Yesterday was quite pleasant in San Francisco. I walked all over the city, and, for some reason, FitBit recorded none of it.
This morning has been cool and still, wtich patchy fog near the water.
The National Weather Service (NWS) in San Francisco forecasts patchy fog in the morning and then mostly sunny day today, with a high temperature of 68 F. The winds will be light from the west-northwest, increasing to 5-9 mph from the west by this afternoon. This evening will be partly cloudy, with a low temperature of 55 F. Winds will be from the west-southwest at 8 mph.
The visible satellite imagery shows a few clouds, though the Bay Area is becoming clearer this morning. Mot of the clouds on this image are actually low fog.
The enhanced infrared satellite imagery show no thick clouds over the state this morning. These images have been excluded from today’s post.
The water vapor imagery shows a few disturbances in the jetstream, but all of them have passed south through the Bay Area, leaving us with deep moisture this morning.
The 12Z upper air sounding from San Francisco shows several nearly saturated conditions below 800 mb. There was 0.73 inches of precipitable water. There was no Convective Available Potential Energy (CAPE) and no Convective Inhibition (CINH) present in the column this morning. There was weak but deep thermal inversion and the 0-3 km average lapse rate was 2.0 C/km. This is the lowest 0-3 km average lapse rate I have ever posted on this blog.
The hodograph shows 4 kts of low-level shear and 32 kts of deep-layer shear this morning. Shear at all levels was a mix of speed and directional changes.
The surface observations (from the SPC Mesoscale Analysis Map) show cool temperatures, moderate humidity (as shown by moderate dewpoint depressions), light winds, and mostly clear skies across the state so far this morning. There are no major frontal boundaries over the state, though there is a cold front to the north and west of the Bay Area.
The surface pressure map shows that there is a slight high pressure system over northern California this morning. There are no strong pressure gradients over the state so far this morning. The RAP shows that no strong gradients are expected to develop over the next six hours.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows only weak flow over the Bay Area today. There is a trough, but it is more pronounced farther south.
The 500 mb NAM chart shows no strong vorticity advection over the state today. This chart has excluded from today’s post.
The 700 mb NAM chart shows no rapidly rising air over the state today. This chart has been excluded from today’s post.
The 850 mb NAM chart shows no strong thermal advection over the Bay Area today. This chart has been excluded from today’s post.
The Precipitation chart shows that there is little chance of precipitation today, statewide. This chart has been excluded from today’s post.
Overall, today will be a mild and still day over the Bay Area. The Cold Air Advection (CAA) was not that strong yesterday, though the temperature was a little cooler last night as compred to the night before. Tonight will be a little colder, not because of CAA, but because of the mostly clear skies this evening.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC