We got a respite yesterday from the showers and thunderstorms that have affected much of the region this past week. Conditions will turn wet again later today and persist into early this week as the jet stream pattern across North America amplifies …. with a large ridge of high pressure in the West, a large trough of low pressure in the central states and another large ridge of high pressure just off the Atlantic Coast. With a deep trough of low pressure in the upper atmosphere extending from Hudson Bay to the lower Mississippi Valley, that places the East under a deep southerly flow of humid air. Meanwhile, a nearly stationary front at the surface splayed across the Appalachians will enhance low-level convergence and ascent of the moist air, triggering showers and thunderstorms. Furthermore, we will have several small jet stream disturbances traveling northeast across the area, also enhancing the shower and thunderstorms. This general pattern will persist through midweek before the aforementioned upper level pattern retrogrades and the offshore Atlantic high builds westward and reduces the risk for showers and thunderstorms at the end of the week and next weekend. At this point, Wednesday will be the day closest to the “transition” to the drier regime, though we still think there will be scattered thunderstorms across the area on Wednesday and also on Independence Day … mainly in the late afternoon and on the western side of the metro area.
In terms of details, the time of day that will feature the highest risk for thunderstorms (most widespread) will be in the late afternoon and early evening, after the partial sunshine we have destabilizes the atmosphere the most. In addition, the most vigorous of the small jet stream disturbances moving north along the East Coast should pass Monday and Monday night which will also bring an opportunity for a period of heavier showers and thunderstorms.