Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM 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... There remains some agreement on the large scale pattern featuring a reloading Eastern U.S. trough and Western U.S. ridging eventually pushing eastward, but plenty of uncertainty in the details. Run to run continuity regarding a compact upper low over west-central Canada continues to pose a problem. Models have flip flopped between whether that energy gets pulled southward with the larger Ontario/Quebec upper low or if it stays totally separate and eventually gets pushed north and east with additional energy into the Northwest/Northern Rockies. Through the 00z/06z guidance, models were showing better agreement for it to hang back over Canada, but recent 12z runs today (available after forecast generation time) suggest it could get pulled more southward into the north-central U.S.. So confidence is the details of this remains very low. Otherwise, lots of uncertain timing of initial energy through the Northwest Sunday-Monday and again as the main East Pacific trough moves into the Coast late period. This impacts how fast the upper ridge over the West moves out into the Plains. The Gulf Coast and Florida remains an issue mid to late week regarding strength/presence of upper troughing/shortwave energy and weaker impulses. Was able to use a general blend of the deterministic guidance to get a good starting point for the first half of the period, but given the new 12z guidance, even that forecast is low confidence. Increased the ensemble means late period to about 50 percent of the blend to help mitigate the differences in the deterministics. Overall, maintained good continuity with the previous WPC forecast. ...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 still with enough uncertainty to preclude a Slight Risk at this point. Farther east, the placement of embedded heavier convection also 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 with some aid from weak upper level impulses/energy. The mean ridge in the West will continue to cause much warmer than average temperatures, 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 next week. Santorelli/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