Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 AM EDT Fri Aug 30 2024 Valid 12Z Mon Sep 02 2024 - 12Z Fri Sep 06 2024 ...Overview... A fairly progressive northern stream upper level pattern will be in place next week during the medium range period. Upper ridging across the Southern U.S. will expand and build into the West as systems ride the top of the ridge from west to east, reinforcing troughing over the Great Lakes and Northeast. This pattern should push a couple of weaker frontal boundaries into the central and southeastern U.S., with periods of stormy weather expected to accompany. Meanwhile, a persistent surface trough and embedded waves near the western Gulf Coast should provide focus for heavy rainfall across parts of Texas. ...Guidance/Predictability Assessment... Models show fairly good agreement on the overall large scale pattern through much of next week, with the typical differences in the details of individual systems. Models agree a compact upper low will move into the Pacific Northwest early week, but continue to show variability in how this interacts with additional northern stream energy past the Rockies and eventual effects on downstream troughing over the Great Lakes to the Northeast. There is also still a fair amount of uncertainty in shortwave energy near the Texas Gulf Coast as it moves inland, with significant impacts to heavy rainfall potential across that region. The WPC forecast for tonight was able to use a general model compromise for the first half of the period, but trended towards majority of the ensemble means by Day 7. Continued some incorporation of the ECMWF and GFS late period for added system definition. ...Weather/Hazards Highlights... The main heavy rainfall focus during the period will be across the South, particularly Texas, as shortwave energy moves inland from the western Gulf. Precipitation coverage and totals remain highly uncertain, but the overall dynamics and anomalous moisture support a heavy to excessive rainfall threat. This is covered by fairly broad marginal risks on the Days 4 and 5 EROs (covering Monday to Tuesday night), with a possible focus across the coast and farther inland across parts of central and west Texas. Into the Southeast, moisture along a sagging frontal boundary should support showers and storms with a marginal risk of flash flooding on Monday. Precipitation and locally heavy downpours look to linger the rest of the week across much of the South, but totals and locations are very uncertain. To the north, some generally light precipitation should accompany the shortwave through the West into the northern Plains. Modestly above normal temperatures across the Northwest on Monday should shift east and moderate into mid week. By mid to late week, increasing heat is expected across much of the West, with moderate to major HeatRisk threats across the Southwest and central valleys of California. From the Southern Plains to the Midwest and the East, temperatures should be near or below normal for this time of the year within a rather pleasant air mass through much 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 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