Holland is famous for its windmills. Did flour prices in medieval and early modern Holland fluctuate based on how windy a month was? Did millers mill more grain when it was windy and build stockpiles?

Holland is consistently windy, the closer to the water the windier. The problem would be more "too much wind" -- a winter storm for example. See the Riso National Laboratory in Denmark for a "wind atlas" of Europe. The wind driven gristmills that were used for making flour in Holland were typically located in cities-- most of them are long gone, but Amsterdam famously had 26 mills ("korenmolens") on the bastions of the city walls; only one remains today.

Grain is much easier to store than flour, which is ruined if it gets wet. There were active grain markets across Europe, but not really anything other than local "flour markets" -- eg you might buy some from a mill, but you wouldn't be transporting large amounts for commercial purposes.

So we have lots of commercial scale grain storage, including in the Netherlands, but very little "flour storage" -- households might keep some extra on hand, but not on a significant scale

In Amsterdam three-fourths of the warehouse capacity was given over to grain storage. "Rowers" were employed to stir the stored grain to prevent germination or spontaneous combustion

"Stockpiling flour" is impractical, too easy to spoil, but the Dutch were early in the business of making very hard durable baked products-- "ship's biscuits", also known as "hardtack"; there were apparently 120 biscuit factories in 1620 in the town of Wormer [Vries, 1981: 15-16]. The Dutch have another kind of twice baked biscuit, a "rusk", which like hardtack can be stored for a long time.

So you can store grain, or you can store some durable baked goods; but you can't easily store flour. Holland has windmills because the wind is generally so reliable; but if there were no wind for an extended period, other mills could have supplied. The Netherlands did have watermills, as at Kollen -- famously painted by Van Gogh, who wrote to a friend

‘Since you left I've been working on a Watermill – the one I asked about in that little inn at the station, where we sat talking with that man whom I told you seemed to suffer from a chronic shortage of small change in his pocket. It's the same sort of thing as the two other water mills that we visited together, but with two red roofs, and one views square on from the front – with poplars around it. It will be magnificent in the autumn.'

. . . this is in Brabant which is inland a bit from Holland, less consistently windy. Speaking of painters, Rembrandt's father was a miller, though he milled malt for the beermakers, rather than flour.

There is a substantial debate among economic historians about the relationship between grain harvests, grain storage, grain trade and the price of grain in early modern Europe, see "Harvests and Grain Prices in Sweden" for an extensive discussion of the complexities and unresolved issues in this analysis.

Sources:

Grain Flour, 1590-1790 - comprehensive review article by Sheila Pelizzon. Most of the quotes above and their sources below are found here. If you want to read one thing to get a handle on cereal production supply chains in early modern Europe, this is it.

Jan de Vries, a retired UC Berkeley Professor, is your go-to source for Dutch economic history

Vries, Jan de (1974). Dutch Rural Economy in the Golden Age, 1500-1700. New Haven: Yale Univ. Press.

Vries, Jan de (1976). The Economy of Europe in an Age of Crisis, 1600-1750. Cambridge: Cambridge Univ. Press.

Vries, Jan de (1981). Barges and Capitalism: Passenger Transportation in the Dutch Economy, 1632- 1839. Utrecht: HES Publishers.

and especially

"The Political Economy of Bread in the Dutch Republic," in Oscar Gelderblom, ed., The Political Economy of the Dutch Republic (Ashgate Publishers, 2009).pp. 85-114.

- for a sense of grain, but not flour, as a continentally and then inter-continentally traded commodity.

I don't have a good data series for Dutch grain prices right now, but there's a comprehensive survey for Sweden in this period:

Harvests and grain prices in Sweden, 1665—1870

- that gives you a sense of how grain prices moved.

European Wind Atlas - comprehensive dataset on windspeeds in Europe, intended for electricity generating windmill developers, but good evidence for why "not enough wind" wouldn't often have been a problem in Holland.