Wardrop Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wardrop Ranch clear sky chart from 2005-11-06 to 2026-04-02.

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	4 5% 2 5% 4 4 4 4 6% 8% 56%	140047
	Night	4 6% 2 5% 4 4 4 3 5% 7% 56%	139267
Transparency	Day	25% 6% 10% 23% 25% 11%	135030
	Night	26% 6% 10% 24% 24% 9%	135292
Seeing	Day	7% 10% 29% 30% 18% 6%	17412
	Night	6% 6% 35% 39% 12% 1	27565

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	1 6% 3 7% 3 3 3 3 5% 8% 58%	4720
	11th to 20th	Day	1 4 2 8% 4 3 3 2 4 6% 63%	4814
	21st to end	Day	2 4 2 8% 4 3 3 3 4 6% 61%	5844
February	1st to 10th	Day	2 7% 3 6% 4 3 3 4 4 8% 56%	1926
	11th to 20th	Day	1 4 2 6% 4 5% 4 3 6% 7% 58%	2049
	21st to end	Day	2 6% 3 6% 4 3 3 2 5% 5% 61%	1730
March	1st to 10th	Day	2 8% 3 4 3 3 3 3 5% 6% 61%	4600
	11th to 20th	Day	4 8% 3 5% 3 4 4 3 5% 7% 54%	4936
	21st to end	Day	3 7% 3 5% 3 4 4 4 6% 8% 54%	6011
April	1st to 10th	Day	5% 8% 1 4 4 4 5% 4 6% 7% 52%	2413
	11th to 20th	Day	6% 9% 3 5% 4 4 5% 4 6% 8% 47%	2371
	21st to end	Day	9% 7% 2 5% 5% 4 5% 4 7% 8% 46%	2400
May	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 5% 6% 50%	5803
	11th to 20th	Day	8% 6% 1 5% 3 4 4 4 7% 9% 49%	6115
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 7% 8% 49%	6925
June	1st to 10th	Day	6% 4 2 5% 4 4 4 5% 8% 9% 51%	2800
	11th to 20th	Day	6% 4 1 3 4 4 5% 5% 7% 9% 53%	2800
	21st to end	Day	4 3 2 5% 4 5% 6% 5% 7% 9% 51%	2800
July	1st to 10th	Day	3 3 1 3 3 4 5% 5% 8% 9% 57%	6339
	11th to 20th	Day	3 2 1 5% 4 5% 5% 5% 8% 11% 51%	6340
	21st to end	Day	4 4 2 6% 4 5% 6% 6% 8% 9% 47%	6864
August	1st to 10th	Day	7% 3 1 5% 4 5% 6% 5% 8% 11% 44%	5655
	11th to 20th	Day	3 2 1 4 4 5% 5% 5% 8% 9% 54%	5366
	21st to end	Day	6% 4 2 6% 5% 5% 6% 5% 7% 10% 46%	5984
September	1st to 10th	Day	4 3 1 4 3 4 3 3 6% 8% 60%	2400
	11th to 20th	Day	6% 2 1 3 3 3 4 3 6% 7% 61%	2344
	21st to end	Day	5% 3 1 3 3 4 4 3 4 6% 66%	2200
October	1st to 10th	Day	4 3 1 2 1 2 2 2 3 4 76%	3381
	11th to 20th	Day	4 4 1 4 2 2 3 3 4 7% 65%	3250
	21st to end	Day	5% 5% 1 3 2 2 2 2 3 5% 70%	3368
November	1st to 10th	Day	2 4 1 3 3 3 4 3 5% 8% 66%	1853
	11th to 20th	Day	2 5% 2 4 3 3 3 2 4 6% 66%	1890
	21st to end	Day	3 6% 3 5% 3 3 2 3 4 6% 63%	1858
December	1st to 10th	Day	1 5% 2 4 3 2 3 2 4 6% 68%	2700
	11th to 20th	Day	1 4 1 3 3 3 3 3 5% 8% 65%	3106
	21st to end	Day	3 6% 3 7% 4 4 4 4 4 7% 55%	4092
January	1st to 10th	Night	2 8% 4 7% 4 3 3 3 4 7% 56%	8201
	11th to 20th	Night	1 5% 2 6% 5% 4 4 3 5% 6% 60%	8232
	21st to end	Night	2 5% 2 7% 4 4 4 3 4 5% 62%	8370
February	1st to 10th	Night	2 7% 3 7% 3 3 3 3 5% 8% 58%	2693
	11th to 20th	Night	2 7% 4 7% 5% 4 4 4 5% 7% 51%	2458
	21st to end	Night	3 6% 3 6% 3 3 3 2 4 5% 63%	2076
March	1st to 10th	Night	2 7% 4 6% 4 3 3 3 4 6% 59%	5494
	11th to 20th	Night	5% 9% 2 5% 3 3 3 3 5% 6% 56%	5273
