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WEATHER REVIEW FEBRUARY 2001
02/12/01
MAJOR BAY AREA SNOW EVENT!
After another 9 days of dry to start February and 15 days overall since our last rains, twin lows plummeted down the coast and brought intermittent heavy rain, thunderstorms and widespread snow down to surface levels east and north of the Bay Area between the 9th and 12th. 2.81" of rain fell here in Pacifica, with many ice pellet showers and lightning on the 10th and 11th. Both upper level lows came straight down the coast after swinging up and over a narrow ridge extending well into the arctic, similar but even more amplified than the January event. The modified-arctic-air-fueled  lows spawned intense convective activity at times, with T'storms, occasionally reaching moderate in intensity (especially on the night of the 10th).  Convective activity was noted in both the forerunning cold fronts and in squalls behind the fronts and near the vortex cores. Both upper lows intensified as they moved south into moister air, and significantly exceeded model expectations. Over 5" liquid equivalent fell in favored mountainous areas, mostly in the Santa Lucias. 3-4" was widespread in other areas, although some lowland areas, less favorable orographically, only received 1.75-2". Overall, the general snow level was 2K' for the weaker Friday event and 1K'-1.5K' for the stringer Sun/Mon. event, however snow fell in many areas at much lower elevations. Mount Hamilton, in the SE of the Bay Area, elev. 4.2K' received 30" of snow, with unofficial reports of 6' drifts. It is unknown if this is the largest single snow accumulation, but recent memory suggests it is. HiWay 17, elev 1.7K' in the Santa Cruz Mountains was closed on the morning of the 12th with 8" of snow. Many trees in the area were felled in part or whole from the weight of the snow. The entire coast mountain ridge line along freeway 280 down the Peninsula was solid white along the ridge line, often extending halfway down the mountain slopes. While I have seen/experienced a number of lower snow level events, this was by far the heaviest snow I've seen locally since the early 60's. Temps dropped to 38F in Pacifica early on the 12th, as the cold core of the second low made it's closest approach to the area but no snow was noted here. Montara Mountain, elev. 2K' in southern Pacifica received a good dusting, which lasted all day. By the 15th, a second upper level low kicked east after sliding/meandering down the coast all the way past the Mexican border. Wrap-around moisture continued in the Bay Area, keeping skies partly cloudy, but no more rain after the 12th here, although showers did develop over the valleys and points south on the 13th. Heavy  wind, rain and snow pummelled the southland,  even  heavier than up here a few days earlier. 5' (feet)of snow was reported on Mt. Blady, with widespread snow down to 3,500'.  Flash flood watches were posted for the entire SoCal coast, and some minor landslides were reported, but no major damage to speak of.  5+" of rain was reported in many locations, including downtown LA. for the entire event.

After the major cold air outflow from the arctic eased up in mid-month, a more zonal, onshore flow developed for what I believe is the first time in almost two years.  Pineapple? I 'm smelling raisins..as in winds coming from the SE.  After only as 4 day lull in the storminess (shortest dry period of the season) a cold upper low @ 45N  on the northern quadrant of a weakening parent west of Pt. Conception shifted north and west off the B.C. coast, and robbed the parent low of upper air support...hence the "stretching out" and weakening of the front. The parent low, quite weak barometrically, spun west of Pt. Conception (should be spelled Concepcion), and shifted energy  north, bringing heavy wind but only moderate rain. This first storm seemed to follow a classic "martyr" pattern...a la the sacrificial lamb that moistens up the atmosphere ahead of the holy army to follow. I don't really see a "Pineapple connection" developing----as yet. The jet(s) are still too far split, and the southern one in particular seems to be sagging south.  Persistent doldrums air south of around 25N seems to be retarding the juicing up of the upper air flow..hence minimal tropical enhancement. What seemed to be missing is a strong suppressed EPAC high flinging moisture up and over it's west/northern flank to serve as fuel for storms to the North (dirty ridges).. Note that, except for a tantalizing hint of a 1,000 mile long west-east flow north of Hawaii during the third week, (good direction, but still somewhat moisture starved), most of the cloud streams across the entire Pacific showed an "outward" bowing, evidence that weather is being produced by advancing cold air. Dirty ridges and the like, show an "inward" bowing to the cloud/moisture stream, which indicates advancing warm air packages. When a persistent dirty ridge fuels a quasi-stationary GOA low, a deep trough can develop over time along the flanks.  
An interesting observation, I was glancing at rainfall PON for the entire West coast, and the farther north you go up to B.C. the less rain PON there has been. While I would say this Winter has been anything BUT El Nino-like down here, the rainfall distribution is disturbingly El Nino-ish. Alaska has had one of the warmest/driest Winters on record, also another El Nino-like feature....yet SST's have shown no anomalous warmth, and the tropics have been extremely quiet, especially the ITCZ. I have often wondered if basic airflow changes precede SST changes, or vice-versa. When the El Nino of 1997-98 died, La Nina-like cold air brought the big chill in December '98. SST's were still warm but fading when the rain pattern shift occurred. This year, SST's are hinting of a return to El Nino conditions, but very minor changes in temps have been noted so far, but rainfall totals (not pattern) suggest otherwise. Very, very curious. So much for the progs of a "normal" Winter..ha, ha.
After nine straight days of rain (17th-25th), skies and lawns finally dried out. A seemingly endless parade of four upper level lows and numerous secondary /eddy lows belted the coast and brought intermittent rains, and occasional convection, but no sustained, heavy rains..at least to Pacifica. We totalled a respectable 4.42" for the entire period, and of the nine rain-days, the largest daily rain came on the 19th when exactly 1" fell. in 4 bursts. Elsewhere, though, especially in SoCal and the mountains south of Monterey, received heavy rains and ground was near/past saturation. Snow once again was reported in the Bay Area hills on the 23rd and 24th, however this time snow was confined to elevations >1.5- 2K' north of the central Bay Area, and rose quickly to 3,500' near Mt. Hamilton. Even though temps were generally still below normal, this rainy period featured a track with a much more west-east component and juicier air along with it. Eureka is currently 65% of normal, while here in Pacifica, our 18.6" rain to date is near normal (19-20") and approaching the low end of our normal annual rain total (yearly norm 23"-30").

                   MONTHLY CLIMATOLOGICAL SUMMARY for FEB. 2001


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  50.6  59.6   2:15p  43.7   4:45a  13.3   0.0  0.00   1.6  13.0   1:00p     E
 2  51.9  60.9   3:30p  46.0   4:30a  11.5   0.0  0.00   1.7  13.0  11:30a     N
 3  56.7  66.5   2:30p  48.2   3:00a   7.7   0.0  0.00   2.7  13.0  10:15a   NNW
 4  61.1  71.7   2:30p  53.1  10:00p   2.6   0.0  0.00   3.1  17.0  11:00a   NNE
 5  52.8  59.4   2:15p  47.3   8:15a  11.7   0.0  0.00   1.9  12.0  10:30p   SSW
 6  48.1  51.3   1:15p  45.1  12:00m  16.8   0.0  0.00   8.4  43.0   6:30p   WNW
 7  47.1  53.4   2:00p  41.7   7:00a  17.4   0.0  0.00   4.0  24.0  12:15a     N
 8  48.6  55.5   1:00p  41.4   7:45a  16.5   0.0  0.00   3.3  26.0   1:15a   NNE
 9  46.3  49.4   4:15p  43.8   8:23p  18.4   0.0  0.78  12.8  40.0   8:45a     S
10  44.7  49.0  11:28a  42.7   6:20a   0.0   0.0  0.30   8.1  26.0  12:08a     S
11  45.5  49.6   3:00p  41.8  10:19p  19.3   0.0  0.72   7.0  34.0   2:06a     S
12  42.0  44.5   5:30p  37.5   4:45a  24.0   0.0  0.43   3.3  13.0  12:34a   SSE
13  48.0  56.1   3:15p  39.6   3:00a  17.2   0.0  0.00   3.2  18.0  11:15p     N
14  48.9  53.9  12:15p  45.1   7:30a  15.5   0.0  0.00   2.4  17.0   1:15a     S
15  49.9  55.8   1:00p  45.2   1:30a  14.5   0.0  0.00   3.2  16.0   3:15p    NE
16  52.0  57.8   1:45p  47.8   1:15a  12.2   0.0  0.00   4.3  27.0   1:00p     S
17  52.4  55.7  12:15p  50.4  11:45p  11.9   0.0  0.76   5.5  30.0   6:45a     S
18  52.1  57.3   2:15p  49.9   7:15a  11.4   0.0  0.03   4.0  28.0   3:30p     S
19  51.0  55.6   1:15p  47.9   6:15a  13.3   0.0  1.00  10.0  41.0   5:15p     S
20  52.2  55.6   3:15p  50.0   4:30a  12.2   0.0  0.34   9.4  37.0   1:00a     S
21  51.8  57.0   3:30p  47.5   9:45p  12.8   0.0  0.35   6.6  41.0   2:30a     S
22  48.9  53.1   2:00p  45.7   7:15p  15.6   0.0  0.62   8.3  32.0   4:30a     S
23  46.7  52.3   2:15p  42.0   5:30a  17.8   0.0  0.08   3.8  21.0   3:00a     S
24  48.6  52.9   1:30p  41.9   6:15a  17.6   0.0  0.81   9.2  37.0   8:30a     S
25  51.3  58.0   1:15p  47.6   8:15a  12.2   0.0  0.41   4.1  24.0   1:15a     N
26  51.3  59.5   2:00p  46.2   6:15a  12.2   0.0  0.00   1.0  10.0  12:15a   WNW
27  53.4  63.4   2:45p  46.3   1:30a  10.2   0.0  0.00   2.2  15.0  11:15a   WNW
28  52.8  60.8  12:45p  45.5  12:00m  11.8   0.0  0.00   3.2  23.0   9:45a   WNW
-------------------------------------------------------------------------------------
    50.2  71.7     4    37.5    12   377.6   0.0  6.63   4.9  43.0     6       S


Max >= 90.0:  0
Max <= 32.0:  0
Min <= 32.0:  0
Min <=  0.0:  0
Max Rain: 1.00 ON  2/19/01
Days of Rain: 13 (>.01 in) 11 (>.1 in) 0 (>1 in)
Heat Base:  65.0  Cool Base:  65.0  Method: (High + Low) / 2