One indicator of atmospheric moisture, known as precipitable water (which is the integrated amount of water in the air from near the jet stream down to the surface), is forecast to be near record levels.

Thursday through Monday, precipitable water levels are forecast to be at least two inches and even 2.5-2.75 inches, which is in historic territory. The highest precipitable water level ever measured in Washington was 2.56 inches on Aug 13, 1955. If the precipitable water reaches 2.33 inches, it would rank among the top 10 highest levels on record.

Surface dew points, direct measures of the humidity, are forecast to climb above 70 degrees Wednesday and range from 75-to-80 degrees at times Friday through the weekend.

Anytime the dew point is over 70 degrees, it feels uncomfortable. When it crests 75 degrees, the humidity becomes oppressive.

Temperatures are also forecast to climb as the week wears on, reaching the low 90s midweek and the mid-90s by the weekend. So the combination of heat and humidity will make it feel hotter than 100 degrees at times.

The culprit for the very steamy air mass is an area of high pressure east of Bermuda in the Atlantic Ocean that is developing today. It is forecast to remain nearly stationary into early next week.

The clockwise flow around this high pressure center will pump extremely moist air from the Gulf of Mexico through the South and toward the Northeast.

Bear in mind the Gulf of Mexico is unusually warm right now, with water temperatures around 88 degrees over a large area, several degrees above normal, which adds to the available heat and moisture than can be transported northward.

With moisture levels so high, any thunderstorms that develop late this week and through the weekend will have the potential to generate torrential downpours. But until Sunday or Monday, storms will tend to be hit-or-miss in the region focusing more toward the mountains.