Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 PM EST Sun Jan 09 2022 Valid 12Z Wed Jan 12 2022 - 12Z Sun Jan 16 2022 ...Overview... General ridging over the western U.S. is expected to continue into the medium-range period as shortwaves dive across central Canada into the northern tier while a lingering low/trough off Baja California is forecast to eventually track into the southern Plains. This split flow pattern could potentially phase near the East Coast where cyclogenesis would be possible by next weekend. Model ensemble means favor this phasing scenario in contrast with the deterministic solutions which continue to indicate a split decision in this regard. ...Guidance/Predictability Assessment... Overall, the ensemble means have maintained relatively good run-to-run consistency in predicting the pattern evolution across the U.S. through the medium-range period. The largest discrepancy was noted with regard to how the upper low/trough off Baja California is handled. The 00Z ECMWF switched to a much slower solution beginning in the short-range, thus keeping this feature well off the coast into the medium-range. The GFS trended toward this slow solution as well starting with the 06Z run. This sudden slow down of the upper low has resulted in a marked lowering of rain chances over the southern Plains midweek. The ensemble means indicate that this upper low/trough will eventually lift toward the Southwest late this week as the next shortwave dives across the Canadian prairies toward the northern Plains. Models then begin to diverge as to whether these two features will eventually phase or remain split as they reach the vicinity of the East Coast by next weekend. It appears that the ensemble means support the phasing scenario in contrast with the deterministic solutions which continue to indicate a split decision in this regard. The ECMWF and CMC have been in favor of phasing and cyclogenesis near the East Coast whereas the GFS supports a more separation between the two streams with its typically faster solution. Prior to the weekend, models and ensembles are in good agreement for a deep trough to exit the East Coast Thu-Fri with a strong signal for cyclogenesis off the East Coast. It appears that the heavy rain would stay off shore with what appears to be a deep cyclone in the making. The GFS has become much more aggressive with cyclogenesis off the East Coast together with a tendency to track it closer to land in recent runs. A multi-model/ensemble blend was used to compose this morning's WPC medium-range forecasts. The 06Z GFS was taken out of the blend beyond Day 5 as it appears to build too much high pressure across the Great Lakes, thereby making the northern stream low too weak. The 00Z GFS was not used as a substitute either because it tracks the low too fast to the east. The rest of the blend consists of the 00Z ECMWF/EC mean, the 06Z GEFS, and the 00Z CMC/CMC mean through Day 7. ...Weather Highlights... Moderate to heavy precipitation continuing into Wednesday across the Olympic Peninsula and northern Cascades should begin to wind down as the associated low pressure system is forecast to weaken. Meanwhile, the southern stream Pacific upper low is forecast to spread precipitation into the Four Corners states into late this week but the chance of rain across the southern Plains and lower Mississippi Valley has decreased considerably on Wed-Thu. Gulf moisture is expected to return along the western Gulf Coast region by Friday and into the weekend. Meanwhile, as the northern stream shortwave and surface low track across the northern tier late week, a swath of wintry precipitation can be expected to spread from west to east from the upper Midwest through the Great Lakes and eventually into New England. Thereafter, we will need to monitor how much the split flow pattern will phase near the East Coast this weekend to determine the extent and types of weather impacts the system may bring to the Eastern Seaboard. Temperature-wise, after a cold start to the day along the East Coast on Wednesday, temperatures will rebound closer to near or above normal by Thursday. The central U.S. will see very mild and dry conditions through midweek, with a widespread high temperatures reaching 10-20F above average. Meanwhile, lows will be 15-25F above normal in the Northern Plains. Cooler air will then overspread the Plains as the split flow pattern migrates toward the East Coast where the potential for cyclogenesis exists by next weekend. Kong 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml