576 FXUS02 KWBC 270555 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 AM EDT Sat Jun 27 2026 Valid 12Z Tue Jun 30 2026 - 12Z Sat Jul 04 2026 ...Significant, dangerous heat wave expected next week for the Central to Eastern U.S... ...Pattern Overview... The pattern during the upcoming medium range looks to be highly amplified most of the period with a strong upper high/ridge over the Eastern half of the U.S. and a deep trough over the West. This trough will be reinforced through the period by a series of shortwaves, with some energy possibly acting to suppress the Eastern ridge slightly by next weekend. In the East, a sprawling upper high will result in increasingly dangerous heat and humidity through much of next week (and possibly beyond into the July 4th Holiday weekend). Showers and thunderstorms will be most likely across the Gulf Coast/Florida region, the southern Rockies, and the Upper Midwest to Great Lakes/Northeast. ...Guidance/Predictability Assessment... The latest guidance maintains good agreement with its depiction of the large scale pattern through most of the medium range period. Confidence and predictability remains high for a large upper ridge initially centered over the Mid-Mississippi Valley early in the period before slowly shifting eastward and weakening slightly by the end of the week. Out West, shortwaves will act to reinforce troughing across the region much of the period. Uncertainty increases by mid week with placement and track of an upper low into the Northwest. The GFS seems most aggressive with this feature and was not preferred. By late week, there is some consensus for western U.S. energy to ride over the top of the Eastern ridge, which may act to suppress it slightly. The ECMWF seems less enthused with this scenario, hanging onto a stronger ridge into the weekend. The WPC forecast for tonight used a blend of the deterministic guidance early on, transitioning to a 50/50 blend of the ECMWF/ECAIFS/CMC with the ensemble means. Overall, maintained good agreement with the previous WPC forecast. ...Weather/Hazards Highlights... The most impactful weather hazard during the medium range period will be a long lasting heat wave affecting much of the central to eastern U.S. beginning during the short range period and lasting through the medium range period. Widespread temperatures into the 90s to low 100s, combined with high humidity, will result in heat indices approaching or exceeding 105-110 in many places. This equates to widespread Major to Extreme HeatRisk from the Midwest/MS Valley eastward to the East Coast. Overnight lows will also be quite warm, with some record high minimums possible, bringing little to no relief from the heat in the nighttime hours. Rain and thunderstorms will develop associated with a frontal system across parts of the Upper Midwest and Great Lakes Tuesday- Wednesday. Some of this activity will likely make its way into parts of the Northeast as well as it rounds the northern periphery of the mid/upper level ridge. While much of this should be fairly progressive, moisture anomalies and instability may support a localized flash flood threat. WPC continues to highlight parts of the Upper Midwest and the interior Northeast with marginal risks on both the Day 4/Tuesday and Day 5/Wednesday Excessive Rainfall Outlook. Elsewhere, moisture funneling between the western trough and the eastern ridge should support showers and thunderstorms across parts of the southern Rockies and southern High Plains for at least the early part of the week. A Marginal Risk ERO remains for Day 4/Tuesday. Diurnally driven showers and storms are also expected from the central Gulf Coast to Florida with moisture increasing south of the upper ridge. Showers may increase across parts of the Ohio Valley and East late week/next weekend as the upper ridge slightly weakens and upper level energy tries to intrude into the region. 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw $$