Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 AM EST Sat Feb 25 2023 Valid 12Z Tue Feb 28 2023 - 12Z Sat Mar 4 2023 ...Significant storm system to track across the Northeast U.S. early to mid next week with heavy inland snow... ...A series of active storms for the West through the period also may lead to emerging late next week storm development across the Southeast states... ...Synoptic Overview... The weather pattern is forecast to remain quite active going into much of next week. The highly anomalous and intense low pressure system that will initially affect California and the Desert Southwest will eventually eject eastward across the central Plains and then reach New England by early Tuesday. Surface high pressure briefly settles in across the eastern U.S. in the wake of this storm for the middle of the week. Meanwhile, a persistent and cold/amplified upper trough position will repeatedly rebuild across the cold and unsettled West. A surface low is forecast to track from the West Coast to the Plains, and eventually the Great Lakes region and Mid-Atlantic/Northeast for the Wednesday to Thursday time period, and is expected to result in another round of widespread precipitation and thunderstorms. Additionally, there may be another round of noteworthy precipitation to emerge across the southeastern U.S. late next week along with a threat for heavy rain and potentially enhanced northern periphery snow/ice, but question marks remain on how this will evolve. ...Guidance/Predictability Assessment... The 00Z model guidance suite initially starts off in very good agreement on the synoptic scale pattern on Tuesday, and thus a multi-deterministic model blend suffices as a starting point in the forecast process. However, substantial differences are noted going into the end of the week, and this made the forecast challenging for the Friday-Saturday time period across the eastern U.S. and the potential for a trailing surface low/upper trough that amplifies. At the time of fronts/pressures composition, teleconnections with the negative height anomaly off the Oregon Coast and the positive height anomaly south of the Aleutians favored a quicker exit of the cold front on Saturday and less of a trailing surface low, so the forecast was based on the ECMWF/ECENS for Thursday night and beyond since the GFS did not fit the teleconnections. The 12Z ECWMF solution also had support from the JMA solution. The 00Z ECMWF adjusted for a position closer to the 00Z CMC, and both of these solutions are south of the GFS. Therefore, forecast confidence is below average for days 6 and 7, and substantial changes to the forecast are possible going forward as future model runs get a better depiction of the pattern evolution. ...Weather/Hazard Highlights... The strong low pressure system crossing the Plains is expected to reach the Northeast U.S. by Monday night, with secondary cyclogenesis south of Long Island by Tuesday morning and this becomes the new dominant low. Moderate to occasionally heavy snow is appearing likely for much of central and northern New England on Tuesday, and a rain/snow mix closer to the coast depending on the exact track of the low. Although the strongest winds should remain offshore, winds could gust 30 to 50 mph at times during this event and may result in coastal flooding at times of high tides. The precipitation is expected to end by Wednesday morning for the Northeast as the low moves out to sea. The Western U.S. will continue to remain unsettled going into the middle of next week as the trough rebuilds, with very heavy snow likely for the Sierra and northern California mountains, and then heavy snow reaches the higher mountain ranges of the Intermountain West as the surface low tracks inland. High winds are also a good possibility ahead of the front with the potential for elevated fire weather concerns for the western High Plains Wednesday and into Thursday. Meanwhile, heavy rain and thunderstorms are likely to develop across portions of the Mid-South late Wednesday into Thursday, and there is now a Marginal Risk area for Day 5 in the excessive rainfall outlook. Additional rainfall is expected going into the end of the week, and some of this may be heavy at times across the southeastern U.S., but the axis of the heaviest rainfall continues to remain uncertain at this juncture. In terms of temperatures, much of the central/eastern U.S. should see multiple days of readings 10-20F above normal, and potentially up to 25 degrees above normal on Wednesday across the Ohio Valley. The West will see a persistent cool pattern through the entire week with the Intermountain West and Rocky Mountains most consistently having highs on the order of 10-20F below normal. 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: 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