FEBRUARY 1999 WEATHER SUMMARY
February started out wet, as the 1st marked 12 days out of the previous 16 with measurable precip. Temps remained on the cool side (only 49.8F mean temp..the first time this year when mean temp for a full month was less than 50F). Frost and light freezes occurred early in the month when rain and winds calmed down...with fog in inland areas a persistent problem. Snow in the local hills fell down to 2K' . (This after snow to 1K' on 1/24 when a very cold trough pushed through). Heavy rain came through area on 2/5 - 2/8 as 2 cold lows embedded in a long fetch of mid-Pacific moisture pummeled the coast. North Bay Counties were harder hit, with some danger of flooding on the Napa and Russian Rivers, but rivers receded quickly once the rains quit. A classic cold front/T-Storm line hit early on 2/06, with hail, lightning and thunder, with heaviest T'storm activity in the South Bay and in Monterey area. Up to 5" rain in Santa Cruz area, though much less over the hill in San Jose. The Sierra received up to 7' in the highest elevations with 4' common at around 7K' for the event. Snow level came down to 2K' on back side of the impulse. With all the snow in the Sierra's, only flurries occurred in Reno, with no snow sticking. On 2/22, thunder associated with a cold trough and an embedded upper low occurred , ending a three day period of mostly light rain. A juicy plume of moisture had hovered over the coast most of the day on 2/20, but lack of upper air support for most of the time contributed to the low rain totals (mostly below 1" in the Bay Area-0.74" here). A basically Zonal flow pattern dominated, with ridging nudging north then mid-Pacific lows riding on 140-160kt jets beating it back down south. Some of the lows brought unusually cold air down behind them, but either lack of moisture or weak dynamics prevented the widespread gullywashers that sometimes occur in these patterns. Most of the heavy rains fell due to orographic enhancement. The last in a series of three dying troughs through here early on 3/01, following a warm front bringing drizzle , fog and light rain most of the day on 2/28. Only .08" recorded here. Warm air advecting ahead of the trough raised dewpoints to 58F, which was the highest in months. With clearing skies, temps to the mid 60's (and 70's elsewhere) are possible. This air mass is clearly warmer and more humid than what we have been experiencing almost all Fall and Winter. It is possible this signals a generic northward shift in the dividing line between wet/dry zones along the Pacific Coast. In years past, a warm, spring-like spell like this would occur between mid Dec. to mid Jan.- a sort of mid-winter break that separated our "early season" rain pattern from the "late season" pattern. This year, while the dry spell occurred right on schedule, it was much colder and lasted much longer than normal and created one of the driest periods during that time frame on record. If the current shift to warmer temps is indeed reflecting a generic shift in the pattern, we might expect below normal rain for the remainder of the late rainy season, as lows are guided farther to the north and drying occurs along the southern troughs. On the other hand, if this is just a delayed "break" in the overall Winter pattern as would normally occur much earlier in the season, a turbulent Spring might be on hand, as cold core lows will be drawn down the coast. With the basic pattern remaining quasi-zonal, I am leaning toward a dry Spring. It will take a few weeks to analyze whether our rains here are nearly over.
La Nina Update: With still almost three months to go in the rainy season, Eureka has now received 100% of their annual rain total (37") and San Francisco with 18", is also nearing annual norms (20.5") with 120% of normal to date. However, just to the south at San Francisco Airport (SFO) which typically receives almost the same rain as The City , only 80% (11.7") of normal to date has fallen and 65% of annual totals. SoCal continues less than 40% of normal to date in most areas (L.A. has received barely 4" as compared to a normal of almost 11"). The Santa Cruz area is an anomaly, as zonal flows have hovered twice over the area this Winter..and near normal rain totals have resulted in a narrow band-maybe 50-75 miles north to south. Sierra snowpack water content in the Cent Sierra (near Tahoe) was just measured at 166% of normal (over 300" of snow currently at top of Kirkwood), but the southern Sierra is only 60% or less. The northern mountains, and especially in the far NW, continue way above normal, with exceptionally hazardous conditions in Washington and the Northern Oregon Cascades. Sea Surface temps immediately off the coast continues 4-5F below normal, hovering around 51-52 degrees. Even San Diego is reporting SST's in the 50's. Water vapor imagry still shows a definate lack of activity in the ITCZ, and very dry air in the western Pacific equatorial region. Based on this alone, it seems likely La Nina will be with us at least a couple more months, and possibly longer.
