Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 PM EST Sun Nov 27 2022 Valid 12Z Wed Nov 30 2022 - 12Z Sun Dec 04 2022 ...Wet/snowy conditions expanding across the West with below normal temperatures... ...Heavy Rain possibly reaching into parts of the East by Wednesday... ...Overview... Most guidance continues to show a mean trough aloft becoming established near the West Coast and a ridge initially centered over western Cuba settling over the Gulf of Mexico, with west-southwesterly flow tending to prevail between these two features. This pattern should lead to cool daytime temperatures to the west of the Rockies along with increasing coverage of rain and snow over the West, with some of this activity potentially heavy. Day-to-day details of individual features within the West Coast upper trough still vary among the guidance so it will take time to resolve forecast specifics. Farther east, a deepening storm system tracking northeastward away from Lake Superior on Wednesday will sweep a strong cold front through the East, accompanied by locally heavy rainfall as well as a broad area of brisk to strong winds. Energy ejecting from the West Coast trough may bring a wavy frontal system into the central and eastern U.S. late this week through the weekend. Some precipitation may develop along this front by the weekend. ...Guidance and Predictability Assessment... The guidance continues to show good clustering and agreement in terms of track and depth of the storm expected to be close to the northeastern shore of Lake Superior by the start of the period on Wednesday. There remains some minor timing differences for the trailing front through the East Wednesday-Wednesday night. Attention shifts out West the rest of the period as a couple of potentially impactful systems impact the Western U.S.. The first, expected to reach the coast by early Thursday, could bring a fairly compact from vigorous wave to the vicinity of northern California later this week. Models show some differences in terms of timing and depth (leading to QPF differences too), but better consensus on the overall track. Previous runs of the UKMET were faster to bring the energy inland, while the 00z ECMWF was slowest/deepest, with the 06z/12z GFS and 00z/12z CMC a good middle ground. FThe 12z UKMET and ECMWF runs today both did trend closer to the GFS/CMC. Upstream, the next system may bring a compact closed low near the Canadian Maritimes or Pacific Northwest next weekend but with much fairly large uncertainties in terms of timing, which continue with todays latest 12z runs. One notable outlier was the CMC as it was much flatter than the better consensus of the ECMWF/GFS and ensembles all suggesting more amplification to the pattern. Although, despite better agreement for a more amplified system, uncerainty remains high on the specifics including timing and depth of this system. The WPC forecast for today (sent before 12z model runs were available) used a general blend between early on with the 00z/06z deterministic runs with more weighting towards the GFS/ECMWF over the CMC/UKMET due to initial issues out West. After day 5, leaned increasingly more towards the ensemble means which served as a good middle ground amidst plenty of uncertainty with the second western U.S. system. ...Weather/Hazard Highlights... A system nearing the Pacific Northwest should continue spreading moisture into the region and the far northern Rockies during Wednesday with some locally moderate to heavy rain and higher elevation snow possible, but also potential for snow in the lowlands as well. Gradual amplification of upper troughing should expand the precipitation shield southeastward through the rest of the week, possibly reaching into central or southern California and the central Rockies. For a period of time late in the week, the front associated with the initial system could draw in some lower latitude moisture/waviness, which would enhance rain/snow totals over some areas--most likely in the vicinity of northern California. Confidence in the specifics of this potential evolution is still not great though. Another system dropping southeastward toward the West Coast may bring another round of precipitation around the weekend. Snow levels in the Northwest could decline to fairly low elevations over some areas. Strong low pressure tracking northeastward over Canada will push a cold front through the eastern U.S. during Wednesday-Wednesday night. Areas of moderate to heavy rain may accompany this front given the vigorous dynamics aloft and strong southerly flow of moisture ahead of the front. This storm system and its front may produce strong winds over some areas of the northeast quadrant of the lower 48. Expect a brief period of lake effect snow after system passage as well. A wavy front reaching the north-central Plains/Upper Midwest by Friday should not have too much precipitation with it as it continues across the northern-central U.S. into the first part of the weekend. More organized rainfall could then develop near the front as it stalls over the east-central U.S., depending on how much moisture the west-southwesterly flow aloft and possibly some low level Gulf inflow contribute. Much of the West and far northern Plains should see below normal temperatures for most of next week. This is especially the case for daytime highs, with coldest anomalies of 10-25F below normal possible over/near Montana mid-late week. Latest forecast trends have been toward slightly less extreme cold over the Northwest late in the week, so any daily records for cold lows/daytime highs may be fairly isolated. Meanwhile, the eastern U.S. will see a brief period of above normal temperatures (up to plus 10-15F anomalies for highs and slightly warmer for morning lows) on Wednesday ahead of the front crossing the region. Then the cold air behind the front will drop readings to moderately below normal over the central and then eastern U.S. Wednesday-Thursday, followed by a rebound to above normal readings from the central-southern Plains into parts of the Southeast. Santorelli/Rausch 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