Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Sun Nov 10 2024 Valid 12Z Wed Nov 13 2024 - 12Z Sun Nov 17 2024 ... Another atmospheric river to bring heavy rain and mountain snow threats to parts of the Northwest mid next week... ...Overview... A fairly progressive pattern is forecast through late next week and into next weekend. A progressive but somewhat amplified trough will progress from the central to eastern U.S. bringing mainly light to moderate much-needed precipitation for the Midwest to Mid- Atlantic/Northeast, with some enhanced rainfall south near the Gulf Coast combined with tropical moisture out of the Gulf. Upper ridging on either side of this trough will promote periods of warmer temperatures across the eastern half of the nation through the period. Meanwhile out west, an atmospheric river will impact parts of the Northwest around midweek bringing heavy rain and snow threats, with additional rounds of precipitation later in the week with trough reloading along the coast. Some model indications the overall pattern over the CONUS may turn more amplified next weekend with troughing over the West/Southwest and stronger ridging over the East. ...Guidance/Predictability Assessment... Model guidance remains reasonably agreeable on the large scale progressive pattern, and exact timing and amplitude of the troughs and ridges are the most uncertain aspects of the forecast. An initial shortwave exiting the Northeast on Wednesday shows some uncertainty with energy that lingers off the coast and interacts with the next trough behind it. The central U.S. trough has trended slower and a little bit more amplified and the WPC forecast trended that direction too. The 18z GFS was the fastest of the guidance with this trough, but the better consensus (along with the AI/ML models) were slower. The new 00z GFS (available after the WPC forecast was generated) did trend slower/sharper than its previous run lending confidence to the change in WPC continuity. Lots of uncertainty out West, especially by next weekend, with the deep troughing. ECMWF has been more amplified/deeper, sending energy farther south than the GFS and CMC, but the latest 00z runs of both the GFS and CMC have trended towards the ECMWF, signaling a possibly more amplified pattern by late next weekend and beyond the medium range period. The WPC forecast for Days 3 and 4, leaned more heavily on the ECMWF, CMC, and UKMET (slower trough into the East). By the middle to latter half of the period though, favored the ensemble means which were a good middle ground solution for the troughing in the West. ...Weather/Hazards Highlights... The main concern for weather hazards will be with a modest atmospheric river set to begin impacting the Pacific Northwest on Tuesday (just before the medium range period begins) and may last a few days. Heavy rain and mountain snow potential will last through Wednesday with ample moisture anomalies and some instability along the coast continuing the need for a marginal risk for parts of western Washington/Oregon and into northwest California on the Day 4/Wednesday ERO. Snow may be heavy in the mountains, particularly the Cascades as the week progresses, and some modest snow amounts into the northern Rockies as well. After Wednesday, precipitation should trend lighter as the moisture moves inland, but some lingering precipitation along the coast may be possible as weaker energy reloads into the larger scale trough. The slower and slightly more amplified trough across the Central U.S. on Wednesday should allow for better tapping of Gulf of Mexico tropical moisture and interaction with a coastal front and the approaching shortwave. Models have ticked upwards in terms of QPF across parts of the central Gulf Coast from Louisiana into Mississippi and western Alabama. As such, a marginal risk was added for this region to the Day 4/Wednesday outlook. Farther north, moisture along the front should bring modest precipitation to the eastern half of the country through about Thursday, but continued model disagreements in the trough position/evolution do cause some spread for the precipitation amounts/intensity on individual days. Most of this precipitation looks to fall as rain given the warmer than normal temperatures, until some ice and snow are possible in higher elevations of the Interior Northeast mid- to later week. Winds may be gusty behind the associated low pressure and frontal system in the northern Rockies to northern Plains Tuesday- Wednesday. While system progression will provide some day-to-day variability, most of the lower 48 to the east of the Rockies should see above normal temperatures much of the week. Meanwhile lingering snow cover in the central/southern Rockies will promote cooler than normal highs there through about Thursday while the West otherwise should trend colder with more amplified troughing moving into the region late week and into next weekend. Santorelli 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