Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EDT Thu Jul 28 2022 Valid 12Z Sun Jul 31 2022 - 12Z Thu Aug 04 2022 ...Dangerous heat wave persists into Sunday over the Northwest/Great Basin before anomalous heat shifts east next week... ...Heavy to excessive rain threat for parts of the Tennessee Valley and southern Mid-Atlantic through Monday, with monsoonal flooding concerns across the Southwest... ...Overview... Upper level ridging sandwiched between a trough over the East Pacific and renewed troughing over the Great Lakes/Northeast should shift slowly eastward with time. A dangerous heat wave will continue into Sunday across the Northwest before the heat headlines then shift east into the north-central states on Monday-Wednesday and eventually the Northeast by next Thursday. Upper ridging and heat/humidity will also linger over the southern Plains and lower Mississippi Valley. Excessive rain threats from the short range will persist through Monday across the Tennessee Valley and southern Mid-Atlantic along a warm from before it lifts north ahead of a cold front through the northern tier states. Meanwhile, a seemingly never ending stream of monsoonal moisture will continue to flow into the Southwest and southern Rockies next week, with some at least localized flooding concerns. ...Guidance Evaluation/Predictability Assessment... The latest models are well clustered with the large scale overall pattern, but offer increasing uncertainties in the details of systems. The greatest uncertainty remains out west regarding a shortwave off the coast, which should shift inland bringing a relief to the heat wave across the Northwest. The GFS remains the quickest model to bring the energy inland, while the remainder of the deterministic models tend to linger it offshore an extra day or so as it waits for the next shortwave to drop into the region around Tuesday. The ECMWF has also been somewhat consistent in keeping a cut off compact closed low off the northern California coast well into next week, which does not have much support from the other models or ensembles at this time. After day 5, the ensemble means seem better equipped to handle the uncertainties in timing of individual shortwaves and flow details, and thus the WPC forecast for the second half of the period leaned more on the means. The GFS was not used for days 3-4 because of how it handles the first Northwest U.S. shortwave, but it was incorporated some (with the ECMWF) to help bring a little extra definition to the pattern days 5-7. This approach fits well with the previous WPC forecast as well. ...Weather/Hazards Highlights... The heat wave in the Northwest/Great Basin continues through Sunday before relief comes in the form of an upper trough around Monday. However, this shifts the anomalous heat east across the northern and central Plains through the first half of next week where daytime highs could once again approach or exceed 100F. Temperatures should also be on the rise from the Ohio Valley into the Northeast as heights begin to build later in the period. Meanwhile, mostly typical or slightly above normal heat and humidity continues for the southern Plains and Southeast through the next week. A quasi-stationary boundary in the short range causing days of heavy rainfall, should begin lifting north as a warm front by the start of the medium range period. However, heavy to excessive rainfall seems likely to continue across parts of the Tennessee Valley and into the southern Mid-Atlantic with slight risks present on the experimental days 4 and 5 ERO. There is potential for an upgrade to the flash flood risk especially for parts of the Tennessee Valley, over areas that may receive repeated days of rainfall in the short range. Elsewhere, persistent monsoonal moisture will continue to support diurnally favored showers/storms with locally heavy to excessive rainfall over an already very soggy Southwest next week. A progressive cold front through the Great Lakes on Sunday may bring some moderate to locally heavy showers as well. 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