APRIL 2001 WEATHER SUMMARY
MAJOR SOLAR ACTIVITY AND COLD!!
Another Solar tie-in? In late March through mid April, a major flare sequence occurred, and has been mentioned in a couple of places as a possible weather (tropospheric) trigger for many unusual global atmospheric dynamics noted this month, including the cold snaps out west. After an X-class flare occurred suddenly in late March ending a six month lull in activity, the largest solar flare(s) in over 25 yrs (est.) occurred on April 2. Magnitude was estimated at X-22 and had an associated CME (some key satellite instruments apparently saturate around X-18 strength, so the X-22 magnitude is subjective). Fortunately, the main jet of material was directed away from Earth, but we still received a powerful glancing blow. This event was followed by two other X-class flares on the 10th, neither of which were in highly geoeffective positions, but still impacted Earth. Our weather seems to have been impacted mostly by an intensification of our year-long pattern of much colder than normal air and it's associated moisture starved upper level systems. Rainfall for the month was a disapointing 1.11", all resulting from upper level lows that continued to track N-S down the coast then inland. Zero days with rainfall>0.5". Temps averaged on the very cool side, with a mean temp of only 50.7F. Mean temps this low are much more common in Jan./Feb. In Pacifica, during the first and second weeks, very unusual frosts (climatologically speaking but certainly not unusual this year) were everywhere. By the second week in April, it was SNOWING at 1,720 on Hiway 9. It was 30 in Napa and 31 in Santa Rosa. Air aloft (850mb) plunged to within 2C of the temps in February when record snows hit No + So Cal. Despite predictions of convection and possible snow down to 1,500-2,000', the air was so dry only a few isolated Cu evolved over the hills here. Freezing temps at sea level are extremely rare so late in the season, and agri-business has been in a tizzy over potential damage which won't be fully known for weeks. We reached our lowest temp, a chilly 40.2F on the 15th before slowly modifying for the remainder of the month. Typically, we have seen our last frost for the year by early-mid March, assuming we get any at all during the Winter. Total rain over six consecutive days (6th-11th) during this moisture starved pattern was .96". I also noted a severe storm east of Los Angeles on the 8th, that caused a 100 car pileup and regrettably one death. Solar activity remained very active (but subsiding) however a moderate, long duration C class flare occurred early in the third week . The entire month was a great laboratory for measuring the direct weather effects of solar storms, as these recent solar wind blasts came on very suddenly after a prolonged downtrend in activity. For those in the know, an excellent signal to noise ratio.
MONTHLY CLIMATOLOGICAL SUMMARY for APR. 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
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1 51.0 57.0 2:00p 47.6 11:15p 12.7 0.0 0.01 5.5 25.0 6:30p SSW
2 49.0 56.0 1:45p 44.6 11:30p 14.7 0.0 0.00 5.8 24.0 12:30a N
3 48.0 53.8 9:30a 42.9 6:15a 16.7 0.0 0.00 4.3 20.0 12:30a N
4 49.8 59.8 1:30p 42.3 3:45a 14.0 0.0 0.00 1.7 12.0 9:15a SSE
5 50.6 60.6 11:00a 44.1 12:45a 12.7 0.0 0.00 3.0 17.0 7:15p SSW
6 48.6 51.7 11:30a 45.4 12:00m 16.4 0.0 0.46 5.1 27.0 11:15a SSW
7 47.4 52.7 2:30p 44.3 6:30a 16.5 0.0 0.10 5.2 29.0 3:45p WNW
8 48.3 54.8 1:00p 43.5 12:00m 15.8 0.0 0.12 3.5 18.0 1:15p SSW
9 48.4 56.2 1:45p 42.0 5:30a 15.9 0.0 0.20 2.3 17.0 6:30p WNW
10 48.9 55.3 10:15a 42.6 5:00a 16.1 0.0 0.02 3.3 24.0 2:00p WNW
11 49.8 53.5 3:15p 46.8 12:00m 14.8 0.0 0.02 4.8 21.0 5:00p SSW
12 50.5 57.9 11:15a 41.9 4:30a 15.1 0.0 0.00 2.5 16.0 9:15p SSE
13 49.1 54.7 1:30p 45.6 11:15p 14.8 0.0 0.00 4.8 26.0 1:30p WNW
14 48.9 55.9 12:30p 42.3 4:15a 15.9 0.0 0.00 2.7 14.0 3:15p SSE
15 49.2 56.9 11:45a 40.9 4:15a 16.1 0.0 0.00 1.9 14.0 2:00p SSW
16 54.2 62.1 2:00p 44.3 2:45a 11.8 0.0 0.00 5.1 27.0 4:15p S
17 58.2 67.2 11:45a 49.9 10:45p 6.5 0.0 0.00 1.8 12.0 12:30a WSW
18 53.6 66.5 8:45a 47.5 6:15a 8.0 0.0 0.18 2.1 16.0 12:30p NW
19 51.8 57.4 12:00p 47.0 2:00a 12.8 0.0 0.00 2.9 18.0 3:45p SSW
20
21
22
23
24
25
26
27
28 53.8 59.4 12:30p 48.7 11:45p 10.9 0.0 0.00 3.7 17.0 5:15p NNW
29 53.5 65.5 8:45a 45.1 5:30a 9.7 0.0 0.00 2.8 16.0 3:30p SSW
30 53.5 59.8 2:45p 50.7 6:00a 9.8 0.0 0.00 3.0 18.0 5:15p SW
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50.7 67.2 17 40.9 15 297.7 0.0 1.11 2.6 29.0 7 SSW
Max >= 90.0: 0
Max <= 32.0: 0
Min <= 32.0: 0
Min <= 0.0: 0
Max Rain: 0.46 ON 4/06/01
Days of Rain: 7 (>.01 in) 4 (>.1 in) 0 (>1 in)
Heat Base: 65.0 Cool Base: 65.0 Method: (High + Low) / 2