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