Whiterock Resort
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whiterock Resort clear sky chart from 2005-11-06 to 2025-10-19.

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 5% 7% 41%	126714
	Night	11% 8% 3 8% 4 4 4 3 5% 6% 44%	123244
Transparency	Day	41% 6% 12% 25% 15% 2	130317
	Night	39% 5% 12% 25% 16% 2	127718
Seeing	Day	15% 11% 32% 27% 13% 3	17185
	Night	15% 10% 34% 30% 10% 1	26977

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	8% 12% 5% 18% 8% 6% 5% 3 4 5% 26%	3783
	11th to 20th	Day	6% 10% 4 12% 6% 5% 8% 5% 5% 6% 33%	4080
	21st to end	Day	9% 11% 6% 13% 6% 5% 4 4 5% 5% 32%	4488
February	1st to 10th	Day	10% 14% 5% 10% 7% 6% 4 3 5% 7% 29%	1800
	11th to 20th	Day	10% 10% 4 9% 5% 5% 5% 3 4 6% 38%	1754
	21st to end	Day	12% 10% 4 8% 5% 5% 4 3 5% 5% 37%	1607
March	1st to 10th	Day	15% 9% 3 7% 3 3 3 2 3 5% 47%	4936
	11th to 20th	Day	12% 7% 2 6% 4 4 4 3 5% 8% 46%	4980
	21st to end	Day	21% 13% 5% 9% 5% 4 4 4 4 6% 25%	5462
April	1st to 10th	Day	16% 10% 3 6% 4 4 4 4 5% 7% 37%	2339
	11th to 20th	Day	16% 10% 3 7% 5% 4 3 3 5% 7% 37%	2393
	21st to end	Day	21% 8% 3 6% 4 4 4 3 5% 6% 35%	2600
May	1st to 10th	Day	14% 8% 2 7% 5% 4 4 4 5% 6% 41%	5862
	11th to 20th	Day	14% 6% 3 5% 4 3 4 3 4 6% 48%	6035
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	6935
June	1st to 10th	Day	10% 6% 2 5% 4 5% 5% 4 6% 9% 44%	2800
	11th to 20th	Day	8% 4 1 6% 5% 5% 5% 5% 7% 9% 45%	2800
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 7% 8% 44%	2800
July	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 7% 9% 44%	6360
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 5% 7% 51%	6067
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 11% 44%	6422
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 9% 45%	4234
	11th to 20th	Day	15% 7% 2 6% 4 4 5% 4 6% 8% 40%	4171
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 6% 8% 47%	4484
September	1st to 10th	Day	11% 5% 1 4 3 3 3 4 5% 6% 54%	2400
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 5% 7% 51%	2251
	21st to end	Day	10% 5% 2 4 3 3 4 4 5% 8% 52%	2172
October	1st to 10th	Day	13% 6% 2 4 4 4 4 2 5% 6% 51%	2000
	11th to 20th	Day	14% 7% 2 5% 4 3 3 3 4 5% 50%	1980
	21st to end	Day	14% 8% 3 6% 3 4 4 3 5% 6% 43%	2090
November	1st to 10th	Day	11% 6% 2 5% 4 4 3 4 5% 8% 48%	1829
	11th to 20th	Day	12% 8% 3 7% 6% 5% 3 4 5% 7% 41%	1600
	21st to end	Day	12% 10% 4 6% 5% 4 3 4 6% 7% 40%	1600
December	1st to 10th	Day	6% 6% 3 6% 5% 4 4 3 5% 6% 51%	2610
	11th to 20th	Day	11% 9% 4 10% 6% 5% 5% 4 6% 7% 34%	3008
	21st to end	Day	18% 13% 5% 16% 6% 4 4 3 4 5% 21%	3982
January	1st to 10th	Night	8% 12% 5% 19% 9% 5% 4 3 4 5% 25%	6164
	11th to 20th	Night	7% 11% 4 9% 6% 5% 7% 4 7% 7% 34%	5900
	21st to end	Night	9% 12% 5% 11% 5% 4 4 3 5% 5% 36%	6490
February	1st to 10th	Night	10% 13% 3 10% 7% 5% 4 3 5% 5% 34%	2600