	21st to end	Night	6% 8% 2 5% 3 4 4 4 6% 8% 50%	5173
April	1st to 10th	Night	5% 7% 2 5% 3 4 4 3 6% 7% 53%	2010
	11th to 20th	Night	9% 9% 3 5% 4 3 4 4 5% 7% 47%	1977
	21st to end	Night	10% 9% 2 5% 4 4 3 3 6% 7% 47%	2000
May	1st to 10th	Night	11% 9% 2 6% 3 3 4 3 5% 6% 48%	4175
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 7% 8% 48%	3796
	21st to end	Night	10% 6% 2 4 3 4 3 4 6% 8% 51%	3972
June	1st to 10th	Night	5% 5% 1 4 3 3 4 5% 6% 12% 53%	1600
	11th to 20th	Night	4 3 1 4 3 4 4 3 7% 8% 59%	1600
	21st to end	Night	4 4 1 4 4 4 4 5% 7% 10% 52%	1600
July	1st to 10th	Night	4 4 1 5% 4 5% 5% 5% 7% 9% 52%	3640
	11th to 20th	Night	4 3 1 5% 4 5% 6% 5% 8% 11% 48%	3640
	21st to end	Night	4 4 2 6% 4 5% 6% 5% 8% 9% 47%	4005
August	1st to 10th	Night	6% 5% 2 5% 4 5% 5% 5% 7% 9% 45%	4156
	11th to 20th	Night	5% 4 2 5% 5% 5% 5% 5% 8% 10% 48%	4483
	21st to end	Night	8% 5% 2 7% 4 4 5% 5% 7% 10% 44%	4993
September	1st to 10th	Night	6% 4 1 4 4 4 4 3 6% 8% 56%	2000
	11th to 20th	Night	6% 3 1 4 3 2 3 3 5% 9% 60%	2055
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 7% 62%	2200
October	1st to 10th	Night	5% 3 1 3 3 2 3 2 4 5% 69%	3788
	11th to 20th	Night	6% 4 1 4 3 3 4 3 5% 8% 57%	3898
	21st to end	Night	4 5% 2 4 3 2 2 2 3 5% 67%	4399
November	1st to 10th	Night	2 4 1 4 2 2 3 3 5% 7% 67%	2665
	11th to 20th	Night	2 5% 2 4 2 3 2 2 5% 6% 67%	2730
	21st to end	Night	4 7% 2 5% 3 3 3 3 5% 7% 59%	2756
December	1st to 10th	Night	1 4 2 3 2 3 2 3 3 6% 71%	4710
	11th to 20th	Night	1 4 2 4 3 3 3 3 5% 8% 63%	5321
	21st to end	Night	3 7% 2 5% 4 4 4 4 5% 7% 55%	7128

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	25% 3 7% 30% 25% 10%	4723
	11th to 20th	Day	21% 4 10% 25% 30% 10%	4814
	21st to end	Day	25% 4 7% 27% 26% 12%	5844
February	1st to 10th	Day	27% 5% 10% 27% 21% 10%	1926
	11th to 20th	Day	25% 5% 9% 28% 25% 8%	2059
	21st to end	Day	25% 3 7% 21% 27% 16%	1730
March	1st to 10th	Day	23% 5% 6% 16% 31% 20%	4600
	11th to 20th	Day	28% 6% 8% 22% 27% 8%	4936
	21st to end	Day	25% 7% 11% 34% 20% 3	6011
April	1st to 10th	Day	28% 6% 13% 23% 22% 8%	2413
	11th to 20th	Day	32% 7% 13% 21% 18% 9%	2374
	21st to end	Day	32% 7% 12% 25% 20% 3	2400
May	1st to 10th	Day	32% 6% 10% 26% 19% 6%	5803
	11th to 20th	Day	28% 9% 10% 20% 22% 11%	6119
	21st to end	Day	28% 10% 13% 24% 18% 7%	6926
June	1st to 10th	Day	26% 8% 16% 24% 17% 9%	2800
	11th to 20th	Day	24% 7% 12% 18% 23% 16%	2800
	21st to end	Day	25% 8% 12% 20% 24% 12%	2800
July	1st to 10th	Day	20% 7% 9% 17% 27% 20%	6271
	11th to 20th	Day	24% 8% 13% 25% 20% 11%	6265
	21st to end	Day	29% 8% 13% 17% 16% 16%	6666
August	1st to 10th	Day	33% 9% 15% 23% 14% 5%	4117
	11th to 20th	Day	25% 7% 13% 19% 22% 13%	3882
	21st to end	Day	26% 6% 12% 21% 25% 10%	4311
September	1st to 10th	Day	21% 5% 9% 23% 26% 16%	2400
	11th to 20th	Day	20% 6% 10% 18% 28% 18%	2344
	21st to end	Day	21% 4 7% 20% 35% 13%	2200
October	1st to 10th	Day	13% 3 6% 15% 37% 25%	3381
	11th to 20th	Day	20% 3 6% 27% 35% 9%	3250
	21st to end	Day	19% 3 5% 21% 39% 14%	3368
November	1st to 10th	Day	18% 3 10% 25% 28% 16%	1853
	11th to 20th	Day	20% 4 6% 25% 35% 11%	1890
	21st to end	Day	23% 3 8% 22% 28% 15%	1858
December	1st to 10th	Day	19% 3 7% 31% 30% 9%	2700
	11th to 20th	Day	17% 5% 8% 28% 30% 12%	3104
	21st to end	Day	26% 6% 8% 27% 25% 9%	4092
January	1st to 10th	Night	28% 4 6% 28% 28% 6%	8202
	11th to 20th	Night	23% 6% 9% 24% 24% 14%	8232
	21st to end	Night	25% 5% 8% 23% 26% 13%	8370
February	1st to 10th	Night	26% 4 10% 26% 25% 9%	2693
	11th to 20th	Night	31% 5% 10% 25% 20% 8%	2458
	21st to end	Night	23% 4 6% 25% 27% 15%	2076
March	1st to 10th	Night	26% 4 6% 15% 35% 13%	5494
	11th to 20th	Night	28% 6% 10% 15% 28% 13%	5273
	21st to end	Night	30% 8% 11% 31% 18% 2	5173
April	1st to 10th	Night	29% 6% 11% 23% 21% 9%	2010
	11th to 20th	Night	34% 6% 12% 23% 18% 6%	1977
	21st to end	Night	37% 7% 11% 25% 17% 4	2000
May	1st to 10th	Night	35% 8% 13% 28% 10% 6%	4173
	11th to 20th	Night	30% 10% 15% 22% 16% 8%	3797
	21st to end	Night	28% 10% 18% 26% 14% 4	3972
June	1st to 10th	Night	24% 8% 21% 26% 15% 6%	1600
	11th to 20th	Night	21% 7% 15% 24% 20% 14%	1600
	21st to end	Night	25% 8% 12% 26% 21% 9%	1600
July	1st to 10th	Night	26% 7% 12% 20% 29% 7%	3600
	11th to 20th	Night	27% 8% 20% 25% 16% 3	3592
	21st to end	Night	29% 8% 16% 17% 21% 8%	3891
August	1st to 10th	Night	37% 10% 16% 22% 12% 3	3018
	11th to 20th	Night	30% 9% 18% 21% 17% 5%	3243
	21st to end	Night	26% 7% 15% 28% 19% 5%	3597
September	1st to 10th	Night	25% 7% 10% 21% 25% 12%	2000
	11th to 20th	Night	20% 6% 11% 23% 25% 15%	2055
	21st to end	Night	21% 5% 9% 23% 30% 11%	2200
October	1st to 10th	Night	18% 5% 7% 19% 33% 19%	3788
	11th to 20th	Night	24% 5% 8% 27% 27% 9%	3898
	21st to end	Night	22% 3 6% 25% 31% 14%	4399
November	1st to 10th	Night	17% 4 10% 24% 29% 16%	2665
	11th to 20th	Night	19% 3 8% 27% 31% 12%	2730
	21st to end	Night	25% 4 9% 22% 29% 11%	2756
December	1st to 10th	Night	16% 3 8% 32% 32% 9%	4710
	11th to 20th	Night	20% 3 6% 28% 35% 7%	5322
	21st to end	Night	27% 5% 8% 24% 26% 10%	7128

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	5% 6% 34% 36% 15% 3	330
	11th to 20th	Day	8% 12% 33% 34% 12% 1	330
	21st to end	Day	3 10% 40% 32% 12% 3	363
February	1st to 10th	Day	5% 13% 42% 30% 7% 2	330
	11th to 20th	Day	3 13% 45% 31% 7% 1	330
	21st to end	Day	3 14% 42% 29% 9% 2	273
March	1st to 10th	Day	4 14% 34% 31% 14% 4	330
	11th to 20th	Day	10% 16% 36% 25% 11% 2	457
	21st to end	Day	12% 21% 35% 21% 9% 2	594
April	1st to 10th	Day	9% 19% 36% 24% 9% 2	505
	11th to 20th	Day	13% 24% 32% 21% 9% 2	492
	21st to end	Day	13% 18% 35% 23% 10% 2	500
