(Recasts, adds details on product markets, updates prices)
By Devika Krishna Kumar and Stephanie Kelly
NEW YORK, May 28 (Reuters) - Unexpected pipeline outages and refinery shutdowns over the past week - in part caused by bad weather in the U.S. Midwest - has roiled cash markets for both crude oil and refined products, traders said on Tuesday.
Volatile trading was seen both in crude markets in the Cushing, Oklahoma hub and for gasoline and diesel traded in the Tulsa, Oklahoma region.
The Ozark pipeline, which flows up to about 360,000 barrels per day (bpd) of crude oil, was shut, market intelligence firm Genscape said in a notice on Tuesday. It was not immediately clear whether flooding had caused the outage on Ozark, though the rains have caused other pipelines in the region to shut in recent days.
The Ozark line flows northeast from Cushing to the Phillips 66 Wood River refinery in Roxana, Illinois, according to Genscape.
The outage had an immediate effect on the U.S. West Texas Intermediate crude cash roll - the three-day period after the front-month futures contract expires, when traders rebalance their positions. The roll trade is closely tied to supply and demand at Cushing, the delivery point for U.S. crude futures.
The WTI June/July cash roll traded on Tuesday at minus 40 cents per barrel, the weakest in more than two years, traders said. The cash roll traded at minus 20 cents per barrel on Friday ahead of the long holiday weekend.
Representatives of MPLX LP, which operates the line, did not immediately comment on the outage.
Flooded areas of Arkansas and Oklahoma were bracing for more rain that will feed the already swollen Arkansas River, forecasters said on Tuesday. Up to 19 inches (48 cm) of rain has fallen in parts of Oklahoma over the month of May, the National Weather Service said, with more on the way.
Tallgrass Energy LP on Friday issued a notice of temporary embargo of deliveries for its Tallgrass Iron Horse Pipeline due to flooding on the Cimarron River in Oklahoma. That came a day after a similar notice for its Pony Express Pipeline, which runs from Guernsey, Wyoming to Cushing.
The 200,000-bpd Diamond pipeline, which runs from Cushing across Arkansas to Valero Energy Corp’s Memphis, Tennessee, refinery was also shut, traders and Genscape said on Tuesday.
Flows on that line were already limited due to planned maintenance work at the gasoline-producing and alkylation units at the Memphis refinery, traders said.
Diamond pipeline is a joint venture between Plains All American Pipeline LP and Valero. Both companies did not respond to requests for comment.
HollyFrontier’s 155,300 bpd Tulsa, Oklahoma, refinery, shut operations as a precaution due to high water. Worries about reduced supply have boosted cash prices for gasoline in the Midwest.
Group Three gasoline RUV-DIFF-G3 traded near the highest for this time of year since at least 2013, the earliest Refinitiv Eikon data available, at 3.75 cents per gallon above futures.
Diesel prices, by contrast, have suffered, because the wet conditions have forced farmers to delay planting, sapping demand for the fuel, used to power farming equipment. Group Three prices on Tuesday for diesel ULSD-DIFF-G3 traded near the lowest seasonally since 2016, traders said.
Reporting by Devika Krishna Kumar and Stephanie Kelly in New York; Additional reporting by Collin Eaton and Erwin Seba in Houston Editing by Tom Brown and Marguerita Choy