Lanphier Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lanphier Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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 4 4 6% 7% 39%	113825
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 41%	115318
Transparency	Day	42% 6% 12% 23% 15% 2	117405
	Night	42% 5% 11% 23% 16% 2	119880
Seeing	Day	16% 10% 28% 26% 15% 5%	16317
	Night	17% 10% 30% 29% 12% 1	26284

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% 10% 6% 16% 7% 5% 5% 3 5% 6% 25%	3617
	11th to 20th	Day	10% 9% 5% 10% 7% 8% 8% 4 6% 5% 26%	3689
	21st to end	Day	16% 16% 7% 10% 4 3 3 2 3 5% 30%	4488
February	1st to 10th	Day	15% 13% 5% 9% 6% 5% 4 3 5% 7% 30%	1800
	11th to 20th	Day	13% 11% 4 8% 7% 5% 5% 3 5% 7% 32%	1931
	21st to end	Day	15% 11% 4 9% 5% 4 3 3 4 6% 35%	1650
March	1st to 10th	Day	17% 13% 3 5% 3 3 3 2 3 4 43%	4480
	11th to 20th	Day	7% 8% 3 5% 4 4 3 4 7% 8% 47%	4929
	21st to end	Day	16% 10% 4 8% 5% 4 5% 4 6% 7% 31%	5825
April	1st to 10th	Day	14% 8% 3 7% 5% 5% 4 4 5% 7% 37%	2400
	11th to 20th	Day	15% 9% 3 7% 4 4 5% 3 5% 6% 39%	2374
	21st to end	Day	18% 7% 3 6% 6% 5% 5% 3 5% 7% 35%	2400
May	1st to 10th	Day	14% 9% 3 7% 5% 5% 5% 4 7% 10% 32%	4115
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 5% 7% 37%	4381
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 45%	4824
June	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 6% 9% 47%	2660
	11th to 20th	Day	9% 4 2 5% 4 4 4 4 6% 7% 50%	2660
	21st to end	Day	6% 6% 2 7% 6% 5% 5% 5% 7% 8% 43%	2660
July	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 5% 7% 9% 40%	4440
	11th to 20th	Day	5% 5% 2 6% 4 4 5% 5% 7% 11% 46%	4440
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 4 8% 11% 39%	4762
August	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 7% 10% 49%	4086
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 42%	3729
	21st to end	Day	5% 5% 2 5% 4 4 6% 4 7% 10% 48%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 7% 50%	2280
	11th to 20th	Day	8% 6% 2 6% 3 4 4 3 5% 6% 51%	2233
	21st to end	Day	8% 6% 2 6% 3 3 4 4 6% 7% 50%	2090
October	1st to 10th	Day	11% 4 2 5% 4 3 4 3 5% 7% 53%	1929
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 4 6% 47%	1900
	21st to end	Day	18% 9% 3 7% 4 4 2 2 5% 6% 41%	2006
November	1st to 10th	Day	10% 8% 2 5% 4 4 3 3 4 7% 50%	1762
	11th to 20th	Day	14% 11% 3 7% 3 3 3 3 5% 6% 42%	1800
	21st to end	Day	16% 11% 4 7% 4 4 4 4 3 5% 37%	1705
December	1st to 10th	Day	8% 8% 4 7% 4 3 4 3 5% 6% 49%	2610
	11th to 20th	Day	14% 12% 6% 9% 5% 4 4 4 5% 7% 30%	3008
	21st to end	Day	25% 18% 6% 12% 4 4 3 3 3 5% 17%	3982
January	1st to 10th	Night	14% 13% 6% 11% 4 4 4 3 4 5% 32%	6348
	11th to 20th	Night	11% 14% 6% 12% 6% 5% 7% 4 4 4 28%	6286
	21st to end	Night	18% 13% 6% 11% 4 3 3 2 4 5% 30%	6490
February	1st to 10th	Night	16% 12% 5% 9% 5% 5% 4 3 5% 6% 32%	2600