MONTHLY CLIMATOLOGICAL SUMMARY for FEB. 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
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1 45.3 54.7 2:00p 39.8 3:30a 17.8 0.0 0.00 1.3 11.0 9:30a WSW
2 47.5 57.3 2:00p 40.8 2:00a 16.0 0.0 0.00 1.6 11.0 2:30p N
3 49.0 55.9 12:00p 44.6 1:30a 14.8 0.0 0.00 1.8 11.0 7:00p SSW
4 49.6 54.9 1:30p 44.6 10:00p 15.3 0.0 0.00 2.8 19.0 2:00a N
5 47.7 54.5 2:30p 42.6 3:30a 16.5 0.0 0.00 2.6 14.0 9:30a SSW
6 50.9 53.2 12:00m 48.1 12:30a 14.3 0.0 1.34 14.9 52.0 11:30a S
7 53.6 55.4 9:00a 50.9 9:30p 11.8 0.0 0.84 8.9 43.0 8:30a S
8 53.3 55.1 2:30p 51.7 12:30a 11.6 0.0 0.39 11.1 47.0 12:00m S
9 46.5 54.6 3:30a 41.1 10:00p 17.2 0.0 0.63 8.5 50.0 3:00a S
10 45.2 51.0 3:00p 40.9 8:30a 19.0 0.0 0.00 2.2 12.0 1:30p NNW
11 46.5 54.1 3:00p 40.0 2:00a 18.0 0.0 0.00 3.6 20.0 11:00a NNE
12 48.8 59.2 3:30p 43.4 6:30a 13.7 0.0 0.00 4.0 18.0 12:30p S
13 49.7 59.1 12:30p 45.4 6:00a 12.8 0.0 0.20 2.2 15.0 7:30p WNW
14 48.6 53.4 1:00p 44.0 9:00p 16.3 0.0 0.01 2.0 16.0 12:30a SSW
15 47.9 55.6 12:00p 41.1 7:30a 16.7 0.0 0.00 1.4 13.0 10:00a SSW
16 52.3 54.6 11:00p 49.0 12:30a 13.2 0.0 1.08 8.8 35.0 1:30p S
17 53.7 59.1 1:30p 47.2 9:30p 11.8 0.0 0.20 1.8 11.0 12:30a S
18 49.3 53.7 12:00p 46.0 12:00m 15.2 0.0 0.53 4.1 37.0 12:30p S
19 49.6 57.7 2:00p 42.9 8:00a 14.7 0.0 0.01 2.7 19.0 10:30a NNE
20 50.0 53.8 11:00a 46.9 12:00m 14.7 0.0 0.71 6.6 32.0 1:00p S
21 48.7 54.5 2:30p 43.6 7:00a 16.0 0.0 0.06 4.6 21.0 9:30p SSW
22 51.7 58.6 2:30p 46.4 12:00m 12.5 0.0 0.05 1.6 14.0 2:30p WSW
23 51.1 60.5 2:30p 45.7 4:30a 11.9 0.0 0.00 1.3 12.0 3:00p WSW
24 51.0 57.4 1:00p 44.1 5:00a 14.3 0.0 0.44 5.3 32.0 8:00p S
25 50.1 55.9 1:30p 46.8 6:30a 13.7 0.0 0.11 3.8 30.0 12:30a SSW
26 48.9 55.8 12:30p 42.5 5:00a 15.8 0.0 0.00 1.5 11.0 4:00p NNE
27 52.8 61.7 3:30p 45.4 12:30a 11.4 0.0 0.00 1.9 14.0 9:30a W
28 56.2 61.8 2:30p 50.5 2:30a 8.8 0.0 0.08 2.9 16.0 3:30a SSW
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49.8 61.8 28 39.8 1 405.4 0.0 6.68 4.1 52.0 6 S
Max >= 90.0: 0
Max <= 32.0: 0
Min <= 32.0: 0
Min <= 0.0: 0
Max Rain: 1.34 ON 2/06/99
Days of Rain: 14 (>.01 in) 11 (>.1 in) 2 (>1 in)
Heat Base: 65.0 Cool Base: 65.0 Method: (High + Low) / 2