A windy evening this last Sunday. Winds at KSQL were 20+KTS and KSFO were 27G40. These high winds were due to a strong pressure gradient in the area as observed by very closely spaced isobar lines on this surface analysis chart.Each line represents a 4 mb difference in pressure. ATIS reports between KSFO and KSAC were confirming that large difference in pressure. KSFO 29.75 vs KSAC 29.58. Converting that to millibar (mbar) yields a 5.8 mbar difference. The delta between KHAF and KSAC was even larger at 7.5 mbar. The NWS aviation forecaster had this to say: IMPRESSIVE SURFACE GRADIENTS LOCALLY SFO-SAC RANGING FROM 5 TO 5.7 MB AND HAF-SFO 2.7 MB THIS EVE. SLIGHTLY LARGER SCALE PRESSURE GRADIENTS ACROSS THE AREA ARE NOT SUPPORTIVE OF PRESENT MEASURED WIND SPEEDS SO THE TREND HAS BEEN FOR LOW TO MID LEVEL WINDS TO LINK UP TO SURFACE WINDS BRINGING STRONG WIND GUSTS DOWN TO THE SURFACE. VICINITY OF KSFO...IMPRESSIVE WIND GUSTS PEAKING NEAR 50 MPH THIS EVE.
