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 2024-10-25.

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	8% 7% 2 6% 4 4 4 3 6% 9% 45%	101004
	Night	10% 10% 3 7% 4 4 4 3 4 7% 45%	98040
Transparency	Day	17% 48% 4 11% 11% 8%	100766
	Night	21% 49% 4 9% 9% 7%	97868
Seeing	Day	10% 11% 28% 33% 14% 3	15420
	Night	13% 7% 16% 31% 26% 6%	24732

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% 4 4 4 3 6% 7% 39%	2763
	11th to 20th	Day	17% 9% 4 10% 6% 5% 3 3 5% 5% 33%	2860
	21st to end	Day	22% 11% 3 7% 5% 4 5% 3 5% 7% 28%	3146
February	1st to 10th	Day	17% 7% 2 6% 3 3 5% 3 5% 5% 45%	1710
	11th to 20th	Day	14% 8% 2 7% 3 4 4 3 6% 8% 40%	1731
	21st to end	Day	12% 8% 2 6% 3 3 4 3 5% 7% 47%	1570
March	1st to 10th	Day	14% 9% 4 9% 6% 6% 5% 4 6% 7% 28%	3428
	11th to 20th	Day	10% 6% 2 5% 4 4 3 3 6% 9% 47%	3490
	21st to end	Day	13% 8% 2 8% 6% 5% 5% 4 7% 9% 34%	3851
April	1st to 10th	Day	13% 8% 2 6% 4 4 4 4 5% 8% 42%	2280
	11th to 20th	Day	9% 7% 3 5% 4 3 3 4 6% 9% 49%	2249
	21st to end	Day	7% 6% 2 5% 3 3 3 3 7% 11% 51%	2280
May	1st to 10th	Day	6% 4 2 4 2 2 2 2 4 6% 65%	3970
	11th to 20th	Day	5% 5% 2 4 3 4 4 4 7% 12% 50%	4097
	21st to end	Day	6% 11% 2 6% 5% 3 3 3 5% 6% 52%	4813
June	1st to 10th	Day	7% 8% 2 5% 4 4 4 4 6% 10% 46%	2660
	11th to 20th	Day	2 5% 2 4 3 3 3 3 6% 10% 58%	2660
	21st to end	Day	4 7% 3 7% 4 4 3 4 6% 9% 49%	2660
July	1st to 10th	Day	1 6% 2 4 2 3 2 2 6% 10% 61%	4367
	11th to 20th	Day	2 5% 3 7% 5% 5% 5% 4 8% 17% 39%	4110
	21st to end	Day	1 11% 3 7% 6% 7% 5% 4 8% 14% 33%	4455
August	1st to 10th	Day	3 9% 4 9% 9% 9% 7% 5% 9% 14% 22%	4091
	11th to 20th	Day	1 8% 3 7% 5% 4 3 3 6% 12% 47%	3855
	21st to end	Day	2 7% 3 7% 5% 5% 4 5% 8% 13% 42%	4180
September	1st to 10th	Day	3 6% 2 5% 4 3 3 3 6% 12% 54%	2280
	11th to 20th	Day	5% 9% 3 6% 4 4 3 4 7% 13% 42%	2280
	21st to end	Day	4 3 1 3 3 3 3 3 6% 10% 61%	2000
October	1st to 10th	Day	5% 4 2 5% 3 3 2 3 6% 8% 61%	1900
	11th to 20th	Day	8% 6% 2 5% 4 4 3 3 6% 8% 52%	1900
	21st to end	Day	9% 5% 2 5% 3 3 2 3 5% 8% 53%	2025
November	1st to 10th	Day	9% 5% 2 5% 3 4 4 4 6% 8% 50%	1855
	11th to 20th	Day	10% 8% 3 6% 4 4 4 4 5% 7% 46%	1710
	21st to end	Day	10% 7% 2 4 3 2 3 4 5% 7% 53%	1536
December	1st to 10th	Day	14% 7% 3 7% 4 4 4 3 6% 7% 43%	1520
	11th to 20th	Day	25% 11% 3 6% 4 3 4 3 5% 6% 30%	1928
	21st to end	Day	20% 9% 3 7% 4 4 4 3 6% 8% 32%	2794
January	1st to 10th	Night	15% 8% 3 6% 4 4 4 4 5% 6% 41%	4186
	11th to 20th	Night	19% 10% 4 9% 6% 6% 5% 3 5% 5% 31%	4110
	21st to end	Night	22% 13% 3 9% 5% 4 4 3 4 6% 28%	4521
February	1st to 10th	Night	16% 7% 2 5% 4 3 4 3 5% 6% 46%	2470
	11th to 20th	Night	12% 9% 3 7% 4 4 4 4 6% 7% 42%	2335
	21st to end	Night	13% 7% 2 6% 4 3 3 3 5% 8% 46%	1884
March	1st to 10th	Night	14% 11% 3 8% 5% 5% 5% 4 6% 6% 33%	3442
	11th to 20th	Night	12% 8% 3 5% 4 3 3 2 4 6% 49%	3490
	21st to end	Night	14% 14% 3 8% 5% 3 4 4 4 6% 34%	3801
April	1st to 10th	Night	10% 8% 3 6% 4 4 4 3 5% 7% 45%	1900
	11th to 20th	Night	11% 8% 2 5% 3 3 3 3 4 6% 51%	1879
	21st to end	Night	5% 6% 2 4 4 4 3 4 5% 9% 54%	1900
May	1st to 10th	Night	6% 7% 2 4 3 2 2 2 3 4 64%	3001
	11th to 20th	Night	3 10% 5% 8% 4 6% 2 2 3 6% 51%	2802
	21st to end	Night	5% 11% 2 4 3 2 2 2 3 5% 62%	2762
June	1st to 10th	Night	5% 9% 3 7% 4 4 4 3 5% 11% 45%	1520
	11th to 20th	Night	2 7% 3 5% 3 4 3 2 4 7% 60%	1520
	21st to end	Night	4 10% 4 6% 4 4 2 2 3 9% 53%	1520
July	1st to 10th	Night	1 8% 3 4 3 2 2 1 3 8% 64%	2590
	11th to 20th	Night	2 11% 4 10% 5% 5% 4 3 4 6% 45%	2860
	21st to end	Night	1 26% 4 9% 5% 4 4 3 4 7% 32%	3109
August	1st to 10th	Night	4 22% 12% 11% 5% 3 2 2 4 7% 26%	2848
	11th to 20th	Night	2 14% 3 7% 4 5% 5% 3 4 7% 48%	2990
	21st to end	Night	2 14% 3 9% 6% 5% 4 4 4 7% 42%	3498
September	1st to 10th	Night	2 8% 2 7% 5% 3 4 4 5% 9% 53%	1900
	11th to 20th	Night	5% 13% 3 6% 4 4 4 2 5% 8% 46%	1900
	21st to end	Night	3 5% 2 6% 4 3 2 2 4 8% 61%	2175
October	1st to 10th	Night	5% 7% 2 5% 3 3 3 3 4 5% 60%	2280
	11th to 20th	Night	6% 8% 3 6% 4 4 3 2 4 6% 54%	2280
	21st to end	Night	7% 6% 2 6% 4 3 4 3 4 6% 55%	2436
November	1st to 10th	Night	9% 7% 2 6% 3 3 3 3 5% 8% 51%	2222
	11th to 20th	Night	10% 7% 3 6% 4 4 4 4 6% 8% 46%	2470
	21st to end	Night	9% 5% 1 4 5% 3 3 3 5% 6% 55%	2641
December	1st to 10th	Night	15% 7% 3 6% 4 3 4 3 5% 6% 43%	2660
	11th to 20th	Night	27% 11% 3 5% 4 3 4 3 5% 6% 29%	3276
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 4 5% 6% 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	27% 40% 7% 21% 4 1	2763
	11th to 20th	Day	43% 39% 7% 7% 2 2	2860
	21st to end	Day	38% 42% 4 11% 4 1	3146
February	1st to 10th	Day	18% 65% 3 7% 5% 1	1710
	11th to 20th	Day	17% 64% 2 7% 7% 3	1740
	21st to end	Day	11% 65% 4 12% 5% 2	1570
March	1st to 10th	Day	36% 44% 5% 7% 7% 1	3428
	11th to 20th	Day	13% 41% 8% 20% 8% 9%	3490
	21st to end	Day	27% 46% 9% 14% 4 1	3851
April	1st to 10th	Day	15% 65% 4 9% 7% 1	2280
	11th to 20th	Day	10% 65% 6% 11% 7% 1	2252
	21st to end	Day	8% 66% 6% 10% 9% 1	2280
May	1st to 10th	Day	10% 40% 8% 19% 15% 8%	3970
	11th to 20th	Day	12% 39% 5% 15% 24% 6%	4100
	21st to end	Day	13% 47% 3 16% 19% 1	4814
June	1st to 10th	Day	8% 65% 4 11% 9% 3	2660
	11th to 20th	Day	6% 65% 3 10% 13% 3	2660
	21st to end	Day	10% 63% 1 4 12% 9%	2660
July	1st to 10th	Day	9% 35% 1 4 10% 42%	4299
	11th to 20th	Day	13% 36% 2 7% 15% 26%	4041
	21st to end	Day	19% 35% 3 7% 18% 17%	4315
August	1st to 10th	Day	27% 37% 4 12% 14% 6%	4076
	11th to 20th	Day	18% 37% 2 8% 25% 10%	3894
	21st to end	Day	16% 38% 4 13% 17% 11%	4179
September	1st to 10th	Day	10% 60% 1 8% 13% 9%	2280
	11th to 20th	Day	12% 60% 2 10% 11% 5%	2280
	21st to end	Day	9% 59% 2 11% 13% 6%	2000
October	1st to 10th	Day	6% 59% 2 8% 13% 13%	1900
	11th to 20th	Day	13% 59% 4 6% 10% 8%	1900
	21st to end	Day	11% 60% 4 8% 9% 8%	2025
November	1st to 10th	Day	8% 58% 4 15% 10% 4	1855
	11th to 20th	Day	17% 59% 4 10% 7% 2	1710
	21st to end	Day	15% 60% 4 7% 11% 3	1536
December	1st to 10th	Day	20% 60% 4 7% 4 4	1520
	11th to 20th	Day	32% 48% 3 5% 8% 3	1928
	21st to end	Day	30% 39% 7% 15% 8% 2	2794
January	1st to 10th	Night	25% 39% 13% 16% 4 2	4186
	11th to 20th	Night	41% 40% 8% 5% 3 2	4110
	21st to end	Night	42% 40% 4 8% 5% 2	4521
February	1st to 10th	Night	18% 64% 4 7% 5% 3	2470
	11th to 20th	Night	16% 64% 3 7% 7% 3	2337
	21st to end	Night	11% 65% 4 14% 5% 2	1884
March	1st to 10th	Night	31% 48% 7% 7% 7% 1	3442
	11th to 20th	Night	17% 42% 5% 14% 14% 8%	3490
	21st to end	Night	31% 47% 6% 12% 4 1	3801
April	1st to 10th	Night	14% 65% 4 9% 7% 1	1900
	11th to 20th	Night	13% 65% 4 10% 6% 2	1879
	21st to end	Night	10% 66% 4 10% 7% 2	1900
May	1st to 10th	Night	13% 42% 6% 17% 14% 9%	3001
	11th to 20th	Night	20% 40% 7% 7% 15% 11%	2803
	21st to end	Night	13% 43% 4 20% 19% 1	2762
June	1st to 10th	Night	13% 65% 1 7% 11% 3	1520
	11th to 20th	Night	9% 64% 2 8% 13% 3	1520
	21st to end	Night	10% 63% 1 3 11% 12%	1520
July	1st to 10th	Night	13% 35% 1 3 5% 43%	2549
	11th to 20th	Night	23% 36% 1 3 6% 30%	2806
	21st to end	Night	30% 36% 2 12% 20%	3011
August	1st to 10th	Night	40% 39% 1 4 11% 5%	2839
	11th to 20th	Night	20% 37% 6% 29% 8%	3017
	21st to end	Night	22% 39% 4 6% 16% 12%	3498
September	1st to 10th	Night	13% 60% 2 5% 12% 9%	1900
	11th to 20th	Night	13% 60% 2 9% 10% 6%	1900
	21st to end	Night	11% 59% 2 10% 10% 8%	2175
October	1st to 10th	Night	7% 59% 1 5% 12% 15%	2280
	11th to 20th	Night	13% 60% 3 7% 8% 9%	2280
	21st to end	Night	13% 60% 3 8% 8% 9%	2436
November	1st to 10th	Night	11% 58% 3 13% 10% 5%	2222
	11th to 20th	Night	16% 60% 4 12% 7% 3	2470
	21st to end	Night	14% 60% 4 9% 9% 4	2641
December	1st to 10th	Night	20% 60% 5% 7% 5% 4	2660
	11th to 20th	Night	31% 50% 3 6% 8% 3	3276
	21st to end	Night	30% 40% 9% 14% 7% 2	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% 30% 26% 12% 2	382
March	1st to 10th	Day	22% 17% 28% 23% 9% 1	460
	11th to 20th	Day	20% 12% 27% 24% 13% 4	460
	21st to end	Day	14% 19% 32% 26% 8% 1	506
April	1st to 10th	Day	16% 17% 32% 21% 10% 2	460
	11th to 20th	Day	13% 21% 31% 24% 9% 3	452
	21st to end	Day	7% 20% 33% 25% 10% 5%	460
May	1st to 10th	Day	10% 17% 34% 27% 10% 2	463
	11th to 20th	Day	12% 14% 34% 29% 9% 2	488
	21st to end	Day	12% 15% 30% 27% 13% 2	529
June	1st to 10th	Day	8% 13% 36% 30% 11% 3	490
	11th to 20th	Day	4 12% 37% 35% 11% 2	490
	21st to end	Day	6% 7% 35% 40% 11% 2	490
July	1st to 10th	Day	8% 5% 30% 45% 12% 1	486
	11th to 20th	Day	2 4 25% 51% 16% 2	484
	21st to end	Day	5% 3 27% 50% 13% 3	531
August	1st to 10th	Day	7% 6% 30% 47% 9% 2	487
	11th to 20th	Day	4 5% 30% 41% 16% 3	477
	21st to end	Day	5% 4 23% 44% 18% 5%	539
September	1st to 10th	Day	5% 3 26% 39% 21% 6%	490
	11th to 20th	Day	7% 11% 27% 36% 15% 5%	490
	21st to end	Day	4 9% 25% 34% 23% 5%	490
October	1st to 10th	Day	5% 8% 26% 31% 21% 9%	490
	11th to 20th	Day	8% 10% 23% 30% 22% 8%	490
	21st to end	Day	11% 7% 23% 30% 22% 7%	514
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	14% 12% 20% 31% 20% 3	628
March	1st to 10th	Night	20% 13% 18% 26% 19% 3	760
	11th to 20th	Night	20% 8% 16% 31% 21% 4	760
	21st to end	Night	15% 10% 27% 28% 17% 2	836
April	1st to 10th	Night	13% 9% 27% 31% 17% 4	760
	11th to 20th	Night	14% 14% 22% 28% 17% 4	751
	21st to end	Night	6% 11% 28% 29% 21% 4	760
May	1st to 10th	Night	8% 7% 26% 31% 24% 4	659
	11th to 20th	Night	9% 4 22% 33% 30% 3	543
	21st to end	Night	14% 10% 19% 33% 18% 4	411
June	1st to 10th	Night	10% 6% 23% 34% 25% 3	380
	11th to 20th	Night	4 7% 22% 42% 22% 3	380
	21st to end	Night	9% 3 16% 38% 30% 4	380
July	1st to 10th	Night	7% 3 13% 42% 28% 7%	393
	11th to 20th	Night	9% 3 9% 38% 31% 10%	552
	21st to end	Night	12% 5% 9% 33% 33% 8%	624
August	1st to 10th	Night	19% 3 13% 30% 29% 6%	567
	11th to 20th	Night	10% 3 16% 34% 30% 8%	664
	21st to end	Night	8% 4 12% 37% 31% 9%	836
September	1st to 10th	Night	4 2 14% 33% 36% 11%	760
	11th to 20th	Night	10% 5% 16% 31% 31% 7%	760
	21st to end	Night	4 5% 13% 30% 37% 11%	760
October	1st to 10th	Night	8% 4 13% 32% 33% 10%	760
	11th to 20th	Night	8% 5% 14% 28% 35% 10%	760
	21st to end	Night	10% 5% 11% 28% 33% 14%	812
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 2024-10-22 17:21:06. Version ac07

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