Extended Forecast Discussion NWS Weather Prediction Center College Park MD 418 PM EDT Thu May 26 2022 Valid 12Z Sun May 29 2022 - 12Z Thu Jun 02 2022 ...Potential for heavy precipitation next week from the northern Rockies to Upper Midwest and then southward to the Central Plains... ...Weather Pattern Overview... Latest guidance continues to show an evolution toward an amplified western trough/eastern ridge aloft Sunday-Tuesday, with the western trough likely most amplified around Monday and the eastern ridge strongest around Tuesday. Consensus then shows a rapid flattening of the mean pattern as the western energy ejects and southern tier ridging retrogrades to some degree. By Thursday an approaching eastern Pacific trough may even support a weak upper ridge over the Interior West. The initial amplified pattern/western upper dynamics will support potential for some areas of heavy precipitation from the northern Rockies into the Plains/Upper Midwest, followed by a transition to more emphasis for heavy rainfall over the central Plains as a wavy front begins to push southeastward. An area of very cool temperatures will progress through the West into the northern Plains early in the week and then modify as it reaches the rest of the Plains. Meanwhile very warm to hot weather initially over the Plains/Midwest will shift into the northern half to two-thirds of the eastern U.S. Duration of warm temperatures over the Northeast is a question mark however, as flow around a broad upper low over eastern Canada may push a front into/through the region. ...Model Guidance and Preferences... The updated forecast accounting for 00Z/06Z guidance started with an operational model composite (more GFS component from the 00Z versus 06Z run) early in the period and then trended toward 50-60 percent total 06Z GEFS/00Z ECMWF mean input as specifics became increasingly uncertain. There are various aspects of the forecast that have been exhibiting spread/trends over recent runs. Issues with the western trough involve how Sunday-Monday energy will ultimately eject from the trough, with peripheral influence from Pacific flow (just offshore the Pacific Northwest as well as upstream) plus central Canada troughing/possible embedded low that have become more pronounced in latest runs and may interact with the ejecting energy. In general the primary trend over the past couple days has been for the western energy to eject a bit faster, but with no real consensus yet for the details. The past couple UKMET runs have been rather extreme with the speed of upstream Pacific flow and southeastward amplitude of troughing that eventually reaches the Plains (the latter being an error in some UKMET runs with a prior ejecting feature around a couple weeks ago). At the same time most guidance has generally trended more pronounced with flow around an upper low crossing far eastern Canada, bringing a better defined cold front through parts of the Northeast and perhaps stalling this front for a time somewhere between the northern Mid-Atlantic and New England (with a lot of spread in the guidance at this time). The 06Z GFS compared more poorly to consensus for the upper low track/cyclonic flow amplitude versus the 00Z run or most other guidance. The 12Z GFS returned somewhat closer to the majority. By next Thursday there is decent agreement on a more progressive/low amplitude shortwave over the Upper Midwest pushing along the central U.S. front from earlier in the week, while a weak upper ridge reaches the West. ...Sensible Weather/Threat Highlights... From Sunday into the early part of the next work week, the upper low moving over the parts of the West along with areas of low level upslope flow should combine to generate a period of moderate to heavy precipitation over the northern Rockies and High Plains while a slowly moving wavy frontal system over the Plains could help to focus locally heavy rainfall as far east as the Upper Midwest. Currently expect heaviest totals over parts of Montana and northern Wyoming with significant snowfall possible in higher elevations of the Rockies. The Storm Prediction Center is also monitoring the potential for severe weather over parts of the Plains/Upper Midwest in the Sunday-Monday time frame. Toward midweek the flatter trend for the upper pattern should begin to push the Plains front southeastward, likely shifting the emphasis for heaviest rainfall into or near the central Plains. The extreme southern tier including Florida may see some scattered diurnally favored convection, aided by energy aloft to the south of the eastern U.S. upper ridge. Parts of the Northeast could see one or more episodes of rainfall with a cold front that moves into/through the region and possibly stalls for a time over New England or the northern Mid-Atlantic. Some rainfall could be locally moderate to heavy but with low confidence in details thus far. Warmest temperature anomalies on Sunday will extend from the southern High Plains into the Midwest, with some locations up to 10-20F above normal. Parts of the central/southern Plains may see the very warm to hot weather persist into early next week but otherwise the emphasis for heat will shift more into the northern half to two-thirds of the East with a broad area of plus 10-20F anomalies and perhaps some daily records, more for morning lows versus daytime highs. The front over the Northeast may bring a cooling trend to parts of that region though. On the other hand, well below normal temperatures will push across the West into the northern Plains Sunday onward, with a broad area of highs 10-20F below normal Sunday-Tuesday. Some lingering minus 10-15F anomalies are possible into Wednesday over the northern-central Plains but further moderation is likely thereafter. A warmer trend over the West will bring moderately above normal highs into the region by Wednesday-Thursday. Rausch 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 Hazards: - Heavy precipitation across portions of the Northern Plains/Rockies, and the Northern Great Basin, Sun-Mon, May 29-May 30. - Heavy rain across portions of the Pacific Northwest, Sun, May 29. - Heavy rain across portions of the Central/Northern Plains, and the Northern Rockies, Sun-Mon, May 29-May 30. - Heavy rain across portions of the Central Plains, Tue-Wed, May 31-Jun 1. - Severe weather across portions of the Central/Northern Plains, and the Middle/Upper Mississippi Valley, Sun, May 29. - Severe weather across portions of the Central/Northern Plains, the Middle/Upper Mississippi Valley, Mon, May 30. - Flooding possible across portions of the Central Plains. - Flooding occurring or imminent across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding likely across portions of the Southern Plains. - Excessive heat across portions of the Southern Plains, Sun, May 29. - High winds across portions of the Central Plains/Rockies/Great Basin, the Southern Rockies/Plains, and the Southwest, Sun-Mon, May 29-May 30. - Enhanced wildfire risk across portions of the Southern Rockies, the Central/Southern Plains, and the Southwest, Sun-Mon, May 29-May 30. 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