Extended Forecast Discussion NWS Weather Prediction Center College Park MD 305 PM EDT Fri Jun 28 2024 Valid 12Z Mon Jul 01 2024 - 12Z Fri Jul 05 2024 ...Hazardous heat from the South and vicinity next week to portions of the East/Southeast and California into the Fourth... ...Overview... An active summer weather pattern will continue to feature a pattern of energetic and progressive northern stream shortwaves through the northern states as a strong ridge shifts slowly over the South, eventually building back into the East and West Coasts. A threat for heavy rains will be across the Upper Midwest Monday- Tuesday, with focus slowly working over the Mid-Mississippi/Ohio Valleys and vicinity through the holiday.It should also remain a wet pattern across the Southwest with a continuous and highly anomalous moisture feed around the western periphery of the ridge. Hazardous heat threats will focus across much of the southern Plains to Southeast/East over the period, building into parts of the Southwest and interior California by mid to later next week. ...Guidance/Predictability Assessment... Guidance forecast spread continues a trend of being lower than normal through medium range time scales in a pattern with above average predictability overall. The WPC product suite was mainly derived for the Monday-Wednesday timeframe from a blend of the 06 UTC GFS and 00 UTC ECMWF/UKMET/Canadian along with the generally compatible 13 UTC National Blend of Models (NBM) and WPC continuity. Applied most blend weighting to the ECMWF/UKMET that depict a stronger and more resilient southern upper ridge that may prove slow to dissipate. Opted to switch the favored blend to best clustered guidance from the ECMWF and GEFS/ECMWF ensemble means along with the NBM for later next week amid slowly growing, but manageable variances. ...Weather/Hazards Highlights... It generally remains the case that 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. Marginal and slight risk ERO areas are planned for Day 5 as the signal for a main axis of heavy convection shifts to/from Kansas/Iowa through Wisconsin/Illinois into the Great Lakes, possible spreading across the Ohio Valley toward the Mid-Atlantic over the holiday period. 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/Schichtel 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