Extended Forecast Discussion NWS Weather Prediction Center College Park MD 117 PM EST Fri Mar 01 2024 Valid 12Z Mon Mar 04 2024 - 12Z Fri Mar 08 2024 ...Wet pattern for parts of the West Coast and the South... ...Overview... Latest guidance for next week generally agrees upon large scale mean troughing over the western half of the lower 48 and upper ridging off the East Coast. This pattern will favor cool conditions over the West with periods of enhanced precipitation over some areas, while above normal temperatures prevail farther east with the Lower Mississippi Valley into the Southeast seeing the best potential for heavy rainfall. Rain may extend farther north across the eastern half of the country as well. ...Guidance/Predictability Assessment... Models and ensembles continue to show agreement for the very large scale pattern, but still with some significant embedded differences that have sensible weather impacts across some areas. There are notably a lot of shortwave/timing differences across the northern tier, though still with a general theme of enough dynamics existing to support some degree of surface frontal evolution. At the same time, a couple of Pacific shortwaves should amplify/move into the West after midweek, with another surface system that may reach the Plains late next week. The 06z/12z GFS seems to be the biggest outlier for both regions, but especially across the West late week. The GFS is much quicker to bring a southern stream compact upper low off the California coast inland, and the new 12z run is especially fast/weaker with this. The ECMWF and CMC support a slower progression and possible embedded closed low over the Southwest next Friday. Ensemble means are quite muted/flatter but do have general positioning closer to the ECMWF and CMC. Also some differences late week with a shortwave through the Southeast, which does have implication for heavy rainfall distribution and timing from the Gulf Coast to the Southeast/East Coast. The WPC forecast was able to use a deterministic model blend for days 3-4, but after that incorporated the ensemble means in place of the GFS and increased ensemble mean contribution amidst increasing flow differences next Thursday-Friday. This approach maintained good continuity with the previous WPC forecast as well. ...Weather/Hazards Highlights... During the first half of the week expect a front lingering over/near the Gulf Coast to provide a focus for rain and thunderstorms that may extend along and north of the Gulf Coast, with a front dropping southeastward from the central U.S. also possibly enhancing Gulf inflow somewhat toward midweek. The Day 4 Excessive Rainfall Outlook valid Monday reflects a Marginal Risk area centered over the Lower Mississippi Valley while the Day 5 Marginal Risk area reflects the consensus eastward progression of heaviest rainfall potential toward the Southeast (while still possibly lingering over the central Gulf Coast region). Expect some rainfall to extend farther north along the advancing central U.S. front as well. From midweek onward the Mid-Atlantic and Northeast may become the most favored region for meaningful rainfall as the wavy front progresses eastward. Meanwhile, upper level and surface systems will promote episodes of rain and higher elevation snow over the West with guidance differences keeping confidence lower than desired for the details. The non-GFS majority cluster would have an early week system focusing a narrow axis of enhanced moisture aimed at the West Coast near the California/Oregon border. The ECMWF/ECens mean still depict fairly modest moisture anomalies with this event whose heavy rainfall may be fairly localized, so have opted not to depict any risk area in the Day 4 ERO for now. A mid-late week system may bring additional rain/snow to the West. How quickly this system progresses through the West will determine whether a rebound in rainfall could occur along/north of the Gulf Coast late in the week. Under the influence of mean troughing aloft, most areas from the West Coast into the Rockies will see highs 5-15F below normal while morning lows will tend to be near or slightly below normal. In contrast, expect well above normal temperatures to prevail over the eastern half or so of the country. Plus 20-30F anomalies will be possible from the central-southern Plains into the Northeast early-mid week with locations from the Midwest into Northeast seeing the best potential for some daily records. Santorelli/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