Cypress Hills Dark-Sky Preserve - West Block
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cypress Hills Dark-Sky Preserve - West Block clear sky chart from 2005-11-06 to 2024-12-24.

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	6% 7% 3 7% 5% 5% 5% 4 6% 8% 43%	105920
	Night	5% 7% 3 7% 5% 5% 5% 4 7% 9% 43%	102813
Transparency	Day	36% 7% 16% 26% 12% 2	105643
	Night	35% 8% 17% 26% 12% 2	102681
Seeing	Day	10% 12% 31% 29% 15% 3	15734
	Night	9% 12% 33% 32% 13% 1	25103

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	2 11% 5% 9% 5% 4 5% 4 7% 11% 36%	2219
	11th to 20th	Day	1 5% 3 12% 7% 5% 8% 7% 9% 10% 32%	2220
	21st to end	Day	1 6% 3 9% 5% 5% 5% 5% 5% 8% 48%	2706
February	1st to 10th	Day	5% 9% 4 10% 6% 6% 7% 6% 8% 8% 30%	1710
	11th to 20th	Day	3 9% 4 9% 7% 6% 8% 6% 9% 10% 29%	1665
	21st to end	Day	4 10% 4 12% 6% 7% 7% 5% 7% 9% 30%	1413
March	1st to 10th	Day	3 7% 3 9% 6% 7% 6% 4 7% 8% 41%	3285
	11th to 20th	Day	6% 7% 3 7% 5% 5% 5% 3 7% 12% 41%	3490
	21st to end	Day	6% 17% 5% 14% 10% 5% 5% 4 6% 6% 23%	3825
April	1st to 10th	Day	6% 10% 3 9% 6% 6% 5% 5% 7% 8% 34%	2279
	11th to 20th	Day	9% 13% 5% 9% 6% 5% 5% 4 6% 7% 31%	2437
	21st to end	Day	10% 11% 3 9% 5% 4 5% 5% 6% 8% 33%	2470
May	1st to 10th	Day	15% 14% 6% 9% 4 5% 4 4 4 5% 30%	4398
	11th to 20th	Day	8% 6% 2 7% 6% 6% 6% 6% 8% 8% 36%	4388
	21st to end	Day	14% 10% 3 9% 6% 6% 5% 4 6% 6% 31%	5154
June	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 6% 7% 36%	2850
	11th to 20th	Day	15% 8% 3 7% 6% 5% 5% 5% 6% 8% 32%	2850
	21st to end	Day	7% 4 2 5% 5% 5% 5% 5% 7% 8% 45%	2850
July	1st to 10th	Day	3 3 2 6% 5% 5% 6% 4 7% 9% 49%	4740
	11th to 20th	Day	4 3 1 4 4 4 4 4 6% 8% 59%	4740
	21st to end	Day	2 2 1 3 3 3 3 3 5% 7% 68%	5095
August	1st to 10th	Day	5% 4 2 5% 4 5% 5% 4 6% 9% 52%	4225
	11th to 20th	Day	4 3 2 4 3 4 5% 5% 8% 10% 52%	4028
	21st to end	Day	5% 3 1 4 3 3 3 4 6% 8% 60%	4521
September	1st to 10th	Day	10% 5% 1 5% 4 3 3 4 5% 7% 52%	2298
	11th to 20th	Day	12% 5% 2 6% 3 4 5% 4 5% 8% 45%	2180
	21st to end	Day	10% 6% 2 4 3 3 4 3 5% 7% 52%	2066
October	1st to 10th	Day	5% 5% 2 5% 3 4 5% 4 6% 9% 51%	3170
	11th to 20th	Day	3 5% 2 6% 4 4 4 4 6% 9% 53%	3150
