Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 AM EDT Mon Apr 18 2022 Valid 12Z Thu Apr 21 2022 - 12Z Mon Apr 25 2022 ***Additional snow and cold weather likely for portions of the Northern Plains this weekend, and heavy snow in the Sierra on Thursday*** ...Weather Pattern Overview... A quasi-zonal flow pattern aloft will initially be in place across much of the central and southern U.S. on Thursday, with a northern stream shortwave and surface low crossing north of the Great Lakes. The pattern becomes more amplified by Friday and into the weekend as a large synoptic scale trough from the Pacific moves inland across the Intermountain West, and this will spur surface cyclogenesis across the Plains by Friday night with showers and storms developing ahead of the trailing front. Meanwhile, a downstream ridge axis builds across the eastern U.S. and results in a considerable warming trend for the weekend. ...Model Guidance Evaluation... The 00Z model guidance suite appears to have above average agreement on the main synoptic scale features through Thursday night, with just some minor differences in cold front timing across the Great Lakes and Northeast. Similar to yesterday, the the GFS remains more progressive with the axis of the main trough axis across the central/northern Plains, and definitely stronger by 12Z Saturday compared to the model consensus. Meanwhile, the 00Z CMC/ECMWF are in closer agreement and depict a closed low evolving over the Dakotas by early Sunday, and this also has support from the 00Z UKMET. The GFS/GEFS is also farther east with the downstream upper ridge axis over the Eastern U.S., which would have implications for the temperature forecasts. By early next week, the models are in good agreement on the depiction of another storm system over the northeast Pacific Ocean, but considerable model spread is apparent across the Rockies and western High Plains in the wake of the departing surface low over the north-central U.S. A nearly multi-deterministic model blend was incorporated as a starting point for Thursday, and then more of the ECMWF/ECENS was used going forward into the weekend along with some of the CMC and GEFS mean. ...Sensible Weather/Threats... In the precipitation department, moderate to heavy rain along with heavy snow in the Sierra will likely be ongoing on Thursday as the deep upper trough moves inland. This spring event will deliver some highly beneficial precipitation to drought-stricken areas of California, with the potential for 1-2+ inches of rain in some areas of central and northern California, and 1-3 feet of snow for the higher elevations of the Sierra. Another round of organized showers and storms are expected to develop across the central U.S. and extending northward to the Great Lakes for the end of the week as Gulf moisture is advected northward ahead of the organizing storm system over the central Plains. Additional moderate to heavy snow is also expected for portions of the northern Rockies for Friday and into the weekend, with an increasing threat for accumulating snow across the Dakotas and eastern Montana/Wyoming next weekend, potentially affecting the same areas that were hammered by the recent blizzard. In terms of temperatures, a major warming trend is forecast for much of the eastern half of the nation going into the weekend, along with increasing humidity levels, in response to deep southerly flow ahead of the central U.S. storm system. One of the caveats in the temperature forecast will be the presence of a back door cold front near the Mid-Atlantic and Northeast U.S. this weekend, with potentially a big contrast over a relatively short distance, so future changes in the forecast are likely. It will likely remain uncomfortably cold from Montana to North Dakota and northern Minnesota with highs running 15-25 degrees below normal. 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, 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