Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Mon Oct 30 2023 Valid 12Z Thu Nov 2 2023 - 12Z Mon Nov 6 2023 ...Synoptic Overview... An expansive surface high will encompass much of the eastern U.S. for the middle to end of the week with the high slowly moving offshore by the weekend. This airmass will slowly moderate after the widespread frost and freeze conditions earlier in the week. However, there will likely be a renewed surge of colder weather 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 Thursday and continuing into the end of the week, with some signal of an atmospheric river event. ...Guidance Evaluation/Predictability Assessment... Model agreement is generally good across the central/eastern U.S. early in the period, but differences become apparent as early as Thursday near the Pacific Northwest as the shortwaves move inland. The 12Z CMC did not fit the consensus well in regards to amplitude and timing of Pacific shortwave energy moving inland, so the fronts/pressures forecast was based on a GFS/ECMWF/UKMET blend with some previous WPC continuity, and then increased use of the ensemble means to about 50-60% going into Sunday/Monday. The 00Z CMC is in better alignment with the consensus compared to its 12Z run. By the end of the period next Monday, the flow is mainly zonal across the nation with more significant differences with shortwave timing, thus the increase in ensemble means. ...Weather/Hazards Highlights... Most of the continental U.S. should be relatively uneventful in terms of impactful rainfall for the 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 for the Wednesday night through Thursday evening time period. Locally heavier rainfall on the west facing slopes may just be enough to cause some minor flood concerns, and therefore a Marginal Risk of excessive rainfall remains valid for the Day 4 period on Thursday. There should be enough of a lull on Day 5 to avoid having a Marginal Risk at this time, but another round of Pacific moisture is expected to arrive over the weekend. A slow moderation trend with temperatures will commence for the central and eastern U.S. by Thursday with highs generally 5-15 degrees below early November averages, compared to the widespread 15-25 negative anomalies expected during the short range forecast period. Temperatures continue to warm going into Friday and the weekend with readings generally near to about 5 degrees above average in most cases. Pleasantly mild conditions should also return to the Rockies and adjacent portions of the central/southern Plains going into next weekend. However, it should continue to remain quite chilly for North Dakota and into northern Montana and Minnesota with highs generally in the upper 20s to upper 30s. 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