Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Fri Dec 30 2022 Valid 12Z Mon Jan 02 2023 - 12Z Fri Jan 06 2023 ...Winter storm threat for the north-central Rockies/Plains and Upper Midwest early next week as a heavy rain/severe weather threat reemerges for the mid-lower Mississippi Valley/Mid-South then Southeast early through midweek... ...More rounds of moderate to heavy precipitation for the West with focus across California next week... ...Overview... A deepened low pressure system forecast to develop into early next week over the central U.S. will likely lead to a winter weather event from the north-central Rockies/Plains through the Upper Midwest, while heavy rain and severe weather appear likely across the South Monday-Wednesday. Meanwhile the West should see additional rounds of moderate to heavy precipitation next week, with highest amounts mainly across California next week. ...Guidance/Predictability Assessment... Models and ensembles again offer a similar mid-larger scale pattern evolution, albeit with ample embedded system differences by Tuesday to shift main local weather focus. That said, there seems to be reasonably good predictability with the depiction of the main highlighted threats to monitor into short range time frames. The most evident variances between guidance and with run to run continuity concerns seem to remains where the commahead heavy snow/ice axis will setup across the north-central states early next week with uncertain main low track/stream phasing, lead low/frontal depections and also the timing and focus with a series of Pacific systems to work into an unsettled West in active flow. Compared to most recent guidance, the latest few runs of the ECMWF and to a lesser extent ECMWF ensembles remain farther to the south with development and track of a deepening central U.S. low early next week and also more progressive and wetter with upcoming bouts of precipitation next week into the West. WPC continuity has been leaning 2/3 of the way toward the more northern track of the central U.S. main low with associated downstream flow depictions as well as near composite for western U.S. system timings, but somewhat on the wet side given reasonable support. Accordingly, the WPC medium range product suite was primarily derived from a composite GFS/ECMWF/UKMET/Canadian model blend valid Monday before transitioning starting Tuesday instead to a composite blend of more compatible guidance from the GEFS/ECMWF ensemble means and the National Blend of Models (NBM). This solution tends to mitigate the embedded system differences consistent with uncertainty and also acts to maintain good WPC product continuity. National Blend QPF was in general adjusted partially toward WPC continuity to provide the most stable run to run depcitions. ...Weather/Hazard Highlights... Upper trough emergence will support heavy snow across the central Rockies this weekend into Monday. Subsequent surface low pressure consolidation across the central High Plains will then bring a swath of snow across the northern half of the Plains into the Upper Midwest, along with increasingly windy conditions and an icy transitional zone. Inflow east of the low and lingering cold air may also support some later period snow/ice downstream from the northern Great Lakes to a cooled Northeast. Meanwhile farther south, the frontal system associated with this low and favorable Gulf moisture/instability and right entrance region upper jet lift should provide a focus for another episode of widespread heavy rain, along with a threat of severe weather as per SPC, across parts of the lower Mississippi Valley/Mid-South through the Southeast Monday-Wednesday. Thereafter, a trailing frontal low pressure system could develop under the right entrance region upper jet and then lift over the East. This could spread some moderate to heavy rain up the Mid-Atlantic states and coastal New England. WPC experimental excessive rainfall outlook (ERO) "slight" risk areas have been issued for Monday and Tuesday across the South. The West Coast states can expect a brief break from the heavy precipitation on Sunday as the trough axis shifts farther to the east. But additional rounds of precipitation are expected as the week progresses. There is quite a bit of uncertainty with the timing of additional heavy precipitation events at this point, but generally amounts look to trend upward by Tuesday-Thursday across California as a stronger frontal system approaches from the Pacific. 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. Milder than average temperatures for winter will be widespread across the eastern half of the country for early next week. Lows of around 15-30F above average and highs around 10-20F above average will be common, even reaching 20-30F anomalies in the Ohio Valley/Great Lakes Tuesday and the Northeast on Wednesday. Daily records for warm lows could be widespread for parts of the central and eastern U.S., while daily record highs are possible as well especially in the Ohio Valley. Meanwhile in the West, the overall wet/snowy pattern will tend to keep daytime temperatures around 5-10F below normal. As the large-scale upper trough moves through the western U.S. into the Plains, near to below average temperatures are expected to work their way from west to east across these areas. 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