Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 AM EST Sun Mar 2 2025 Valid 12Z Wed Mar 5 2025 - 12Z Sun Mar 9 2025 ...Heavy rain and strong winds expected for the Eastern Seaboard Wednesday into early Thursday... ...General Overview... The weather pattern across the continental U.S. will be quite active mid-week into the weekend with two storm systems of interest. The first and strongest low pressure system will be gathering strength across the Midwest and Great Lakes on Wednesday in response to an amplifying upper level shortwave crossing the Midwest. Heavy rainfall, strong to severe thunderstorms, and strong winds will be making weather headlines from the Southeast U.S. to the Mid-Atlantic and Northeast, and the storm system exits the East Coast by Thursday morning. A second and weaker storm system develops over the Rockies on Thursday and likely reaches the central Plains on Friday, with additional showers and thunderstorms expected. There may be additional low pressure development over southern Texas next weekend. ...Guidance/Predictability Assessment... At the time of fronts/pressures preparation, there was good overall model agreement with the big storm system crossing the Great Lakes and into the Northeast states through Thursday afternoon, and therefore a general model compromise works as a starting point in the forecast process. Things are less certain with the second storm system that follows behind it on Friday across the central Plains. The guidance diverged quite a bit going into Friday night and next weekend, with the GFS/GEFS indicating a much more progressive solution with a lead surface low that is generally weaker, in contrast to the much slower CMC, with the ECMWF falling in between. The GFS depicts a separate and stronger low developing over southern Texas by Saturday night ahead of a amplifying trough. In regards to the building southern stream trough over the southwestern U.S. next weekend, the suite of ML guidance, along with the AIFS, supported a solution more in line with the GFS/GEFS over the southern Rockies, instead of the CMC/ECMWF that are displaced to the east across the central Plains. Therefore, the model blend was weighted a little more to the GEFS/GFS for the second half of the forecast period, with the ensemble means accounting for about 70% of the blend by next Sunday owing to greater than average uncertainty. ...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 a triple point low forming near eastern Maine by Friday morning. 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. 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