Prolonged period of 'potentially dangerous heat' becoming more likely for the Northwest, weather service warns

(CNN)More than 260 million people in the United States are forecast to experience highs of at least 90 degrees by the end of this week as a new heat wave envelops the Northwest, threatening the region with record-breaking, dangerous temperatures.

"There is increasing confidence in another prolonged stretch of exceptionally hot weather by mid to late next week, and potentially as early as Tuesday across portions of the Pacific (Northwest)," warned the National Weather Service in Portland, Oregon.
Other regions are also expected to sweat it out with the above-average temperatures, with the central United States experiencing it early in the week, and then the Northeast by the middle of the week.
    In total, more than 60 daily records could be broken nationwide by next weekend.

      Heat alerts issued for Northwest

        An excessive heat watch is already in effect for portions of Washington, Oregon and California, and additional heat alerts will likely be added in the coming days as the incoming heat wave grips the region, the National Weather Service said.
        A ridge of high pressure along with a rise in the jet stream will shift east from the North Pacific, reaching the Northwest by the middle of the week.
          This area of high pressure will act similarly to a heat dome, essentially trapping and producing extreme heat while keeping the area it encompasses dry.
          The good news is this weather pattern setup will not favor heat as intense as the heat dome in late June, which brought widespread temperatures in the triple digits and led to hundreds of deaths across the greater region.
          "While it will be hot, the overall pattern is nothing like the record breaking heat towards the end of June," the Portland National Weather Service office said.
          "Although this upcoming heat wave will likely not ultimately match the late June event in terms of magnitude, there is still an increasing probability of a prolonged period of potentially dangerous heat."
          High temperatures for most in the Northwest on Monday will be in the 70s and 80s, which is right around average, but will increase to the 90s and 100s beginning Wednesday, becoming about 20 degrees above the normal temperature for this time of year.
          Forecast high temperatures for the Northwest.
          Only the mountain peaks and immediate coast will escape the heat, with temperatures hovering in the 70s and 80s.
          The most dangerous heat will be during the latter half of the week, especially Thursday and Friday, for cities such as Seattle, Portland and Medford, Oregon.
          Portland is currently forecast to reach at least 100 degrees for three consecutive days starting Wednesday. That's equivalent in length to the late-June heat wave for the city, but that time temperatures reached 116 degrees, shattering the all-time record for the city.
          Temperatures this week will likely be about 10 degrees shy of that record, but the city is still predicted to see daily record highs.
          In Seattle, high temperatures could reach the mid- to upper 90s beginning Wednesday or Thursday, likely breaking the record high for the day.
          The lack of significant cooling overnight could also make this heat wave more hazardous for this part of the country.
          "Overnight lows should also be quite warm during this time, running in the upper 60s or low 70s and potentially contributing to an increased risk for heat related illnesses during this time," warned the weather service.
          Along with this heat will be dry conditions, with no rain expected for the Northwest through the weekend once the ridge moves in midweek.
          A drought continues to cripple this part of the country, helping fuel wildfires, and the heat will make the drought conditions even worse.
          The ridge of high pressure will drift to the east by next weekend, bringing significantly above-average temperatures to the interior Northwest and southwestern Canada before temperatures cool slightly next week.
          Climate Prediction Center's temperature outlook from August 14-18.
          Highs should remain above average across the Northwestern United States for the extended future.

          Heat wave this week for the Northeast, too

          A different area of high pressure will also bring above-average temperatures to much of the East this week, especially the Northeast.
          Widespread high temperatures of 5 to 15 degrees above average will be common across the central United States and interior Northeast to begin the week.
          Highs will be in the 90s and 100s in the southern Plains, while it will be in the 80s and 90s for the Midwest during this time frame.
          Heat advisories are in effect for more than 25 million people, including Dallas, Oklahoma City, Kansas City and St. Louis.
          As the high pressure shifts east, so will the heat, becoming most significant for the Northeast late in the workweek. Some cities may even break their daily record high temperatures.
          Cities such as New York, Boston and Washington, DC, are forecast to hit the low to mid-90s from Wednesday through Friday, but it will likely feel like the 100s in some locations when factoring in the high humidity levels.
          Forecast high temperatures for the Northeast.
          The National Weather Service in New York said it "looks like there is increasing potential for heat advisory criteria to be met Wednesday through Friday of next week for much of the region."
            Given the hot and humid air mass and weak storm systems sweeping through to the north, there will be the chance for scattered thunderstorms much of this week in the Northeastern United States. There is even the risk for some severe storms, especially in the Midwest.
            A cold front is then expected to sweep through the Northeast this weekend, ushering in relief from the heat and sticky conditions as well as ending the chance of rain.