Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 PM EDT Wed Aug 10 2022 Valid 12Z Sat Aug 13 2022 - 12Z Wed Aug 17 2022 ...Monsoonal moisture/rainfall threat continues for the Southwest and Intermountain West/Rockies... ...Excessive heat threat across the Plains, with warming temperatures in the Northwest next week... ...Overview... A fairly stagnant trough-ridge-trough pattern is forecast this weekend across the contiguous U.S.. Shortwaves will deepen and then maintain a trough in the East, an upper low off the West Coast lifts northeastward into British Columbia, and a warm upper high meanders near the Central/Southern High Plains. Upper ridging is also forecast to expand into the West by Tuesday-Wednesday of next week, increasing temperatures to well above average, particularly in the Northwest. The ridge aloft will also continue to support monsoonal moisture streaming into the Southwest, Intermountain West and Rockies through much of next week. A lingering frontal boundary over Florida will provide a focus for rainfall there, while possible shortwave energy rounding the ridge could lead to rounds of showers/thunderstorms across the Midwest/Upper Great Lakes this weekend, with rain chances expanding south and east into early next week. ...Guidance Evaluation/Predictability Assessment... The latest guidance is in good agreement on the broad synoptic pattern of dipole troughs along the coasts and ridging across the central-western part of the country during the medium range. The 00z EC/ECE had the least run-to-run/ensemble member spread with respect to the eastern trough axis, in particular. On day 3 a general model blend of the 00z EC/CMC/UK and 06z GFS were joined by the 00z GFS to account for some discrepancies in the 00z EC and 06z GFS. The gmb was continued on day 4 with the exception of the 00z GFS. The 00z ECE and 06z GEFS were added to the blend on day 5 as they seemed to resolve the eastern U.S. trough reasonably well compared to the deterministics. The 00z ECE was favored in the blend on through day 7 as it carries little to no spread over the lower 48 and displays the overall pattern comparitively to model consensus. ...Weather/Hazards Highlights... Parts of the West have seen persistent monsoonal moisture over the past couple of months, and the rest of this week and into next week will continue that pattern. In fact, notable moisture anomalies are forecast to stream into parts of the Great Basin and the Rockies and produce rain and thunderstorms. A Slight Risk of Excessive Rainfall was introduced today for Saturday and Sunday over portions of northwestern Arizona, including Mohave, Yavapai and Coconino counties. Rain totals may increase by Monday-Tuesday for the Northern/Central Rockies in particular. Meanwhile, a moist airmass and a lingering frontal boundary will cause showers and thunderstorms across the Florida Peninsula into early next week. Farther north, shortwave impulses rounding the ridge could lead to rain and storms across the Midwest/Upper Great Lakes into the Ohio Valley this weekend, but with low confidence on the specifics. Then rain chances could increase for the Ohio Valley to Appalachians and the East Coast early next week along a cold front, but the details remain uncertain there as well. Very warm to hot temperatures around 10-15F above average, though mainly not to record-breaking levels, are forecast across the Northern and especially the Central Plains over the weekend, with some gradual moderation and shift southward through the workweek, though highs could still reach 100F in the Southern Plains. As the upper ridge expands into the Northwest, this will warm up temperatures there and cause highs 10-20F above normal by Tuesday-Wednesday. Meanwhile, below normal highs are possible in the east-central U.S. behind the cold front, with the most persistent cooler than average weather in the Ohio and Tennessee Valleys toward the Mid-Atlantic. Given the rainfall and cloudiness over the Southwest and Great Basin into the Rockies, highs are likely to be several degrees below normal there through much of next week. Kebede/Tate 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