Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 PM EST Sun Mar 2 2025 Valid 12Z Wed Mar 05 2025 - 12Z Sun Mar 09 2025 ...Deep low pressure system could bring blizzard conditions across the upper Midwest Wednesday morning as well as heavy rain, strong thunderstorms, and strong winds for the East Coast into early Thursday... ...General Overview... A deep cyclone near peak intensity will likely track across the Great Lakes on Wednesday with a potent cold front sweeping through the eastern U.S. before the cyclone weakens and moves away into the Canadian Maritimes Thursday into Friday. Unsettled weather associated with a couple of upper troughs will attempt to merge over the southwestern portion of the country through midweek followed by uncertain timing, track and intensity on the ejection of the merged upper trough into the mid-section of the country late in the week. ...Guidance/Predictability Assessment... Ensemble means from global dynamic models continue to show good agreement on the above-mentioned pattern evolution across mainland U.S. through the medium range period. There continues to be some residual tendency for the deep cyclone to track farther north across the Great Lakes while the potent cold front trailing south from the cyclone to advance faster across the East Coast on Wednesday. Meanwhile, uncertainty remains abound on both the deterministic and ensemble mean guidance for the next system over the Southwest which is forecast to eject eastward into the mid-section of the country late this week. There has been a general model consensus to eject this system farther north into the central Plains on Friday where a deeper low pressure system would tend to form and then track toward the east-northeast. The GFS/GEFS solutions have been on the fastest side; the CMC/CMC mean solutions have been the slowest, with the ECMWF/EC mean in between these extremes. The model spread diverges further by the weekend as the system tracks toward the East Coast. The WPC medium-range forecast package begins with a consensus of the deterministic and ensemble mean guidance but then transitions to 55% based on the 06Z GFS/GEFS, 35% from the 00Z EC/EC mean, and 10% from the 00Z CMC for this weekend, which is consistent with the previous WPC blend. However, the latest from EC-AIFS and the 12Z ECMWF appear to favor more of the southern stream wave development than the northern stream. This scenario will be monitored in future WPC forecast updates. ...Weather/Hazards Highlights... An amplified upper level trough/closed low reaches the Midwest by Wednesday morning, along with a very strong surface low that will track eastward across the Great Lakes and into Quebec, with the possibility of blizzard conditions Wednesday morning on the basc- side of the cyclone across the upper Midwest. Meanwhile, a strong low level jet will advect copious moisture northward across the East Coast region Wednesday into Thursday morning, producing widespread moderate to heavy rainfall from the eastern Carolinas to New England. The heaviest rain is likely to be from eastern Pennsylvania to southern Maine, where a Marginal Risk remains for the new Day 4 outlook. Parts of this region still have some snow on the ground, so this will contribute to run-off issues. A second storm system is expected to follow behind this, and bring additional rounds of showers and thunderstorms to many of these same areas, but the current thinking is that it will not be as intense as the midweek storm system. Some strong thunderstorms will also be possible with this event late in the week into Saturday across the southern U.S., depending on how low level boundaries evolve. Before this system reaches the Plains, it will affect central and southern California with moderate showers and heavy Sierra snowfall on Wednesday. Given recent burn scar sensitivities across portions of southern California, a Marginal Risk of excessive rainfall is planned for both Days 4 and 5, mainly across the terrain. Temperatures are expected to be mild across the eastern third of the U.S. on Wednesday ahead of the big storm system, followed by a return to more seasonal conditions to close out the work week. Cooler than average readings are likely from the Intermountain West to the western High Plains in conjunction with the upper trough situated across the southern Rockies. Looking ahead to next Sunday, there may be warm-up across the north-central U.S., but this is less certain at this point in time. Kong/Hamrick 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