Extended Forecast Discussion NWS Weather Prediction Center College Park MD 150 PM EDT Sun Oct 29 2023 Valid 12Z Wed Nov 01 2023 - 12Z Sun Nov 05 2023 ...Synoptic Overview... An expansive surface high will encompass much of the central and eastern U.S. for the middle of the week with the cold front clearing the Florida coast by late Wednesday. This airmass will bring the coldest air of the season for most areas, with widespread frost and freeze conditions during the overnight hours across much of the south-central states to the East Coast. The airmass gradually modifies by the end of the week, and a renewed surge of colder weather arrives for the Northern Plains and Upper Midwest by Friday into next weekend. A storm system moving inland across the Pacific Northwest and Northern Rockies is expected to increase precipitation across these areas by Wednesday and continuing into the end of the week, with some signal of an atmospheric river event. ...Guidance Evaluation/Predictability Assessment... The 00/06z guidance captured the overall synoptic evolution across the lower 48 reasonably well during the medium range period. A fairly zonal pattern across much of the country helped with this. An upper trough emerging from the eastern Pacific over the Pacific Northwest. The latest guidance has trended stronger and more wet with the east Pac system this coming Thursday/Friday. That being said, there's still some uncertainty around the timing and strength of the system. Given the zonal pattern through the period, a general model blend consisting of the 00z EC/CMC/UKMET and 06z GFS were utilized through day 5 before a transition to a predominantly 00z ECE/CMCE and 06z GEFS based blend. ...Weather/Hazards Highlights... Most of the continental U.S. should be relatively uneventful in terms of impactful rainfall for the middle to end of the week. The exception to this will be across western Oregon and Washington where a potential atmospheric river event may produce a few inches of rainfall from the coastal ranges of Northern California to the Olympic Mountains over the Day 4 and 5 time period. At this time, it appears the greatest moisture flux towards the coast would be during the transition period between day 4 and 5 (06z Thursday -- 18z Friday). Thus, the marginal risk that was issued overnight for day 4 was extended into day 5 with some expansion into the coastal ranges of northern California. Some lake effect snow is likely from Michigan to Upstate New York as a strong surge of cold air advection rushes across the warmer lake waters on Wednesday, with a few inches of accumulation possible for some areas, but not looking like a major event by any means. Looking ahead to the end of the week, precipitation increases across much of the northwestern states with potentially heavy snow for the higher mountain ranges. Parts of northern California may also get rain by the end of the week. The cold airmass ushered in by the strong cold front engulfs all of the central and eastern U.S., by Wednesday. Widespread anomalies on the order of 10 to 20 degrees below average for this time of year are expected from Texas to the East coast on Wednesday for highs. The first frost/freeze of the season is expected for a vast expanse of the south-central U.S. and also extending into the major metro areas of the Northeast U.S. going into the middle to end of the week. This airmass should then modify going into Friday and beyond with temperatures closer to average as a more zonal flow pattern evolves. Kebede/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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw