Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Thu Jun 6 2024 Valid 12Z Sun Jun 09 2024 - 12Z Thu Jun 13 2024 ...Warmer than average temperatures continue for the West into next week, though less extreme than the short range period... ...Overview... Into early next week, upper troughing is forecast for the eastern U.S., which may get renewed into the middle of next week with another shortwave. Periods of upper ridging are likely for much of the western and central U.S., though could be disrupted by shortwave energies at times. Warm to hot temperatures will continue across the West during the medium range period, though moderated a bit compared to the short range. A front should focus moisture near the Rockies early next week, causing showers and storms there and farther east across the southern tier. Rounds of rain and storms are also possible across the Eastern Seaboard next week, and heavy amounts may come into Florida by Tuesday-Wednesday. ...Guidance/Predictability Assessment... Model guidance is finally coming into somewhat more reasonable agreement with the forecast features described above. An upper low meandering around Ontario/Quebec to start the period Sunday and shortwave energy coming through the southwestern side will push troughing through the eastern U.S. early in the week, with some uncertainty for when it pushes into the western Atlantic around midweek. For the past couple of model cycles, models have been more agreeable with the track and timing of a shortwave likely forming a closed low moving across south-central Canada, which looks to combine with a shortwave moving through the Northwest Sunday to expand troughing into the north-central U.S. by around Tuesday and providing better predictability for a low/pressure frontal system associated with it. This pushes into the eastern U.S. by Wednesday- Thursday with typical levels of spread. Meanwhile in the West, models continue to show support for mean ridging, though disrupted on the northern side with the northwestern to north-central U.S. shortwave mentioned above Sunday-Monday. By Wednesday-Thursday the ridge may slowly be pushed east into the central U.S. as a larger- scale upper low moves through the northeastern Pacific (with some spread in timing/placement) while a southern stream upper low also approaches the Southeast. The WPC forecast was based on a blend of the 18Z GFS, 12Z ECMWF, and 12Z CMC early in the forecast period. Included the GEFS and EC ensemble means by Day 5 and increased their proportion to almost half by the end of the period as spread increased. ...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 into Sunday, with a surface front helping to focus showers and thunderstorms in an environment with plenty of instability. For the Day 4/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. The faster movement of the front will mostly preclude excessive rain there, but the front continuing to stall across the central Rockies to southern High Plains may produce additional rounds of convection with potential for heavy rain rates, so a Marginal Risk is delineated for Day 5/Sunday in those areas. Rounds of rain are also possible for the Eastern Seaboard as fronts come through. The heaviest rain is likely across Florida into Tuesday-Wednesday as well above moisture pools along the stalling front. The mean ridge in the West will continue to cause much warmer than average temperatures there, albeit not quite as hot as in the short range period. The highest temperature anomalies of 10-20F above normal are forecast for the Great Basin, warming a bit and expanding eastward as the week progresses into the northern Rockies and Plains. Temperatures will also rise a few degrees in the Desert Southwest to bring temperatures back above 110F in some places. Meanwhile, most areas east of the Rockies should trend to slightly below normal behind the cold front. Warmer than average temperatures that could set daily records in the Florida peninsula into Sunday will eventually moderate as rain chances increase. 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