Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Wed Jul 27 2022 Valid 12Z Sat Jul 30 2022 - 12Z Wed Aug 03 2022 ...Dangerous heat wave to focus over the Northwest/Great Basin through the weekend, with anomalous heat moving into the north-central U.S. late period... ...Heavy to excessive rain threat from the central Plains to the southern Mid-Atlantic this weekend, with a lingering threat in the Southwest into next week... ...Overview... A dangerous heat wave will continue into this coming weekend across the Northwest, with high heat then set to spread to the north-central states next week. Upper ridging and heat/humidity will also linger over the southern Plains and lower Mississippi Valley to the south of a wavy quasi-stationary front. This front will be a focus for multi-day heavy rain threats from the south-central Plains to the southern Mid-Atlantic with excessive rainfall likely in some places. Renewed troughing will take shape across the Great Lakes and Northeast into next week, while a seemingly never ending stream of monsoonal moisture continues to flow into the Southwest and southern Rockies. ...Guidance Evaluation/Predictability Assessment... Deterministic models and ensemble means remain fairly well clustered with the large-scale pattern and evolution of the expansive western/southern U.S. ridge and the trough digging into the Northeast this weekend. Some model differences remain in regards to the distribution and timing of individual energies within the trough, particularly as weaker shortwaves move through the Great Lakes acting to maintain some kind of general troughiness across the region. Many of these differences are small scale, and well within the normal degree of spread for the medium range. By around Tuesday, the GFS becomes fairly fast with one shortwave, resulting in a flatter overall look compared to the ECMWF, CMC, and ensemble means. Out West, there are lingering questions in the timing of a shortwave entering the Northwest, which would have some implications for excessive heat details in that region. The GFS and UKMET have been the quickest to bring this energy onshore, while the ensemble means support something a little slower, now a bit more in line with the ECMWF, some runs of the Canadian and climatology. The models suggest the overall pattern may become more amplified by the middle of next week with troughing over the West and East sandwiching a building heat dome over the Four Corners and into the Plains. The WPC medium range product suite mainly utilized a blend of the seemingly reasonable and overall compatible GFS/ECMWF/UKMET/Canadian models this weekend, switching to the ensemble means and some deterministic ECMWF and CMC thereafter to mitigate growing smaller scale embedded system variance. This maintains good WPC product continuity. ...Weather/Hazards Highlights... Heat headlines will continue into the weekend for the Northwest/Great Basin with highs in the low to mid 100s for the Columbia Basin, and even 90s expected as far west as Portland and Seattle. These much above normal temperatures combined with little to no relief overnight from the heat, could create a dangerous heat threat for many across the region. Records for highs/warm lows could also be set across interior portions of the Northwest. There is some forecast uncertainty with the timing of when the temperatures will moderate again, but current forecasts suggest by early next week temperatures could once again bounce back closer to normal as the ridge shifts into the northern Plains. This looks to create a building heat dome over the central part of the nation by around next Tuesday, once again bringing another period of above normal heat to much of the Plains states. Excessive heat during the short range across the south-central states should finally moderate by the medium range, though more typical summertime heat and humidity will continue from the southern Plains to the Southeast. A quasi-stationary boundary draped from the south-central Plains to the southern Mid-Atlantic will continue to focus a threat for heavy to excessive rainfall into the medium range period with some areas likely to see repeated rounds of heavy rainfall increasing the risk for at least localized flash flooding. The days 4 and 5 experimental EROs have expansive slight risks depicted along this boundary from the central Appalachians/southern Mid-Atlantic and back into to the central Plains. A cold front to the north may bring some locally moderate to heavy rainfall to parts of the Upper Midwest on Sunday. Meanwhile, persistent monsoonal moisture will continue to support diurnally favored showers/storms with some locally heavy to excessive rainfall over an already very soggy Four Corners and southern Rockies region into the middle of 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, 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