Extended Forecast Discussion NWS Weather Prediction Center College Park MD 216 AM EDT Fri May 28 2021 Valid 12Z Mon May 31 2021 - 12Z Fri Jun 04 2021 ...Record breaking temperatures likely in parts of the West next week... ...Heavy rain potential over portions of the southern and central Plains... ...Overview and Guidance Evaluation and Preferences... The pattern during the first half of the medium range period should be rather stagnant as amplified ridging anchors over the West Coast and mean troughing becomes established over the Central states. This translates to possibly record breaking heat out West and the potential for rounds of moderate to heavy rainfall for portions of the Southern/Central Plains. By late next week, a shortwave entering the Pacific Northwest should suppress the upper ridge south and eastward, and push the Central trough into the East. The 12z/18z guidance was generally in above average agreement with the overall pattern, though with typical uncertainties in the details of individual features. ECMWF was a tad slow/stronger than the consensus with an exiting Eastern U.S. shortwave on Monday, though a general model blend seemed to mitigate this. Some variability with individual bursts of energy embedded within the main trough across the Plains, which at this time scale are impossible to pin down anyways. Some timing and evolution differences begin to arise late week regarding the trough as it shifts eastward and also with the next wave coming into the Pacific Northwest. The WPC blend relied on a general deterministic model blend days 3-5 eventually reaching a 50/50 deterministic vs ensemble means by days 6 and 7 to help mitigate these lower predictability details. This approach fit well with previous WPC continuity as well. ...Weather Highlights/Hazards... The main focus for rainfall during the period will be over the central/southern Plains as Gulf of Mexico moisture intercepts a slow moving cold front. Some locations could see several inches of rain with the best chance at this point from parts of northern Texas into Oklahoma. Much of this area is already over saturated due to above normal precipitation recently which would only increase flooding concerns across the region. High pressure building in behind the front may also aid low level upslope flow to enhance convective development over the High Plains. Rain and scattered thunderstorms are expected to spread eastward into the Mississippi Valley, the Ohio/Tennessee Valleys, and parts of the East by mid to late next week ahead of the main trough, but with less certainty on any areas of focused heavy rainfall totals. Meanwhile, the West should stay dry beneath upper level ridging with maybe some scattered precipitation as shortwave energy moves across the region later next week. Main concern for temperatures during the medium range period is from California into the Great Basin where daytime highs 20 to 25 degrees above average could approach or exceed record values, centered around next Tuesday/Wednesday. As the upper ridge weakens and shifts, values may moderate a bit but still are expected to be above normal across much of the West and into the northern Plains. The south-central U.S./High Plains will be below normal under cloudy and stormy skies the first half of the period, while the Eastern U.S. sits near normal all next week. Santorelli 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml