Thunderstorms will develop over a wide swath of the central U.S. and parts of the Rocky Mountains Wednesday as the Ring of Fire pattern continues. Scattered storms will fire due to a variety of triggers late this afternoon into this evening, bringing damaging wind gusts, large hail, and perhaps a tornado or two in their paths. As the pattern continues, thunderstorms will continue to threaten parts of the Central U.S. into the weekend.

As cloud debris clears from a decaying MCS Wednesday afternoon, isolated thunderstorms will develop over central Iowa and eastern Nebraska by the early evening. These storms will merge into a southward racing squall line, a type of MCS. There is a very slight chance that discrete storms early in the evening will be capable of producing brief tornadoes over Central Iowa, before the formation of the squall line. Otherwise, the main threat will be widespread damaging wind gusts ahead of the squall line and large hail in a few embedded cells within it.

These storms will have an overabundance of triggers, so they will quickly become widespread. Remnants of a weakening MCS that brought widespread wind damage and hail with diameters of up to two inches will be the first trigger, initiating convection when cloud debris clears by late afternoon. Behind it, a cold front will help merge the new storms’ outflows into a linear structure and propel them southward. Fueled by temperatures near 90 degrees and dew points in the middle 60s, many of these storms will indubitably develop strong hail cores. The resulting squall line will align itself on a southwest to northeast axis between east central Nebraska and southeast Iowa. The strongest storms will persist over southwestern Iowa and southeastern Nebraska late into the night, maintaining a slight risk to produce strong wind gusts.




Further west, a low pressure system will develop east of the Rocky mountains due to a complicated process called Lee Cyclogenesis, where “Lee” refers to the lee side of the Rocky Mountains. The low will travel east northeastward, prompting the development of scattered thunderstorms on its east side over the central Plains, where warm advection and flow up the lee side of the Rocky Mountains will contribute to thunderstorm development. In an environment even more buoyant than that over Iowa, the outflows of these storms will result in the development of a separate MCS over near the intersection of Colorado, Kansas and Nebraska, expanding southward into Kansas and northern Oklahoma late in the evening, but traveling eastward into the night.

The strongest storms will develop just after sunset near and south of the intersection of Colorado, Kansas and Nebraska. Scattered to possibly widespread severe weather is expected here, with threats being large hail and powerful wind gusts Wednesday evening. A brief tornado or two cannot be ruled out in discrete storms that develop ahead before the MCS. Aided by an intensifying low-level jet stream transporting moist Gulf of Mexico air, these storms will persist through the night over central Nebraska and Kansas, maintaining a threat for damaging wind gusts.

Over the Northern Rockies, isolated thunderstorms will develop in the afternoon on the northwestern side of the newly-developed low pressure system, where wind will be directed to flow up the Rocky Mountain slopes. Storms will develop over eastern slopes, but the strongest storms will form over central Wyoming, where instability will be strongest.

Thursday, severe weather will become more widespread over the northern Rockies and western Dakotas as moist flow intensifies up the lee side of the Rocky Mountains. Some of these storms will be capable of producing damaging wind gusts and up to quarter-sized hail. Scattered storms will develop late in the afternoon along eastern slopes in a modestly unstable air-mass. Storms will merge over parts of Montana and Wyoming into several MCSs but where this occurs is uncertain due to the placement of small shortwave troughs in the flow of the jet stream. Storms will be most widespread near these shortwaves and near jet streaks, which are currently expected over central Wyoming and eastern Montana. Away from these localized features, thunderstorm development will be aided by lift associated with an broad incoming upper-level trough of low pressure. Additional storm development associated with this flow of moisture is expected further south and east into the central Plains.

Further south, a pesky north-south aligned dryline over western Texas will trigger isolated storms. With strong daytime heating and abundance of buoyancy, these storms may be capable of producing large hail.

The dome of high pressure scorching the southern Plains will shift southward Friday. Instability will remain, so this shift will permit more storms to develop over the Plains with lesser sources of lift. Outflow from Thursday night’s storms may trigger storm development over the central Plains, especially over Nebraska, where the most kinks in the flow of the jet stream are likely to develop.




In the central Mississippi Valley, a small but robust shortwave may spawn new thunderstorm development Friday morning through early Friday afternoon. The ultimate strength of these storms is contingent upon the timing of this shortwave. The shortwave will slow down as it propagates southeastward, so if it approaches in the morning, storms will be weaker and the severe threat will be limited further east into the Midwest. If it arrives later in the morning or early afternoon, stronger thunderstorms are expected to be stronger. Regardless, storms are likely to develop over a smaller area compared to previous events this week.

Friday does not mark the end to the rounds of thunderstorms for the Central U.S. The dome of high pressure is expected to remain over Texas, sending buoyant air northward into the Plains. More disturbances are expected to ride over this ridge, spawning further thunderstorm development. Meanwhile, a broad area of upper-level low pressure is expected to arrive on the West Coast Friday night. We will know more about this weekend’s threats as these events near.



Author

Josh is a lifelong nature and weather enthusiast as well as the Head Meteorologist at WeatherOptics. He began regularly forecasting for New Jersey, Long Island and New York City in 2014 on social media, contributing to community pages such as SBU Weather. He holds degrees in Physics and in Atmospheric and Oceanic Sciences from Stony Brook University, from which he graduated in 2018. In the Fall of 2018 Josh will start graduate school for his M.S. in Marine and Atmospheric Sciences at Stony Brook, continuing his research on approaches to non-convective wind gust forecasting.

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