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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
------------------------------------------------------------------------------------
 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
-------------------------------------------------------------------------------------
    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