	11th to 20th	Night	14% 10% 4 9% 6% 3 4 3 4 5% 38%	2353
	21st to end	Night	15% 10% 3 8% 4 4 4 3 4 5% 40%	1980
March	1st to 10th	Night	19% 11% 3 6% 3 3 3 2 3 5% 40%	5373
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 5% 6% 51%	5072
	21st to end	Night	18% 10% 4 7% 5% 5% 4 4 5% 6% 32%	5102
April	1st to 10th	Night	12% 8% 3 6% 4 5% 4 4 5% 7% 42%	2000
	11th to 20th	Night	14% 6% 3 5% 4 4 4 3 5% 7% 44%	1975
	21st to end	Night	19% 8% 3 6% 4 4 4 5% 3 5% 39%	2000
May	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 4 6% 8% 35%	2987
	11th to 20th	Night	16% 6% 2 6% 4 4 4 3 6% 8% 41%	2526
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 9% 45%	2743
June	1st to 10th	Night	8% 6% 2 5% 3 3 4 4 6% 9% 51%	1520
	11th to 20th	Night	7% 5% 2 5% 4 4 4 4 6% 8% 51%	1520
	21st to end	Night	7% 4 2 6% 4 5% 4 4 7% 9% 49%	1520
July	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	2530
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 9% 57%	2530
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 8% 10% 44%	2798
August	1st to 10th	Night	6% 4 2 4 3 2 4 4 6% 10% 55%	2853
	11th to 20th	Night	7% 4 2 5% 4 4 5% 3 5% 8% 52%	3100
	21st to end	Night	5% 3 1 5% 3 4 4 4 7% 10% 53%	3476
September	1st to 10th	Night	10% 4 2 5% 3 3 3 3 5% 7% 55%	1900
	11th to 20th	Night	7% 5% 2 6% 3 3 3 3 5% 8% 54%	1928
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 7% 53%	2090
October	1st to 10th	Night	9% 4 1 5% 4 3 4 3 5% 6% 55%	2247
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 5% 7% 51%	2280
	21st to end	Night	17% 8% 2 6% 4 3 4 3 5% 5% 43%	2590
November	1st to 10th	Night	10% 7% 2 5% 4 3 3 2 4 6% 53%	2536
	11th to 20th	Night	12% 8% 3 6% 4 3 3 3 4 6% 48%	2600
	21st to end	Night	16% 11% 3 6% 4 3 4 3 4 6% 40%	2690
December	1st to 10th	Night	12% 9% 3 7% 5% 3 3 3 4 6% 46%	4580
	11th to 20th	Night	15% 9% 4 9% 4 4 4 4 5% 6% 36%	5199
	21st to end	Night	25% 18% 6% 10% 5% 4 4 3 4 4 18%	6996

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	60% 5% 8% 18% 8% 1	3618
	11th to 20th	Day	59% 4 11% 14% 10% 2	3689
	21st to end	Day	59% 3 9% 19% 9% 1	4488
February	1st to 10th	Day	55% 5% 11% 19% 8% 1	1800
	11th to 20th	Day	51% 5% 10% 20% 12% 1	1941
	21st to end	Day	51% 3 10% 22% 11% 2	1650
March	1st to 10th	Day	46% 3 7% 22% 20% 2	4480
	11th to 20th	Day	33% 5% 11% 30% 19% 1	4929
	21st to end	Day	51% 6% 15% 21% 6% 1	5827
April	1st to 10th	Day	46% 6% 12% 23% 14% 1	2400
	11th to 20th	Day	46% 5% 9% 24% 14% 2	2374
	21st to end	Day	48% 7% 12% 20% 12% 2	2400
May	1st to 10th	Day	45% 8% 14% 22% 9% 1	4151
	11th to 20th	Day	45% 7% 11% 27% 9%	4385
	21st to end	Day	35% 8% 10% 22% 24% 2	4837
June	1st to 10th	Day	31% 9% 13% 27% 17% 3	2660
	11th to 20th	Day	32% 7% 11% 25% 23% 3	2660
	21st to end	Day	35% 9% 13% 22% 17% 3	2660
July	1st to 10th	Day	39% 8% 12% 26% 13% 2	4371
	11th to 20th	Day	30% 8% 15% 27% 19% 1	4365
	21st to end	Day	35% 10% 19% 23% 13% 1	4612
