Extended Forecast Discussion NWS Weather Prediction Center College Park MD 131 PM EST Mon Jan 02 2023 Valid 12Z Thu Jan 05 2023 - 12Z Mon Jan 09 2023 ...Heavy precipitation threats into California likely resume this weekend... ...Guidance/Predictability Assessment and Weather/Hazard Highlights... Global guidance continues to agree to weaken a deep cyclone off the Pacific Northwest coast on Thursday and set up a mean low farther northwest that persists into next week, keeping an active pattern for the West Coast (particularly California) as shortwave energy rounds the low. Precip from the midweek atmospheric river ahead of the cyclone over California persists Thursday before a brief reprieve Friday. Many areas, especially burn scars, are likely to be sensitive to additional rainfall by then given the ample recent and forecast rainfall. An experimental Day 4 Excessive Rainfall Outlook (ERO) "slight" risk area along with high probabilities for Sierra snowfalls in the WPC Winter Weather Outlook (WWO) persist. Guidance also shows some favorable flow into the Pacific Northwest for especially southward facing terrain and periodic shortwave/terrain enhanced snow potential farther inland across the Intermountain West toward the Rockies with system translations. By the weekend, there is still uncertainty of timing, strength, and placement of Pacific lows/frontal systems bringing the next surges of moisture into the West Coast and may be noteworthy in California, particularly from recent GFS runs (including the 12Z from today) as well as the CMC and UKMET while the ECMWF keeps forcing/precipitation offshore. Some uncertainty remains with a Friday re-invigoration of low pressure over New England Friday. Recent GFS runs (including the 12Z from today) have a more negatively tilted upper low over the eastern Great Lakes which allows a stronger coastal low off New England and snow over much of the northeast Friday/Friday night. Meanwhile the latest CMC/UKMET/ECMWF have a weaker/more progressive flow that does not result in much late work week precip over the Northeast. However, members of the ECENS and CMCE have a similar feature, so this is something to monitor and a reason why the forecast trends from deterministic guidance to ensembles on Day 5. Meanwhile, lead upper-level troughing moving through the Intermountain West is forecast to reach the Great Plains by Saturday and help develop a modest frontal wave that is subsequently forecast to track east, but with latitudinal uncertainty with guidance taking it over the Midwest or Tennessee Valley this weekend. in guidance has it toward the Great Lakes then off the East Coast by Monday. Compared to the models and considering system development, the 01 UTC NBM 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 into the Mid-Atlantic. WPC QPF and associated weather grids were adjusted to accommodate. Overall, a composite blend of the GFS/ECMWF/Canadian/UKMET seems to provide a reasonable forecast basis into Friday before WPC guidance preferences begin to switch to a GEFS/ECMWF/CMCE ensemble mean preference amid modestly growing forecast spread through the rest of this medium range period. Slightly warmer than normal conditions generally prevail for the Northwest, Central, and Eastern sections of the CONUS Friday into next week while temperatures in the Southwest are near to below normal under troughing. Jackson 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