PICO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PICO clear sky chart from 2005-11-06 to 2026-02-16.

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	12% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	130883
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 41%	130229
Transparency	Day	43% 4 12% 25% 15% 2	134443
	Night	43% 4 11% 24% 16% 2	134745
Seeing	Day	15% 10% 26% 26% 17% 6%	17345
	Night	17% 10% 29% 30% 14% 1	27291

By Month

Percentage Cloud Cover SE (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	12% 10% 6% 13% 6% 5% 4 3 5% 6% 30%	4691
	11th to 20th	Day	8% 10% 4 11% 8% 9% 7% 5% 5% 5% 28%	4710
	21st to end	Day	16% 16% 5% 11% 6% 4 4 3 4 4 27%	5794
February	1st to 10th	Day	15% 12% 5% 9% 6% 4 4 3 5% 6% 30%	1948
	11th to 20th	Day	14% 11% 3 8% 7% 5% 4 4 5% 8% 31%	1998
	21st to end	Day	16% 12% 3 7% 5% 4 4 2 5% 5% 35%	1650
March	1st to 10th	Day	16% 14% 3 6% 3 3 3 2 3 5% 41%	4480
	11th to 20th	Day	9% 10% 2 5% 3 3 4 4 6% 8% 47%	4791
	21st to end	Day	16% 11% 4 8% 5% 5% 5% 4 5% 7% 31%	5918
April	1st to 10th	Day	13% 8% 3 7% 6% 4 5% 4 6% 8% 36%	2400
	11th to 20th	Day	16% 9% 3 7% 4 4 4 3 4 6% 40%	2374
	21st to end	Day	18% 7% 2 6% 5% 5% 4 3 5% 7% 37%	2400
May	1st to 10th	Day	17% 8% 2 7% 5% 5% 5% 4 7% 11% 29%	5816
	11th to 20th	Day	16% 8% 3 6% 4 4 4 3 6% 8% 37%	6077
	21st to end	Day	10% 7% 3 7% 5% 6% 5% 4 7% 8% 37%	6935
June	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 7% 9% 46%	2800
	11th to 20th	Day	8% 5% 2 5% 5% 4 5% 4 6% 9% 48%	2800
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 4 7% 10% 43%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	6360
	11th to 20th	Day	7% 7% 3 8% 5% 6% 6% 5% 8% 11% 36%	6360
	21st to end	Day	9% 6% 3 6% 5% 5% 5% 5% 8% 11% 36%	6924
August	1st to 10th	Day	8% 3 1 4 3 3 4 4 7% 10% 53%	4139
	11th to 20th	Day	9% 5% 2 7% 5% 4 6% 5% 7% 10% 41%	3849
	21st to end	Day	5% 4 2 6% 4 4 5% 4 7% 11% 49%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 8% 48%	2400
	11th to 20th	Day	8% 5% 3 5% 3 4 5% 4 5% 6% 51%	2309
	21st to end	Day	9% 6% 2 5% 4 4 3 4 5% 7% 52%	2200
October	1st to 10th	Day	9% 5% 1 5% 3 4 3 3 5% 7% 54%	2103
	11th to 20th	Day	14% 6% 2 6% 3 3 4 3 5% 6% 47%	2000
	21st to end	Day	18% 7% 2 6% 4 3 3 3 4 6% 42%	2072
November	1st to 10th	Day	10% 7% 2 5% 4 3 3 3 5% 6% 52%	1852
	11th to 20th	Day	15% 9% 3 6% 4 3 3 4 5% 7% 42%	1890
	21st to end	Day	15% 12% 4 8% 5% 4 3 3 5% 4 37%	1883
December	1st to 10th	Day	8% 10% 4 7% 5% 3 3 3 5% 6% 46%	2690
	11th to 20th	Day	14% 11% 5% 11% 5% 5% 5% 3 5% 6% 29%	3088
	21st to end	Day	25% 17% 5% 12% 5% 4 3 3 3 4 18%	4070
January	1st to 10th	Night	13% 12% 5% 11% 5% 4 4 3 4 6% 35%	8232
	11th to 20th	Night	9% 12% 5% 11% 5% 5% 7% 4 4 5% 32%	8280
	21st to end	Night	16% 11% 5% 9% 5% 4 4 3 4 5% 32%	8404
February	1st to 10th	Night	16% 11% 4 9% 6% 5% 4 3 5% 6% 32%	2671
	11th to 20th	Night	15% 9% 4 8% 5% 4 4 4 4 5% 38%	2399
	21st to end	Night	18% 8% 3 9% 4 4 3 2 4 6% 39%	1980
March	1st to 10th	Night	18% 14% 4 6% 3 3 3 2 3 4 39%	5373
	11th to 20th	Night	11% 7% 2 5% 4 3 4 3 4 6% 50%	5212
	21st to end	Night	17% 10% 3 8% 5% 5% 4 4 5% 6% 33%	5010
April	1st to 10th	Night	13% 8% 3 7% 4 5% 3 3 5% 7% 44%	2000
	11th to 20th	Night	15% 8% 2 6% 3 3 4 3 5% 7% 45%	1975
	21st to end	Night	18% 7% 3 7% 5% 4 4 4 5% 6% 37%	2000
May	1st to 10th	Night	17% 10% 3 8% 5% 4 4 4 5% 7% 34%	4079
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 6% 10% 39%	3824
	21st to end	Night	12% 7% 2 7% 5% 4 5% 4 6% 8% 39%	3942
June	1st to 10th	Night	7% 5% 2 6% 4 4 4 3 7% 8% 50%	1600
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 6% 9% 51%	1600
	21st to end	Night	6% 5% 2 6% 4 4 4 4 7% 10% 48%	1600
July	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 6% 9% 47%	3618
	11th to 20th	Night	5% 5% 2 7% 4 4 5% 5% 7% 11% 44%	3617
	21st to end	Night	7% 6% 3 7% 5% 4 5% 5% 8% 10% 40%	3947
August	1st to 10th	Night	5% 4 2 4 4 4 4 4 7% 9% 55%	3010
	11th to 20th	Night	7% 4 1 6% 4 5% 5% 3 7% 8% 49%	3200
	21st to end	Night	5% 2 1 4 3 4 4 4 5% 9% 57%	3586
September	1st to 10th	Night	10% 5% 2 5% 3 3 4 4 4 8% 53%	2000
	11th to 20th	Night	7% 4 2 5% 4 3 3 3 6% 8% 55%	2070
	21st to end	Night	10% 6% 2 4 3 4 4 3 5% 7% 53%	2200
October	1st to 10th	Night	9% 4 2 5% 4 3 4 3 4 7% 57%	2294
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 53%	2400
	21st to end	Night	17% 9% 2 5% 4 3 4 3 4 6% 42%	2766
November	1st to 10th	Night	10% 6% 3 5% 4 3 4 3 5% 6% 52%	2666
	11th to 20th	Night	12% 8% 2 6% 4 3 3 3 5% 6% 48%	2730
	21st to end	Night	18% 9% 4 6% 4 3 3 3 4 6% 40%	2735
December	1st to 10th	Night	12% 8% 3 7% 4 4 3 3 4 6% 45%	4720
	11th to 20th	Night	16% 9% 4 8% 5% 4 4 3 5% 6% 36%	5339
	21st to end	Night	27% 16% 5% 9% 5% 4 4 3 4 4 19%	7150

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	55% 3 10% 22% 9% 1	4692
	11th to 20th	Day	55% 3 12% 16% 11% 2	4710
	21st to end	Day	61% 2 7% 19% 8% 2	5794
February	1st to 10th	Day	54% 3 13% 20% 9% 1	1948
	11th to 20th	Day	52% 4 10% 21% 12% 1	2008
	21st to end	Day	50% 3 8% 24% 12% 3	1650
March	1st to 10th	Day	48% 2 5% 23% 18% 3	4480
	11th to 20th	Day	36% 3 12% 29% 19% 2	4791
	21st to end	Day	53% 3 12% 23% 7% 1	5920
April	1st to 10th	Day	45% 3 13% 24% 14% 1	2400
	11th to 20th	Day	46% 3 10% 25% 13% 2	2374
	21st to end	Day	47% 4 13% 23% 11% 2	2400
May	1st to 10th	Day	48% 5% 14% 22% 11%	5852
	11th to 20th	Day	45% 5% 11% 25% 13% 1	6081
	21st to end	Day	42% 5% 11% 25% 16% 1	6949
June	1st to 10th	Day	34% 5% 15% 27% 17% 3	2800
	11th to 20th	Day	33% 6% 10% 27% 21% 3	2800
	21st to end	Day	35% 6% 15% 24% 17% 3	2800
July	1st to 10th	Day	34% 5% 11% 31% 17% 2	6291
	11th to 20th	Day	39% 8% 14% 25% 13% 1	6285
	21st to end	Day	38% 9% 18% 26% 9% 1	6728
August	1st to 10th	Day	26% 6% 15% 38% 14% 1	4124
	11th to 20th	Day	37% 6% 15% 27% 14% 1	3885
	21st to end	Day	27% 6% 15% 32% 16% 4	4311
September	1st to 10th	Day	34% 4 11% 26% 21% 4	2400
	11th to 20th	Day	32% 4 9% 26% 26% 3	2309
	21st to end	Day	32% 5% 8% 27% 25% 3	2200
October	1st to 10th	Day	20% 3 8% 22% 43% 4	3428
	11th to 20th	Day	27% 2 8% 22% 36% 4	3240
	21st to end	Day	37% 3 7% 26% 26% 2	3323
November	1st to 10th	Day	33% 3 12% 28% 19% 4	1852
	11th to 20th	Day	42% 2 9% 26% 16% 4	1890
	21st to end	Day	51% 2 10% 24% 12% 1	1883
December	1st to 10th	Day	39% 3 16% 30% 12%	2690
	11th to 20th	Day	56% 4 8% 23% 8% 1	3085
	21st to end	Day	71% 2 11% 12% 4	4070
January	1st to 10th	Night	52% 3 13% 24% 8%	8233
	11th to 20th	Night	54% 3 8% 18% 14% 3	8280
	21st to end	Night	56% 3 9% 21% 10% 2	8404
February	1st to 10th	Night	54% 3 10% 21% 10% 1	2671
	11th to 20th	Night	48% 3 9% 23% 14% 2	2400
	21st to end	Night	49% 2 9% 24% 14% 2	1980
March	1st to 10th	Night	51% 2 6% 22% 16% 2	5373
	11th to 20th	Night	36% 2 10% 28% 20% 4	5212
	21st to end	Night	52% 3 9% 26% 9% 1	5010
April	1st to 10th	Night	41% 3 11% 26% 17% 2	2000
	11th to 20th	Night	40% 3 10% 25% 18% 4	1975
	21st to end	Night	48% 4 10% 21% 14% 3	2000
May	1st to 10th	Night	50% 4 14% 21% 10% 1	4106
	11th to 20th	Night	41% 5% 12% 26% 14% 2	3825
	21st to end	Night	42% 4 13% 22% 17% 2	3950
June	1st to 10th	Night	31% 5% 13% 29% 19% 3	1600
	11th to 20th	Night	30% 4 11% 26% 25% 4	1600
	21st to end	Night	30% 6% 15% 25% 18% 6%	1600
July	1st to 10th	Night	34% 4 11% 28% 21% 2	3580
	11th to 20th	Night	30% 9% 15% 29% 15% 2	3572
	21st to end	Night	36% 9% 17% 24% 14% 1	3832
August	1st to 10th	Night	24% 6% 16% 37% 16% 1	3001
	11th to 20th	Night	31% 6% 12% 32% 18% 1	3230
	21st to end	Night	23% 6% 14% 35% 18% 4	3586
September	1st to 10th	Night	30% 3 9% 28% 23% 7%	2000
	11th to 20th	Night	27% 5% 8% 28% 28% 4	2070
	21st to end	Night	31% 4 9% 23% 27% 5%	2200
October	1st to 10th	Night	20% 3 7% 22% 45% 4	3749
	11th to 20th	Night	24% 2 7% 25% 37% 4	3899
	21st to end	Night	34% 3 8% 25% 25% 5%	4465
November	1st to 10th	Night	33% 4 10% 26% 22% 5%	2666
	11th to 20th	Night	39% 2 9% 27% 20% 3	2730
	21st to end	Night	47% 3 10% 24% 15% 1	2735
December	1st to 10th	Night	42% 3 11% 29% 15% 1	4720
	11th to 20th	Night	48% 4 12% 24% 11% 1	5341
	21st to end	Night	69% 3 10% 13% 5%	7150

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	19% 18% 35% 21% 6% 1	330
	11th to 20th	Day	27% 19% 35% 16% 3	330
	21st to end	Day	21% 20% 39% 16% 4	363
February	1st to 10th	Day	23% 15% 42% 16% 4	330
	11th to 20th	Day	25% 20% 35% 15% 3 1	315
	21st to end	Day	25% 13% 44% 16% 3	249
March	1st to 10th	Day	22% 19% 39% 16% 4	300
	11th to 20th	Day	25% 19% 36% 15% 4 1	300
	21st to end	Day	31% 16% 30% 17% 5%	527
April	1st to 10th	Day	19% 16% 33% 24% 7% 1	500
	11th to 20th	Day	23% 16% 28% 20% 10% 2	492
	21st to end	Day	20% 13% 36% 20% 8% 2	500
May	1st to 10th	Day	20% 12% 30% 26% 11% 2	503
	11th to 20th	Day	18% 10% 26% 25% 17% 4	613
	21st to end	Day	10% 8% 31% 30% 14% 6%	789
June	1st to 10th	Day	10% 6% 24% 30% 23% 8%	730
	11th to 20th	Day	11% 5% 21% 34% 24% 5%	730
	21st to end	Day	7% 5% 26% 33% 21% 8%	730
July	1st to 10th	Day	11% 3 13% 29% 27% 17%	721
	11th to 20th	Day	6% 3 19% 35% 26% 10%	718
	21st to end	Day	10% 2 14% 32% 32% 10%	794
August	1st to 10th	Day	9% 2 14% 34% 29% 11%	650
	11th to 20th	Day	9% 3 16% 30% 27% 15%	519
	21st to end	Day	8% 1 14% 30% 36% 12%	583
September	1st to 10th	Day	11% 5% 16% 30% 27% 11%	530
	11th to 20th	Day	8% 2 12% 32% 33% 13%	530
	21st to end	Day	10% 8% 24% 23% 24% 11%	530
October	1st to 10th	Day	10% 7% 22% 33% 23% 5%	433
	11th to 20th	Day	14% 17% 31% 25% 10% 3	330
	21st to end	Day	27% 16% 31% 21% 4 1	363
November	1st to 10th	Day	15% 15% 32% 23% 12% 3	330
	11th to 20th	Day	19% 17% 35% 18% 8% 2	330
	21st to end	Day	28% 15% 29% 21% 7%	330
December	1st to 10th	Day	14% 19% 42% 18% 5% 3	330
	11th to 20th	Day	20% 18% 33% 24% 4	330
	21st to end	Day	26% 21% 36% 11% 6%	363
January	1st to 10th	Night	18% 16% 38% 24% 4	1050
	11th to 20th	Night	21% 18% 37% 20% 4	1050
	21st to end	Night	20% 15% 38% 24% 3	1155
February	1st to 10th	Night	22% 14% 38% 24% 3	991
	11th to 20th	Night	20% 18% 36% 24% 2	804
	21st to end	Night	24% 14% 38% 22% 2	660
March	1st to 10th	Night	22% 15% 36% 24% 3	800
	11th to 20th	Night	22% 13% 34% 26% 5%	702
	21st to end	Night	25% 12% 30% 27% 5%	660
April	1st to 10th	Night	17% 15% 34% 28% 6%	600
	11th to 20th	Night	18% 11% 35% 27% 9%	593
	21st to end	Night	22% 9% 33% 29% 7% 1	600
May	1st to 10th	Night	18% 8% 34% 31% 10% 1	600
	11th to 20th	Night	16% 6% 26% 34% 17% 2	591
	21st to end	Night	11% 5% 25% 36% 20% 4	650
June	1st to 10th	Night	9% 4 20% 42% 24%	600
	11th to 20th	Night	8% 3 22% 44% 22% 2	600
	21st to end	Night	7% 4 24% 37% 28% 1	600
July	1st to 10th	Night	10% 2 11% 33% 39% 5%	585
	11th to 20th	Night	5% 3 12% 45% 31% 4	582
	21st to end	Night	8% 2 12% 41% 34% 3	657
August	1st to 10th	Night	9% 2 11% 43% 31% 4	597
	11th to 20th	Night	6% 2 12% 42% 34% 4	594
	21st to end	Night	5% 1 11% 39% 38% 5%	660
September	1st to 10th	Night	12% 3 13% 37% 31% 4	600
	11th to 20th	Night	7% 3 13% 38% 34% 5%	670
	21st to end	Night	12% 5% 21% 31% 27% 4	800
October	1st to 10th	Night	11% 3 23% 37% 22% 4	800
	11th to 20th	Night	16% 12% 28% 30% 14% 1	800
	21st to end	Night	22% 12% 33% 27% 6%	880
November	1st to 10th	Night	13% 8% 39% 30% 9%	820
	11th to 20th	Night	17% 14% 35% 26% 7%	840
	21st to end	Night	25% 12% 31% 27% 6%	845
December	1st to 10th	Night	22% 12% 36% 25% 5%	1050
	11th to 20th	Night	23% 10% 34% 28% 5%	1050
	21st to end	Night	29% 15% 33% 21% 2	1155

Page generated at 2026-02-13 00:42:17. Version ac07

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