Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Tue Jan 03 2023 Valid 12Z Fri Jan 06 2023 - 12Z Tue Jan 10 2023 ...Significant heavy precipitation threats for California to resume this weekend and early next week... ...Guidance/Predictability Assessment and Weather/Hazard Highlights... This Friday should serve as a relatively light precipitation over most of the West given shorter term forecasts, but ejecting impulses may produce some central Great Basin/Rockies snows while deep layered/moist southerly flow up along/off the West Coast should begin to produce some enhanced precipitation for favored areas of coastal northern Califirnia and the Pacific Northwest. The WPC experimental Day 5 Excessive Rainfall Outlook (ERO) renews by Saturday a "slight" risk area for northern California. The threat for additional rounds of heavy rainfall with ample runoff issues are likely to persist and expand southward over the state Sunday through Tuesday in a dangerously wet pattern with multiple rivers of moisture working inland ahead of a series of uncertain/deepened eastern Pacific storms. Many areas, especially burn scars, are likely to be sensitive to additional rainfall given the ample recent and forecast rainfall. High probabilities for Sierra snowfalls are also depicted in the WPC Winter Weather Outlook (WWO) Sunday-Tuesday. Guidance also shows some favorable flow into the Northwest for especially southward facing terrain and modest shortwave/terrain enhanced snow potential working into the Great Basin. Elsewhere, guidance solutions have become better clustered with a Friday re-invigoration of low pressure over New England as a supporting closed upper trough/low passages across the region. This may support some plowable snows across Interior New England as wrapping moisture is squeezed out in a cooling environment. Meanwhile, upper-level troughing moving through the West is forecast to reach the Plains by Saturday and help develop a modest surface frontal wave that may subsequently track with some uncertainty eastward across the Mid-Mississippi Valley to the Mid-Atlantic this weekend. Compared to the models, the NBM still seems to be missing the modest precipitation potential that may produce some light wintry weather over the Midwest as well as a trailing area of showers down trough the south-central U.S. as well as downstream to the Mid-Atlantic this weekend and the South/Southeast into early next week. WPC QPF and weather grids were accordingly adjusted. Overall, a composite blend of best clustered guidance from the latest GFS/ECMWF and GEFS/ECMWF ensemble means seems to provide a reasonable forecast basis Friday into Saturday before WPC guidance preferences switch in earnest to the compatible GEFS/ECMWF ensemble means amid modestly growing forecast spread through the rest of this forecast period. 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