It actually rained in The City today (San Francisco, CA)… not very much just 0.02″. It did, however, set a record for today, since it has never rained in recorded weather history on July 18th.

From today’s area forecast discussion:

bq.. IT HAS BEEN A RECORD SETTING MORNING. DOWNTOWN SAN FRANCISCO HAS HAD 0.02 INCHES OF RAIN THIS MORNING…WHICH IS A RECORD FOR THIS DATE. THE PREVIOUS RECORD FOR DOWNTOWN SAN FRANCISCO WAS…ZERO! RECORDS HAVE BEEN KEPT FOR DOWNTOWN SAN FRANCISCO FOR MORE THAN 150 YEARS! LIGHT TO MODERATE RAIN HAS FALLEN LAST NIGHT AND THIS MORNING ACROSS MOST OF THE BAY AREA NORTH OF SAN JOSE. RAINFALL TOTALS HAVE BEEN MORE THAN 0.2 OF AN INCH IN PLACES OF THE NORTH BAY…WITH 0.1 INCHES OR LESS ACROSS THE BAY AREA…AND EVEN UP TO 0.02 INCHES IN LA HONDA AND BEN LOMOND.

p.. Here’s the doppler radar image showing the system a little later in the day.

And the 1 KM visible satellite image.

The “Day Forest Fire”:1 down in Southern California is a big one. So far it was burned 74,052 acres. How big is that? Check out the yesterday’s smoke blotting out the sky around Santa Barbara, California.

The fire is so large that it shows up on the IR satellite image too.

[1(Incident Information System on the Day fire)]http://www.inciweb.org/incident/475/

Here’s a classic example of coastal fog in central/northern California.

From this “MODIS”:1 near real-time satellite image, you can see the stratus clouds (aka, fog) being pushed down the coast from the northwest to the southeast. The afternoon weather is great if you live in a south-facing area like parts of Marin county and or Santa Cruz, but not so good for north- or west-facing areas such as the western parts of San Francisco… unless you really like fog that is.

I don’t know the exact time this photo was taken, but it was probably in the afternoon, since most of the coast was foggy yesterday morning with clearing on parts of the coast in the afternoon.

[2(Wikipedia on the Santa Cruz Mountains)]http://en.wikipedia.org/wiki/Santa_Cruz_Mountains

[1(MODIS image homepage)]http://rapidfire.sci.gsfc.nasa.gov/subsets/

Yup… gonna snow locally again this weekend. The weather models have been predicting this for about a week now; pretty much indicating a sure thing in the weather prediction business.

Here’s what the National Weather Service says about this weekend from this afternoon’s “area forecast discussion”:1 for the Bay Area.

bq.. NO DOUBT THE BIG STORY HERE WILL ONCE AGAIN BE VERY LOW SNOW LEVELS ESPECIALLY FOR MID MARCH. BY 18Z FRIDAY THE GFS HAS 700MB TEMPS OF -15 WITH 1000-500MB THICKNESS VALUES AROUND 525 DM. THIS TRANSLATES TO A SNOW LEVEL OF AT LEAST 2000 FEET…POSSIBLY LOWER. BY SATURDAY MORNING ANOTHER REINFORCING SHOT OF COLD AIR DROPS DOWN WITH 700 MB TEMPS TO -16 (VERY COLD) AND 1000-500MB THICKNESS TO AROUND 523 DM. IN CONVECTIVE SHOWERS AT NIGHT OR EARLY MORNING THIS COULD BRING SNOW LEVELS TO NEAR SEA LEVEL.

p. Again, Z is Greenwich Mean Time, MB is millibars, DM is decameters and temperatures are in degrees Celsius. The 1000-500MB thickness is a good proxy for how cold the air will be from the surface up to 500MB of pressure. Cold air is denser than warm air, so cold air will have a lower 1000-500MB heights. 525MB height is pretty low… especially for March.

What is driving the potential for snow this weekend? Well, it’s artic air being driven down from Alaska. Here’s an animated image of the 850MB temperatures (which correlate strongly to surface temperatures) from Wednesday to late on Friday.

[1(Bay Area AFD)]http://www.srh.noaa.gov/fwd/productviewnation.php?pil=MTRAFDMTR&version=0

The other day I wrote a post that linked to the “W6BUL-5″:1 lightning-detection page. I was curious how this apparent hobbyist meteorologist had built a lightning-detector/display application. Searching on the term “stormvue” (which is displayed as the W6BUL-5 lightning-detection application loads) brings up “Astrogenic Systems”:2 as the first hit on Google.

One of the products that Astrogenic sells is called “StormVue”:3 which is designed to work with “Boltek lightning detectors”:4 (Stormvue is the front end of Astrogenic’s NexStorm application that runs $135).

Boltek makes a product called “StormTracker”:5 which is a $500 PC-based lightning detector antenna/PC-card solution. In Boltek’s words…

bq.. Boltek’s StormTracker uses state-of-the-art technology to make real-time lightning detection affordable. How does the StormTracker work? The StormTracker is an add-on to your IBM PC or compatible computer allowing you to not only tell if lightning is near but see where it is. StormTracker detects lightning strikes up to 300 miles away and plots them in real time on a map of your area.

StormTracker’s antenna is a small black box (3″x2″x1-1/2″) which may be mounted indoors (in a wood framed house for example) or outdoors. The antenna is typically mounted ten to twenty feet above the ground, away from large metal objects and sources of electrical noise such as televisions and computer monitors.

p.

A variety of third-party applications are designed to work with StormTracker including Astrogenic’s StormVue/NexStorm.

Pretty essoteric, but it’s pretty amazing what is possible with technology these days. I mean, who would have thought that for around $600 you could create your own real time, web-based lightning-detection application?

[5(StormTrackers homepage)]http://www.boltek.com/stracker.htm

[4(Bolteks homepage)]http://www.boltek.com/default.htm

[3(Stormvues homepage)]http://www.astrogenic.com/stormvue.html

[2(Astrogenics homepage)]http://www.astrogenic.com/

[1(W6BUL-5 lightning detection page for California)]http://members.dslextreme.com/users/eltorodelrio/Lightning/StormVue.html