Extended Forecast Discussion NWS Weather Prediction Center College Park MD 145 PM EST Wed Mar 01 2023 Valid 12Z Sat Mar 04 2023 - 12Z Wed Mar 08 2023 ...Synoptic Overview... The strong low pressure system over the eastern U.S. should depart from the Northeast by late Saturday with surface high pressure building across the eastern third of the nation through Monday. In its wake, the overall large scale pattern should then evolve with a slow moving upper trough across much of the western U.S. through the weekend and into early next week, with continuation of unsettled conditions and below normal temperatures over much of the West. The primary Pacific system of note will drop southward from the Gulf of Alaska and reach the offshore waters of the Pacific Northwest during the weekend and then weaken as it idles off the coast. Downstream of this ridge will be a broad ridge axis across the central U.S. with the main upper high over the central Gulf of Mexico. Some weak shortwave energy is expected to track across the northern periphery of this ridge, but nothing particularly strong is currently expected. ...Guidance/Predictability Assessment... The latest runs of the guidance continue to have above average agreement with wavy pattern that becomes more amplified with the trough over the western states. As such, the first couple of days of the extended forecast was comprised equal weighting of the 00Z ECWMF, CMC, UKMET and 06Z GFS. By the beginning of the new week model differences increase a bit but overall the clustering of all of the features are about average and within the normal degree of spread for the Day 6 and 7 time period. To help reduce some of this uncertainty the EC ensemble means and GEFS means were included. ...Weather/Hazard Highlights... A deep upper trough will remain anchored in place over the West Coast this weekend and persist into the first half of next week. This trough along with an embedded surface low pressures will increase the potential for coastal rain and heavy inland snow from the Pacific Northwest into northern California. Some of the highest accumulations are expected to align along the central West Coast into the Sierra Nevada, adding to the already very impressive snow pack over the region. Lesser amounts will spread across portions of the Northern and Central Rockies. With low confidence in specifics, shortwave energy streaming eastward from the main West Coast trough could produce one or more areas of light snow from the Northern Plains into the Great Lakes, with scattered light rain possible for locations farther south. For the Northeast U.S., some lingering snow and coastal rain/wind is likely through early Saturday afternoon, with improving conditions going into Sunday as the surface low departs the region. Ridging across the Gulf of Mexico will keep much of the south-central states and the Southeast warmer than normal, with many locations with temperatures 10 to 15 degrees F above early March averages along with increasing humidity levels from Texas to the Southeast states. The West will continue to feel like the middle of January through the weekend with the Intermountain West and Rocky Mountains consistently having highs on the order of 10 to 20 degrees F below normal, which will equate to highs in the 20s and 30s for most areas north of the Utah/Arizona border. Campbell/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