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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