Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Fri Aug 05 2022 Valid 12Z Mon Aug 08 2022 - 12Z Fri Aug 12 2022 ...Monsoonal pattern remains active across the Southwest with additional heavy rainfall likely... ...Overview... The overall weather pattern across the contiguous U.S. next week will be gradually amplifying as shortwaves combine to deepen a trough in the East, while an upper high drifts from the Four Corners to High Plains and a slow-moving upper low off the West Coast lifts northward and across the Pacific Northwest around Wednesday-Thursday. Moisture inflow into a cold front ahead of the eastern trough will lead to potentially heavy rain and thunderstorms as the front pushes southeastward across the Ohio and Tennessee Valleys toward the Gulf Coast and across the Eastern Seaboard. Additionally, persistent monsoonal moisture looks to continue across portions of the West leading to additional heavy rainfall, with even some expansion northward across the Intermountain West as the week progresses. ...Guidance Evaluation/Predictability Assessment... While model guidance is agreeable with the large scale pattern and evolution described above, differences in the details remain that do have impacts on the sensible weather such as frontal position and rainfall placement and amounts. A shortwave moving across the north-central to northeastern U.S. early in the workweek shows notable model differences. Specifically, the past few GFS runs have been quite variable with its handling of the feature, as the 12Z seemed reasonably close to other guidance though a bit stronger, the 18Z was weaker but faster than consensus, and now the 00Z indicates split energy with one shortwave moving even faster across the Northeast while another lingers over the north-central U.S. Monday-Tuesday. The ECMWF/UKMET/CMC have shown better consensus and continuity with this feature, so the WPC forecast leaned more toward that cluster but did include a bit of the 12Z and 18Z GFS runs. Other than that, slight differences in energy as the eastern trough deepens were well within normal medium range spread. Model guidance also has reasonably good agreement for the upper high/ridge gradually shifting east through the week as well. There has been some model variability with the upper low over the eastern Pacific, however--in terms of the 12Z/18Z model cycle, the UKMET was a little slower than other models and the ensemble means. The 00Z GFS and CMC trended slightly slower but the 00Z ECMWF actually trended faster/farther east with the timing and track of the upper low nearing the Pacific Northwest around Wednesday, so there is still continued spread. Thus the WPC forecast was based on a blend favoring the 12Z ECMWF/CMC with lesser components of the GFS/UKMET early in the period, with introduction and increasing proportions of the ensemble means by the latter part of the week amid increasing uncertainty with the details especially in the West. ...Weather/Hazards Highlights... As the medium range period begins Monday, rain and thunderstorms are expected to stretch from the Mid-Mississippi Valley across portions of the Ohio Valley and Great Lakes region to northern New England along and ahead of a cold front. Rain and storms will shift southeast each day as the front progresses, sliding across the Eastern Seaboard and Lower Ohio/Tennessee Valleys Tuesday-Wednesday and lingering in the Southeast Thursday-Friday. Some heavy rain rates and amounts could lead to potential for flash flooding in these areas, especially over sensitive locations that have received abundant rainfall recently, though some waffling in model guidance lowers confidence in the details. Meanwhile, monsoonal moisture continues to impact the Southwest with enhanced rainfall. Another wet day is likely on Monday, with some indications of a focus near the Colorado/New Mexico border (where conditions are already quite wet) that has prompted a Slight Risk issuance in the experimental Day 4 ERO. While rain amounts may gradually lessen in this area as the week progresses, the moisture plume is likely to expand farther north into the Intermountain West and Great Basin with some locally heavy totals possible here as well. Very warm to hot temperatures around 10-15F above average, though not quite to record-breaking levels, are forecast to shift from the Northwest Monday into the northern and then central Plains as the workweek progresses and the upper ridge axis moves east. Farther east, slightly above average highs in the Northeast/Mid-Atlantic early in the workweek will moderate to right around normal behind the cold front, while some below normal highs are possible in the Ohio and Tennessee Valleys. Given the rainfall and cloudiness over the Southwest and Great Basin, highs are likely to be several degrees below normal there. 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