Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Tue Apr 12 2022 Valid 12Z Fri Apr 15 2022 - 12Z Tue Apr 19 2022 ...Overview... Lower amplitude mean flow aloft should prevail over the lower 48 at least from Friday through the weekend, behind a departing deep upper low which may take its time drifting across eastern Canada into next week. Guidance generally shows a shortwave and associated rain/snow progressing into and through the West during the weekend then into the Plains/Mississippi Valley by early next week. By early next week an upper trough reaching the eastern Pacific early next week may serve to amplify the downstream ridge crossing the West and trough heading into the East, with the Pacific trough likely entering the West next Tuesday and bringing another episode of precipitation to the region. Within what has been an agreeable forecast of the large scale pattern, persistent significant detail differences at the surface and aloft keep confidence lower than desired for coverage and intensity of precipitation--especially over the eastern half of the country from Sunday onward but also to some degree over the West. ...Guidance Evaluation/Predictability Assessment... The first half of the period started with a composite of latest operational runs. This part of the forecast involved primarily timing issues, with the GFS beginning to stray a bit faster than most other guidance for the surface front and supporting dynamics crossing New England during the weekend and spread/variability persisting for the system reaching the West by Saturday. The western system has some degree of complexity, involving potential interaction of a trough/upper low off the Pacific Northwest/Vancouver Island and separate shortwave just to the south. Through the 06Z cycle the GFS was on the faster side of the spread but the new 12Z UKMET has adjusted closer to the GFS, leaving the 00Z ECMWF/ECMWF mean a little on the slower side and the 12Z CMC essentially a compromise. The new 12Z ECMWF has nudged to a middle ground as well. By the first part of next week, detail issues with the incoming western system lead to additional divergence of solutions at the surface and aloft over the East. The ECMWF through 00Z continued to be the most consistent model in principle with development of an embedded closed low along with surface system whose track is over the mid-latitudes of the East, with its mean and the CMC/CMC mean favoring similar timing which is slower than the GFS/GEFS mean. The new 12Z GFS/CMC keep the core of the upper trough farther north which leads to a much farther north surface low track than what other guidance had been showing through the 00Z/06Z cycles. The 12Z GEFS mean has adjusted the surface track at least partially in the 12Z GFS/CMC direction. Meanwhile the new 12Z UKMET becomes a fast extreme with greater strength than consensus. The 12Z ECMWF has adjusted its upper system northward somewhat but not to the extent of the GFS/CMC. The upper trough reaching the West by Tuesday was closer to consensus in the 00Z GFS versus the faster 06Z run, while the 12Z version has reverted back to the majority. The new CMC/ECMWF are fairly consistent. The early-period blend based on 00Z-06Z based guidance transitioned to a model/mean mix tilted somewhat more toward the ECMWF/ECMWF mean relative to the GFS/GEFS, with 06Z GFS input switching to the 00Z run late. ...Weather Highlights/Threats... The departing low pressure system north of the Great Lakes will likely continue to bring gusty winds into Friday across the northern tier, resulting in blowing a drifting of snow and possible hazardous travel conditions in regions that received heavy snowfall in prior days. This system may also produce some generally light precipitation across the Great Lakes/Northeast. Moisture and instability interacting with a warm front lifting through the Southeast and Lower Mississippi Valley next weekend and approach of a cold front from the north should bring areas of moderate to locally heavy rainfall to parts of those areas, but for now with low confidence in exact placement of heaviest totals. Farther west, a system forecast to reach the West by Saturday should focus rain/mountain snow over the central and northern West Coast into the northern Rockies late this week into the weekend. Currently the best signal for heaviest totals is from southwest Oregon into northern California but still with some uncertainty over exact location and magnitude. Moisture should spread east beyond the Rockies Sunday onward as low pressure/fronts reach the central/eastern U.S. At least some precipitation across the northern tier may be in the form of snow while rainfall coverage/intensity over the East will depend on currently uncertain system details. The central Rockies/High Plains could see a brief period of strong winds around Sunday with system passage. Expect another episode of precipitation from the Pacific Northwest/northern California into the northern Rockies early next week, with some enhanced totals possible over favored coastal/terrain areas. The core of below normal temperatures across the northern High Plains will likely persist into early next week, with daytime highs generally 20-30F below normal. Locally colder readings (especially for daytime highs) are possible late this week into the weekend with some lingering daily records for lows/cold highs possible mainly on Friday. Over the West, temperatures should moderate in between systems as a period of upper ridging moves through. Friday-Saturday will feature chilly readings over the northern half of the region (minus 10-15F anomalies for highs) and closer to normal temperatures farther south. As the upper ridge builds over the region by the start of next week, northern locations should trend toward normal and southern areas above normal. The Great Basin and Southwest could see highs as warm as 10-15F above normal. The East should stay near normal this weekend, but the system potentially reaching the Midwest/East early next week could draw some of the chilly northern Plains air southward and eastward behind it, with expanding coverage of minus 10-20F anomalies. The southern Plains will see highs 10-15F above normal Friday-Sunday followed by a cooling trend. Rausch/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, 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