Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Jun 18 2022 Valid 12Z Tue Jun 21 2022 - 12Z Sat Jun 25 2022 ...Expansive area of heat to shift from the Midwest into the South next week... ...Overview and Guidance/Predictability Evaluation... The overall pattern during the medium range period features a persistant and very warm upper level ridge expanding across the Southern U.S. as weak and progressive systems ride overtop through the northern tier. The guidance constinues to show reasonably good agreement on the large scale pattern through the period, though with some lingering differences in the details and timing of individual systems. Recent runs of the deterministic models have trended faster with an amplified trough off the Northeast early next week, which would allow for more ridge building and warmth across the Mid-Atlantic states. But the ensemble means are still slower suggesting a fair bit of uncertainty still with regards to temperatures across the region next week. Elsewhere, the most notable difference is the CMC seems to break down the western edge of the ridge too fast allowing for a more amplified and faster shortwave into the Northwest and moving into the northern Plains late next week. Meanwhile, the ECMWF and GFS have consistently suggested a farther westward expansion of the southern ridge and thus the shortwave axis tends to linger more over the Northwest/western Canada into next weekend, which has more support from the ensemble means. The WPC blend for tonight favored the deterministic models early on, and increasing the ensemble means late period (in place of the CMC). ...Sensible Weather/Threat Highlights... The biggest weather hazard during the medium range period will be a dome of heat and anomalous warmth across much of the eastern half of the country next week. The greatest anomalies (generally 10-15+ above normal) will shift from the Midwest on Tuesday into the South Wednesday-Friday, meaning high temperatures in the mid to upper 90s and low 100s likely and little relief overnight as low temperatures hover in the mid to upper 70s. Widespread record high max and min temperatures are likely in many places. Northward streaming anomalous moisture west of the ridge will bring an unusually early monsoon type pattern to parts of the Four Corners states and vicinity, mainly early in the week, supporting an increase in coverage and intensity of rainfall across the region with at least local flood and flash flood threats. By mid week, there are still mixed signals over how much rainfall the interaction of this moisture with the western front advancing into the Plains will produce. However, the potential for some training/repeat activity may have to be monitored as models continue to show this Plains front becoming aligned west-east along the southern edge of the westerlies by Wednesday-Thursday. Farther east, an area of showers and thunderstorms may push across the Great Lakes and possibly into the Northeast ahead of an advancing warm front, with some activity possibly on the heavy side earlier in the 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, experimental excessive rainfall outlook, 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/#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