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 2025-03-12.

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	13% 12% 5% 11% 5% 4 4 3 5% 6% 32%	108186
	Night	14% 15% 6% 13% 6% 4 4 3 4 5% 26%	110963
Transparency	Day	53% 5% 11% 20% 10% 1	111717
	Night	61% 5% 10% 16% 8% 1	115559
Seeing	Day	19% 13% 29% 25% 11% 2	16178
	Night	22% 13% 27% 26% 10% 1	26410

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	11% 22% 14% 33% 5% 4 2 1 2 2 4	3617
	11th to 20th	Day	11% 16% 10% 29% 13% 9% 4 2 2 1 2	3620
	21st to end	Day	13% 18% 11% 20% 9% 5% 6% 2 3 3 10%	3982
February	1st to 10th	Day	10% 19% 7% 19% 16% 7% 3 2 3 4 12%	1700
	11th to 20th	Day	12% 15% 8% 18% 13% 6% 5% 2 3 4 15%	1948
	21st to end	Day	13% 18% 6% 15% 10% 5% 4 2 4 5% 19%	1650
March	1st to 10th	Day	12% 13% 5% 10% 6% 4 4 3 5% 6% 32%	3220
	11th to 20th	Day	9% 11% 6% 17% 6% 4 4 3 5% 6% 30%	3357
	21st to end	Day	17% 13% 7% 17% 5% 4 3 2 4 4 23%	4005
April	1st to 10th	Day	17% 15% 4 9% 5% 4 4 3 5% 6% 30%	2280
	11th to 20th	Day	19% 13% 4 6% 4 3 3 3 4 6% 35%	2328
	21st to end	Day	16% 10% 3 9% 4 4 4 3 5% 7% 35%	2470
May	1st to 10th	Day	13% 8% 3 6% 4 3 4 3 5% 6% 44%	4082
	11th to 20th	Day	10% 7% 2 6% 4 3 4 3 5% 6% 49%	4293
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 5% 7% 44%	4824
June	1st to 10th	Day	12% 5% 2 6% 4 5% 4 4 5% 7% 45%	2660
	11th to 20th	Day	11% 4 2 6% 4 5% 5% 4 6% 10% 44%	2660
	21st to end	Day	13% 6% 2 5% 4 4 4 3 7% 8% 44%	2660
July	1st to 10th	Day	18% 7% 2 5% 3 3 4 3 6% 8% 41%	4440
	11th to 20th	Day	8% 4 1 4 3 3 4 3 6% 8% 56%	4440
	21st to end	Day	9% 4 2 5% 4 4 3 4 6% 8% 52%	4813
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 7% 9% 43%	4300
	11th to 20th	Day	15% 5% 2 4 3 3 3 3 5% 6% 51%	4044
	21st to end	Day	13% 6% 3 6% 4 4 4 3 4 5% 47%	4286
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 7% 44%	2275
	11th to 20th	Day	14% 5% 2 5% 3 3 5% 3 6% 8% 46%	2090
	21st to end	Day	16% 7% 2 7% 4 4 4 4 7% 8% 38%	2090
October	1st to 10th	Day	18% 10% 3 7% 4 4 4 3 4 8% 36%	2090
	11th to 20th	Day	23% 17% 4 9% 6% 4 4 3 4 5% 21%	1788
	21st to end	Day	25% 17% 4 10% 6% 4 4 3 4 5% 18%	1881
November	1st to 10th	Day	18% 20% 3 7% 4 4 4 3 4 7% 27%	1762
	11th to 20th	Day	14% 26% 8% 11% 6% 4 3 3 5% 4 16%	1800
	21st to end	Day	18% 27% 10% 12% 4 3 3 3 3 4 14%	1715
December	1st to 10th	Day	11% 35% 13% 17% 7% 4 3 1 2 2 6%	2294
	11th to 20th	Day	11% 28% 14% 19% 8% 4 4 2 3 3 5%	2740
	21st to end	Day	20% 23% 12% 15% 6% 4 4 3 2 3 7%	3982
January	1st to 10th	Night	11% 22% 11% 34% 6% 3 2 1 1 1 7%	6348
	11th to 20th	Night	10% 17% 9% 24% 17% 9% 3 2 2 2 5%	6360
	21st to end	Night	11% 20% 11% 19% 9% 7% 5% 2 3 3 10%	6996
February	1st to 10th	Night	11% 18% 7% 19% 14% 6% 4 3 3 3 12%	2695
	11th to 20th	Night	12% 16% 6% 18% 10% 6% 5% 3 4 4 16%	2338
	21st to end	Night	14% 18% 6% 15% 7% 5% 3 3 5% 6% 21%	1980