	11th to 20th	Night	10% 11% 4 7% 5% 5% 5% 4 5% 6% 39%	2533
	21st to end	Night	10% 8% 3 9% 4 5% 4 2 4 5% 46%	2038
March	1st to 10th	Night	15% 7% 2 5% 3 2 3 2 4 5% 51%	4919
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 5% 7% 52%	4980
	21st to end	Night	16% 11% 4 11% 5% 4 4 4 5% 6% 30%	5467
April	1st to 10th	Night	12% 9% 2 6% 5% 3 4 4 4 7% 45%	2060
	11th to 20th	Night	13% 9% 4 6% 5% 3 4 3 5% 7% 42%	1952
	21st to end	Night	17% 8% 3 7% 4 4 3 3 4 8% 40%	1800
May	1st to 10th	Night	15% 7% 2 5% 4 3 4 3 4 6% 49%	4053
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 7% 52%	3880
	21st to end	Night	18% 8% 3 6% 4 4 4 3 5% 6% 42%	3942
June	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 51%	1600
	11th to 20th	Night	7% 5% 2 5% 4 3 4 4 8% 9% 50%	1600
	21st to end	Night	5% 4 1 6% 4 5% 4 5% 6% 8% 53%	1600
July	1st to 10th	Night	6% 4 2 5% 4 4 5% 5% 6% 9% 50%	3618
	11th to 20th	Night	7% 5% 2 4 3 3 3 3 5% 9% 56%	3892
	21st to end	Night	6% 4 2 6% 4 4 5% 4 7% 9% 49%	4449
August	1st to 10th	Night	5% 4 1 6% 4 4 4 4 5% 9% 55%	2926
	11th to 20th	Night	9% 7% 2 5% 3 3 4 3 5% 7% 52%	2888
	21st to end	Night	8% 5% 2 4 3 3 4 3 5% 8% 56%	3417
September	1st to 10th	Night	8% 4 2 4 4 3 3 3 4 7% 57%	2000
	11th to 20th	Night	9% 5% 3 4 3 3 4 3 6% 7% 54%	2145
	21st to end	Night	9% 4 2 5% 3 3 3 3 4 6% 58%	2207
October	1st to 10th	Night	12% 6% 2 5% 3 3 4 2 5% 6% 53%	2400
	11th to 20th	Night	14% 6% 3 5% 3 3 3 2 4 6% 51%	2377
	21st to end	Night	15% 7% 2 7% 3 4 3 3 4 6% 47%	2508
November	1st to 10th	Night	9% 6% 2 5% 4 3 4 3 5% 6% 54%	2464
	11th to 20th	Night	11% 7% 2 7% 4 3 3 3 6% 6% 46%	2800
	21st to end	Night	11% 9% 3 7% 4 3 4 3 5% 6% 44%	2800
December	1st to 10th	Night	5% 8% 3 7% 5% 4 4 3 6% 6% 48%	4580
	11th to 20th	Night	10% 8% 4 11% 5% 5% 4 4 5% 5% 37%	5199
	21st to end	Night	18% 15% 5% 13% 5% 4 4 3 4 4 26%	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% 4 10% 17% 7%	3784
	11th to 20th	Day	51% 4 10% 20% 13% 2	4080
	21st to end	Day	53% 4 12% 21% 9% 1	4488
February	1st to 10th	Day	56% 4 10% 19% 10% 1	1800
	11th to 20th	Day	48% 4 11% 21% 14% 2	1763
	21st to end	Day	48% 5% 12% 20% 12% 3	1607
March	1st to 10th	Day	42% 3 7% 28% 17% 3	4936
	11th to 20th	Day	37% 5% 8% 27% 20% 3	4980
	21st to end	Day	60% 6% 14% 15% 4 1	5464
April	1st to 10th	Day	46% 6% 11% 27% 10% 1	2339
	11th to 20th	Day	48% 5% 12% 21% 12% 2	2393
	21st to end	Day	49% 5% 10% 22% 12% 1	2600
May	1st to 10th	Day	42% 6% 9% 25% 16% 1	5900
	11th to 20th	Day	38% 5% 8% 28% 18% 3	6039
	21st to end	Day	45% 7% 11% 22% 14% 1	6949
June	1st to 10th	Day	36% 7% 15% 26% 14% 2	2800
	11th to 20th	Day	32% 8% 14% 27% 18% 1	2800
	21st to end	Day	36% 7% 15% 25% 14% 3	2800
July	1st to 10th	Day	34% 7% 15% 32% 10% 1	6291
	11th to 20th	Day	32% 7% 12% 30% 17% 2	5994
	21st to end	Day	30% 9% 20% 27% 13% 1	6240
August	1st to 10th	Day	34% 8% 15% 27% 16% 1	4220
