121 FXUS02 KWBC 300618 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 218 AM EDT Tue Jun 30 2026 Valid 12Z Fri Jul 03 2026 - 12Z Tue Jul 07 2026 ...Significant, dangerous, and record breaking heat wave expected to last into next weekend for the Central to Eastern U.S... ...Pattern Overview... The period begins with a strong ridge anchored over the eastern half of the country, continuing to support a significant and dangerous heat wave which will begin during the short range period. Energy out West should eventually make its way into the Northern Plains and Great Lakes, working to suppress the ridge, bringing an end to the heat wave by around Sunday for most places. This should also allow ridging to build back into the Southwest region for later in the period. Showers and storms initially across the Northern tier will eventually expand into the Ohio Valley and the East next weekend as the ridge weakens. ...Guidance/Predictability Assessment... The latest guidance continues to show good agreement with the synoptic scale pattern but uncertainty remains with the details/evolution of energy traversing the flow in the West and the timing of ridge break down over the East. Most of the guidance show the Heat Wave peaking in the Thursday-Friday time frame, and by the weekend confidence is increasing that energy from the West should work into the Great Lakes weakening the ridge and overall oppressive heat. How quickly and how much the ridge is suppressed is still in question. The amplitude of the shortwave feature remains uncertain but there seems to be some trend towards slightly less amplified flow by early next week. There are not really any clear outliers in the latest model cycle, so the WPC fronts/pressures forecast was based on a general model blend of the deterministic guidance for the first half of the period, gradually increasing weighting of the ensemble means to just over half of the blend by the latter half. This generally maintained good agreement with the previous WPC forecast, with sensible weather adjustments to the NBM focused primarily for Max T and afternoon Dewpoints underneath the ridge. ...Weather/Hazards Highlights... A significant and major heat wave set to begin by the middle of this week will peak at the start of the medium range period over much of the Central to Eastern U.S.. Widespread and daily record breaking maximum temperatures into the 90s to low 100s, combined with high humidity, will result in heat indices approaching or exceeding 105-110 in many places. Some of these values may break all time records as well. This equates to widespread Major to Extreme HeatRisk from the Midwest/Mississippi Valley eastward to the East Coast. Overnight lows will also be quite warm, with numerous record high minimums possible, bringing little to no relief from the heat in the nighttime hours. Heat may finally begin to abate from west to east this weekend, with upper temperature limits possibly restricted by increasing clouds/convection as ridge breakdown begins. Above normal temperatures should expand westward into the Southern and Central Plains as well, with temperatures out West near to below normal underneath of general troughing. Rain and thunderstorms associated with a slow moving frontal boundary will impact parts of the Northern Plains to Upper Midwest and Great Lakes into next weekend. Moisture anomalies and instability within fairly weak flow may support at least a localized flash flood threat. WPC highlights much of this region within a Marginal Risk for the Day 4/Friday and Day 5/Saturday Excessive Rainfall Outlooks. Storm chances will expand this weekend and early next week across much of the Ohio/Tennessee Valleys and East as the upper ridge weakens but still warm temperatures support a moist and unstable environment for afternoon convection ahead of a frontal system. This region is also included in the Day 5 Marginal ERO. Elsewhere, diurnally driven showers and storms are expected from parts of the central Gulf Coast to Florida most of the period with moisture increasing south of the upper ridge. Showers may refire again later in the period for parts of the Southern/Central Rockies and High Plains, as well as the northern tier ahead of additional shortwave energy. 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 $$