891 FXUS21 KWNC 261841 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT June 26 2026 SYNOPSIS: Extreme heat is likely to continue from week-1 into the July 4 holiday 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 likely 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 interior western CONUS. This transition may also favor frontal activity and rounds of heavy precipitation across portions of the Northeast and Mid-Atlantic early in the period. Mid-level low pressure off the West Coast early in week-2 increases chances for episodes of high winds across the Pacific Northwest and California. HAZARDS High risk of extreme heat across portions of the eastern Great Plains, Mississippi, Ohio, and Tennessee Valleys, Appalachians, Southeast, and Mid-Atlantic, Sat, Jul 4. Moderate risk of extreme heat from the Great Plains to the Eastern Seaboard (excluding portions of the Great Lakes, Northeast, and Gulf Coast), Sat-Sun, Jul 4-5. Slight risk of extreme heat across much of the Great Basin, Rockies, Great Plains, and the eastern CONUS, Sat-Tue, Jul 4-7. Slight risk of heavy precipitation across portions of the Northeast, Ohio Valley, and Mid-Atlantic, Sat-Mon, Jul 4-6. Slight risk of high winds for portions of California and the Pacific Northwest, Sat-Tue, Jul 4-7. DETAILED SUMMARY FOR MONDAY JUNE 29 - FRIDAY JULY 03: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY JULY 04 - FRIDAY JULY 10: 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 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 4). Additionally, the uncalibrated 0z deterministic ECMWF depicts heat index values greater than 105 deg F across the Mid-Atlantic. While the GEFS is arguably less robust with the most extreme heat into the 4th of July, 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. However, a high risk (greater than 60 percent chance) for extreme heat remains valid for July 4 over the central and southern portions of the Mid-Atlantic into the Southeast given the best tool agreement and continued indication for record high temperatures in the National Blend of Models (NBM). The high risk extends westward through parts of the Tennessee Valley, Midwest, 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 60 percent chance of heat index values exceeding 100 (105) deg F into parts of the Northern (Central) 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. Another key consideration is the Nation's 250th Anniversary on July 4, with numerous outdoor activities planned. Staying hydrated and limiting exposure to very hot, humid weather is very important, especially vulnerable populations including older adults. A moderate risk (40-60 percent chance) of extreme heat is posted from the Great Plains to the Eastern Seaboard for July 4-5. As previously discussed, there is more uncertainty in regards to how long the heat will persist across the East, especially across the northern Mid-Atlantic where signals are more mixed. There is higher confidence regarding the core of the heat potential becoming focused across the Great Plains, where triple digit temperatures are possible. By day-10, the 0z ECMWF, GEFS, and Canadian ensembles all depict a 595-596 dm ridge across the Four Corners, which would result in extreme heat conditions emerging across portions of the Interior West. Therefore, a broader slight risk (20-40 percent chance) of extreme heat is valid July 4-7, encompassing the moderate risk, and also including portions of the Rockies and Great Basin. Extreme heat is favored to persist across the West throughout all of week-2, and perhaps continue to expand into the Desert Southwest and California Central Valley. However, models indicate weak troughing and enhanced northwesterly mid-level flow developing downstream of the ridge which would lead to diminishing heat risk across the eastern U.S. later in the period. Because the slight and moderate risks cover large areas, their valid time periods generally capture the heat risk over all locations included. However, the transient nature of the ridge makes it difficult to accurately depict the heat progression, and it is likely that additional extensions in time will be needed in future updates to the western portions of the moderate and slight risks as the heat diminishes in the East. Tied to westward shifting ridging, and the potential progression of frontal activity, enhanced precipitation and potential thunderstorms are possible across parts of the Ohio Valley, Lower Northeast, and Mid-Atlantic. While signals are weak, consideration is given to the overall synoptic pattern and increased impacts on July 4. 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 4-6. At the base of anomalous troughing favored early in week-2 across the West Coast of the CONUS and northeast Pacific, a slight risk of high winds remains posted for July 4-7. This risk area is shifted farther south into California compared to yesterday, consistent with the GEFS and ECMWF PETs indicating at least a 20 percent chance of wind speeds exceeding the 85th climatological percentile and 25-mph. Across the southwestern CONUS, the ridge axis is forecast to move into 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 region will continue to be monitored in the upcoming outlooks. Transient shortwaves moving across Alaska favor periods of enhanced precipitation across much of the state, along with a tilt toward below-average temperatures. However, no areas of hazardous weather are expected. FORECASTER: Thomas Collow $$