	11th to 20th	Day	41% 6% 11% 29% 12% 1	4210
	21st to end	Day	33% 7% 15% 26% 17% 3	4483
September	1st to 10th	Day	31% 6% 11% 29% 20% 4	2400
	11th to 20th	Day	32% 6% 12% 31% 18% 1	2251
	21st to end	Day	30% 5% 11% 30% 23% 1	2172
October	1st to 10th	Day	21% 3 6% 27% 41% 2	3260
	11th to 20th	Day	26% 3 12% 31% 23% 6%	3220
	21st to end	Day	37% 5% 8% 29% 19% 4	3428
November	1st to 10th	Day	35% 5% 16% 23% 18% 3	1829
	11th to 20th	Day	43% 5% 12% 23% 17% 1	1600
	21st to end	Day	44% 4 15% 24% 13% 1	1600
December	1st to 10th	Day	33% 4 19% 31% 12% 1	2610
	11th to 20th	Day	49% 6% 16% 22% 8%	3005
	21st to end	Day	65% 4 10% 15% 5% 1	3982
January	1st to 10th	Night	61% 5% 11% 14% 9% 1	6164
	11th to 20th	Night	46% 5% 12% 18% 16% 3	5900
	21st to end	Night	50% 5% 10% 19% 15% 1	6490
February	1st to 10th	Night	53% 4 10% 20% 11% 2	2600
	11th to 20th	Night	45% 4 11% 23% 14% 3	2534
	21st to end	Night	42% 3 11% 22% 19% 3	2038
March	1st to 10th	Night	37% 3 7% 32% 19% 3	4919
	11th to 20th	Night	32% 4 8% 33% 18% 5%	4980
	21st to end	Night	53% 8% 14% 17% 5% 2	5467
April	1st to 10th	Night	40% 5% 11% 26% 16% 2	2060
	11th to 20th	Night	42% 5% 10% 24% 16% 3	1952
	21st to end	Night	45% 5% 12% 23% 14% 1	1800
May	1st to 10th	Night	37% 5% 9% 28% 20% 1	4080
	11th to 20th	Night	32% 6% 11% 24% 21% 6%	3881
	21st to end	Night	43% 6% 12% 22% 15% 2	3950
June	1st to 10th	Night	29% 6% 15% 31% 15% 4	1600
	11th to 20th	Night	28% 8% 13% 25% 23% 4	1600
	21st to end	Night	27% 7% 15% 29% 20% 3	1600
July	1st to 10th	Night	28% 7% 16% 33% 15% 2	3580
	11th to 20th	Night	26% 6% 15% 31% 20% 2	3846
	21st to end	Night	28% 10% 19% 28% 14% 1	4320
August	1st to 10th	Night	26% 6% 17% 31% 18% 2	2916
	11th to 20th	Night	32% 6% 14% 31% 16% 2	2915
	21st to end	Night	27% 6% 16% 27% 19% 6%	3417
September	1st to 10th	Night	28% 5% 11% 28% 24% 4	2000
	11th to 20th	Night	29% 5% 12% 34% 19% 1	2145
	21st to end	Night	28% 4 9% 29% 26% 3	2207
October	1st to 10th	Night	21% 3 6% 22% 45% 2	3920
	11th to 20th	Night	27% 3 9% 27% 27% 6%	3876
	21st to end	Night	38% 4 10% 27% 19% 2	4120
November	1st to 10th	Night	31% 4 15% 25% 20% 4	2464
	11th to 20th	Night	38% 4 14% 25% 17% 2	2800
	21st to end	Night	41% 4 10% 28% 14% 2	2800
December	1st to 10th	Night	36% 4 13% 36% 11% 1	4580
	11th to 20th	Night	47% 6% 13% 25% 8%	5201
	21st to end	Night	63% 4 10% 17% 7%	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	19% 15% 35% 22% 7% 1	300
	11th to 20th	Day	19% 16% 42% 21% 2 1	300
	21st to end	Day	20% 11% 41% 23% 4 1	330
February	1st to 10th	Day	18% 17% 44% 17% 3	300
	11th to 20th	Day	15% 22% 39% 19% 4 1	300
	21st to end	Day	22% 20% 39% 16% 3	249
March	1st to 10th	Day	17% 19% 44% 14% 5% 1	300
	11th to 20th	Day	26% 13% 37% 17% 6%	300
	21st to end	Day	32% 16% 34% 15% 3	330
April	1st to 10th	Day	27% 15% 35% 19% 5%	439
	11th to 20th	Day	22% 17% 34% 20% 6%	511
