Tule fog — California Central Valley

11 airports · ten-year record · rebuilt daily
Tule fog is the Central Valley's dense winter radiation fog: it forms on calm, clear nights after the first autumn rains, pools in the valley floor, and can last for days — the deadliest weather hazard on California highways and the reason valley airports lose whole mornings from November through February. The table below is the ten-year airport record; the National Weather Service Hanford office publishes a seasonal Fog Severity Index for the valley and official forecasts, and every airport page here links its own terminal forecast.
September is off season — these airports together average about 0 hours below CAT I minima in September, against 397 in January, the peak month.
January: ~397 hJanFebruary: ~74 hFebMarch: ~17 hMarApril: ~1 hAprMay: ~2 hMayJune: ~0 hJunJuly: ~0 hJulAugust: ~0 hAugSeptember: ~0 hSepOctober: ~7 hOctNovember: ~149 hNovDecember: ~392 hDec
airportnamecountryfog h/yrpeakILSforecast
KVISVisalia Municipal AirportUS189Jan and DecCAT Iverifying
KMCEMerced Regional Macready FieldUS135Jan and DecCAT Iverifying
KSCKStockton Metropolitan AirportUS110Jan and DecCAT Iverifying
KSMFSacramento International AirportUS107Dec and JanCAT IIIverifying
KMODModesto City Co-Harry Sham FieldUS94Jan and DecCAT Iverifying
KFATFresno Yosemite International AirportUS88Dec and JanCAT IIIverifying
KMHRSacramento Mather AirportUS85Jan and DecCAT Iverifying
KSACSacramento Executive AirportUS73Jan and DecCAT Iverifying
KMYVYuba County AirportUS54Jan and DecCAT Iverifying
KBFLMeadows FieldUS50Dec and JanCAT Iverifying
KRDDRedding Municipal AirportUS39Dec and NovCAT Iverifying

Hours/yr = time below CAT I approach minima (visibility under ~½ mile or ceiling under 200 ft), ten-year average of hourly observations. "Forecast" shows whether the airport's calibrated Fog Atlas percentage has passed live verification; every other airport carries official guidance and climatology only.

When is tule fog season?

November through February, peaking in December and January; dense fog is rare in the valley from April to September.

Which Central Valley airport is foggiest?

See the ranked table on this page — hours per year below CAT I approach minima, ten-year average.

Machine access: data.json.

Live world fog map · all airports · by city · forecast verification · methodology · about · llms.txt. Not for operational use.