SEPTEMBER 1999 MONTHLY REVIEW
2 major lightning storms highlited this month. The first, on the 8th-9th.
brought continuous activity for almost 15 hours straight in Pacifica, and
the second on the 22nd, lightning but no rain for almost 6 hrs before dawn.
By all accounts, the 8th-9th was the most intense and long lasting of
any lightning event in Bay Area history. At it's peak, the NWS reported 217
hits in a 15 minute period along a line stretching from Salinas to just north
of the Bay Area. Locally, I counted 17 hits in 1 minute around 2100 hrs on
the 8th. Lightning was observed from 6 different cells all working simultaneously
at that time all around the Bay. Massive cloud to cloud and cloud to
ground strokes were observed, with some of the cloud to cloud chaining along
the underside of the cells - one stretching from south of Half Moon Bay to
Daly City, a distance of almost 30 linear miles. Some discharges lasted for
up to 2 seconds as repeat strokes seemed to continue indefinitely. Peak intensity
locally occurred at 0430 on the 9th, culminating a virtually sleepless night,
with deafening thunder and massive cloud to ground lightning striking the
hill in back (250 yards. or so) of my house. The storm was triggered by another
of our now-typical cool cutoff lows which suddenly tapped into moisture from
dying hurricane Gregg, off Baja California. The morning of the 8th started
out clear, and satellite imagery showed only a few high clouds off Pt. Concepcion
and the typical stratus along the coast. The squall line formed in a matter
of hours along the NE edge of the low starting around 1200 hrs and by 1630
hrs, the first thunder was heard in Pacifica. Upper level air, warm
and moist, rode up and over the cool sea air below, with temps at sea
level in the 50's and high foggy conditions, but clear and temps in the mid
60's at elevations >1,000'. Heavy downpours in the area produced rains
>1", however, a meager 0.15" fell here, most in one quick burst.
Even some brief, minor street flooding was reported. One lightning
strike hit a huge tire disposal site in the Sierra foothills, and started
over 7,000,000 tires ablaze. Officials are concerned that this fire may burn
for months, as there is no current way known how to extinguish it. Many stations
in the area reported "Black Rain" as oily smoke mixed with rain to form
off-colored precip.
The second event occured almost 2 weeks later on the 22nd, as moisture from
Hurricane Hilary got trapped in the circulation of yet another cutoff low
off the SoCal coast, and brought a repeat performance of lightning which
lasted about 6 hours. No measurable rain fell here, although we get some
occassional big drops. Temperature-wise, most of the month had temps averaging
cooler than normal and close to August numbers. A highly unusual low temp
of 47.9F was noted on the 5th. September is usually the start of our warmest
period of the year, however it wasn't until the last week of the month that
we got to 80F and above (topping out at 87F on the 28th). Even with the last
5 days of above average temps (and warm nights from offshore winds), the
mean temp for the month was only 61.2F. SST has remained in the mid 50's
and appears stabilizing. 60F water is still 60 miles offshore, and La Nina
seems unwilling to break her hold on the area.
On the Flora/Fauna front, many trees have started to drop leaves
prematurely....some such as the local Elm trees are 3-4 weeks ahead of schedule.
Our local flock of Golden Crown Sparrows returned exactly to schedule on
the 28th, but not in typical numbers. Normally, the birds arrive in good
numbers quite quickly, but so far only a few have been noted on my backyard
feeder. Despite the warm temps at the end of the month, the sky has a hazy
quality to it, and conditions "feel" like Autumn. Another round of La Nina
appears set for this Winter, however with most of the residual heat from
the El Nino of two years ago now a distant memory, I think lower than normal
rains are in the offing and much below temps in the central coast regions
may bring major damage to crops and other ecologically sensitive areas.
