Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EDT Fri Apr 1 2022 Valid 12Z Mon Apr 4 2022 - 12Z Fri Apr 8 2022 ...Heavy rainfall/convection and runoff threat to focus across the South next week... ...Pacific Northwest heavy rain and terrain/mountain heavy snow threat inland to the northern Rockies... 19Z Update: The 12Z guidance suite has a very good overall depiction of the amplifying pattern as the deep upper trough builds over the north-central U.S. next week. Although still slightly progressive, the 12Z run of the GFS has trended closer to the non-NCEP model consensus, and therefore a deterministic model blend sufficed as a good starting point in the forecast process. However, differences are more apparent for the northwestern U.S. as the next system approaches, with the GFS well ahead of the model consensus by Friday, and a CMC/ECMWF/ECENS blend approach works well for the West Coast region. In terms of the heavy rainfall threat across the Deep South and Gulf Coast region, the corridor of heaviest rainfall is favored from the Red River Valley of TX/OK eastward to central AL and the southern Appalachians, with some scattered 3+ inch totals within the realm of possibility. Multiple rounds of strong to severe storms and likely a squall line are also expected across many of these same areas. The previous discussion follows below. /Hamrick -------------------- ...Overview... The large scale pattern will undergo a dramatic change over the course of the period, as fairly low-amplitude progressive flow leading into the start of the period early Monday transitions to a western ridge/east-central U.S. upper trough with a closed low currently expected to track from the northern Plains into the Great Lakes by around Wednesday-Friday. A strong jet arriving into the Northwest early in the week will initially focus heavy precipitation over that part of the country and then the developing upper trough/associated surface evolution will spread precipitation across much of the eastern half of the lower 48 with heaviest totals forecast to be across the South. The upper ridge building into the West will bring another episode of unseasonably warm temperatures to that part of the country. ...Guidance Evaluation/Predictability Assessment... Latest models and means offer good agreement with the overall pattern evolution while exhibiting some typical detail differences that have medium to low predictability. Of particular note, latest GFS runs have been on the southern side of the spread for the upper low that tracks over the Plains and Midwest late Tuesday through Wednesday and GFS runs have tended to be more eager to bring Pacific shortwave energy into the northern part of the western ridge late in the period (which the new 00Z ECMWF has adjusted toward). As the main system of interest reaches the East late in the week, differences are fairly modest for a days 6-7 forecast with the GFS/GEFS slightly northeast of the ECMWF/CMC and their means. A starting point consisting of a 12Z/18Z model blend early and then a model/ensemble mean blend later on provided a good intermediate solution with only modest refinements to continuity. ...Weather Highlights/Threats... A strong upper jet pushing into the Northwest early next week will bring an episode of enhanced coastal/terrain rain and mountain snow to the Pacific Northwest with significant totals extending into the northern Rockies. After this moisture departs, the upper ridge building into the West will bring dry weather to much of the region Wednesday-Friday. Downstream upper trough amplification and surface low/front evolution will promote active weather over the central/eastern U.S. With typical run-to-run refinements and some spread in the details, there is a persistent signal for heavy rainfall potential from near the southeastern Plains into the Southeast during the first half of the week. This region has the best overlap of moist Gulf inflow and instability, along with focus from a couple surface fronts. The Storm Prediction Center is also monitoring this system for strong to severe convection, with more details forthcoming as predictability improves over future guidance runs. Other parts of the central/eastern U.S. could see pockets of locally moderate to heavy rain as well. Meanwhile some snow could be possible along the northern tier, on the cold side of the upper low track, as well as into parts of New England. The upper ridge building into the West will support another period of well above normal temperatures across the region by Wednesday-Friday. The greatest anomalies for daytime highs should be from California and southern Oregon into the Great Basin, with highs 10-20F above normal and some locations reaching 20-25F above normal. Some daily records for highs/warm lows will be possible late in the week. Ahead of the ridge, cool air under the amplifying upper trough will bring highs down to 5-15F below normal over the northern Rockies on Tuesday and progressing into the east-central U.S. by Friday. Leading warm/moist flow ahead of the upper trough/surface system will bring a couple days of above normal readings (especially for morning lows) to the East around Wednesday-Thursday. Rausch/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