204 FXUS02 KWBC 260612 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 212 AM EDT Fri Jun 26 2026 Valid 12Z Mon Jun 29 2026 - 12Z Fri Jul 03 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 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 snow possible at the highest elevations of the Northern Rockies associated with one compact upper low early in the period. 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 continues to show good agreement on the large scale forecast, but plenty of uncertainty still in the details. Out West, guidance is showing better agreement now on an initial upper low over Montana on Monday lifting more northward, keeping the upper ridge over the East in tact. This system should spin up deep lee cyclogenesis over the northern/central Plains, with the progress of this system slow to move eastward due to the potent upper-high/ridge over the East. Energy and shortwaves into the Western trough will act to reinforce this trough through next week. The guidance shows another upper low dropping into the Pacific Northwest late week, but uncertainty on the evolution and details of this. WPC was able to use a mostly deterministic/AI guidance blend for the first half of the period, transitioning to a 50/50 blend of the ensemble means with the EC/EC-AIFS by Day 7. Generally 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 this weekend and lasting through next week, and likely into the July 4th Holiday weekend as well. 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 HeatRisk across the entire region, with areas of extreme HeatRisk in parts of the Midwest and Ohio Valley underneath the core of the upper high. 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 mountain snow will be ongoing into Monday for much of the Northern Rockies, with several inches of snow accumulation for the highest mountain ranges. Ahead of this, rain and thunderstorms may develop across parts of the Upper Midwest and Great Lakes into Tuesday ahead/north of a lifting warm front through the region. While much of this should be fairly progressive, moisture anomalies and instability may support a localized flash flood threat. WPC highlights parts of the Upper Midwest and the interior Northeast with marginal risks on the Day 5/Tuesday 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. Diurnally driven showers and storms are also expected from the central Gulf Coast to Florida with moisture increasing south of the upper ridge. 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 $$