Extended Forecast Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Mon May 09 2022 Valid 12Z Thu May 12 2022 - 12Z Mon May 16 2022 ...Blocky pattern favors record heat from the Southern Plains/Lower Mississippi Valley to the Midwest/Northeast along with episodes of central U.S. convection and an emerging onshore rainfall focus to the Carolinas... ...Emerging heat threat for California and the Southwest by early next week... ...Overview... The blocky pattern into later this week will still feature a mean trough aloft over the West, amplified upper ridging from the southern Plains through Great Lakes/Northeast, and an upper low off the Southeast coast. Temperatures will likely challenge daily records under and near the upper ridge axis late this week while parts of the West will see chilly weather with rain and higher elevation snow. Between these regimes, a storm system emerging over the northern Plains may produce some areas of heavy rainfall where wet ground conditions already exist. Then during the weekend and early next week most guidance shows the pattern transitioning toward a western ridge/east-central U.S. trough configuration. This evolution should finally push the rainfall focus to the east of the Plains. The initial upper low tracking into the Southeast around Friday due to a retrograding Atlantic ridge should quickly lift northward and open up during the weekend, with associated rainfall spreading into and north from the Carolinas. The ridge building over the West will lead to increasing coverage of very warm to hot temperatures over the southern half of the West during Saturday-Monday. ...Guidance Evaluation/Preferences... The 06 UTC GFS/GEFS and 00 UTC UKMET/Canadian/ECMWF/ECMWF ensemble mean seem reasonably well clustered into Day 3/4 (Thursday/Friday) and a composite solution seems to offers a good forecast basis in conjuncture with the 13 UTC National Blend of Models. These GFS/ECMWF runs, along with latest 12 UTC versions, remain best compatible with the GEFS/ECMWF ensemble means into days 5-7 and this favored blend maintains good WPC product continuity. ...Weather/Threat Highlights... The strong upper ridge extending from the southern Plains through the Great Lakes/Northeast as of Thursday will promote much above normal temperatures from much of the Plains and Mississippi Valley through the Great Lakes and Northeast late this week. Highs/morning lows will be at least 10-20F above normal with some embedded plus 20-25F anomalies possible from the central Plains into Great Lakes, and locations across a fairly broad area may challenge daily records. After Friday expect the above normal temperatures to be more confined to the Great Lakes/Northeast and the far southern Plains/western Gulf Coast region. There will be a lingering potential for daily records over the Northeast into Saturday and over eastern Texas and vicinity through the end of the period. The frontal system and upper dynamics crossing the Northwest late this week will produce a brief period of enhanced rain and high elevation snow as well as highs 5-15F below normal. Meanwhile the southern part of the West should moderate to slightly above normal by Friday. Then arrival of the upper ridge will extend the warming trend over the West through the weekend. Highs of 10-20F above normal should expand from California eastward from Saturday onward and some locations could reach record highs by Sunday-Monday. Northern areas of the West should be closer to normal and one or more fronts may produce periods of light to moderate precipitation over the Pacific Northwest. Late this week the system emerging from the West and developing over the northern Plains before tracking into southern Canada, along with associated fronts, may produce areas of heavy rainfall over parts of the far northern tier where some areas are quite sensitive to added rain due to very wet ground conditions. The experimental Day 4 (Thursday-Thursday night) Excessive Rainfall Outlook shows a Slight Risk area over parts of northern North Dakota and Minnesota where there is the best overlap of guidance signals for significant rain and instability, along with high soil moisture. Depending on system evolution, areas farther west back to the northern High Plains could also see significant rainfall. Some locally moderate to heavy showers and thunderstorms will be possible farther south along the wavy trailing front (which may hang up for about a day as western energy catches up to it) but so far with less agreement for specifics. The Storm Prediction Center is also monitoring the potential for severe weather, so check the latest outlooks for updated information. Rainfall and the focusing front should become more progressive from Saturday onward, leading to a drier trend over the Plains. Retrogression of the western Atlantic upper low into the Southeast toward the end of the week should spread enhanced rains into the Carolinas and vicinity by Friday with some of this moisture spreading northward across the Mid-Atlantic/Northeast this weekend. Highest totals should be over or near the eastern Carolinas. Amounts farther north should trend lighter due to decreasing focus of moisture as the upper low opens up while it lifts northward. Schichtel/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 rain across portions of the Upper Mississippi Valley and the Northern Plains, Thu, May 12. - Severe weather across portions of the Central/Northern Plains, and the Upper Mississippi Valley, Thu, May 12. - Flooding possible across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding occurring or imminent across portions of the Great Plains, the Middle/Upper Mississippi Valley, and the Mid-Atlantic. - Flooding likely across portions of the Middle/Upper Mississippi Valley, and the Northern Plains. - Excessive heat across portions of California and the Southwest, Sun-Mon, May 15-May 16. - Excessive heat across portions of the Great Plains, the Mid-Atlantic, the Mississippi Valley, the Central Appalachians, the Tennessee/Ohio Valleys, the Great Lakes, the Northeast, and the Southeast, Thu-Sat, May 12-May 14. - Enhanced wildfire risk across portions of the Southern Rockies, and the Central/Southern Plains, Thu, May 12. - Flooding possible across portions of mainland Alaska, Thu-Fri, May 12-May 13. 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