Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Fri Sep 2 2022 Valid 12Z Mon Sep 5 2022 - 12Z Fri Sep 9 2022 ***Prolonged heat wave for portions of the Western U.S. into early next week*** ...General Overview... The main weather headline going into next week will continue to be the anomalous upper level ridge that will be anchored across the western U.S., and thus a continuance of the ongoing heat wave from the West Coast to the Northern Plains. Some good news is potentially on the weather horizon as a strong shortwave trough tries to break down the ridge across the Pacific Northwest and suppresses the ridge some. Across the eastern U.S., a broad upper trough will likely be in place for the beginning of the week that should weaken with time, and moisture from a possible tropical disturbance may begin approaching the southwestern U.S. by the end of the week. ...Guidance Evaluation/Predictability Assessment... The 00Z model guidance suite initially has a good overall synoptic scale depiction of the overall pattern on Monday. By mid week, timing differences are apparent with the arrival of the Pacific Northwest trough that will eventually erode the upper ridge across the western U.S., with the GFS indicating a slower arrival. Towards the end of the week, the GFS is more robust with the upper ridge over the Plains, whereas the ECWMF and CMC break it down faster. Taking these factors into account, the WPC fronts/pressures forecast was primarily derived from a multi-model consensus through early Tuesday, followed by a gradual increase of the ensemble means to account for increasing mesoscale uncertainties by the middle to end of the week. ...Weather/Hazards Highlights... It will continue to be very hot by early September standards across most of the western U.S. and extending across much of the northern Plains and even into the Upper Midwest through the middle of the week. Afternoon highs are expected to be on the order of 10-20 degrees above average, and the same holds true for overnight low, providing only limited respite from the heat. This will equate to highs 110-115 degrees for the lower elevations of the Desert Southwest, and widespread 90s for the Intermountain West and extending northeast across Montana and the Dakotas. Multiple daily records will likely be exceeded. Another factor to consider is the duration of the heat wave since it will be very hot for the upcoming Labor Weekend as well. This will increase heat stress for those working outdoors and for those without air conditioning. It is interesting to note there will likely be very little in the way of below average low temperatures anywhere across the continental U.S. next week, although highs may run several degrees below average across portions of the South and Gulf Coast region owing to increased clouds and rainfall. In terms of rainfall, a quasi-stationary frontal boundary draped across the southern tier states, with waves of low pressure along it, will be the general focus for multiple rounds of showers and thunderstorms. This is expected to extend from Texas and Deep South, to the Appalachians and Mid-Atlantic/Northeast. The tropics are also expected to become more active by the end of the week with a possible disturbance moving inland across western Mexico and potentially bringing a surge of moisture northward to New Mexico and Texas late in the period, although this remains quite uncertain at this juncture. Another tropical disturbance could also enter the western Atlantic east of the Bahamas by the middle to end of the week, based on recent National Hurricane Center outlooks. Hamrick 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