The afternoon NW thermal at Shoreline Lake is a sea-breeze circulation: cool Pacific marine air enters via the Golden Gate and the San Bruno gap and is pulled down the Bay toward the hot Santa Clara Valley. Coarse forecast models miss it; this model is trained specifically on it.
A logistic-regression model trained on 10 years of METAR observations (Moffett Field as ground truth β a good day is a peak of β₯ 12 kt from the NW between 14:00 and 18:00). Inputs each morning: forecast temperature contrast between the South Valley (San Martin) and the coast (Half Moon Bay), 850 hPa wind and temperature, marine-layer inversion depth, coastal cloud observations, sea-breeze onset at SFO, persistence, and season.
The headline is the expected peak strength β for winging that matters more than a yes/no, since it decides the wing size. A regression on the same features predicts the afternoon peak to Β±1.8 kt (r = 0.67); the 5-dot scale runs too light β marginal β good β strong β send it. The GO/NO chip is the old binary call (85% accuracy vs 78% base rate). Full model history β
Data: Iowa Environmental Mesonet (METAR), Open-Meteo (forecasts, pressure levels), NDBC buoy 46012. All times shown are 24h Pacific.