August	1st to 10th	Day	28% 8% 18% 34% 11% 1	4072
	11th to 20th	Day	37% 7% 13% 28% 14% 1	3765
	21st to end	Day	28% 8% 16% 29% 15% 4	4179
September	1st to 10th	Day	34% 6% 10% 24% 20% 6%	2280
	11th to 20th	Day	33% 5% 9% 25% 23% 5%	2233
	21st to end	Day	32% 6% 9% 28% 22% 2	2090
October	1st to 10th	Day	23% 4 8% 17% 45% 3	3202
	11th to 20th	Day	26% 3 8% 22% 35% 5%	3140
	21st to end	Day	40% 4 7% 26% 21% 2	3283
November	1st to 10th	Day	36% 4 14% 24% 18% 4	1762
	11th to 20th	Day	42% 4 11% 24% 16% 3	1800
	21st to end	Day	50% 5% 10% 24% 10%	1705
December	1st to 10th	Day	37% 4 17% 31% 11%	2610
	11th to 20th	Day	52% 5% 11% 22% 8% 2	3005
	21st to end	Day	72% 3 10% 10% 4	3982
January	1st to 10th	Night	55% 4 12% 22% 7%	6348
	11th to 20th	Night	60% 4 9% 14% 10% 3	6286
	21st to end	Night	58% 3 8% 19% 11% 1	6490
February	1st to 10th	Night	54% 4 11% 18% 11% 2	2600
	11th to 20th	Night	49% 3 10% 22% 14% 2	2354
	21st to end	Night	47% 4 11% 22% 14% 3	1980
March	1st to 10th	Night	48% 4 6% 23% 17% 2	5373
	11th to 20th	Night	35% 5% 8% 29% 19% 4	5072
	21st to end	Night	51% 6% 10% 23% 8% 1	5102
April	1st to 10th	Night	41% 5% 11% 24% 15% 3	2000
	11th to 20th	Night	40% 4 10% 25% 17% 3	1975
	21st to end	Night	47% 5% 10% 20% 15% 3	2000
May	1st to 10th	Night	45% 8% 15% 21% 10% 1	3015
	11th to 20th	Night	41% 7% 13% 27% 11% 1	2527
	21st to end	Night	33% 8% 13% 20% 22% 4	2751
June	1st to 10th	Night	27% 8% 14% 28% 18% 5%	1520
	11th to 20th	Night	30% 7% 11% 23% 24% 5%	1520
	21st to end	Night	31% 7% 15% 24% 19% 5%	1520
July	1st to 10th	Night	39% 6% 11% 29% 13% 2	2490
	11th to 20th	Night	20% 7% 14% 35% 22% 2	2482
	21st to end	Night	31% 9% 19% 22% 17% 2	2709
August	1st to 10th	Night	23% 7% 18% 33% 17% 1	2843
	11th to 20th	Night	29% 7% 13% 32% 19% 1	3130
	21st to end	Night	24% 7% 17% 32% 15% 4	3476
September	1st to 10th	Night	29% 5% 10% 25% 22% 8%	1900
	11th to 20th	Night	29% 5% 8% 25% 27% 5%	1928
	21st to end	Night	32% 5% 9% 25% 25% 5%	2090
October	1st to 10th	Night	21% 3 7% 21% 44% 4	3754
	11th to 20th	Night	24% 3 8% 23% 37% 5%	3779
	21st to end	Night	35% 4 10% 23% 24% 5%	4263
November	1st to 10th	Night	33% 4 11% 26% 20% 5%	2536
	11th to 20th	Night	38% 4 9% 26% 20% 2	2600
	21st to end	Night	47% 3 10% 23% 15% 1	2690
December	1st to 10th	Night	41% 3 11% 31% 13% 1	4580
	11th to 20th	Night	49% 5% 12% 22% 11% 1	5201
	21st to end	Night	70% 5% 9% 11% 4	6996

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	23% 19% 34% 17% 6%	300
	11th to 20th	Day	26% 17% 40% 15% 2	300
	21st to end	Day	20% 15% 40% 20% 4	330
February	1st to 10th	Day	26% 15% 41% 14% 4	300
	11th to 20th	Day	24% 19% 34% 19% 4	300
	21st to end	Day	24% 15% 47% 14% 1	249
March	1st to 10th	Day	22% 20% 40% 15% 3	300
	11th to 20th	Day	26% 18% 34% 17% 4	300
	21st to end	Day	30% 16% 32% 17% 5%	486
April	1st to 10th	Day	21% 17% 32% 24% 6% 1	500
	11th to 20th	Day	21% 18% 31% 20% 10% 1	492
