Extended Forecast Discussion NWS Weather Prediction Center College Park MD 238 AM EDT Fri Jun 28 2024 Valid 12Z Mon Jul 01 2024 - 12Z Fri Jul 05 2024 ...General Overview... The beginning of July will feature a high quality airmass across much of the Eastern U.S. behind a departing cold front, with drier and cooler conditions compared to the heat and humidity expected over the weekend. Meanwhile, excessive heat will continue to make weather headlines across the south-central U.S. where the upper level ridge axis will be, and some of this heat reaches the East Coast region in time for the Fourth of July holiday with the surface high moving offshore. Rain and storms are likely across the Midwest states for the first half of the week, and monsoonal moisture across the Southwest will maintain scattered showers and storms. ...Guidance/Predictability Assessment... The 00Z model guidance suite is in good synoptic scale agreement for the beginning of the week, and a general model compromise suffices as a good starting point in the forecast process. The NBM appeared a little too light with QPF across the Four Corners region with respect to the monsoon, so these values were raised roughly 30 percent or so. Forecast uncertainties increase the most across the northwestern U.S. for the second half of the week, with recent runs of the GFS/GEFS becoming more at odds with the ECMWF/CMC solutions regarding the upper ridge placement and the downstream trough across the Northern Rockies and the Dakotas. Upon examination of the machine learning guidance, there was better support for the CMC/ECMWF solutions for the Fourth and into Friday, so the GFS was tapered down by this time, and there was more of the ECENS than the GEFS used as a result. ...Weather/Hazards Highlights... Widespread showers and storms are expected to be ongoing across the Upper Midwest on Monday ahead of a frontal boundary and an upper level impulse moving through the region. Although the overall forecast rainfall totals are currently expected to be in the 1-2 inch range, this would be falling on highly saturated grounds in many cases, which would be an aggravating factor when it comes to flooding potential. Therefore, the Slight Risk remains valid for the new Day 4 ERO across much of Minnesota and portions of adjacent states. Elsewhere, moisture pooling ahead of the cold front approaching the Southeast U.S. coast may lead to some repeated rounds of storms with high rainfall rates on Monday, where a Day 4 Marginal Risk area is planned. Monsoonal flow into the Southwest states will continue the daily threat for showers and storms through much of the period. Marginal risks remain in place across parts of Arizona, New Mexico, and southern Colorado for both the Day 4 and 5 EROs, with the potential for upgrades to a Slight Risk in subsequent updates depending on short range rainfall. This pattern is likely to persist into next Wednesday as well given the lingering and deepened moisture channel on the upper ridge western periphery. It will continue to remain hot and humid across the Southern U.S. for much of next week, with the hottest conditions centered across Texas and Oklahoma where triple digit high temperatures are likely. Some of this heat likely reaches the Mid-Atlantic region by the end of the week with highs in the middle to upper 90s. It will also be getting hotter for the inland lower elevations of California and into the Arizona Deserts with widespread 100-110 degree readings likely, and locally higher for the normally warmer locations. 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 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