| Wind and weather regimes at Great Falls, Montana - :13637 | National Weather Service (NWS)
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Wind and weather regimes at Great Falls, Montana
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    This is a discussion of the surface wind at Great FalIs, Montana, including its seasonal and diurnal variations, and its relation to weather patterns and temperature. Methods are presented for classifying and forecasting the significant windshifts from southwesterly directions which accompany dry weather, to northerly directions which accompany the storm patterns. A convenient parameter which measures both the surface pressure gradient and the downslope effect of southwesterly winds is the difference in altimeter settings between Helena and Great FaIIs, known as the H-G gradient. Changes in this parameter accompanying windshifts are forecast by the Gulf Index System. This is based upon the idea of (I) Verifying the movement of short-waves of significant ampIitude across the west coast of Canada, and (2) Extrapolating and tracking the resultant pressure changes southeastward from the Gulf of Alaska Into Montana. The windshift at Great FaIIs occurs between 6 and 24 hours after the rising pressure at Juneau reaches a value at least 3 mbs above that of the faIIing pressure at Great FalIs. Verification data is given for 3 seasons, along with other suggestions for making wind forecasts.

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