	21st to end	Day	24% 17% 34% 19% 6% 2	700
May	1st to 10th	Day	23% 13% 30% 23% 9% 1	703
	11th to 20th	Day	21% 12% 30% 24% 11% 2	725
	21st to end	Day	19% 11% 29% 25% 14% 3	789
June	1st to 10th	Day	9% 7% 27% 31% 21% 5%	730
	11th to 20th	Day	9% 6% 32% 35% 16% 3	730
	21st to end	Day	8% 9% 38% 28% 14% 3	730
July	1st to 10th	Day	7% 4 21% 34% 24% 10%	721
	11th to 20th	Day	6% 4 28% 35% 21% 7%	718
	21st to end	Day	6% 2 23% 41% 23% 4	794
August	1st to 10th	Day	8% 5% 24% 37% 21% 5%	726
	11th to 20th	Day	11% 5% 20% 34% 25% 4	715
	21st to end	Day	10% 3 23% 38% 20% 5%	690
September	1st to 10th	Day	13% 6% 25% 32% 17% 6%	530
	11th to 20th	Day	9% 4 31% 33% 18% 5%	381
	21st to end	Day	12% 12% 27% 32% 14% 4	330
October	1st to 10th	Day	18% 9% 30% 27% 14% 3	330
	11th to 20th	Day	18% 17% 38% 21% 6% 1	324
	21st to end	Day	19% 17% 35% 20% 7% 1	330
November	1st to 10th	Day	16% 16% 37% 22% 7% 2	300
	11th to 20th	Day	21% 20% 35% 17% 7%	300
	21st to end	Day	20% 16% 40% 19% 6%	300
December	1st to 10th	Day	10% 15% 45% 23% 7%	300
	11th to 20th	Day	16% 17% 38% 20% 7% 1	300
	21st to end	Day	23% 17% 41% 15% 3	330
January	1st to 10th	Night	14% 15% 38% 27% 6%	1000
	11th to 20th	Night	15% 16% 39% 23% 6% 1	1000
	21st to end	Night	19% 12% 38% 25% 5%	1100
February	1st to 10th	Night	17% 13% 43% 24% 4	1000
	11th to 20th	Night	17% 14% 42% 22% 4	979
	21st to end	Night	15% 17% 42% 21% 4 2	718
March	1st to 10th	Night	18% 11% 38% 25% 7% 1	600
	11th to 20th	Night	18% 9% 38% 28% 8%	600
	21st to end	Night	23% 15% 37% 19% 5% 1	660
April	1st to 10th	Night	19% 16% 39% 22% 4	600
	11th to 20th	Night	18% 15% 34% 28% 5% 1	593
	21st to end	Night	21% 13% 35% 25% 7% 1	600
May	1st to 10th	Night	18% 9% 34% 30% 9%	600
	11th to 20th	Night	18% 9% 29% 32% 12%	591
	21st to end	Night	17% 7% 27% 35% 13%	650
June	1st to 10th	Night	8% 6% 26% 42% 18%	600
	11th to 20th	Night	9% 4 30% 44% 13%	600
	21st to end	Night	8% 5% 35% 39% 13% 1	600
July	1st to 10th	Night	6% 2 18% 44% 29% 2	585
	11th to 20th	Night	4 1 22% 49% 21% 2	582
	21st to end	Night	4 2 18% 50% 24% 1	657
August	1st to 10th	Night	8% 2 22% 42% 24% 1	597
	11th to 20th	Night	8% 3 19% 44% 23% 3	594
	21st to end	Night	9% 3 22% 40% 24% 2	660
September	1st to 10th	Night	10% 6% 21% 38% 23% 3	600
	11th to 20th	Night	11% 3 28% 39% 18% 1	600
	21st to end	Night	11% 5% 31% 35% 17% 1	607
October	1st to 10th	Night	15% 9% 33% 30% 13% 1	800
	11th to 20th	Night	17% 13% 37% 27% 7%	793
	21st to end	Night	20% 12% 33% 27% 8%	836
November	1st to 10th	Night	12% 13% 37% 31% 7%	875
	11th to 20th	Night	15% 16% 40% 22% 6%	1000
	21st to end	Night	17% 13% 38% 25% 8% 1	1000
December	1st to 10th	Night	15% 13% 42% 23% 6%	1000
	11th to 20th	Night	17% 12% 38% 27% 5% 1	1000
	21st to end	Night	20% 15% 37% 24% 4	1100

Page generated at 2025-10-16 00:50:24. Version ac07

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