Extended Forecast Discussion NWS Weather Prediction Center College Park MD 147 AM EST Thu Feb 27 2025 Valid 12Z Sun Mar 02 2025 - 12Z Thu Mar 06 2025 ...Coast to coast U.S. southern tier system to monitor... ...Overview... The medium range period will feature a rather progressive upper flow pattern across the lower 48 states as a couple of systems traverse coast to coast. Amplified northern stream troughing over the East will be established this weekend, but will shift eastward early next week and be replaced by upper ridging. Meanwhile, a lead southern stream cutoff low over the southern High Plains on Sunday will lift north and east and get absorbed into the larger scale flow into early next week over the south- central U.S.. Behind this, a deep trough/closed low will move increasingly into the West Sunday/Monday. Weather/hazard focus with this emerging and amplified southern stream system will track from the Southwest through the south-central then into the East by the middle of next week. The guidance signal has grown for an associated and increasingly widespread swath of windy and wet/unsettled weather to monitor in these areas. A third amplified trough approaches the West Coast next Thursday. ...Guidance/Predictability Assessment... Models and ensembles this cycle are showing better clustering for both the initial cut off low over the southern High Plains, and the next trough into the West on Sunday-Monday. There are some lingering differences in the exact positioning of the low and timing, which could have sensible weather impacts, particularly in placement of rainfall over the southern Plains. These details though may take until the short range to fully iron out. The UKMET was notably south of consensus with the trough across the West into Monday, so it was not used in the forecast blend tonight. There is better consistency and clustering between the GFS, ECMWF, and CMC as the shortwave lifts into the Upper Midwest/Great Lakes mid next week. A third deep trough approaches the West Coast next Wednesday into Thursday, but does slow a lot of run to run and model to model variability. The WPC forecast blend for tonight consisted of the GFS, ECMWF, and CMC for the first half of the period. Gradually transitioned to 60 percent of the ensemble means by the end of the period, primarily to address the late period uncertainty over the West Coast. Used the EC and CMC to compliment the ensemble means as well. ...Weather/Hazards Highlights... The southern stream upper low moving into the southern Plains on Sunday may lead to increasing moisture for this region. This also has a high wind threat across that broad area. There also appears to be a better signal for the precipitation to spread farther east/northeast across the southern Plains and eastward early next week. The northern stream trough moving through the eastern Pacific and into the West next weekend will also bring precipitation chances back for the West Coast, and spreading across the Great Basin/Rockies. As this trough moves into the Central U.S. around Tuesday-Wednesday next week, it should tap moisture from the Gulf to fuel more widespread rains across the Eastern half of the U.S.. SPC also highlights a threat for severe weather over the south- central states given support. There is also the potential for moderate to at least locally heavy rainfall and with ambient moist soil conditions in some areas. Gusty winds could accompany this system, depending on how deep the parent surface low gets. Another round of moderate rain and elevation snow moves into California next Wednesday ahead of the third system. Much above normal temperatures over the Rockies and Plains states on Sunday will gradually progress eastward with time and moderate. The greatest anomalies, 15 to 20 degrees above normal, will be across the northern Plains through Monday. Temperatures across much of the East will be considerably colder than normal on Sunday, but should moderate back to normal Monday-Tuesday, and warmer than normal Wednesday. By next Thursday, much of the country may be near or within a few degrees of normal. 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