Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Tue May 24 2022 Valid 12Z Fri May 27 2022 - 12Z Tue May 31 2022 ...Weather Pattern Overview... An upper trough with possible embedded closed low will be crossing the eastern U.S. late this week into the weekend, with some uncertainty over how quickly it and the associated surface wave/frontal system will ultimately clear the East Coast. Meanwhile, a shortwave reaching the northwestern U.S. by Friday will be at the leading edge of a larger scale mean trough that should amplify over the West during the weekend and early next week. A strong ridge will build over an increasing portion of the eastern half of the country as the western trough deepens. Primary regions of focus for precipitation will be over the East with the late week system, and then from the Northwest through the northern-central Plains into western Great Lakes with a leading frontal system and embedded waves that set up over the central U.S. as the pattern amplifies while a trailing Pacific system also enhances precipitation over parts of the West. The southern High Plains will likely see well above normal temperatures through the period. Farther north, the above normal anomalies will push eastward and expand with time while below normal readings spread across the Northwest and into the Great Basin/northern Plains. ...Model Guidance and Preferences... Through the 00Z/06Z model cycles, most guidance exhibited a pronounced slower trend with the upper trough/low crossing the East. The CMC was the one faster holdout, though the 06Z GFS did nudge a bit faster than the 00Z version. New 12Z runs have really lowered the confidence in any scenario though, as the GFS/UKMET/ECMWF have trended faster by way of some combination of faster progression of the initial trough and/or greater interaction with a more amplified northern stream trough while the CMC has jumped back to the 00Z ECMWF. Meanwhile the models are still in the process of trying to resolve the details of Pacific dynamics that support a system tracking toward the Northwest around Saturday. The 06Z GFS was the deep extreme and the new 12Z GFS has trended closer to other solutions. On the other hand the 12Z ECMWF has become a weak/suppressed extreme. Guidance agrees fairly well that incoming Pacific energy will dig into the western U.S., but with typical differences for the details. Recent ensemble mean trends imply at least a moderate degree of support for latest GFS/ECMWF/CMC runs that show an embedded closed low for a period of time. Based on the array of 00Z/06Z guidance, the updated forecast started with a blend of 06Z GFS and 00Z ECMWF/UKMET/CMC early in the period with the least weight on the CMC due to its faster eastern upper trough. Then the forecast transitioned to a blend of 06Z GFS/00Z ECMWF and their ensemble means. The new guidance is suggesting a potential faster reversal for the initial eastern system but better stability for the large scale pattern by early next week. ...Sensible Weather/Threat Highlights... Areas of heavy rainfall with the initial eastern system should be tapering off by Friday, although a corridor of showers and storms is still possible across the East Coast states ahead of a weakening cold front. There is the potential for some repeated rounds of convection with heavy rain across portions of the southern Mid-Atlantic/Carolinas but the potential for any flooding appears marginal. Pockets of heavy rainfall are also possible across portions of the Northeast, although the system should be more progressive there. As rainfall diminishes in coverage/intensity over the East, the dominant focus for precipitation will extend from the Northwest through the northern-central Plains into western Great Lakes. Showers and storms will initially develop across the Northern Plains and Upper Midwest in response to a developing low pressure/frontal system over the north-central U.S. while some precipitation extends back into the northern Rockies and vicinity. A system expected to reach the Northwest around Saturday could bring an episode of enhanced precipitation to parts of the region, followed by this moisture streaming across the Rockies and interacting with the wavy frontal system set up over the Plains. Colder trends over the Northwest/northern Rockies should increase the potential for some late season high elevation snow by around Sunday-Monday while some areas of heavy rainfall could develop over northern tier areas as well. It will take additional time to resolve the details within an amplified pattern that would tend to increase the potential for a heavy precipitation event. Temperatures will warm up considerably across the Plains by the end of the week with highs reaching 10-20F above normal over some areas, including 100-105F or so readings over western Texas where some daily records could be challenged. The southern High Plains will remain on the hot side into early next week but with highs declining at least a few degrees. Meanwhile the heat will build eastward to include the Great Lakes/Ohio Valley and eventually the East Coast through the weekend and into early next week, compliments of the building upper ridge and southerly flow ahead of the wavy mean front setting up over the Plains. In contrast, over the course of the period much cooler weather will spread across the Northwest/northern Rockies and then into the Great Basin and Northern Plains as upper troughing deepens over the western U.S. Within this area, highs of 10-20F below normal will be most likely Sunday-Tuesday. 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