Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 PM EST Sun Feb 23 2025 Valid 12Z Wed Feb 26 2025 - 12Z Sun Mar 02 2025 ...Overview... The upper flow pattern should remain rather progressive through much of the medium range period. At the start of the period on Wednesday, a shortwave atop the north-central U.S. should eventually deepen over the East Thursday into Friday, with secondary reinforcing energy by Saturday. A ridge axis over the West will be undercut by a southern stream cutoff low moving inland across Southern California and the Southwest this weekend. Another deep and elongated upper trough looks to move into the West Coast next Sunday. ...Guidance/Predictability Assessment... There continues to be reasonable agreement on the large scale pattern during the medium range period, but still plenty of uncertainty in the details, some of which could have notable sensible weather impacts. Into Thursday, a shortwave moving through the deepening east-central U.S. trough leads to some minor model differences in the associated surface low position over the Great Lakes or so, with the GFS/UKMET farther east of the CMC/EC. A position in between appears best considering the AI models as well, and the 12Z models have converged better on a position. Then by Friday-Sunday, the next shortwave and surface low will track from south-central Canada through the Great Lakes region and Northeast. The 00Z ECMWF appeared to be a northern outlier compared to the dynamical and AI guidance on Friday and then became slow by Sunday. The 12Z EC looked more reasonable but there is still some model spread to keep an eye on. Farther west, models continue to waffle on the timing and position of the southern stream upper low as it moves into southern California on Friday. The 00Z/06Z deterministic models were actually pretty agreeable on the timing, with the EC and CMC ensemble means in line, but the GEFS means were faster. But the newer 12Z EC/GFS runs jumped farther west and maintain a bit slower of a track into the Southwest to southern Plains through the weekend. So still some model variations there to monitor. To the north there is also model spread with the trough moving across the eastern Pacific toward the Pacific Northwest/California next weekend. GFS runs are particularly slow and close off an upper low well offshore northern California; the EC and other guidance including both EC-based and GFS-based AI models have the trough coming in faster than the GFS and CMC. Thus leaned toward the EC/EC mean for this feature. The WPC forecast used a blend of deterministic models favoring the GFS and ECMWF early in the period. As the period progressed, quickly ramped up the proportion of ensemble means, particularly the EC mean, given the increasing spread with multiple features. ...Weather/Hazards Highlights... A cold front shifting across the Ohio/Tennessee Valleys into the Eastern Seaboard will spread generally light to moderate precipitation across this region Wednesday into Thursday. Some precipitation could be snow in the northern part of the precipitation shield across the Interior Northeast. A clipper system should bring an additional round of precipitation to the Great Lakes and Northeast Friday into Saturday. A building ridge should keep conditions quiet and dry across the West Wednesday and Thursday, other than a little light precipitation possible in the Pacific Northwest. The southern stream upper low moving across southern California Friday and inland next weekend may lead to light showers over California, the Southwest, and into the south-central U.S., with increasing rain chances in the southern Plains by next Sunday as moisture increases. The northern stream trough moving through the eastern Pacific and into the West next weekend will also bring precipitation back into the forecast for the West Coast and Great Basin. By the start of the period on Wednesday, much of the lower 48 will be much above normal in terms of temperatures, with decent coverage of plus 10-20 degree anomalies. The northern/central Plains can expect the highest anomalies of 20 to locally 30 degrees above normal, with 60s for highs as far north as Nebraska or perhaps even South Dakota at times. The Southwest and Great Basin can also expect warmer than average conditions underneath the building upper ridge. Parts of the Desert Southwest could reach into the 90s especially Wednesday, and some sites could set daily record high max/min temperatures in the vicinity. Areas east of the Mississippi should also see warm conditions into Wednesday, but are likely to cool back to near normal (or slightly below in spots) by late week underneath upper troughing. Tate/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 (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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