/Olympics and Cascades of the Pacific Northwest along with a signifciant threat for terrain enhanced elevation snow set to also spread early-mid next week into the mountains of northern California inland across the north-central Great Basin/Rockies as depicted in the WPC Winter Weather Outlook probabilities in NDFD. Meanwhile, an intially closed/separated southern stream system is slated to lift from the southern Plains through the Ohio Valley this weekend. This will act to focus across the South enhanced rain/convection given upper and surface system support to pool moisture/instability to fuel activity. There is a some guidance signal for locally moderate to heavy rainfall given the risk of repeat/training cells with overall slow system translation, albeit with details less certain given the nature of closed features. A WPC experimental med-range ERO considered a "slight" risk of excessive rainfall for the central Gulf coast states Saturday, but held off for now given uncertainties with convective details and antecedent conditions. Nevertheless, also expect a swath of moderately heavy rainfall to lift across the Ohio Valley/Appalachains and across the Eastern Seaboard through early next week with the lead system and with rejuvinating backside upper trough energy feed that may spawn modest coastal/frontal genesis and moisture from the Atlantic in addition to lingering Gulf moisture. 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, experimental excessive rainfall outlook, 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/#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