March	1st to 10th	Night	16% 11% 5% 7% 4 3 3 3 4 6% 38%	3853
	11th to 20th	Night	8% 15% 5% 10% 5% 4 4 3 5% 7% 34%	3631
	21st to end	Night	15% 13% 6% 12% 5% 5% 4 4 4 5% 26%	3640
April	1st to 10th	Night	18% 14% 3 8% 4 4 5% 3 5% 6% 30%	1900
	11th to 20th	Night	20% 10% 4 6% 4 4 4 4 4 6% 34%	1801
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 6% 36%	1710
May	1st to 10th	Night	16% 8% 2 6% 4 4 5% 3 5% 6% 41%	2813
	11th to 20th	Night	13% 8% 2 7% 4 4 5% 4 6% 7% 41%	2606
	21st to end	Night	18% 6% 2 5% 3 4 3 4 7% 7% 41%	2743
June	1st to 10th	Night	14% 7% 2 6% 5% 4 5% 3 5% 7% 43%	1520
	11th to 20th	Night	13% 6% 2 6% 5% 5% 4 5% 6% 9% 42%	1520
	21st to end	Night	11% 8% 3 6% 4 4 4 4 5% 8% 45%	1520
July	1st to 10th	Night	14% 7% 3 6% 4 4 5% 4 6% 8% 41%	2530
	11th to 20th	Night	7% 5% 2 5% 4 3 4 3 5% 8% 54%	2530
	21st to end	Night	9% 5% 2 7% 4 4 4 4 5% 7% 49%	2750
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 3 4 7% 43%	2633
	11th to 20th	Night	14% 5% 2 4 4 3 3 3 6% 6% 49%	2785
	21st to end	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 47%	3368
September	1st to 10th	Night	13% 6% 3 6% 3 3 3 3 4 7% 49%	1900
	11th to 20th	Night	14% 5% 2 6% 3 4 4 3 5% 7% 48%	2075
	21st to end	Night	17% 7% 3 6% 5% 4 4 3 6% 7% 38%	2090
October	1st to 10th	Night	18% 10% 3 7% 5% 4 3 3 4 5% 37%	2090
	11th to 20th	Night	23% 14% 4 8% 5% 4 4 3 4 5% 25%	2387
	21st to end	Night	24% 17% 5% 9% 6% 4 3 3 4 5% 22%	2717
November	1st to 10th	Night	16% 18% 4 7% 5% 5% 4 3 5% 6% 27%	2536
	11th to 20th	Night	15% 24% 7% 14% 5% 4 4 3 3 4 18%	2600
	21st to end	Night	16% 25% 9% 12% 4 4 4 3 4 4 14%	2680
December	1st to 10th	Night	11% 26% 16% 17% 6% 4 3 2 3 3 8%	4877
	11th to 20th	Night	13% 24% 10% 21% 9% 4 3 2 3 3 8%	5445
	21st to end	Night	22% 21% 10% 15% 5% 4 3 2 3 3 12%	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	91% 2 4 2	3618
	11th to 20th	Day	92% 3 2 2	3620
	21st to end	Day	83% 3 8% 4 1	3982
February	1st to 10th	Day	80% 3 7% 9% 1	1700
	11th to 20th	Day	74% 6% 9% 8% 3	1958
	21st to end	Day	67% 7% 9% 11% 4 1	1650
March	1st to 10th	Day	51% 7% 13% 19% 10% 1	3220
	11th to 20th	Day	53% 7% 13% 19% 6% 1	3357
	21st to end	Day	63% 7% 9% 15% 6% 1	4005
April	1st to 10th	Day	55% 6% 10% 19% 10%	2280
	11th to 20th	Day	50% 6% 8% 20% 15% 2	2328
	21st to end	Day	47% 7% 11% 17% 16% 2	2470
May	1st to 10th	Day	39% 7% 10% 25% 18% 2	4120
	11th to 20th	Day	35% 6% 11% 27% 18% 2	4297
	21st to end	Day	36% 9% 11% 23% 19% 2	4837
June	1st to 10th	Day	37% 7% 12% 27% 15% 2	2660
	11th to 20th	Day	35% 7% 13% 24% 19% 1	2660
	21st to end	Day	37% 7% 16% 25% 15% 1	2660
July	1st to 10th	Day	42% 5% 15% 25% 12% 2	4371
	11th to 20th	Day	26% 5% 15% 38% 14% 2	4365
	21st to end	Day	30% 5% 13% 30% 20% 1	4662
August	1st to 10th	Day	36% 5% 16% 30% 12% 1	4285
