139 FXUS02 KWBC 261907 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 PM 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 maintains good agreement with its depiction of the large scale pattern through most of the medium range period. The feature that will continue to have the most predictability is the large and sprawling 594+dm mid/upper level ridge that will initially be centered over the Mid-Mississippi Valley early in the period before slowly shifting eastward into the central Appalachians by the end of next week. Upstream of this ridge, a mean mid/upper level trough will drive the pattern across the Western U.S., with a series of relatively lower predictability shortwaves reinforcing the trough through most of next week. Given the above, the WPC forecast was derived using a blend of mostly deterministic and machine learning guidance through Day 5 before shifting more weight (60/40 split) to the EC and GEFS ensemble means for Days 6 and 7. This approach limited the impacts of smaller scale spatial and temporal differences (mainly with troughing in the Western U.S.) later in the period while maintaining continuity 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. Some of this activity will likely make its way into parts of the Northeast by midweek 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 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. A Marginal Risk ERO has been introduced for Day 4/Monday and maintained for Day 5/Tuesday to account for any localized flash flooding concerns. Diurnally driven showers and storms are also expected from the central Gulf Coast to Florida with moisture increasing south of the upper ridge. Santorelli/Miller 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 $$