Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EDT Sat May 29 2021 Valid 12Z Tue Jun 01 2021 - 12Z Sat Jun 05 2021 ...Record warmth likely Tuesday into Thursday across parts of the West... ...Locally heavy rain possible mid-week from the southern Plains into the Mississippi Valley... ...Overview and Guidance Evaluation and Preferences... A fairly amplified pattern should be in place to start the medium range period as strong ridging holds over the West and broad troughing is maintained from the Central to Eastern states. A shortwave entering the Pacific Northwest around next Thursday should kick the Western U.S. ridge into the Rockies while the Central U.S. trough amplifies somewhat and heights build again into the East. The trough will continue to move slowly eastward as the pattern may become more zonal and progressive with another round of shortwave energy entering the West Coast by next weekend. The latest model guidance continues to show fairly good predictability and agreement on the overall pattern through much of the period. This allowed for a majority deterministic model blend through day 5. Forecast uncertainty begins to increase later in the period especially regarding timing and evolution in the details of the Central U.S. trough as it lifts towards the Northeast late next week. Some previous model runs hint at a possible close low emerging from this trough, although the latest GFS/CMC runs suggest a little weaker/more progressive feature with possible southern stream energy attempting to hang back while northern stream energy races into the Northeast. WPC prefers a blend more towards the ensemble means by days 6-7, with some contribution from the ECMWF which has shown a little bit better run to run continuity. The approach also maintains good continuity with the previous WPC forecast. ...Weather Highlights/Hazards... The main focus for rainfall with be along and ahead of the Central U.S. troughing as moisture pools along a weakening frontal boundary. The best chance for moderate to locally heavy rainfall will be from central Texas into Arkansas on Tuesday, where much of this region has already seen much above normal rainfall in the past couple of weeks. From Wednesday onward, the activity should shift eastward into the Tennessee/Ohio Valleys and the Northeast along a quasi-stationary front, 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 15-25F above normal may meet or exceed daily records. Expect widespread warm near record morning lows as well across this same region into Thursday. As the upper ridge weakens and shifts east, values may moderate a bit but still are expected to be above normal across much of the West and into the northern Plains and Upper Midwest. The south-central U.S./High Plains will be below normal under cloudy and stormy skies Tuesday and Wednesday, while the Eastern and Southeast U.S. sits near normal the entire period. 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