Natural gas futures were lower during U.S. morning hours on Tuesday, as investors cashed out of the market to lock in gains from the previous session’s strong rally.

On the New York Mercantile Exchange, natural gas futures for delivery in June traded at USD4.348 per million British thermal units during U.S. morning trade, down 1% on the day.       

Nymex natural gas prices fell by as much as 1.4% earlier in the day to hit a session low of USD4.330 per million British thermal units.

Natural gas futures rallied nearly 4% on Monday to re-approach a 21-month high, as sentiment on the commodity remained upbeat amid easing concerns over U.S. inventory levels.

Total U.S. natural gas storage stood at 1.734 trillion cubic feet as of last week, 32% lower than last year at this time and 5.1% below the five-year average for this time of year. 

Early injection estimates for this Thursday’s storage data range from 25 billion cubic feet to 40 billion cubic feet. 

Inventories rose by 31 billion cubic feet in the same week a year earlier, while the five-year average change for the week is a rise of 67 billion cubic feet.

Natural gas prices found additional support as weather forecasts pointed to below-average temperatures for the Midwest and South later in the coming week, which was expected to boost demand for the fuel.

But investors were hesitant to extend the sharp rally with spring's low-demand shoulder season looming.

Gas use usually hits a seasonal low with spring's mild temperatures, before warmer weather increases demand for gas-fired electricity generation to power air conditioning.

Nymex gas prices have risen sharply in recent weeks, gaining almost 37% since mid-February, boosted by calls for colder temperatures in major consuming regions across the U.S. that helped tighten the market. 

The June contract rose to a 21-month high of USD4.428 per million British thermal units on April 19.

Elsewhere on the NYMEX, light sweet crude oil futures for delivery in June fell 1.1% to trade at USD93.44 a barrel, while heating oil for June delivery declined 1.2% to trade at USD2.832 per gallon.