Conditions will be ripe this afternoon into this evening for strong thunderstorms across much of the country. Strong to perhaps isolated severe storms are expected over the interior Northwest and the Southeast but stronger and more widespread storms are expected over New Mexico and western Texas tonight into this evening.
The progressive but dynamic upper-air pattern that has resulted in recent flooding in the Eastern U.S. and record heat in the central U.S. will continue to bring unsettled weather for much of the contiguous U.S. The ridge of high pressure over northern Mexico and southern Texas will shift eastward today, inviting a trough of low pressure to arrive onshore tonight over the Pacific Northwest. Meanwhile, a shortwave trough will ride over the ridge and across the Four Corners region before ejecting into the Rocky Mountains. As it does so, it will generate lift out ahead of it and drag a cold front across New Mexico. In the Ohio Valley and the Southeast, a cold front associated with a robust trough crossing the Great Lakes will slide towards the coast and generate thunderstorms ahead of it.
The worst of today’s storms will occur over New Mexico and southwestern Texas. Ahead of the shortwave trough, the environment will be moderately unstable with strong clockwise change in wind direction and speed with height. These conditions will support the development of isolated supercells along and east of eastward facing mountain slopes in New Mexico by mid-afternoon before evolving into linear structures. These supercells will be capable of producing large hail, powerful wind gusts, and possibly isolated tornadoes. The area with the best chance for tornado development will be over central New Mexico, where scattered discrete storms will initially develop.
Later this afternoon into the evening, thunderstorms over New Mexico will merge and evolve into linear systems and will travel east-southeastward into Texas. The best thermodynamics for these linear systems to maintain severe characteristics through the evening will be over southeastern New Mexico and southwestern Texas. Threats associated with these storms will be confined to damaging wind gusts from the outflow ahead of the storms, although a small risk of hail will also be present.
Storms are less welcome in the rain-weary Southeast and Appalachia. A warm and very humid environment will serve as fuel to storms that develop ahead of the cold front between late morning and early evening, from northwest to southeast. These conditions should be satisfactory for the development of scattered storms with brief but torrential downpours and small hail. The saving grace here will be the lack of wind shear. Without it, the storms’ own downdrafts will cut off their updrafts from the moist environment, making them short-lived and thwarting the potential for large hail. Storms will generally be scattered but some multicellular lines may develop, especially over the Ohio River Valley and over Appalachia. The primary severe threat with these storms will be strong wind gusts from the storms’ outflow boundaries but small hail cannot be discounted.
In the interior Northwest, the eastward shift of the ridge over northern Mexico and southern Texas will invite a trough to propagate eastward, generating lift ahead of it in conjunction with upsloping over the northern Rockies. With these sources of upward motion and an abundance of directional change in wind speed and direction with height, the marginally unstable environment over eastern Washington, northwestern Oregon, and northern Idaho should be enough to generate scattered thunderstorms, some of which may be capable of producing damaging winds and large hail. Storms will develop late this afternoon over Oregon and Washington and migrate into Idaho around sunset.
More unsettled weather is expected this week as this progressive upper-air pattern refuses to yield. Be sure to check back as these future events unfold.