	21st to end	Day	21% 15% 36% 20% 7% 1	500
May	1st to 10th	Day	19% 13% 33% 26% 8% 2	503
	11th to 20th	Day	18% 11% 27% 27% 14% 3	657
	21st to end	Day	12% 8% 33% 26% 14% 7%	734
June	1st to 10th	Day	9% 7% 23% 31% 24% 7%	680
	11th to 20th	Day	10% 5% 22% 36% 21% 5%	680
	21st to end	Day	8% 6% 31% 33% 18% 4	680
July	1st to 10th	Day	11% 3 15% 30% 27% 14%	671
	11th to 20th	Day	6% 4 21% 34% 25% 10%	668
	21st to end	Day	10% 2 18% 32% 31% 8%	739
August	1st to 10th	Day	8% 3 16% 38% 26% 9%	671
	11th to 20th	Day	8% 5% 19% 28% 26% 14%	479
	21st to end	Day	7% 2 16% 31% 33% 10%	539
September	1st to 10th	Day	13% 4 18% 28% 28% 9%	490
	11th to 20th	Day	9% 2 14% 32% 30% 12%	490
	21st to end	Day	10% 11% 22% 26% 22% 9%	490
October	1st to 10th	Day	12% 9% 26% 32% 16% 5%	329
	11th to 20th	Day	16% 18% 32% 24% 8% 1	300
	21st to end	Day	31% 14% 32% 18% 5%	330
November	1st to 10th	Day	13% 16% 34% 23% 10% 5%	300
	11th to 20th	Day	23% 16% 33% 17% 9% 2	300
	21st to end	Day	24% 14% 37% 19% 6%	300
December	1st to 10th	Day	14% 24% 37% 16% 5% 4	300
	11th to 20th	Day	21% 19% 36% 19% 4	300
	21st to end	Day	28% 20% 35% 14% 2	330
January	1st to 10th	Night	19% 14% 40% 23% 5%	1000
	11th to 20th	Night	21% 16% 37% 21% 4	1000
	21st to end	Night	21% 14% 36% 26% 3	1100
February	1st to 10th	Night	23% 14% 37% 23% 3	1000
	11th to 20th	Night	21% 15% 35% 26% 2	798
	21st to end	Night	21% 16% 37% 23% 3	660
March	1st to 10th	Night	22% 15% 36% 23% 4	800
	11th to 20th	Night	20% 12% 34% 28% 6%	640
	21st to end	Night	27% 11% 33% 23% 6%	660
April	1st to 10th	Night	18% 15% 37% 26% 4	600
	11th to 20th	Night	17% 13% 34% 27% 9%	593
	21st to end	Night	21% 10% 37% 26% 6% 1	600
May	1st to 10th	Night	18% 6% 38% 29% 9% 1	600
	11th to 20th	Night	18% 4 27% 36% 12% 1	563
	21st to end	Night	11% 5% 27% 33% 21% 3	617
June	1st to 10th	Night	9% 4 21% 46% 20%	570
	11th to 20th	Night	10% 3 23% 43% 19% 2	570
	21st to end	Night	8% 2 28% 41% 19% 1	570
July	1st to 10th	Night	11% 2 11% 36% 35% 5%	555
	11th to 20th	Night	5% 2 19% 40% 32% 3	552
	21st to end	Night	7% 14% 45% 31% 2	624
August	1st to 10th	Night	8% 2 12% 44% 30% 4	567
	11th to 20th	Night	8% 1 14% 39% 33% 6%	564
	21st to end	Night	5% 1 13% 39% 39% 2	627
September	1st to 10th	Night	12% 3 16% 37% 28% 4	570
	11th to 20th	Night	9% 1 17% 38% 31% 4	598
	21st to end	Night	10% 8% 23% 32% 23% 4	760
October	1st to 10th	Night	11% 4 30% 31% 22% 2	760
	11th to 20th	Night	16% 11% 31% 29% 12% 1	760
	21st to end	Night	22% 12% 34% 24% 7%	836
November	1st to 10th	Night	14% 10% 40% 27% 9%	780
	11th to 20th	Night	18% 13% 37% 25% 6% 1	800
	21st to end	Night	22% 14% 35% 24% 5%	890
December	1st to 10th	Night	21% 12% 39% 23% 5% 1	1000
	11th to 20th	Night	23% 11% 35% 25% 6%	1000
	21st to end	Night	26% 17% 32% 22% 2	1100

Page generated at 2025-05-08 08:33:55. Version ac07

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