Golden Gate Weather Services

In answer to numerous questions, yes it has been warmer than normal this July in the San Francisco Bay Area. But it is nowhere near record territory. As an intermediate point between the cool coast and hot interior valleys, San Jose works well as a single summertime temperature metric.

Through yesterday, San Jose's mean maximum temperature for the month was 84.3 degrees, or 2.4 degrees above the July normal of 81.9 degrees. It is interesting to note, that the last time San Jose had an above normal July was in 2006, a year when the average maximum was 85.2. The record was 1996 when the mean maxima was 87.2 degrees. Given forecast temperatures of a few degrees above normal for the remainder of the month, this year's numbers will edge up slightly.


Likewise, San Jose has had five days of 90 degrees or greater and will probably add a couple more days by the end month. The normal number of July 90 degree days is four. The record for 90 degree days is 12, set in 2006.  


Jan Null, CCM
Certified Consulting Meteorologist
Golden gate Weather Services
Phone: (408) 379-7500
Email: jan.null@sjsu.edu

This Friday, June 30th, marks the end of a rather remarkable California rainfall season. Here are some of the numbers highlighting the past very wet 12 months.

Jan Null, CCM
Golden Gate Weather Services
http://ggweather.com
@ggweather

With the warm weather I’ve been hearing about LOTS of really hot outlier temperatures being reported from car thermometers; and their owners wondering why they’re so different from official temperature reports. To clarify, let’s look first at how the official temperatures are measured.

There are four general guidelines for accurately measuring air temperatures.
- The thermometer must be outside of direct sunlight., otherwise you are measuring the sun’s intense shortwave energy and not the air temperature.
- It should also be in a well ventilated environment that’s representative of surrounding air, not in an enclosed area.
- Official temperatures are taken at about 5 feet above a natural surface and not a heat-retaining surface like concrete or asphalt. There can be as much as a 25 degree difference between air right above the ground and that at 5 feet.

- And measurements should also be far enough away from other heat emitting sources like walls and vehicles as to not be biased.

Conversely, the thermometers on most cars violate just about every one of the above guidelines. They are usually located under the front grillwork or adjacent body panel, only a foot or two above the highway or parking lot. Especially when a car has been sitting it is measuring the air heated by the parking surface plus any residual heat being given off by the vehicle itself. Even when a car is moving the temperature readings are upwardly biased by the heat given off by the roadway and the vehicle. It’s been my experience that car outside temperatures at startup on a warm day can be more than 10 degrees to toasty, and even while they seem generally to be at least 5 degrees too warm.


Similarly, the readings from locations like bank thermometers and some backyard thermometers don’t do a good job of accurately capturing the air temperature for some of the same reasons.

So when you next start up your car and see a dashboard outside temperature reading of 120° you can take solace in the fact that it’s probably only 105°!

Jan Null, CCM
Golden Gate Weather Services

No, it's NOT yet the End of the Rainfall Season!!

Despite proclamations by several individuals, the most recent rainfall does NOT mark the end of California's rainfall season. Yes, the amounts drop off significantly as we transition into late spring and summer, but climatologically it would be quite unusual not to have rain in May and June. For example, the last time that San Francisco had zero rain for the months of May and June was in 1978!

Below are the normal rainfall amounts and the normal number of days of rain across California for May and June.


Jan Null, CCM
Golden Gate Weather Services
http://ggweather.com
jnull@ggweather.com

It's time to take a quick look back at the good, the bad and the ugly of the CPC Winter Precipitation and Temperature Outlooks from this past winter. Because of the probabilistic nature of this outlooks this review, like previous reviews, is very subjective. But at least in the West, when their sub-headline for the just finished winter was "Drought expected to persist in California" followed the previous winter's busted above normal El Niño forecast, the efficacy of the product certainly needed scrutiny. See or details CPC Winter 2016-17 Seasonal and Monthly Precipitation and Temperature Outlooks in Review:




Jan Null, CCM
Golden Gate Weather Services
jnull@ggweather.com