Extended Forecast Discussion NWS Weather Prediction Center College Park MD 138 PM EDT Sat Jun 20 2020 Valid 12Z Tue Jun 23 2020 - 12Z Sat Jun 27 2020 ...Guidance/Predictability Assessment... A GFS/ECMWF/UKMET composite seems to produce a reasonable forecast starting point early in the medium range period, but opted to quickly transition from Wed onward to the more compatible GEFS/NAEFS/ECMWF ensemble means and the National Blend of Models in a period of rapidly increasing forecast spread and run to run continuity issues. In particular, recent ECMWF runs have been showing greater West Gulf Coast/TX spin-up and heavy QPF potential next week than most other guidance. The ECMWF runs still seem overdone with amounts, but Gulf of Mexico moisture and persistent/favorable upper trough proximity common to most guidance does offer some heavy rainfall threat more consistent with the aforementioned preferred blends. Out West, guidance has also been all over the place from run to run with potential digging of mid-upper level troughing and associated surface feature progressions through the Northwest and north-central Intermountain West/Rockies/Plains. Forecast confidence is low, but the composite ensemble solution has moderate troughing. ...Overview and Weather/Hazard Highlights†Frontal setup over the central U.S. and progression eastward through the Eastern Seaboard through next midweek should focus lead moisture to fuel widespread and some locally heavy showers and thunderstorms. Guidance continues to suggest the Southern Plains and Lower Mississippi Valley may have the greatest potential for locally heavy rainfall and runoff issues. Much above normal temperatures should moderate Tuesday and Wednesday across the Great Lakes then Northeast with frontal rains/passage. The trailing frontal zone stalling back through the southern and central U.S. will linger next week and remain a focus for shower and thunderstorm development. Uncertain energies ejecting from the West could invigorate convective rainfall development, with some strong cells possible over the north-central U.S. late week into next weekend. Meanwhile out West, upper-level mean ridging should dominate over the Southwest for much of next week and early week Northwestern U.S. upper ridging should keep conditions mostly dry. Cold frontal passages through the Northwest and the Northern Rockies/Plains later next week though may bring some showers over the region, with organized activity most likely to focus along a lingering boundary in the northern Rockies/High Plains. Temperatures across much of the West are forecast to be above to well above normal into mid-late next week, with daytime highs ranging 10 to 15+ degrees above average. Temperatures may moderate into next weekend as uncertain height falls dig over Northwest into the northern Great Basin. Schichtel/Santorelli Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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