MONTHLY CLIMATOLOGICAL SUMMARY for SEP. 1999
NAME: HOME CITY: Pacifica STATE: Ca ELEV: 540' LAT: 37.36'N LONG: 122.27'W
TEMPERATURE (°F), RAIN (in), WIND SPEED (mph)
HEAT COOL AVG
MEAN DEG DEG WIND DOM
DAY TEMP HIGH TIME LOW TIME DAYS DAYS RAIN SPEED HIGH TIME DIR
------------------------------------------------------------------------------------
1 58.7 69.6 12:30p 49.5 6:30a 5.5 0.0 0.00 2.8 16.0 5:30p S
2 62.1 71.5 2:30p 55.7 4:30a 1.4 0.0 0.00 3.2 20.0 4:00p N
3 58.2 67.0 3:00p 51.3 5:00a 5.8 0.0 0.02 2.0 12.0 1:30p NE
4 58.2 68.3 2:30p 52.4 7:30a 4.6 0.0 0.00 2.0 9.0 2:00p SSW
5 58.6 70.6 2:00p 47.9 7:00a 5.8 0.0 0.00 1.7 9.0 2:00p SSW
6 61.7 75.9 3:00p 51.1 7:30a 1.5 0.0 0.00 1.6 8.0 12:30p E
7 61.6 75.8 2:00p 51.0 7:00a 1.6 0.0 0.00 1.5 10.0 2:00p SW
8 59.4 67.6 3:00p 55.3 12:30a 3.6 0.0 0.09 2.1 18.0 10:30p WSW
9 60.0 66.5 2:00p 57.3 9:00a 3.1 0.0 0.07 3.1 22.0 2:00a W
10 61.6 72.5 2:00p 55.2 12:00m 1.2 0.0 0.00 3.8 17.0 5:00a S
11 60.9 71.2 2:00p 54.8 1:30a 2.0 0.0 0.00 2.0 12.0 2:30p SSE
12 60.7 70.9 3:00p 54.6 1:30a 2.3 0.0 0.00 1.7 11.0 3:00p W
13 60.2 67.4 2:00p 55.7 2:30a 3.4 0.0 0.00 2.1 11.0 9:00p NNW
14 57.9 62.1 2:00p 55.7 12:00m 6.1 0.0 0.00 3.3 14.0 6:00p SSW
15 56.5 60.7 11:30a 54.4 12:00m 7.4 0.0 0.00 2.6 11.0 8:00p SSW
16 58.3 67.1 1:30p 53.6 6:00a 4.7 0.0 0.00 2.2 11.0 3:00a W
17 59.4 70.1 1:00p 54.0 7:30a 3.0 0.0 0.00 1.9 10.0 11:00a W
18 58.0 66.3 2:30p 53.3 3:00a 5.2 0.0 0.00 3.4 15.0 2:30p SSW
19 60.2 67.3 2:30p 55.0 6:30a 3.8 0.0 0.00 3.5 17.0 1:00p S
20 61.4 69.0 1:00p 56.2 12:00m 2.4 0.0 0.00 2.0 12.0 4:00p S
21 59.0 67.6 1:00p 52.4 4:00a 5.0 0.0 0.00 2.0 9.0 1:30p ESE
22 59.8 67.2 1:00p 56.1 1:00a 3.4 0.0 0.00 1.7 14.0 1:00p S
23 59.2 68.7 1:30p 54.9 11:00p 3.2 0.0 0.00 1.9 18.0 11:30a SSW
24 60.3 73.4 2:00p 52.9 8:00a 1.8 0.0 0.00 1.6 10.0 1:30p W
25 60.1 71.6 3:30p 51.1 7:00a 3.7 0.0 0.00 1.6 11.0 1:00p SSE
26 65.1 84.5 1:30p 54.4 7:30a 0.0 4.4 0.00 1.7 13.0 1:00p N
27 69.6 84.8 1:30p 57.2 12:30a 0.0 6.0 0.00 2.3 20.0 1:00p SSW
28 72.3 87.1 4:00p 57.4 12:00m 0.0 7.3 0.00 2.9 23.0 11:30a SSW
29 69.0 81.2 11:00a 56.4 2:30a 0.0 3.8 0.00 1.9 14.0 8:30a SW
30 67.0 81.3 2:00p 57.7 12:00m 0.0 4.5 0.00 1.2 8.0 1:30p SW
-------------------------------------------------------------------------------------
61.2 87.1 28 47.9 5 91.3 26.0 0.18 2.2 23.0 28 SSW
Max >= 90.0: 0
Max <= 32.0: 0
Min <= 32.0: 0
Min <= 0.0: 0
Max Rain: 0.09 ON 9/08/99
Days of Rain: 3 (>.01 in) 0 (>.1 in) 0 (>1 in)
Heat Base: 65.0 Cool Base: 65.0 Method: (High + Low) / 2