May	1st to 10th	Day	12% 16% 32% 26% 11% 3	658
	11th to 20th	Day	12% 10% 30% 29% 15% 4	725
	21st to end	Day	9% 13% 29% 28% 17% 5%	789
June	1st to 10th	Day	7% 8% 26% 29% 22% 8%	730
	11th to 20th	Day	5% 9% 29% 32% 20% 5%	730
	21st to end	Day	4 7% 26% 35% 22% 6%	730
July	1st to 10th	Day	6% 4 18% 34% 30% 8%	721
	11th to 20th	Day	4 2 16% 35% 33% 11%	718
	21st to end	Day	5% 2 15% 33% 33% 12%	780
August	1st to 10th	Day	7% 2 21% 35% 23% 11%	527
	11th to 20th	Day	4 3 20% 36% 25% 12%	517
	21st to end	Day	6% 3 24% 33% 26% 8%	583
September	1st to 10th	Day	5% 4 24% 32% 24% 11%	530
	11th to 20th	Day	4 6% 28% 30% 23% 10%	474
	21st to end	Day	7% 5% 20% 29% 27% 12%	330
October	1st to 10th	Day	7% 10% 21% 27% 22% 14%	330
	11th to 20th	Day	2 13% 31% 28% 19% 7%	330
	21st to end	Day	8% 10% 34% 29% 15% 5%	363
November	1st to 10th	Day	4 10% 31% 32% 18% 4	330
	11th to 20th	Day	4 9% 30% 40% 15% 3	330
	21st to end	Day	5% 9% 34% 36% 13% 3	330
December	1st to 10th	Day	4 13% 39% 27% 15% 3	330
	11th to 20th	Day	4 10% 41% 34% 9% 2	330
	21st to end	Day	7% 12% 38% 32% 11% 1	363
January	1st to 10th	Night	4 5% 40% 40% 10% 2	1050
	11th to 20th	Night	5% 8% 40% 38% 9% 1	1045
	21st to end	Night	3 5% 40% 42% 10% 1	924
February	1st to 10th	Night	4 7% 48% 36% 5% 1	840
	11th to 20th	Night	5% 8% 48% 33% 6%	824
	21st to end	Night	5% 8% 48% 34% 5%	692
March	1st to 10th	Night	5% 8% 45% 35% 7%	840
	11th to 20th	Night	8% 8% 41% 34% 9%	840
	21st to end	Night	8% 10% 42% 32% 8%	733
April	1st to 10th	Night	9% 10% 46% 29% 6%	603
	11th to 20th	Night	13% 13% 38% 30% 6%	593
	21st to end	Night	15% 11% 34% 33% 8%	600
May	1st to 10th	Night	12% 10% 33% 36% 9% 1	600
	11th to 20th	Night	15% 5% 31% 37% 11% 1	591
	21st to end	Night	11% 7% 34% 35% 12% 1	650
June	1st to 10th	Night	7% 4 29% 42% 16% 2	600
	11th to 20th	Night	5% 4 36% 42% 13%	600
	21st to end	Night	3 3 29% 45% 18% 1	600
July	1st to 10th	Night	6% 2 22% 44% 24% 2	585
	11th to 20th	Night	2 1 19% 49% 26% 3	582
	21st to end	Night	7% 2 16% 42% 32% 1	657
August	1st to 10th	Night	6% 2 20% 46% 24% 2	597
	11th to 20th	Night	5% 2 22% 51% 19% 1	594
	21st to end	Night	6% 2 20% 48% 21% 3	660
September	1st to 10th	Night	6% 1 24% 48% 19% 2	600
	11th to 20th	Night	7% 3 26% 44% 18% 2	600
	21st to end	Night	6% 4 26% 46% 16% 3	600
October	1st to 10th	Night	9% 4 34% 34% 16% 3	720
	11th to 20th	Night	5% 6% 32% 41% 14% 3	800
	21st to end	Night	7% 7% 34% 35% 15% 2	965
November	1st to 10th	Night	4 6% 35% 40% 13% 1	1025
	11th to 20th	Night	4 6% 38% 41% 9% 1	1050
	21st to end	Night	7% 8% 35% 37% 12% 2	1050
December	1st to 10th	Night	3 7% 40% 38% 11% 1	1050
	11th to 20th	Night	5% 6% 44% 33% 11% 1	1050
	21st to end	Night	6% 9% 42% 36% 7% 1	1155

Page generated at 2026-03-30 00:18:46. Version ac07

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