395 FXUS21 KWNC 271805 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT June 27 2026 SYNOPSIS: Extreme heat is likely to continue from week-1 into the July 4th holiday weekend across many areas of the central and eastern contiguous U.S. (CONUS) associated with anomalous mid-level high pressure. Anticipated high dewpoints favor heat index values exceeding 100 to 105 deg F over many areas with warm nights limiting overnight relief. As the mid-level high shifts westward, some heat relief is forecast across the Eastern Seaboard, but with extreme heat potential increasing across parts of the western CONUS. This transition may also favor frontal activity and heavy precipitation across portions of the Northeast and Mid-Atlantic early in the period. Surface high pressure off the West Coast in week-2 increases chances for episodes of high winds across the Pacific Northwest and California through much of the period. HAZARDS Moderate risk of extreme heat for the eastern Great Plains, Mississippi and Tennessee Valleys, Southeast, and Mid-Atlantic, Sun, Jul 5. Slight risk of extreme heat across much of the central and eastern CONUS, Sun-Tue, Jul 5-7. Slight risk of extreme heat across much of the Great Basin, Southwest, and Rockies, Sun-Thu, Jul 5-9. Slight risk of heavy precipitation across portions of the Mid-Atlantic, Central Appalachians, and eastern Ohio Valley, Sun-Mon, Jul 5-6. Slight risk of high winds for portions of California and the Pacific Northwest, Sun-Sat, Jul 5-11. DETAILED SUMMARY FOR TUESDAY JUNE 30 - SATURDAY JULY 04: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SUNDAY JULY 05 - SATURDAY JULY 11: A major heat wave is forecast to be ongoing across much of the central and eastern CONUS at the start of week-2. For the Eastern Seaboard, the peak of the heat is likely to occur during the late week-1 timeframe, with mid-level ridging retrograding farther to the west at the beginning of week-2. Despite these trends, the ECMWF Probabilistic Extreme Tool (PET) continues to indicate greater than a 60 percent chance maximum temperatures exceed the 85th climatological percentile on day-8 (July 5). Additionally, the uncalibrated 0z deterministic ECMWF depicts heat index values around 105 deg F across the Mid-Atlantic. The GEFS PET is less robust with chances for extreme heat by day 8. However, it still depicts actual temperatures in the 90s deg F extending through the northern Mid-Atlantic and possibly near to above 100 deg F across parts of the Carolinas. Given some of the relatively cooler signals emerging over more northern areas, the risks of extreme heat have been adjusted slightly southward compared to yesterday across the East. The National Blend of Models (NBM) records tool shows a dramatic reduction in near or record breaking heat by July 5th across the eastern CONUS. As such, the high risk of extreme heat has been allowed to time off into the week-1 period. A moderate risk (greater than 40 percent chance) for extreme heat remains valid for July 5th over the central and southern portions of the Mid-Atlantic into the Southeast given the best tool agreement and continued chances for heat index values to exceed 105 degF. The moderate risk extends westward through parts of the Tennessee Valley, Mississippi Valley and eastern Plains underneath the ridge axis and consistent with a very humid air mass in place, with skill weighted heat risk tools indicating at least a 40 percent chance of heat index values exceeding 100 (105) deg F into parts of the Northern (Central & Southern) Plains. The NBM also depicts widespread record high minimum temperatures throughout much of the eastern U.S. (potentially only dropping into the mid- to upper 70s deg F), resulting in little overnight relief from the heat. Staying hydrated and limiting exposure to very hot, humid weather is very important, especially for vulnerable populations including older adults. A slight risk (20-40 percent chance) of extreme heat encompassing the moderate risk is posted from the Great Plains to the Eastern Seaboard for July 5-7. By day-9, the 0z ECMWF, GEFS, and Canadian ensembles all depict a 594-596 dm ridge across the Four Corners, which could result in extreme heat conditions emerging across portions of the Interior West and persisting through at least the middle of week-2. The Weather Prediction Center (WPC) Probabilistic HeatRisk tool shows increasing signals for major HeatRisk across the West by the beginning of week-2. Therefore, an additional slight risk (20-40 percent chance) of extreme heat is valid July 5-9, across much of the interior western US, excluding most areas west of the Sierra Nevada and the Northern Rockies. Tied to westward shifting ridging, and the potential progression of frontal activity, enhanced precipitation and potential thunderstorms are possible across parts of the eastern Ohio Valley, central Appalachians, and Mid-Atlantic. While signals are weak, consideration is given to the overall synoptic pattern and increased impacts on July 4th weekend. Both the GEFS and ECMWF PETs indicate at least a 20 percent chance of 3-day precipitation totals exceeding the 85th climatological percentile across parts of the region. Uncalibrated tools are marginally supportive as well with enhanced chances of precipitation totals reaching 1-inch, and locally higher amounts possible in thunderstorms. Therefore, a slight risk of heavy precipitation is posted for the aforementioned areas, July 5-6. Surface high pressure off the West Coast and thermal low pressure over the Great Basin increase chances for episodes of high winds during week-2. The GEFS and ECMWF PETs indicate at least a 20 percent chance of wind speeds exceeding the 85th climatological percentile and 25-mph. Therefore, a slight risk of high winds is posted across this region. Across the southwestern CONUS, the ridge axis is forecast to move towards a more favorable position for enhanced monsoonal moisture advection and increased precipitation over parts of the Desert Southwest. Although PETs show increased chances of 3-day precipitation exceeding the 85th climatological percentile over the Desert Southwest and into the Central Rockies during the second half of week-2, both raw and calibrated precipitation amounts in the ensemble means remain fairly low, precluding a corresponding precipitation hazard at this time. Localized thunderstorms are still possible and this area will continue to be monitored with ensemble guidance indicating precipitable water increasing during the week-2 period. Transient shortwaves moving across Alaska favor periods of enhanced precipitation across much of the state, along with a tilt toward below-average temperatures. However, precipitation and temperature values are expected to remain below hazardous thresholds. FORECASTER: Ryan Bolt $$