Extended Forecast Discussion NWS Weather Prediction Center College Park MD 313 PM EDT Tue Mar 26 2024 Valid 12Z Fri Mar 29 2024 - 12Z Tue Apr 02 2024 ...Rounds of heavy rain and high elevation snow likely across California, The Great Basin, and the central/southern Rockies... ...Overview... Snow and rain may continue Friday in Maine as a low pressure system is slow to exit. Meanwhile, an upper low is forecast to slowly move down the California coast late Friday through Sunday before slowly tracking over the Southwest into the middle of next week. This feature and its surface low will direct moisture into California and produce heavy rain and higher elevation snow for California, much of the Southwest/Great Basin and central/southern Rockies. Farther downstream, increasing moisture should combine with northern stream troughing to produce low pressure that tracks east from the central Plains Sunday through the Northeast Tuesday. Expansive precipitation coverage is likely with this system with snow and freezing rain possible on the north side of the system. ...Guidance/Predictability Assessment... The 00Z/06Z deterministic guidance were in good agreement with the low/trough in the Southwest and broad ridge over southeast/northern tier shortwave activity through Sunday. In particular, the 00Z ECMWF/06Z GFS are similar with the CA low and its reinforcing trough on Sunday that allows some eastward movement to begin while the 00Z CMC/UKMET were more closed. However, the 12Z runs are in better agreement with a less closed system by Sunday. The WPC forecast was based on a multi-model blend favoring the 00Z/06Z EC/GFS until Day 5 when some ensemble means began to be included. ...Weather/Hazards Highlights... Surface low pressure in the western Atlantic tracking toward the Canadian Maritimes will cause rain/snow to linger across Maine through Friday. For the western U.S., an active and unsettled period is expected as a persistent jet on the southeast side of an upper low directs moisture into California eastward. A modest atmospheric river should start to take aim at California late Friday with heavy rain ahead of the associated cold front. The timing of this front is a bit sooner than previous, so a Day 4 Slight Risk has been raised for portions of Santa Barbara and Ventura Counties. Otherwise the Dy 4 Marginal Risk looks to be in good shape from coastal California toward the foothills of the Sierra Nevada. The higher elevations of the Sierra Nevada can expect heavy snow. By Saturday, anomalous moisture likely reaching above the 95th percentile continues to be directed at southern California. Notable upslope flow into the Transverse Ranges means heavy rainfall could occur, so a Slight Risk is continued for upslope portions of the Transverse Range below the snowy higher elevations. The Marginal Risk is expanded farther east through southern Nevada as timing of as moisture spreading east has also become earlier. Ample moisture remains in place into Sunday- Monday across much of California into the Desert Southwest and Great Basin and into the Rockies. Moderate to heavy snow is likely in the higher elevations of the Intermountain West. Farther east, shortwaves generally riding along the northern side of a central U.S. ridge could combine with moisture to produce some light to moderate precipitation Friday into the weekend across the north-central U.S. and Great Lakes region into Ohio Valley and northern Mid-Atlantic. Heavier precip is likely to develop with a low pressure system tracking east from the central Plain through the Northeast Sunday-Tuesday. Chances for wintry precipitation are increasing across the northern Plains and Upper Midwest by the weekend, and stretching into the Great Lakes region and higher elevations of the Northeast by Monday. Chilly temperatures linger across the north-central U.S. through Monday, but farther south from the central to southern Plains/Mississippi Valley, notable warmth is expected late week into the weekend as upper ridging builds. Temperatures of 10-20 degrees above average will become widespread, with highs in the 70s and 80s reaching Kansas and Missouri while highs climb into the 90s if not 100F in southern Texas. The above normal temperatures are likely to expand east into the Ohio/Tennessee Valleys, Mid- Atlantic, and Southeast by early next week. A cold front is forecast to finally drop temperatures in the south-central U.S. by Tuesday, focusing this warmth in the Southeast. Meanwhile in the West, near to above normal lows but near to below normal highs are forecast, consistent with the clouds and precipitation there. One exception may be over the Pacific Northwest where enough upper ridging should build in to push highs a above normal Saturday through early next week. Jackson 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/ https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml