How long could the Kronstadt rebels have held out?

In February 1921, large-scale workers' strikes took place in Petrograd over the continuously worsening plight of the population. The Kronstadt sailors rose in sympathy and, on February 28, held a meeting during which a 15-point resolution calling for an end to Bolshevik dictatorship was passed. On March 2, the Communist government issued an ultimatum to the sailors, and five days later, ordered attacks on Kronstadt. The initial assaults were repulsed but defenses were breached on March 17, and by the 19th, the Red Army had retaken control of the city.

Now a key factor in the rebellion's defeat was the fact that the water in the bay was still iced over, allowing the Red Army to storm the city by foot. This leads to two questions:

a) When did the ice melt in 1921?

b) Assuming the rebellion starts just before the ice melts, how long could it have held out against the Red Army? How long a siege could Kronstadt have sustained, assuming no meaningful outside reinforcements?

If I'm not mistaken the Ice in the North Baltic generally stays frozen until Mid April, but then that estimate is WWII's numbers, I can't offer an exact date for 1921.

But for the sake of discussion, once the Ice Melts Kronstadt, can hold out as long as the food supply lasts once the water melts. If they can get more from Western and Central Europe, from where I'm not sure, they can even last until the winter of 1921-22. Any Red Army attempts to launch an amphibious operation before the waters freeze are going to have to face a very powerful (Proportionally speaking) fleet and then a large number of sailors and militia fighting them, anyone who makes it to the island itself rather then the bottom of Baltic will be facing a tough fight. If the Red Army waits until the winter the rebels on Kronstadt will be doomed, you would probably see alot of folks making the run across the ice to Finland before the Red Army gets to the island.

The real issue though is the political one, If the mutineers leaders can keep their Anti-Soviet Revolt together, and if Lenin can maintain stability in Petrograd as a rebellion simmers in site of the leadership, the White Forces at this point are mostly finished but its possible that Left Opposition groups can still cause his regime some major headaches elsewhere if the Bolshevik Dictatorship cant defeat a lone mutiny. And if the Rebellion lasts long enough, will Lenin be able to launch the New Economic Plan in such an environment.

Japhy said:

If I'm not mistaken the Ice in the North Baltic generally stays frozen until Mid April, but then that estimate is WWII's numbers, I can't offer an exact date for 1921.

But for the sake of discussion, once the Ice Melts Kronstadt, can hold out as long as the food supply lasts once the water melts.

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According to Wikipedia, the Gulf of Finland is frozen from late November to late April. So if we assume a later start to the rebellion, Kronstadt could be nigh-impregnable short of organizing a large-scale amphibious operation until late Autumn. However, what about food and ammunition? Would they have enough to last this long, or would they run out before then?