Extended Forecast Discussion NWS Weather Prediction Center College Park MD 209 AM EST Mon Jan 10 2022 Valid 12Z Thu Jan 13 2022 - 12Z Mon Jan 17 2022 ...Overview... A complex split flow pattern will occur during the medium range period, with progressive shortwaves diving through the north-central and eastern U.S. while southern stream energy initially lingers well offshore Baja California before additional Pacific energy drops into the West and disrupts mean ridging there. At the surface, a Miller-A type cyclone could develop this weekend and move from the Southeast into the western Atlantic, but with quite a bit of uncertainty with its track and thus the impacts along the Eastern Seaboard. ...Guidance/Predictability Assessment... Given the complexity of the pattern, confidence is somewhat low for the details of the medium range forecast. However, there are some general commonalities among recent models. The initial southern stream energy/troughing well west of Baja California on Thursday continues to trend toward mainly weakening off the coast before tracking over the Southwest more slowly as it joins up with additional energy dropping south through the West, as opposed to a faster closed low moving eastward that most guidance showed about a day ago. The UKMET was first to show this type of solution that guidance has now trended toward. There are still some uncertainties with the magnitude of the upstream energy dropping southward from the Pacific and the interaction with the initial southern stream energy and the existing mean ridge across the West on Friday, but the large variations in ensemble member 500mb heights for example make it difficult to determine outliers at this time. Meanwhile in the East, a trough axis has good agreement early in the period Thursday but differences in shortwave energy tracking through the mean trough lead the 00Z GFS to close off a mid-upper low by Friday in the western Atlantic, which is not favored by other guidance. Regardless, the trough could dig somewhat, and guidance shows an associated surface low deepening considerably in the western Atlantic on Friday into Saturday, but mainly far enough offshore of the U.S. not to cause much precipitation over the Eastern Seaboard--though, winds could be a concern with a tightening pressure gradient near the New England coast. Then by the weekend, energy diving southeastward into the north-central U.S. will deepen a possibly positively-tilted (at least on Saturday) trough that tracks into the eastern U.S. on Sunday. This trough also may be supported by the western energy, but there remains some disagreement with their interaction, and most guidance seems to leave energy behind in the Southwest and form and maintain a closed low there over the weekend, with the 12Z ECMWF the main exception as a second northern stream shortwave crossing into the north-central U.S. could dominate and phase with the southern stream energy. With phasing and shortwave intensity differences, predictability remains low and this affects the surface pattern as well. Deterministic guidance for the 12/18Z/incoming 00Z cycle varied quite a bit with their low tracks over the central/eastern U.S. and western Atlantic. For the WPC medium range fronts/pressures forecast, a blend of the 18Z GFS and 00Z ECMWF, CMC, and UKMET worked for the beginning of the period, with fairly even weighting given the uncertainty in any particular outliers, and transitioned toward utilizing more of the ensemble means as the period progressed. ...Weather Highlights... Some light precipitation is likely for parts of the Southwest and into the Four Corners states for the latter part of the week given the upper low's influence, while precipitation chances continue to decrease across the south-central U.S. given model trends. Then as the northern stream shortwave and surface low track across the northern tier late week, a swath of wintry precipitation is currently expected to spread from west to east from the upper Midwest through the Great Lakes and eventually into New England. Areas farther south such as the Ohio Valley, much of the Appalachians, and the Mid-Atlantic could also see winter weather, but dependent on the low track and the potential for the split flow pattern to phase in the upper levels, which are quite uncertain at this point. Meanwhile, the south-central and southeastern U.S. should see light to moderate rain along the southern extent of the cold front on Saturday. Temperature-wise, the central U.S. will see very mild and dry conditions on Thursday and into Friday, with widespread high temperatures reaching 10-25F above average. Meanwhile, lows will be 15-25F above normal in the Northern Plains. Temperatures should moderate somewhat by the weekend there, while colder than average temperatures are forecast for the Northeast on Friday into the weekend. Tate 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