Here's why grocery stores are struggling to stock their empty shelves

New York (CNNBusiness) Grocery store shelves across America are wiped clean, and they're staying empty as stores struggle to quickly restock everyday necessities such as milk, bread, meat, canned soups and cleaning products.

Disgruntled shoppers have unleashed their frustration on social media over the last several days, posting photos on Twitter of bare shelves at Trader Joe's locations, Giant Foods and Publix stores, among many others.

After contending with two years of a pandemic and supply chain-related problems , grocery stores still aren't getting the break they had hoped for. Rather, they are now confronting a host of other setbacks.

As the highly contagious variant of the Covid-19 virus continues to sicken workers, it's creating staffing shortages for critical functions like transportation and logistics, which in turn are affecting delivery of products and restocking of store shelves across the country.

Albertsons' CEO Vivek Sankaran acknowledged that products are in tight supply during the company's earnings call with analysts Tuesday.

"I think as a business, we've all learned to manage it. We've all learned to make sure that the stores are still very presentable, give the consumers as much choice as we can get," Sankaran said during the call.

Even so, he added, Omicron has put "a bit of a dent" on efforts to improve supply chain gaps. "We would expect more supply challenges over the next four to six weeks," Sankaran said.

Grocery stores are operating with less than their normal workforces, according to the National Grocers Association, and many of its members have less than 50% of their normal workforce.

"While there is plenty of food in the supply chain, we anticipate consumers will continue to experience sporadic disruptions in certain product categories as we have seen over the past year and half due to the continued supply and labor challenges," said Greg Ferrara, the group's president and CEO.

"From farms to food makers to grocery stores, it's across the board," said Lempert. "During the pandemic, these operations have had to implement social distancing protocols and they're not really built for that and it has impacted production."

"The trucking industry has an aging workforce on top of a shortage," Lempert said. "It's really been a problem for the last several years."

At Trader Joe's stores, shoppers over the weekend saw messages attached to empty shelves blaming weather emergencies for delivery delays.

Not to mention climate change, which is an ongoing serious and longer term threat to food supply. "Fires and droughts are damaging crops such as wheat, corn and soybean in the US and coffee crops in Brazil," he said. "We can't ignore it."

More and more of us have taken to cooking and eating at home through the pandemic that's contributing to the grocery supply crunch, too, said Lempert.

Grocery stores certainly are aware of the empty shelves, Lempert said, and they are trying to mitigate panic buying, which only worsens it the situation.

One strategy: Fanning out products. They're doing this by putting out both limited varieties and limited quantities of each product in an attempt to prevent hoarding and stretch out their supplies between deliveries.

"Pre-pandemic you might have seen five different varieties of milk across the front row and 10 cartons deep. Now it will be five across and maybe two rows deep," said Lempert.

-- CNN's Nathaniel Meyersohn and Danielle Wiener-Bronner contributed to this story