Extended Forecast Discussion NWS Weather Prediction Center College Park MD 208 AM EST Sun Jan 01 2023 Valid 12Z Wed Jan 04 2023 - 12Z Sun Jan 08 2023 ...Significant multi-day heavy precipitation event this week into the West with primary focus across California... ...Guidance/Predictability Assessment... Models and ensembles are gradually converging on a better clustered pattern and system forecast at medium range time scales. While differences including local weather focus remain, an overall GFS/ECMWF/UKMET/Canadian model composite along with the National Blend of Models and WPC continuity seems to offer a reasonable forecast starting point mid-later this week and increased incorporation of the compatible GEFS/ECMWF ensemble means seems to offer a good forecast continuation into next weekend amid gradually growing forecast spread in active flow. ...Weather/Hazard Highlights... There is some chance for snow in marginally cooled air from the lower Great Lakes through the northern Northeast through midweek with system passage. Meanwhile to the south, a wavy frontal system will develop and spread some moderate rain up the Eastern Seaboard midweek, with uncertain additional/modest frontal wave formation offshore possibly lingering some light QPF into the Mid-Atlantic/coastal Northeast into later next week. Prior to this, much milder than average temperatures will linger across much of the Eastern Seaboard into midweek. Lows of around 15-30F above average will be common. Daily records will likely be widespread across the broad region. It remains the expectation that additional rounds of precipitation are also expected to work across the West Coast this week in a very wet pattern to start 2023, but still primarily with a focus on California. Amounts look to trend upward again in earnest by Wednesday-Thursday across California as a system approaches from the Pacific with another potential Atmospheric River event to shift steadily southward across the state over time. Many areas are likely to be sensitive to additional rainfall by then given the ample recent rainfall and additional rain during the short range period and then will be an additional chance for an uptick in precipitation with additional system approach latter week. WPC experimental medium range Excessive Rainfall Outlook (ERO) "slight" risk areas have been issued for the Wednesday-Thursday episode. There is also a multi-day threat for heavy snow that will focus over the Sierra this week, but also spread northward through the Cascades and with some gusto inland across the Intermountain West toward the Rockies over time with system translation. This threat is addressed in the WPC Winter Weather Outlook (WWO) and other products. System/energy translation and associated/modest surface system genesis is then expected to work downstream across the central to east central U.S. heading into next weekend, but with limited QPF potential. 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