	11th to 20th	Day	35% 4 13% 33% 14% 1	4083
	21st to end	Day	39% 4 15% 29% 12% 1	4285
September	1st to 10th	Day	39% 8% 13% 26% 14% 1	2275
	11th to 20th	Day	35% 7% 18% 29% 11% 1	2090
	21st to end	Day	43% 7% 15% 26% 9%	2090
October	1st to 10th	Day	33% 4 10% 34% 19% 1	3480
	11th to 20th	Day	58% 3 10% 19% 9%	2939
	21st to end	Day	63% 4 14% 16% 3	3081
November	1st to 10th	Day	60% 6% 10% 17% 7%	1762
	11th to 20th	Day	72% 5% 10% 10% 4	1800
	21st to end	Day	76% 5% 11% 6% 1	1715
December	1st to 10th	Day	89% 2 4 4 1	2294
	11th to 20th	Day	88% 4 6% 2 1	2736
	21st to end	Day	83% 5% 5% 5% 1	3982
January	1st to 10th	Night	89% 2 5% 4	6348
	11th to 20th	Night	89% 3 4 3	6360
	21st to end	Night	81% 5% 7% 7% 1	6996
February	1st to 10th	Night	78% 4 7% 8% 2	2695
	11th to 20th	Night	72% 6% 8% 12% 3	2339
	21st to end	Night	65% 6% 13% 13% 4	1980
March	1st to 10th	Night	48% 5% 16% 22% 8%	3853
	11th to 20th	Night	50% 6% 12% 23% 8% 1	3631
	21st to end	Night	59% 6% 10% 17% 7% 1	3640
April	1st to 10th	Night	55% 6% 10% 19% 10% 1	1900
	11th to 20th	Night	50% 6% 9% 20% 13% 3	1801
	21st to end	Night	48% 6% 10% 20% 13% 3	1710
May	1st to 10th	Night	43% 6% 12% 19% 17% 3	2840
	11th to 20th	Night	41% 6% 10% 27% 15% 1	2607
	21st to end	Night	41% 6% 13% 19% 15% 5%	2751
June	1st to 10th	Night	40% 6% 11% 28% 13% 2	1520
	11th to 20th	Night	39% 6% 12% 23% 17% 3	1520
	21st to end	Night	37% 7% 12% 26% 15% 2	1520
July	1st to 10th	Night	42% 4 14% 23% 13% 4	2490
	11th to 20th	Night	29% 4 15% 31% 18% 2	2482
	21st to end	Night	35% 6% 11% 25% 20% 2	2662
August	1st to 10th	Night	42% 6% 13% 26% 13% 1	2624
	11th to 20th	Night	35% 4 16% 30% 15% 1	2812
	21st to end	Night	38% 5% 15% 23% 18% 1	3368
September	1st to 10th	Night	36% 6% 15% 23% 20% 1	1900
	11th to 20th	Night	38% 5% 15% 28% 13% 1	2075
	21st to end	Night	45% 6% 15% 25% 9%	2090
October	1st to 10th	Night	43% 3 9% 33% 11% 1	3480
	11th to 20th	Night	54% 3 10% 22% 11%	3962
	21st to end	Night	57% 3 14% 20% 6%	4467
November	1st to 10th	Night	59% 6% 11% 17% 6% 1	2536
	11th to 20th	Night	73% 4 9% 9% 5% 1	2600
	21st to end	Night	75% 5% 10% 8% 1	2680
December	1st to 10th	Night	84% 4 6% 6% 1	4877
	11th to 20th	Night	84% 4 6% 4 1	5447
	21st to end	Night	79% 5% 9% 5% 3	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	20% 24% 36% 14% 5% 1	300
	11th to 20th	Day	25% 21% 37% 15% 2	300
	21st to end	Day	25% 18% 34% 20% 3	330
February	1st to 10th	Day	20% 29% 32% 13% 5% 1	300
	11th to 20th	Day	21% 28% 33% 15% 3	300
	21st to end	Day	23% 26% 40% 10% 1	249
March	1st to 10th	Day	21% 25% 39% 13% 2	300
	11th to 20th	Day	19% 20% 33% 20% 8% 1	382
	21st to end	Day	28% 16% 26% 23% 6% 1	506
April	1st to 10th	Day	23% 18% 31% 21% 5% 1	460
	11th to 20th	Day	26% 18% 29% 17% 8% 2	452
	21st to end	Day	18% 17% 30% 24% 8% 2	460
May	1st to 10th	Day	19% 14% 31% 25% 8% 2	463
