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Froude Project Insights: Analyzing NWFS Events at GSP This Winter

The Froude Project at GSP provides an analysis of NWFS (Narrowly-Viewing Flow Systems) events using the Froude number (Fr), which is a vital indicator of wind interactions with topographical barriers. This winter season, our observations highlight the first warning-level NWFS event, with previous minor events showing Fr values of 1.5 or less. Understanding the implications of Fr, especially when approaching or dropping below 1, is critical. We consider factors like the time lag of air masses and seek community insights to enhance our forecasting efforts.

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Froude Project Insights: Analyzing NWFS Events at GSP This Winter

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  1. Froude # Project at GSP • As a reminder: • Fr = U/NH • U is the wind speed orthogonal to the barrier • N is the Brunt-Vaisala frequency • H is the height of the barrier • Fr is calculated each hour as a 850-950mb layer average • We use 320 degrees as the wind direction that is orthogonal to the mountain barrier and assume a barrier height of 3500 feet • Calculated from the GFS, NAM, RUC, local WRF, and there is also a composite Fr group • So far this winter season, no high impact NWFS events until the recent storm

  2. Froude # Project at GSP • First “warning” type of NWFS event this season • Previous (minor) events tended to have Fr values of 1.5 or less • NWFS seems to shut off completely close to 1 and below • Also have to consider the time lag of the airmass making through the upstream edit area to the upslope areas (~3 hrs?) • Would be nice to have at least one more “warning” type of event to compare to this one • Any thoughts or ideas are very welcome!

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