Bay Area residents, particularly those in the North Bay, might want to keep their rain gear handy as meteorologists closely monitor a storm system brewing in the Gulf of Alaska that is anticipated to impact California later this week. According to a recent forecast, the National Weather Service (NWS) San Francisco has noted a shift to a drier pattern, but things could change towards the weekend.
With light offshore winds keeping fire danger somewhat at bay through Thursday morning, the weather focus shifts to increasing moisture that could lead to rainfall. While the drying trend prevails midweek, a "slight chance of rain for the North Bay" is on the horizon, per NWS San Francisco's issuance. However, there's a caveat: Models present a mixed bag of predictions further south, leaving the rest of the area shrouded in atmospheric ambiguity. "Please stay tuned to the forecast for the latest developments," the statement by NWS San Francisco reads, alerting to an escalated uncertainty towards the weekend.
NWS Bay Area took to social media to shed some light on these forecast variations and explain the complexities behind predicting this potential wet weather. Ensemble models work by running a set of equations to predict the weather. In some of those simulations, the NWS Bay Area post explained that the initial conditions or the model assumptions are changed slightly to account for atmospheric uncertainties. These subtle tweaks in initial states can significantly alter the projection of the storm's impact, making long-term forecasts exceedingly prone to change.
A more detailed look reveals conflicting interpretations from different models per NWS: The GFS ensemble hints at a "slightly wetter scenario," while the ECMWF ensemble conjures visions of a "drier and potentially windier outcome." This disparity sows doubt on the impending climatic conditions and carries substantial implications for fire crews. As per the recent NWS Bay Area post, Santa Rosa faces a "55% chance of measurable rain" this Sunday. However, the likelihood of surpassing 0.1 inches of rain is pegged at a mere 10%—a pivotal statistic for firefighting operations trying to forecast fire weather concerns.
Back to the weekend storm: The GFS ensemble favors a slightly wetter system, while the ECMWF ensemble shows a drier and potentially windier outcome. This leads to uncertainty over the impacts of this system to the area, especially when it comes to rain or fire weather concerns.
— NWS Bay Area 🌉 (@NWSBayArea) October 23, 2024
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