Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 PM EDT Mon Mar 21 2022 Valid 12Z Thu Mar 24 2022 - 12Z Mon Mar 28 2022 ...Overview... Expect an amplified upper level pattern from late this week into early next week, with some degree of progression. An eastern Pacific trough should move into the West by around next Monday while the mean ridge persisting over the West into the weekend pushes into the central U.S. This gradual shift in the pattern will eventually bring some moisture into the West and moderation of potential record warmth over California and the Great Basin/Southwest. Meanwhile the elongated upper low/trough over the east-central U.S. as of early Thursday and the associated precipitation will lift away fairly quickly but upstream shortwaves will reinforce a fairly deep mean trough over the East, producing chilly temperatures along with one or more episodes of mostly light rain/snow over the northern half of the region. ...Guidance Evaluation/Predictability Assessment... The latest cycle of guidance shows decent agreement with the large scale pattern but there are persistent detail uncertainties. For the system over the East as of early Thursday, consensus shows a triple point wave over the Mid-Atlantic becoming the more dominant feature Friday-Saturday as it tracks over/near New England and into the Canadian Maritimes. Track differences are generally within typical spread for a few days out in time. Into Saturday, a faster trend in the 12Z CMC versus its questionably slow 00Z version has improved clustering for the shortwave initially rounding the western ridge and then digging into the eastern mean trough. Thus far there is not much of a signal for flow to separate within the trough as depicted in the new 12Z UKMET by early Sunday. The reinforcing trough energy should support offshore low pressure by early Sunday, most likely off the Northeast and then tracking into/near the Canadian Maritimes per the model and ensemble majority. At least before today's 12Z cycle, over the past couple days the ECMWF/ECMWF mean have generally been more consistent than the GFS/GEFS with the handling of the eastern Pacific upper trough moving into the West. The main adjustment in the ECMWF/ECMWF mean has been a slightly faster trend. On the other hand GFS runs have varied considerably for the handling of individual components of the overall trough and upstream flow. 12Z/20 through 00Z/21 runs were quick to separate flow within the trough, leading to an upper low hanging back well offshore into early next week. More recent 06Z/12Z runs have adjusted faster and better fit within the ECMWF-ECens/CMC-CMCens cluster. However the 06Z GFS differed from most solutions in bringing enough southern stream energy into the Plains late in the period to raise eastern U.S. heights more than consensus (00Z and new 12Z runs appeared more reasonable). The GEFS mean has trended a bit slower over the past day. Individual ensemble member spread becomes very broad late in the period so confidence in any particular solution is only moderate at best, and now the 12Z ECMWF's change to more flow separation and slower upper low further highlight the uncertainty here. Review of 00Z/06Z guidance led to using the 06Z GFS/ECMWF and lesser weight of the 00Z UKMET/CMC for the first half of the forecast, and downplaying the slow CMC for the reinforcing eastern U.S. trough. The rest of the period transitioned to a model/mean blend and eventually split GFS input among the 00Z/06Z runs as one run or the other had more or less appealing traits depending on the region. The end result provided good continuity in principle. ...Weather Highlights/Threats... An occluded low pressure system will be in place over the Upper Great Lakes early Thursday, with lingering light precipitation there but with heavier amounts possible along its associated cold front near the East Coast. Expect mainly rain but snow will be possible over northern New England, and the snow could linger into Friday over Maine near a developing coastal low. Shortwave energy and weak low pressure/frontal systems could lead to light precipitation spreading from the northern Rockies/Plains Thursday into the Great Lakes region to the central/northern Appalachians and Northeast late week into the weekend. Some of this precipitation may be in the form of snow over higher elevations/northern latitudes. The central/eastern U.S. evolution may lead to a period of brisk to strong winds from the northern Plains late this week into the East during the weekend. Precipitation ahead of the approaching eastern Pacific upper trough will likely reach the Pacific Northwest around Friday and then spread across more of the West thereafter. Most of this activity should be in the light to moderate range but some locally heavier totals could be possible depending on exact system details. Coverage and intensity of this precipitation becomes increasingly uncertain by late weekend into early next week. Unseasonably warm temperatures will build and expand underneath upper ridging from the western U.S. into the Plains. Highs that are 10-20F above normal will be common over California and the Central Great Basin/Southwest Thursday and Friday, with some plus 20-25F anomalies appearing in the Great Basin Saturday and moving to the northern/central High Plains early next week as the upper ridge axis shifts. Daily record temperatures could be tied or set across California and eastward. The most likely scenario has an increasing portion of the West seeing highs closer to normal by next Monday but there is lower potential that above normal readings could persist a little longer. Meanwhile, cooler air underneath the upper trough/low over the central into eastern U.S. should moderate as it moves eastward, with temperatures generally 10F or less below normal. However, additional cold fronts and upper energy will bring below normal temperatures to parts of the eastern third of the U.S. by Sunday, with the Great Lakes and central Appalachians seeing 10-15F below normal highs. Rausch/Tate 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 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml