Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Wed Jun 5 2024 Valid 12Z Sat Jun 08 2024 - 12Z Wed Jun 12 2024 ...Warmer than average temperatures continue for the West into the weekend and early next week, though less extreme than the short range period... ...Overview... A reloading upper trough will be present in the eastern U.S. this weekend into early next week, while mean upper ridging is forecast for the western U.S. (though disrupted at times by shortwave energies). Warm to hot temperatures will continue across the West during the medium range period, though moderated a bit compared to the short range. The forecast pattern should support multiple rounds of showers/storms over the central or south-central Rockies, Plains, and Mississippi Valley as systems ride the ridge and frontal boundaries help to focus moisture. Rain chances should eventually reach the Southeast into next week. Meanwhile, periods of light to modest rain are likely in the northeastern U.S. underneath the slow-moving trough/low. ...Guidance/Predictability Assessment... Model guidance generally agrees with the weekend pattern of upper ridging in the West (with a couple of shortwave disruptions) and troughing in the East, but continue to see differences in the details even in the early-mid period that will affect sensible weather. By Sunday-Monday, notable differences arise with potential for energy to round the western side of the trough and dig troughing into the east-central CONUS. GFS runs were strong enough with this shortwave to close off a small low; the 18Z run was not too far off from the ECMWF/CMC in placement over the Mid- Mississippi to Ohio Valleys Monday, but the 12Z GFS seemed too slow. Now 00Z guidance has trended away from this digging energy for the most part, though the 00Z ECMWF keeps it and thus maintains troughing across the East into Tuesday-Wednesday. The timing of the trough moving out of the East (or rebuilding) is also affected by a couple of uncertain upstream features that may or may not combine or interact--namely, shortwave troughing expected to come into the Northwest Sunday moving east and energy moving southeast from west-central Canada. Models (both dynamical and AI/machine learning) show a variety of solutions with these tracks and evolution, keeping confidence low. Elsewhere, ECMWF runs have been strong with an upper low dropping into the eastern Pacific Sunday- Monday and stalling through the first half of the week. The 00Z GFS and CMC do show this feature now, but weaker than the ECMWF. The WPC forecast was based on a blend of deterministic models favoring the 18Z GFS and 12Z ECMWF early in the period, but increased the proportion of ensemble means in the blend to half Day 6 and more Day 7 given the increasing uncertainty. ...Weather/Hazards Highlights... Ample moisture from the Gulf and Pacific moisture advecting around the upper ridge will combine across the southern/central Rockies and Plains this weekend, with one or more surface boundaries helping to focus multiple rounds of showers and thunderstorms in an environment with plenty of instability. While there is still some uncertainty in the exact placement of convection on any given day, the ingredients are in place for heavy rain amounts and rain rates that could cause flooding concerns. For Day 4/Saturday, a Slight Risk in the ERO remains in place across the Oklahoma/Kansas/Missouri/Arkansas intersection and expanded to the east, as models continue to show a heavy rainfall axis of 3-5 inches in these areas. The Marginal Risk expands back into the central High Plains. By Sunday, the cold front should press south a bit and shift the flooding risk south with it. As a first take at the Day 5/Sunday ERO, have a broad Marginal Risk from the southern/central Rockies east into the southern Plains and into the Mid-South. Southern parts of the Rockies and High Plains around northeastern New Mexico or so have shown the greatest consistency in moderate to heavy rain amounts, but was not confident that the impacts would rise to the Slight Risk level there. Farther east, the placement of embedded heavier convection remains uncertain as there is not a lot of run-to-run continuity. But an embedded Slight Risk is possible somewhere across the south-central U.S. on Sunday if models converge better on a location of focus, and if it overlaps areas that have seen significant rains recently. The front should continue to press southeast into Monday and could spread rain chances to the Gulf Coast and Southeast. After some light showers in the interior West Saturday, weak upper troughing farther north will bring in modest rain to the northern Rockies Sunday and continue rain chances across the central/southern Rockies Monday. Meanwhile, rounds of rain and possible thunderstorms are expected across the Lower Great Lakes to the Northeast underneath the upper trough. These rainfall amounts look to be sub-Marginal Risk levels. The mean ridge in the West will continue to cause much warmer than average temperatures there, but by the weekend some southern stream troughing disrupting the ridge should moderate temperatures (and HeatRisk) somewhat in the Southwest compared to the short range period. Higher temperature anomalies of 15-20F above normal, locally higher, will be in the Northwest Saturday and just a touch below that by early next week when a northern stream shortwave moves through. By Tuesday-Wednesday the warm anomalies look to expand back south as well as east into the northern Plains though. Meanwhile, most areas east of the Rockies should trend to slightly below normal behind the cold front. This will eventually include Texas and Florida (where highs several degrees above normal may lead to some daily records) after a hot weekend. 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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw