Pacifica
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pacifica clear sky chart from 2005-11-06 to 2024-02-25.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	10% 7% 3 5% 5% 3 4 4 6% 10% 43%	78594
	Night	11% 9% 3 6% 5% 3 4 4 5% 7% 44%	80744
Transparency	Day	25% 36% 6% 12% 14% 8%	78316
	Night	28% 35% 6% 12% 12% 8%	80544
Seeing	Day	11% 11% 28% 33% 14% 3	14446
	Night	13% 7% 16% 31% 26% 6%	23910

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 8% 3 6% 5% 3 4 4 6% 8% 39%	2763
	11th to 20th	Day	17% 9% 4 9% 7% 4 4 4 5% 5% 33%	2860
	21st to end	Day	22% 11% 4 6% 6% 3 5% 5% 5% 7% 28%	3146
February	1st to 10th	Day	18% 6% 2 5% 4 2 4 4 4 5% 45%	1710
	11th to 20th	Day	15% 8% 3 6% 4 3 4 4 6% 8% 40%	1731
	21st to end	Day	13% 8% 2 5% 4 2 4 3 5% 7% 48%	1521
March	1st to 10th	Day	17% 7% 3 6% 4 3 4 4 7% 9% 35%	1966
	11th to 20th	Day	16% 9% 3 6% 6% 2 5% 5% 5% 8% 35%	1980
	21st to end	Day	12% 6% 2 6% 5% 3 4 4 6% 8% 44%	2192
April	1st to 10th	Day	14% 7% 3 5% 5% 3 5% 5% 5% 8% 41%	2160
	11th to 20th	Day	9% 6% 3 4 4 2 3 4 5% 9% 50%	2129
	21st to end	Day	7% 5% 2 5% 3 2 4 4 6% 11% 51%	2160
May	1st to 10th	Day	6% 6% 3 5% 4 3 4 3 6% 9% 50%	2252
	11th to 20th	Day	8% 7% 3 5% 4 3 4 4 6% 10% 46%	2314
	21st to end	Day	10% 11% 3 6% 5% 3 3 5% 5% 7% 42%	2723
June	1st to 10th	Day	7% 7% 3 4 4 3 4 5% 6% 10% 46%	2520
	11th to 20th	Day	3 5% 2 4 4 2 3 3 6% 10% 58%	2520
	21st to end	Day	4 7% 3 6% 5% 3 3 4 6% 9% 48%	2520
July	1st to 10th	Day	3 9% 4 6% 5% 3 3 4 9% 15% 40%	2493
	11th to 20th	Day	4 8% 4 7% 6% 3 5% 5% 9% 15% 34%	2340
	21st to end	Day	1 7% 3 6% 6% 3 4 6% 10% 19% 36%	2546
August	1st to 10th	Day	4 11% 3 7% 8% 4 4 6% 8% 13% 32%	2328
	11th to 20th	Day	3 7% 2 6% 6% 3 4 5% 9% 15% 41%	2205
	21st to end	Day	3 7% 3 6% 6% 3 4 6% 9% 13% 39%	2376
September	1st to 10th	Day	3 5% 3 4 4 2 2 4 6% 12% 54%	2160
	11th to 20th	Day	5% 9% 3 5% 5% 3 3 5% 7% 12% 43%	2160
	21st to end	Day	4 3 1 3 4 2 3 3 6% 10% 61%	1896
October	1st to 10th	Day	5% 4 2 4 4 2 2 3 6% 8% 60%	1800
	11th to 20th	Day	9% 5% 2 5% 4 2 4 4 5% 8% 52%	1800
	21st to end	Day	9% 5% 2 4 4 2 3 4 5% 8% 53%	1980
November	1st to 10th	Day	9% 4 2 4 5% 2 4 5% 5% 9% 50%	1855
	11th to 20th	Day	10% 7% 3 5% 5% 2 5% 5% 4 7% 47%	1710
	21st to end	Day	11% 6% 3 3 4 2 3 4 4 8% 53%	1536
December	1st to 10th	Day	14% 7% 3 7% 4 3 4 4 6% 7% 43%	1520
	11th to 20th	Day	25% 11% 3 5% 5% 2 4 4 5% 6% 30%	1928
	21st to end	Day	21% 9% 3 6% 5% 3 4 4 6% 9% 32%	2794
January	1st to 10th	Night	15% 8% 3 5% 5% 3 4 5% 5% 6% 42%	4186
	11th to 20th	Night	19% 9% 4 7% 7% 4 5% 4 5% 5% 31%	4110
	21st to end	Night	22% 12% 3 7% 6% 3 4 3 4 6% 28%	4521
February	1st to 10th	Night	17% 6% 2 4 4 2 4 3 5% 6% 46%	2470
	11th to 20th	Night	12% 8% 3 6% 4 3 4 4 6% 7% 42%	2335
	21st to end	Night	13% 6% 2 5% 5% 3 3 4 5% 8% 46%	1829
March	1st to 10th	Night	18% 9% 2 5% 5% 3 4 5% 5% 5% 37%	1990
	11th to 20th	Night	16% 8% 2 6% 5% 3 4 4 5% 8% 38%	1980
	21st to end	Night	14% 8% 2 5% 4 2 4 4 3 6% 47%	2163
April	1st to 10th	Night	11% 7% 4 6% 5% 3 4 4 5% 7% 45%	1800
	11th to 20th	Night	11% 8% 2 4 4 2 3 4 4 6% 52%	1779
	21st to end	Night	6% 5% 2 4 4 3 4 4 5% 9% 55%	1800
May	1st to 10th	Night	6% 9% 2 5% 5% 2 3 3 4 7% 53%	1705
	11th to 20th	Night	5% 10% 3 7% 5% 3 4 3 3 8% 48%	1576
	21st to end	Night	10% 14% 3 5% 5% 2 3 3 3 8% 45%	1552
June	1st to 10th	Night	6% 9% 3 6% 4 3 4 4 5% 10% 46%	1440
	11th to 20th	Night	2 6% 3 4 4 3 3 3 4 8% 59%	1440
	21st to end	Night	4 10% 4 5% 5% 2 3 3 3 8% 54%	1440
July	1st to 10th	Night	2 13% 3 5% 6% 3 4 2 4 12% 48%	1462
	11th to 20th	Night	3 11% 3 7% 7% 4 5% 5% 5% 10% 41%	1620
	21st to end	Night	3 14% 5% 11% 8% 3 6% 5% 5% 7% 33%	1773
August	1st to 10th	Night	6% 20% 5% 7% 5% 3 2 4 5% 10% 34%	1611
	11th to 20th	Night	3 11% 3 10% 6% 4 5% 5% 6% 10% 37%	1696
	21st to end	Night	3 12% 3 9% 8% 4 4 5% 5% 9% 39%	1980
September	1st to 10th	Night	2 7% 2 6% 5% 2 3 5% 4 9% 55%	1800
	11th to 20th	Night	4 13% 3 5% 5% 3 3 3 5% 8% 47%	1800
	21st to end	Night	3 5% 2 5% 4 2 2 3 4 8% 62%	2059
October	1st to 10th	Night	6% 7% 2 5% 4 2 3 3 4 6% 60%	2160
	11th to 20th	Night	7% 7% 3 6% 4 3 4 3 4 6% 54%	2160
	21st to end	Night	7% 6% 2 6% 4 2 4 3 4 6% 55%	2376
November	1st to 10th	Night	9% 6% 2 5% 4 2 3 4 4 8% 51%	2222
	11th to 20th	Night	10% 6% 3 5% 4 3 4 4 5% 8% 46%	2470
	21st to end	Night	9% 4 2 4 5% 2 3 4 5% 6% 55%	2641
December	1st to 10th	Night	16% 7% 3 5% 5% 3 4 4 5% 6% 44%	2660
	11th to 20th	Night	27% 10% 3 4 4 2 4 4 5% 6% 29%	3276
	21st to end	Night	17% 8% 4 7% 6% 4 4 5% 5% 7% 34%	4862

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	31% 28% 10% 22% 6% 2	2763
	11th to 20th	Day	41% 28% 8% 10% 8% 5%	2860
	21st to end	Day	48% 25% 5% 11% 9% 3	3146
February	1st to 10th	Day	26% 34% 5% 14% 14% 7%	1710
	11th to 20th	Day	28% 37% 7% 13% 11% 4	1740
	21st to end	Day	27% 35% 6% 15% 12% 4	1521
March	1st to 10th	Day	27% 38% 8% 15% 10% 2	1966
	11th to 20th	Day	32% 37% 9% 13% 7% 2	1980
	21st to end	Day	27% 39% 8% 14% 10% 2	2192
April	1st to 10th	Day	26% 38% 8% 12% 13% 3	2160
	11th to 20th	Day	22% 37% 10% 14% 13% 4	2132
	21st to end	Day	19% 38% 7% 19% 14% 3	2160
May	1st to 10th	Day	18% 38% 6% 15% 19% 5%	2252
	11th to 20th	Day	18% 38% 6% 18% 15% 5%	2317
	21st to end	Day	22% 39% 9% 14% 15% 1	2724
June	1st to 10th	Day	24% 38% 8% 14% 14% 2	2520
	11th to 20th	Day	16% 36% 6% 12% 23% 8%	2520
	21st to end	Day	20% 37% 2 8% 21% 12%	2520
July	1st to 10th	Day	17% 38% 2 5% 16% 21%	2425
	11th to 20th	Day	23% 36% 5% 5% 16% 16%	2271
	21st to end	Day	20% 38% 3 6% 16% 17%	2405
August	1st to 10th	Day	25% 37% 2 7% 17% 12%	2312
	11th to 20th	Day	16% 35% 3 8% 22% 17%	2205
	21st to end	Day	20% 36% 3 7% 19% 15%	2376
September	1st to 10th	Day	14% 35% 2 6% 19% 24%	2160
	11th to 20th	Day	23% 37% 3 13% 17% 7%	2160
	21st to end	Day	11% 36% 3 15% 20% 15%	1896
October	1st to 10th	Day	18% 36% 5% 12% 19% 10%	1800
	11th to 20th	Day	19% 35% 6% 14% 14% 12%	1800
	21st to end	Day	19% 37% 6% 15% 12% 11%	1980
November	1st to 10th	Day	23% 42% 7% 13% 9% 6%	1855
	11th to 20th	Day	24% 41% 5% 12% 13% 5%	1710
	21st to end	Day	18% 40% 6% 12% 16% 8%	1536
December	1st to 10th	Day	22% 40% 7% 11% 14% 5%	1520
	11th to 20th	Day	42% 32% 7% 9% 8% 2	1928
	21st to end	Day	41% 29% 10% 14% 6% 1	2794
January	1st to 10th	Night	30% 28% 15% 19% 6% 2	4186
	11th to 20th	Night	42% 28% 9% 9% 7% 5%	4110
	21st to end	Night	50% 24% 5% 9% 8% 4	4521
February	1st to 10th	Night	24% 35% 6% 14% 14% 8%	2470
	11th to 20th	Night	27% 36% 8% 12% 13% 4	2337
	21st to end	Night	26% 36% 7% 17% 12% 3	1829
March	1st to 10th	Night	28% 38% 8% 13% 10% 3	1990
	11th to 20th	Night	30% 38% 6% 15% 9% 3	1980
	21st to end	Night	28% 38% 8% 13% 10% 3	2163
April	1st to 10th	Night	26% 38% 8% 14% 11% 3	1800
	11th to 20th	Night	22% 37% 7% 15% 14% 5%	1779
	21st to end	Night	18% 37% 6% 20% 14% 5%	1800
May	1st to 10th	Night	17% 37% 4 15% 19% 7%	1705
	11th to 20th	Night	22% 38% 3 14% 18% 5%	1577
	21st to end	Night	21% 38% 7% 16% 16% 1	1552
June	1st to 10th	Night	24% 38% 6% 13% 16% 3	1440
	11th to 20th	Night	16% 36% 5% 9% 23% 12%	1440
	21st to end	Night	22% 36% 2 9% 15% 16%	1440
July	1st to 10th	Night	17% 35% 3 3 17% 24%	1421
	11th to 20th	Night	24% 38% 3 5% 6% 23%	1566
	21st to end	Night	33% 37% 3 2 9% 16%	1674
August	1st to 10th	Night	29% 35% 3 6% 11% 15%	1602
	11th to 20th	Night	26% 36% 3 6% 12% 18%	1696
	21st to end	Night	23% 36% 3 5% 15% 19%	1980
September	1st to 10th	Night	16% 36% 2 4 14% 27%	1800
	11th to 20th	Night	26% 38% 3 10% 14% 9%	1800
	21st to end	Night	15% 35% 2 12% 20% 15%	2059
October	1st to 10th	Night	22% 36% 6% 10% 14% 13%	2160
	11th to 20th	Night	22% 36% 3 11% 13% 15%	2160
	21st to end	Night	20% 38% 3 14% 15% 12%	2376
November	1st to 10th	Night	22% 42% 7% 13% 9% 7%	2222
	11th to 20th	Night	21% 40% 6% 16% 11% 5%	2470
	21st to end	Night	17% 39% 6% 13% 15% 10%	2641
December	1st to 10th	Night	23% 39% 5% 12% 14% 7%	2660
	11th to 20th	Night	42% 34% 5% 9% 9% 1	3276
	21st to end	Night	41% 29% 11% 11% 6% 1	4862

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	26% 12% 28% 20% 13% 1	313
	11th to 20th	Day	19% 10% 23% 34% 13% 1	370
	21st to end	Day	14% 9% 29% 32% 14% 2	407
February	1st to 10th	Day	16% 12% 27% 26% 17% 2	370
	11th to 20th	Day	17% 17% 31% 24% 11% 1	396
	21st to end	Day	13% 16% 31% 26% 12% 2	363
March	1st to 10th	Day	20% 18% 29% 23% 9% 1	420
	11th to 20th	Day	21% 12% 28% 24% 12% 4	420
	21st to end	Day	12% 19% 33% 26% 8% 2	462
April	1st to 10th	Day	17% 17% 33% 21% 10% 2	420
	11th to 20th	Day	12% 22% 33% 23% 8% 2	412
	21st to end	Day	7% 21% 32% 25% 10% 5%	420
May	1st to 10th	Day	10% 17% 34% 27% 9% 2	423
	11th to 20th	Day	13% 15% 35% 26% 9% 2	448
	21st to end	Day	12% 16% 31% 27% 11% 2	485
June	1st to 10th	Day	8% 14% 35% 30% 11% 3	450
	11th to 20th	Day	4 12% 36% 35% 11% 2	450
	21st to end	Day	6% 7% 34% 40% 11% 2	450
July	1st to 10th	Day	8% 5% 32% 44% 10% 1	446
	11th to 20th	Day	3 4 24% 50% 17% 2	444
	21st to end	Day	5% 3 26% 50% 14% 3	487
August	1st to 10th	Day	7% 6% 30% 46% 9% 2	447
	11th to 20th	Day	4 3 28% 44% 18% 4	437
	21st to end	Day	5% 3 23% 45% 18% 4	495
September	1st to 10th	Day	5% 4 24% 40% 21% 6%	450
	11th to 20th	Day	6% 9% 28% 37% 15% 6%	450
	21st to end	Day	4 9% 25% 34% 22% 6%	450
October	1st to 10th	Day	5% 8% 26% 31% 20% 9%	450
	11th to 20th	Day	7% 10% 22% 30% 23% 8%	450
	21st to end	Day	11% 7% 22% 30% 22% 7%	495
November	1st to 10th	Day	10% 11% 22% 29% 24% 6%	451
	11th to 20th	Day	10% 8% 15% 33% 28% 7%	270
	21st to end	Day	10% 6% 27% 34% 20% 3	187
December	1st to 10th	Day	19% 11% 19% 28% 19% 4	180
	11th to 20th	Day	15% 15% 22% 32% 14% 1	180
	21st to end	Day	21% 12% 27% 30% 10% 1	198
January	1st to 10th	Night	21% 8% 14% 30% 23% 5%	760
	11th to 20th	Night	17% 7% 14% 31% 25% 6%	760
	21st to end	Night	19% 7% 13% 33% 25% 4	836
February	1st to 10th	Night	18% 7% 16% 30% 24% 4	760
	11th to 20th	Night	15% 13% 17% 30% 21% 5%	744
	21st to end	Night	15% 12% 20% 30% 20% 3	610
March	1st to 10th	Night	20% 12% 18% 25% 20% 3	720
	11th to 20th	Night	20% 7% 16% 31% 22% 4	720
	21st to end	Night	15% 9% 27% 29% 18% 2	792
April	1st to 10th	Night	13% 9% 27% 30% 17% 4	720
	11th to 20th	Night	14% 14% 23% 28% 16% 5%	711
	21st to end	Night	6% 11% 29% 28% 21% 4	720
May	1st to 10th	Night	8% 7% 26% 31% 24% 4	625
	11th to 20th	Night	9% 4 22% 32% 29% 4	514
	21st to end	Night	15% 11% 20% 32% 18% 5%	389
June	1st to 10th	Night	10% 6% 23% 33% 26% 3	360
	11th to 20th	Night	5% 6% 21% 42% 23% 3	360
	21st to end	Night	9% 3 15% 38% 31% 5%	360
July	1st to 10th	Night	7% 3 13% 40% 29% 8%	371
	11th to 20th	Night	10% 3 8% 37% 32% 10%	522
	21st to end	Night	12% 5% 8% 32% 34% 9%	591
August	1st to 10th	Night	19% 3 13% 29% 30% 7%	537
	11th to 20th	Night	10% 3 14% 34% 31% 8%	628
	21st to end	Night	8% 4 12% 36% 32% 9%	792
September	1st to 10th	Night	4 2 13% 33% 36% 12%	720
	11th to 20th	Night	10% 4 15% 32% 32% 8%	720
	21st to end	Night	4 5% 13% 29% 37% 12%	720
October	1st to 10th	Night	8% 4 13% 32% 33% 10%	720
	11th to 20th	Night	8% 5% 13% 28% 36% 11%	720
	21st to end	Night	11% 5% 11% 27% 33% 14%	792
November	1st to 10th	Night	10% 5% 14% 28% 35% 9%	740
	11th to 20th	Night	13% 3 12% 33% 32% 7%	760
	21st to end	Night	10% 7% 12% 38% 28% 5%	760
December	1st to 10th	Night	18% 8% 13% 33% 23% 6%	760
	11th to 20th	Night	25% 7% 14% 28% 21% 4	760
	21st to end	Night	21% 11% 17% 29% 20% 1	836

Page generated at 2024-02-22 03:05:42. Version ac07

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