	11th to 20th	Day	14% 8% 33% 32% 10% 2	608
	21st to end	Day	13% 9% 27% 33% 16% 2	734
June	1st to 10th	Day	14% 8% 31% 30% 15% 3	680
	11th to 20th	Day	14% 8% 30% 34% 12% 3	680
	21st to end	Day	16% 7% 26% 35% 13% 3	680
July	1st to 10th	Day	10% 4 23% 38% 20% 5%	671
	11th to 20th	Day	11% 6% 25% 35% 18% 5%	668
	21st to end	Day	8% 3 26% 41% 18% 4	739
August	1st to 10th	Day	10% 4 23% 34% 23% 5%	605
	11th to 20th	Day	14% 5% 20% 34% 19% 9%	479
	21st to end	Day	17% 7% 24% 30% 19% 3	539
September	1st to 10th	Day	22% 7% 25% 24% 17% 5%	490
	11th to 20th	Day	11% 7% 24% 33% 20% 4	490
	21st to end	Day	19% 11% 23% 27% 16% 4	490
October	1st to 10th	Day	21% 17% 28% 19% 13% 2	490
	11th to 20th	Day	32% 16% 32% 17% 3	342
	21st to end	Day	37% 16% 31% 12% 4	330
November	1st to 10th	Day	30% 19% 28% 17% 7%	300
	11th to 20th	Day	25% 24% 38% 9% 3	300
	21st to end	Day	26% 25% 34% 13% 2	300
December	1st to 10th	Day	34% 21% 29% 11% 5%	206
	11th to 20th	Day	27% 28% 32% 9% 3	225
	21st to end	Day	30% 25% 32% 9% 2 2	330
January	1st to 10th	Night	22% 21% 34% 18% 4	1000
	11th to 20th	Night	24% 24% 29% 18% 5%	1000
	21st to end	Night	22% 16% 34% 22% 5% 1	1100
February	1st to 10th	Night	20% 20% 32% 21% 6% 1	923
	11th to 20th	Night	21% 21% 30% 23% 4	783
	21st to end	Night	24% 20% 30% 23% 3	660
March	1st to 10th	Night	19% 15% 33% 25% 7% 1	800
	11th to 20th	Night	17% 16% 35% 25% 7% 1	767
	21st to end	Night	21% 12% 29% 29% 7% 1	736
April	1st to 10th	Night	22% 11% 32% 26% 6% 1	570
	11th to 20th	Night	24% 11% 30% 26% 8% 1	563
	21st to end	Night	20% 8% 28% 32% 11% 1	570
May	1st to 10th	Night	19% 7% 28% 34% 11% 1	570
	11th to 20th	Night	17% 7% 27% 35% 12% 2	561
	21st to end	Night	15% 4 26% 34% 20% 2	617
June	1st to 10th	Night	16% 5% 24% 39% 15% 1	570
	11th to 20th	Night	14% 6% 20% 40% 17% 2	570
	21st to end	Night	14% 4 23% 37% 21% 1	570
July	1st to 10th	Night	11% 3 17% 41% 24% 3	555
	11th to 20th	Night	11% 3 20% 35% 28% 3	552
	21st to end	Night	10% 3 21% 38% 25% 2	624
August	1st to 10th	Night	9% 3 21% 37% 28% 2	567
	11th to 20th	Night	11% 4 20% 33% 28% 5%	564
	21st to end	Night	15% 4 20% 41% 19% 2	627
September	1st to 10th	Night	17% 5% 22% 32% 21% 4	570
	11th to 20th	Night	17% 5% 21% 32% 21% 5%	745
	21st to end	Night	22% 8% 20% 28% 18% 4	760
October	1st to 10th	Night	26% 11% 22% 25% 14% 2	760
	11th to 20th	Night	32% 14% 24% 24% 5%	760
	21st to end	Night	35% 14% 24% 21% 5% 1	836
November	1st to 10th	Night	28% 15% 28% 24% 4 1	780
	11th to 20th	Night	31% 20% 30% 16% 4	800
	21st to end	Night	30% 19% 30% 18% 3	880
December	1st to 10th	Night	29% 23% 30% 15% 3	1000
	11th to 20th	Night	27% 21% 33% 14% 4 1	1000
	21st to end	Night	31% 19% 33% 15% 2	1100

Page generated at 2025-03-09 08:08:42. Version ac07

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