Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Thu Dec 28 2023 Valid 12Z Sun Dec 31 2023 - 12Z Thu Jan 04 2024 ...Overview... The latest models and ensembles still advertise a pattern transition toward a series of Pacific shortwaves (some with an embedded upper low) affecting some locations near the West Coast and then tracking across the southern tier. After a leading trough passes through the eastern U.S. early next week, Western Canada mean ridging should be persistent enough to support a downstream trough extending into the northeastern quadrant of the lower 48 by mid-late week. This pattern should confine the majority of precipitation and somewhat below normal high temperatures to parts of the West Coast and the Gulf Coast states/Southeast. The Great Lakes could see some light snow around Sunday and Wednesday-Thursday. Warmest temperature anomalies will likely be near the Canadian border. ...Guidance/Predictability Assessment... The most uncertainty during the medium range period was in the West. A general model blend consisting of the 00z EC/CMC/UKMET and 06z GFS, with more weighting toward the 00z EC, was used on day 3. A more evenly distributed general model blend was implemented on day 4 due to spread in the guidance regarding yet another West Coast system. It's worth noting that the Euro has trended closer to the coast and closer in line with what the GFS has been signaling over the last 24 hours regarding the West Coast low. This even distribution continues into day 5 when the 06z GEFS and 00z ECENS means were introduced. The Canadian ensemble was left out due to it's more progressive solution with respect to the central U.S. trough. The 06z GFS had a deeper upper low over the Rockies/Plains than the rest of the guidance as well. There's a lot of ensemble spread regarding the early-mid week trough entering the West on days 6 and 7. ...Weather/Hazards Highlights... The weak system crossing the Great Lakes through Sunday may produce a little light snow near its path. The trailing front may produce areas of rain across the Gulf Coast/Southeast Sunday-Monday but with continued uncertainty over coverage/amounts due to detail differences in the guidance for southern stream energy emerging from the Southwest and the orientation/timing of northern stream energy. At the very least, this activity should be progressive enough to keep most totals in the light to moderate range. Another weak wave and trailing cyclonic flow may produce a little lake effect snow by mid-late week. It will be a close call as to whether a system brushing southern California will bring any moisture to that part of the state. As the upper trough continues eastward, expect some rain to spread along and near the Gulf Coast by midweek, with uncertain northward coverage by the time the moisture reaches the East Coast by Thursday. Currently expect most of this moisture to stay far enough south to maintain rain as the primary precipitation type. A better defined system forecast to approach the West Coast by Wednesday and move into the Southwest by Thursday may bring organized precipitation to the West Coast and some areas farther inland, with relatively higher totals most likely over favored terrain in portions of California. The greatest temperature anomalies during the period should be of the above normal variety across the far northern tier near the Canadian border with some locations seeing multiple days with readings 10-20F or so above normal. Morning lows will tend to be farther above normal than daytime highs. On the other hand, aside from the southern Plains being above normal on Sunday ahead of a front, most areas from California eastward across the southern tier should see near to below normal high temperatures during the period. Low temperatures will also be below normal on some days, such as Sunday morning when readings in the low to mid 30s may lead to frost or freezes over portions of northern Florida. Kebede/Rausch 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw