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 2024-11-30.

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% 4 5% 4 6% 8% 39%	101465
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 41%	98196
Transparency	Day	42% 4 12% 25% 16% 2	105069
	Night	42% 3 10% 25% 17% 2	102733
Seeing	Day	15% 9% 26% 26% 17% 6%	15737
	Night	17% 9% 29% 30% 14% 1	25569

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	13% 11% 7% 12% 5% 5% 4 3 5% 6% 28%	2527
	11th to 20th	Day	14% 10% 5% 10% 8% 9% 8% 6% 6% 4 20%	2530
	21st to end	Day	22% 20% 6% 9% 4 3 3 2 4 5% 21%	3117
February	1st to 10th	Day	15% 13% 5% 9% 6% 4 4 3 5% 6% 30%	1762
	11th to 20th	Day	14% 11% 3 8% 7% 5% 5% 4 5% 8% 32%	1848
	21st to end	Day	16% 13% 3 8% 5% 4 4 2 6% 5% 34%	1570
March	1st to 10th	Day	19% 15% 4 6% 4 4 3 3 3 5% 34%	3120
	11th to 20th	Day	10% 9% 2 6% 4 3 4 4 6% 7% 45%	3347
	21st to end	Day	16% 11% 4 9% 5% 5% 5% 3 5% 7% 30%	4130
April	1st to 10th	Day	13% 8% 3 7% 6% 4 5% 4 6% 8% 37%	2280
	11th to 20th	Day	16% 9% 3 7% 4 4 4 3 4 6% 41%	2254
	21st to end	Day	19% 7% 2 6% 5% 5% 4 3 5% 7% 38%	2280
May	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 5% 8% 12% 30%	4050
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 6% 9% 36%	4227
	21st to end	Day	8% 6% 2 6% 4 6% 5% 5% 6% 9% 44%	4824
June	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 5% 7% 9% 46%	2660
	11th to 20th	Day	8% 5% 2 5% 5% 4 4 4 6% 9% 49%	2660
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 4 7% 10% 42%	2660
July	1st to 10th	Day	12% 5% 3 7% 4 4 6% 4 7% 9% 39%	4440
	11th to 20th	Day	5% 5% 2 6% 4 5% 6% 4 8% 10% 45%	4440
	21st to end	Day	8% 5% 3 7% 5% 6% 5% 5% 9% 10% 37%	4813
August	1st to 10th	Day	8% 3 1 4 3 4 4 4 7% 10% 52%	4012
	11th to 20th	Day	9% 5% 2 7% 5% 4 6% 5% 7% 10% 40%	3729
	21st to end	Day	5% 4 2 6% 4 5% 5% 4 7% 11% 49%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 5% 7% 48%	2280
	11th to 20th	Day	9% 5% 3 5% 3 5% 5% 4 5% 7% 49%	2194
	21st to end	Day	9% 5% 2 5% 4 4 3 4 5% 7% 52%	2090
October	1st to 10th	Day	10% 5% 1 5% 3 4 4 3 5% 7% 54%	1998
	11th to 20th	Day	14% 7% 2 5% 3 3 4 3 5% 6% 48%	1900
	21st to end	Day	18% 7% 2 6% 4 3 3 3 5% 6% 42%	1969
November	1st to 10th	Day	10% 7% 2 5% 4 3 3 3 5% 6% 52%	1762
	11th to 20th	Day	15% 9% 3 6% 4 3 3 4 5% 7% 42%	1800
	21st to end	Day	15% 11% 4 7% 5% 4 3 3 5% 5% 38%	1791
December	1st to 10th	Day	14% 13% 5% 7% 6% 4 4 3 5% 7% 33%	1520
	11th to 20th	Day	15% 12% 4 10% 5% 5% 5% 4 5% 7% 28%	1918
	21st to end	Day	21% 17% 6% 13% 5% 4 4 3 4 5% 19%	2783
January	1st to 10th	Night	14% 13% 6% 10% 5% 4 4 3 4 6% 31%	4428
	11th to 20th	Night	13% 16% 6% 12% 6% 5% 8% 4 3 4 25%	4440
	21st to end	Night	24% 14% 7% 10% 4 3 3 2 3 5% 23%	4534
February	1st to 10th	Night	17% 11% 4 9% 6% 5% 4 3 5% 5% 31%	2417
	11th to 20th	Night	14% 9% 4 8% 5% 4 4 4 5% 5% 39%	2218
	21st to end	Night	19% 9% 3 9% 4 4 3 3 4 6% 37%	1884
March	1st to 10th	Night	19% 15% 3 6% 3 4 3 3 3 5% 37%	3733
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 50%	3642
	21st to end	Night	18% 10% 3 8% 5% 4 4 4 5% 6% 34%	3500
April	1st to 10th	Night	13% 8% 2 6% 4 4 3 3 5% 7% 45%	1900
	11th to 20th	Night	15% 8% 2 5% 3 3 4 3 4 7% 45%	1875
	21st to end	Night	19% 7% 3 7% 5% 4 4 4 5% 5% 38%	1900
May	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 6% 7% 36%	2845
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 5% 7% 41%	2669
	21st to end	Night	8% 7% 2 6% 5% 5% 5% 4 6% 9% 42%	2743
June	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 7% 8% 50%	1520
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 6% 9% 52%	1520
	21st to end	Night	7% 5% 2 6% 4 4 4 4 7% 10% 48%	1520
July	1st to 10th	Night	12% 5% 2 7% 4 3 4 3 6% 9% 45%	2530
	11th to 20th	Night	4 3 2 5% 4 3 3 4 6% 11% 55%	2530
	21st to end	Night	7% 7% 2 7% 4 4 5% 5% 8% 12% 40%	2750
August	1st to 10th	Night	5% 4 2 4 3 4 4 4 7% 9% 55%	2917
	11th to 20th	Night	7% 4 1 6% 4 4 5% 3 7% 8% 49%	3100
	21st to end	Night	5% 2 1 4 3 4 4 4 5% 9% 57%	3476
September	1st to 10th	Night	11% 5% 2 5% 3 3 4 4 4 8% 53%	1900
	11th to 20th	Night	7% 4 2 6% 4 3 4 3 6% 8% 54%	1966
	21st to end	Night	9% 6% 2 4 3 4 4 4 5% 7% 53%	2090
October	1st to 10th	Night	9% 4 1 5% 4 3 4 3 4 7% 57%	2179
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 6% 53%	2280
	21st to end	Night	17% 8% 2 5% 4 3 4 3 5% 6% 43%	2627
November	1st to 10th	Night	10% 6% 3 5% 4 3 4 3 5% 5% 53%	2536
	11th to 20th	Night	13% 8% 2 6% 4 3 3 2 5% 6% 47%	2600
	21st to end	Night	18% 9% 3 6% 4 3 3 3 4 6% 41%	2604
December	1st to 10th	Night	16% 10% 3 8% 5% 5% 4 4 5% 7% 33%	2660
	11th to 20th	Night	17% 9% 4 8% 4 4 4 3 4 4 39%	3279
	21st to end	Night	24% 17% 6% 9% 6% 4 4 3 4 4 20%	4884

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	57% 3 8% 24% 8%	2528
	11th to 20th	Day	65% 2 14% 14% 6%	2530
	21st to end	Day	67% 2 8% 16% 7%	3117
February	1st to 10th	Day	55% 3 12% 19% 10% 1	1762
	11th to 20th	Day	50% 4 11% 22% 12% 1	1858
	21st to end	Day	52% 3 8% 24% 11% 3	1570
March	1st to 10th	Day	55% 3 6% 21% 13% 2	3120
	11th to 20th	Day	38% 3 14% 24% 18% 2	3347
	21st to end	Day	55% 3 13% 23% 6% 1	4130
April	1st to 10th	Day	44% 3 13% 24% 14% 1	2280
	11th to 20th	Day	46% 3 11% 25% 13% 3	2254
	21st to end	Day	47% 4 13% 23% 11% 2	2280
May	1st to 10th	Day	46% 4 16% 26% 7%	4088
	11th to 20th	Day	46% 4 12% 27% 10%	4231
	21st to end	Day	36% 4 12% 24% 22% 2	4837
June	1st to 10th	Day	33% 5% 15% 27% 17% 3	2660
	11th to 20th	Day	31% 6% 10% 27% 22% 3	2660
	21st to end	Day	35% 6% 15% 24% 16% 3	2660
July	1st to 10th	Day	39% 5% 10% 30% 13% 2	4371
	11th to 20th	Day	31% 6% 14% 29% 18% 2	4365
	21st to end	Day	37% 9% 18% 24% 12% 1	4662
August	1st to 10th	Day	26% 6% 15% 38% 14% 1	3997
	11th to 20th	Day	37% 6% 14% 27% 15% 1	3765
	21st to end	Day	28% 6% 16% 32% 15% 4	4179
September	1st to 10th	Day	34% 4 11% 26% 20% 4	2280
	11th to 20th	Day	33% 4 9% 26% 25% 3	2194
	21st to end	Day	32% 5% 8% 28% 24% 3	2090
October	1st to 10th	Day	20% 3 8% 23% 43% 4	3323
	11th to 20th	Day	27% 2 8% 23% 36% 4	3140
	21st to end	Day	36% 3 8% 26% 26% 2	3220
November	1st to 10th	Day	34% 3 13% 27% 19% 5%	1762
	11th to 20th	Day	42% 2 9% 26% 17% 5%	1800
	21st to end	Day	51% 2 10% 25% 12% 1	1791
December	1st to 10th	Day	51% 3 14% 21% 10% 1	1520
	11th to 20th	Day	55% 4 7% 26% 7% 2	1915
	21st to end	Day	68% 2 10% 13% 6% 1	2783
January	1st to 10th	Night	55% 2 11% 22% 9%	4428
	11th to 20th	Night	65% 2 9% 17% 8%	4440
	21st to end	Night	66% 2 7% 17% 7% 1	4534
February	1st to 10th	Night	54% 3 10% 20% 11% 2	2417
	11th to 20th	Night	47% 4 9% 23% 15% 2	2219
	21st to end	Night	50% 2 9% 23% 13% 2	1884
March	1st to 10th	Night	52% 2 8% 24% 13% 1	3733
	11th to 20th	Night	36% 2 12% 27% 21% 3	3642
	21st to end	Night	52% 2 10% 27% 8% 1	3500
April	1st to 10th	Night	40% 3 11% 26% 17% 2	1900
	11th to 20th	Night	40% 2 11% 25% 18% 4	1875
	21st to end	Night	48% 4 10% 21% 15% 3	1900
May	1st to 10th	Night	48% 3 17% 22% 10% 1	2872
	11th to 20th	Night	42% 4 13% 28% 11% 1	2670
	21st to end	Night	39% 4 12% 22% 21% 2	2751
June	1st to 10th	Night	31% 5% 13% 29% 19% 4	1520
	11th to 20th	Night	28% 4 11% 27% 25% 5%	1520
	21st to end	Night	31% 6% 15% 24% 18% 6%	1520
July	1st to 10th	Night	36% 4 11% 27% 18% 3	2490
	11th to 20th	Night	22% 6% 12% 36% 21% 3	2482
	21st to end	Night	35% 8% 16% 22% 17% 2	2662
August	1st to 10th	Night	23% 6% 16% 38% 16% 1	2908
	11th to 20th	Night	32% 6% 12% 31% 19% 1	3130
	21st to end	Night	24% 6% 14% 35% 18% 4	3476
September	1st to 10th	Night	31% 3 9% 28% 22% 7%	1900
	11th to 20th	Night	28% 5% 8% 28% 27% 5%	1966
	21st to end	Night	31% 4 9% 24% 27% 5%	2090
October	1st to 10th	Night	20% 3 7% 22% 45% 4	3634
	11th to 20th	Night	24% 2 7% 25% 37% 4	3779
	21st to end	Night	33% 3 8% 26% 25% 5%	4326
November	1st to 10th	Night	33% 4 10% 26% 21% 6%	2536
	11th to 20th	Night	39% 2 9% 27% 20% 3	2600
	21st to end	Night	46% 3 10% 24% 16% 1	2604
December	1st to 10th	Night	50% 3 12% 22% 12% 1	2660
	11th to 20th	Night	48% 2 11% 26% 12% 1	3281
	21st to end	Night	70% 2 7% 13% 7% 1	4884

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	20% 17% 34% 21% 6% 1	270
	11th to 20th	Day	29% 16% 34% 18% 3	270
	21st to end	Day	22% 19% 36% 18% 5%	297
February	1st to 10th	Day	26% 15% 40% 16% 3	270
	11th to 20th	Day	24% 19% 34% 17% 4 1	270
	21st to end	Day	26% 12% 44% 16% 3	225
March	1st to 10th	Day	22% 19% 39% 16% 4	270
	11th to 20th	Day	26% 19% 36% 16% 4 1	270
	21st to end	Day	31% 15% 31% 18% 6%	484
April	1st to 10th	Day	18% 15% 35% 25% 7% 1	460
	11th to 20th	Day	22% 16% 29% 21% 10% 2	452
	21st to end	Day	21% 13% 35% 21% 8% 2	460
May	1st to 10th	Day	20% 11% 30% 26% 11% 2	463
	11th to 20th	Day	18% 8% 27% 26% 17% 4	568
	21st to end	Day	10% 8% 30% 31% 15% 7%	734
June	1st to 10th	Day	9% 5% 24% 30% 23% 8%	680
	11th to 20th	Day	10% 5% 21% 34% 24% 6%	680
	21st to end	Day	8% 5% 28% 31% 20% 8%	680
July	1st to 10th	Day	11% 3 13% 28% 26% 18%	671
	11th to 20th	Day	6% 3 19% 35% 27% 11%	668
	21st to end	Day	10% 2 15% 32% 31% 10%	739
August	1st to 10th	Day	10% 1 14% 33% 30% 11%	604
	11th to 20th	Day	10% 3 17% 30% 25% 15%	479
	21st to end	Day	8% 1 12% 29% 37% 12%	539
September	1st to 10th	Day	12% 4 15% 29% 27% 12%	490
	11th to 20th	Day	9% 2 12% 32% 32% 13%	490
	21st to end	Day	11% 8% 24% 23% 23% 10%	490
October	1st to 10th	Day	11% 7% 22% 32% 22% 5%	398
	11th to 20th	Day	15% 17% 31% 25% 10% 3	300
	21st to end	Day	26% 16% 30% 23% 4 1	330
November	1st to 10th	Day	15% 13% 32% 24% 13% 4	300
	11th to 20th	Day	21% 16% 35% 18% 9% 2	300
	21st to end	Day	26% 15% 30% 21% 7%	299
December	1st to 10th	Day	15% 18% 40% 19% 5% 3	270
	11th to 20th	Day	20% 15% 34% 26% 4	270
	21st to end	Day	26% 21% 35% 11% 7%	297
January	1st to 10th	Night	18% 16% 37% 25% 4	950
	11th to 20th	Night	22% 15% 37% 21% 5%	950
	21st to end	Night	21% 14% 37% 25% 3	1045
February	1st to 10th	Night	23% 13% 37% 24% 3	897
	11th to 20th	Night	18% 17% 38% 25% 2	743
	21st to end	Night	25% 15% 37% 21% 2	628
March	1st to 10th	Night	22% 14% 37% 24% 3	760
	11th to 20th	Night	22% 12% 34% 26% 5%	667
	21st to end	Night	25% 11% 31% 28% 5%	627
April	1st to 10th	Night	17% 14% 35% 28% 6%	570
	11th to 20th	Night	18% 10% 35% 27% 9%	563
	21st to end	Night	22% 9% 33% 28% 7% 1	570
May	1st to 10th	Night	18% 7% 33% 31% 10% 1	570
	11th to 20th	Night	16% 5% 26% 34% 17% 2	561
	21st to end	Night	10% 4 25% 37% 20% 4	617
June	1st to 10th	Night	9% 4 19% 43% 25%	570
	11th to 20th	Night	8% 2 22% 44% 23% 2	570
	21st to end	Night	8% 4 25% 35% 27% 1	570
July	1st to 10th	Night	11% 2 11% 32% 39% 6%	555
	11th to 20th	Night	5% 3 12% 45% 31% 4	552
	21st to end	Night	8% 2 12% 41% 34% 3	624
August	1st to 10th	Night	9% 2 10% 42% 32% 4	567
	11th to 20th	Night	6% 1 12% 41% 34% 4	564
	21st to end	Night	6% 1 11% 38% 38% 5%	627
September	1st to 10th	Night	12% 3 13% 37% 31% 4	570
	11th to 20th	Night	8% 3 14% 37% 34% 5%	636
	21st to end	Night	11% 5% 22% 31% 27% 4	760
October	1st to 10th	Night	11% 3 24% 36% 22% 4	760
	11th to 20th	Night	16% 12% 29% 28% 14% 1	760
	21st to end	Night	21% 12% 32% 28% 6%	836
November	1st to 10th	Night	14% 7% 38% 31% 10% 1	780
	11th to 20th	Night	18% 14% 34% 26% 8% 1	800
	21st to end	Night	24% 11% 31% 27% 6%	805
December	1st to 10th	Night	21% 12% 35% 25% 6% 1	950
	11th to 20th	Night	23% 8% 34% 30% 6%	950
	21st to end	Night	28% 15% 33% 22% 3	1045

Page generated at 2024-11-27 16:30:53. Version ac07

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