Extended Forecast Discussion NWS Weather Prediction Center College Park MD 145 PM EST Sat Dec 30 2023 Valid 12Z Tue Jan 02 2024 - 12Z Sat Jan 06 2024 ...Overview... The latest guidance shows a progressive flow pattern with systems of modest amplitude moving west to east across the Lower 48. Systems with the best moisture tap are forecast to travel through the subtropics/southern tier of the country. This type of pattern keeps the Lower 48 generally milder than average except for some tendency towards cooler than average conditions in the southern tier of the country (especially the Southeast) and causes the bulk of the precipitation confined to the West Coast and the Gulf Coast/Southeast with locally heavy rain possible in some spots. Overall, this pattern is typical of what one would expect with the ongoing warm ENSO/El Nino climate anomaly. ...Guidance/Predictability Assessment... The guidance shows good agreement and the expected flow pattern, with issues generally constrained to late next week/next weekend near the Great Lakes/Northeast (where the 06z GFS is stronger with a system than the remainder of the guidance) and the Pacific Northwest (where the 00z ECMWF is stronger with a system moving nearby). An overall blend of the deterministic guidance seemed to provide a good starting point early on, before using up to 40% of the 00z NAEFS/ECMWF ensemble means late to deal with the main two detail issues within the 500 hPa, pressure, wind, and QPF patterns. The remainder of the grids were heavily weighted towards the 13z NBM starting point. ...Weather/Hazards Highlights... An initial upper low/shortwave moving out of the Southwest should begin to tap Gulf of Mexico moisture and some instability to fuel widespread showers and thunderstorms across parts of the Southern Plains/Lower Mississippi Valley on Tuesday. There is some overlap between the heavier rainfall/QPF signal and the more sensitive areas due to a recent wet pattern near the Middle/Upper Texas coast, so a marginal risk was maintained on the Day 4/Tuesday into early Wednesday Excessive Rainfall Outlook covering much of southeast Texas and southwest Louisiana. This activity should shift east along the central Gulf Coast into the Southeast on Wednesday, with another marginal risk for Day 5/Wednesday into early Thursday, this time confined mainly along the north-central and northeast Gulf Coast. The second low 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. This should also eventually bring heavy rainfall back into Texas and the Gulf Coast late week/next weekend. Due to the heavy rainfall expected on Tuesday into early Wednesday across southeast TX and southwest LA, this following system will also need to be watched for increased flooding concerns. Elsewhere, northern tier systems may bring light precipitation to parts of the Great Lakes/Northeast periodically next week, with precipitation moving into the Pacific Northwest later in the week as well. The greatest temperature anomalies during the period should focus across the far northern tier near the Canadian border and into the Great Lakes/Northeast with some locations seeing multiple days with readings 10-20F or so above normal, with morning lows tending to be farther above normal than daytime highs. Most areas from California eastward across the southern tier, particularly the Southeast, should see near to below normal high temperatures during the period as a series of upper level systems move through. Roth/Santorelli 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