Extended Forecast Discussion NWS Weather Prediction Center College Park MD 322 AM EDT Thu Aug 22 2024 Valid 12Z Sun Aug 25 2024 - 12Z Thu Aug 29 2024 ...Overview... The ongoing blocky flow patttern over the country is expected to increasingly transition into early next week. This is as ample eastern Pacific upper trough energy finally lifts in earnest inland across the West and into Canada as quite a warming upper ridging that has been anchored over the south-central U.S. elongates over the east-central U.S.. This temporarily eases monsoonal flow into the Southwest before an expected overall modest mid-later period return. Well to the north, pattern evolution will lead to opportunities for more progressive and energetic northern stream upper trough energy and cooling airmasses to work into the West and downstream over the U.S. northern tier states mid-later next week. ...Guidance/Predictability Assessment... Models and ensemble solutions continue to provide less than stellar model to model and run to run embedded system timing variances through medium range time scales, but forecast spread has overall decreased versus the past few days. Accordingly, the WPC medium range product suite was primarily derived from a model and ensemble blend with enhanced weighting applied to solutions on the slightly less progressive side of the full envelope of guidance given recent flow nature, but the result is not as slowed as continuity. ...Weather/Hazards Highlights... Amplified upper troughing will finally eject inland over the West/Northwest this weekend and provide a period with cooled and unsettled conditions. This may include rains and spotty high elevation mountain snows across the northern Intermountain West/Rockies. Rains/convection may also develop downstream over the north-central U.S. early next week given focus from possible moderate cyclogenesis/frontogenesis, with modest focus shifting downstream as the week progresses with system/frontal translation. Renewed northern stream upper trough appraoch and digging back into the Northwest into mid-later next week offers potential for development and digging/intrusion of unsettled and cooled flow. Upper ridging building from the south-central U.S. through the east-central U.S. will allow summertime temperatures to spread across these regions to include values upwards of 10 degrees above normal. Heat risk guidance identifies an associated region with upwards to major level impacts with main focus set to shift slowly from the south-central Plains and Mid-Mississippi Valley Sunday southeastward through the South-Southeast into next midweek. A lingering trailing front stalling across Florida will maintain periodic rain/thunderstorm chances there and into Southeast U.S. coastal areas into next week. Moist flow and pattern longevity may lead to possible local runoff issues, especially for urban areas. Schichtel 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw