114 FXUS02 KWBC 271953 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 353 PM 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... A strong ridge will be anchored over the eastern half of the country, supporting a sprawling dangerous heat wave and high humidity. Meanwhile an amplified trough will be over the West becoming reinforced as multiple impulses move through within the flow, with some energy possibly acting to suppress the Eastern ridge slightly by next 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 overall pattern has had pretty decent run to run agreement with the some uncertainties with the timing/location of an upper low for the Northwest as various shortwave energies fire through the trough in the West. 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. 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 used a compromise of the deterministic guidance early on, transitioning to 60 deterministic/40 GEFS and EC ensemble means. ...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. Campbell/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 $$