Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 PM EST Thu Feb 27 2025 Valid 12Z Sun Mar 02 2025 - 12Z Thu Mar 06 2025 ...Severe weather and heavy rain potential likely to focus in Lower/Middle Mississippi Valley and Mid-South on Tuesday and perhaps the East on Wednesday... ...Overview... The medium range period will feature a rather progressive upper flow pattern across the lower 48 states as a couple of troughs traverse coast to coast. While troughing exits the East early week, a 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. Meanwhile upstream, a deep trough/closed low will move into the West Sunday/Monday, spreading some modest precipitation and winds across the region. As this system emerges, reasonably deep low pressure system will form over the central Plains by Tuesday and track northeast Wednesday-Thursday. Ahead of its associated cold front, severe weather and heavy rain with flooding potential are possible across the south-central into east-central U.S. peaking on Tuesday, with some perhaps continuing into Wednesday in the East. Another amplified trough approaches the West Coast next Thursday. ...Guidance/Predictability Assessment... Most model and ensemble guidance is reasonably agreeable with the first few systems of note during the medium range period, namely with the East trough pulling away, the southern Rockies/High Plains small southern stream low getting absorbed, and the trough moving from the eastern Pacific into the West. While smaller scale differences exist, and could impact sensible weather like QPF, a multi-model blend of deterministic guidance could be used as a starting point, particularly the 00Z ECMWF, 00Z/06Z GFS, and 00Z CMC. The main outlier was the 00Z UKMET, which was farther inland/faster with the West trough compared to other guidance, so leaned away from that. That initially West trough maintains reasonable model agreement for the mid-late medium range period as it shifts into the Plains and beyond and causes a surface low to develop and track northeast. The upper trough tracking toward the West by mid-late week shows more variability in model guidance. Operational GFS runs from 00Z/06Z and now 12Z have held the upper low farther back into the Pacific compared to other guidance--including the GFS-based AI models that showed a trough axis farther east. This gave confidence to not prefer the deterministic GFS solutions. Meanwhile the ECMWF runs are slightly on the faster side of the envelope. EC-based AI models are mixed with some faster and some slower. The ensemble means were rather agreeable and showed an in between solution (more toward the EC than the GFS though). Thus the WPC forecast quickly ramped up the proportion of the ensemble means by Day 6 and especially 7 to combat the increasing spread with the West trough in particular. ...Weather/Hazards Highlights... The initial southern stream upper low moving into the southern Plains on Sunday could lead to some modest rainfall across that region. Behind it, some high winds are possible across the southern Rockies to High Plains. The trough coming into the western U.S. early next week will also lead to some precipitation spreading across the West Coast into the Great Basin and Rockies, with lower elevation rain and higher elevation snow as well as gusty winds. A true atmospheric river is not expected and this should limit precipitation totals to be modest in most areas. However, as this trough moves into the central U.S. by Tuesday, it should tap moisture from the Gulf to fuel more widespread and heavy rains from the southern to eastern U.S. The heaviest rainfall totals are currently expected from the Lower/Middle Mississippi Valley to Southeast and Tennessee/Ohio Valleys on Tuesday. Some areas have wet antecedent soil conditions, which would exacerbate flood potential. Severe weather is also a notable threat over the south- central states per SPC. Precipitation should overspread the East on Wednesday, and SPC continues to show severe potential in the Southeast to southern Mid-Atlantic. Areas of heavy rainfall become even more uncertain with placement at that time, but may become problematic in terms of flooding if heavy rain falls on snow- covered areas of the Northeast, per the National Water Center. Northwest of the low track, it may be cold enough to support snow across the north-central Plains into the Great Lakes, but totals are uncertain. Gusty winds are also possible depending on how deep the surface low gets. Another round of moderate rain and elevation snow should move into California Wednesday-Thursday with the next upper trough. 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 25 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. 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