Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Mon Nov 28 2022 Valid 12Z Thu Dec 01 2022 - 12Z Mon Dec 05 2022 ...Wet/snowy conditions expanding across the West with below normal temperatures... ...Overview... Latest models and ensemble means are consistent in showing a late week through weekend upper pattern featuring west-southwesterly mean flow between West Coast upper troughing and a Gulf of Mexico ridge. The pattern should persist into early next week over most areas but with the overall trough axis moving inland over the West with the ejection of the second of two primary shortwaves. This large scale flow will favor below normal daytime temperatures over most areas to the west of the Rockies, as well as the northern High Plains at times, while the West sees episodes of locally significant rain and higher elevation snow. Most of the eastern half of the country will be dry late this week but rainfall should increase in coverage and intensity over east-central areas during the weekend as moisture interacts with a front that a Friday-Saturday Canadian surface low brings into the region. ...Guidance and Predictability Assessment... With the departure of a strong upper shortwave and surface low pressure from eastern North America early in the period, the main focus of the forecast shifts to the west with a couple of individual shortwaves within the West Coast mean trough. While notable differences still exist, there has been some improvement over the past couple of model cycles. The first shortwave should be just off the West Coast as of early Thursday and then progress inland with time, supporting a surface system that ultimately tracks into eastern Canada while pushing a trailing cold front all the way through to the East. The 06z (and 12z) runs of the GFS continue to be too fast with the shortwave with a better consensus for postioning from the ECMWF, CMC, and UKMET which formed the basis of the WPC forecast the first half of the period. The second system will likely approach the Northwest coast (possibly as a closed low) by Saturday. There are some notable differences still on timing, positioning, and depth of this system with the GFS still wanting to pull the low farther south down the CA coast before it begins to move inland early next week. The CMC also seems too fast, so it was not included in the blend past day 5. The WPC forecast favored the ensemble means with the ECMWF days 6 and 7. ...Weather/Hazard Highlights... The first primary system to affect the West should bring highest totals of rain and mountain snow to California late this week (northern-central areas Thursday and pushing farther south by Friday) with some moisture also extending into the northern-central Rockies. This system may incorporate some offshore lower-latitude moisture/waviness to enhance amounts but a somewhat faster trend of this system over the past day or so has lowered the potential for the heavier totals that some guidance had been advertising. The trailing system should bring increasing rain and mountain snow to areas along the northern half of the West Coast around Friday, with best focus drifting south into northwestern California and the Sierra Nevada during the weekend. Again the northern two-thirds of the Rockies will see meaningful snow from this event, albeit with somewhat lower liquid equivalents than expected near the West Coast. Snow levels in the Northwest could decline to fairly low elevations over some areas. Gusty winds may also accompany this system as it exits the rockies into the Northern Plains late this week. The Northeast should see breezy to windy conditions on Thursday as strong low pressure departs over eastern Canada, with lake effect snow gradually trending lighter with time. A wavy front reaching the north-central Plains/Upper Midwest by Friday may bring some light rain or snow to the far northern tier and possibly other areas of light rain as it continues eastward. More organized rainfall could then develop over the east-central U.S. during the weekend as the front stalls and interacts with moisture in the west-southwesterly flow aloft and possibly low level Gulf inflow. A fair degree of uncertainty still exists for specifics, but there is has been an increasing signal for the best rainfall focus to be centered over the Ohio/Tennessee/Mississippi Valley region. The moisture within the west-southwesterly flow aloft could also produce some rainfall over or near the far southern Rockies but with low confidence at this time. Much of the West should see below normal high temperatures from late this week into the start of next week, with most locations 5-15F below normal. There may be a few isolated daily records for cold morning lows/daytime highs near the West Coast late this week. The northern High Plains (especially Montana) may see a couple separate episodes of colder readings, with highs up to 20-30F below normal on Friday and Monday. The eastern U.S. will see a brief period of moderately below normal temperatures Thursday into Friday and then a rebound to above normal readings ahead of the next front. Above normal temperatures should become more pronounced across the southern tier during the weekend and early next week. Morning lows may become particularly anomalous with some plus 20-25F readings possible over and near the southern Plains by Sunday-Monday. 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