	21st to end	Day	4 6% 3 7% 5% 3 4 4 7% 8% 50%	3093
November	1st to 10th	Day	8% 11% 5% 9% 6% 5% 5% 4 6% 7% 35%	1568
	11th to 20th	Day	3 7% 2 7% 7% 6% 6% 5% 8% 9% 41%	1600
	21st to end	Day	4 10% 3 9% 5% 6% 8% 6% 6% 8% 35%	1600
December	1st to 10th	Day	3 11% 3 9% 8% 7% 8% 5% 6% 8% 32%	1419
	11th to 20th	Day	3 8% 3 8% 8% 6% 7% 5% 7% 8% 36%	1755
	21st to end	Day	2 7% 3 7% 4 5% 5% 4 7% 7% 49%	2463
January	1st to 10th	Night	2 7% 3 7% 5% 6% 6% 5% 9% 12% 36%	4726
	11th to 20th	Night	2 6% 5% 12% 7% 7% 6% 5% 7% 9% 34%	4740
	21st to end	Night	1 6% 3 7% 6% 5% 5% 5% 8% 9% 44%	4980
February	1st to 10th	Night	4 9% 3 10% 7% 7% 6% 5% 8% 9% 32%	2470
	11th to 20th	Night	2 8% 4 8% 7% 7% 7% 6% 9% 9% 32%	2402
	21st to end	Night	3 8% 4 10% 8% 6% 6% 4 7% 11% 33%	2041
March	1st to 10th	Night	3 7% 4 9% 7% 7% 7% 6% 7% 9% 33%	3583
	11th to 20th	Night	6% 7% 2 5% 3 4 5% 4 7% 10% 47%	3490
	21st to end	Night	8% 15% 6% 14% 10% 7% 6% 4 6% 6% 18%	3828
April	1st to 10th	Night	6% 10% 4 9% 7% 6% 5% 5% 6% 9% 34%	1898
	11th to 20th	Night	9% 9% 4 8% 5% 5% 5% 5% 7% 9% 34%	1691
	21st to end	Night	9% 9% 4 9% 5% 5% 6% 4 6% 8% 37%	1710
May	1st to 10th	Night	15% 12% 3 8% 5% 5% 5% 4 5% 5% 33%	2558
	11th to 20th	Night	6% 6% 2 7% 5% 5% 6% 6% 8% 9% 40%	2517
	21st to end	Night	12% 7% 3 8% 6% 6% 6% 5% 7% 8% 34%	2418
June	1st to 10th	Night	14% 7% 2 6% 5% 5% 5% 4 6% 7% 41%	1330
	11th to 20th	Night	8% 7% 2 8% 5% 5% 5% 4 5% 7% 44%	1330
	21st to end	Night	6% 4 1 4 3 3 5% 4 6% 10% 54%	1330
July	1st to 10th	Night	3 3 1 4 3 4 5% 4 7% 10% 58%	2220
	11th to 20th	Night	3 2 1 4 2 3 4 3 6% 8% 64%	2220
	21st to end	Night	2 1 1 2 2 2 3 3 5% 8% 69%	2444
August	1st to 10th	Night	8% 4 2 4 3 3 3 3 5% 7% 57%	2711
	11th to 20th	Night	3 3 2 5% 4 4 5% 5% 8% 10% 51%	2811
	21st to end	Night	9% 4 2 4 4 3 4 3 4 6% 57%	3146
September	1st to 10th	Night	9% 5% 1 6% 3 4 4 3 5% 7% 54%	1881
	11th to 20th	Night	9% 8% 2 5% 4 4 4 4 5% 8% 48%	1998
	21st to end	Night	6% 5% 2 6% 4 4 3 3 6% 8% 52%	2114
October	1st to 10th	Night	5% 5% 2 5% 3 4 5% 5% 6% 8% 53%	3800
	11th to 20th	Night	5% 6% 2 6% 4 4 5% 4 6% 9% 51%	3778
	21st to end	Night	4 6% 3 6% 4 4 5% 4 6% 8% 51%	4416
November	1st to 10th	Night	8% 9% 3 7% 5% 6% 6% 5% 7% 8% 36%	2730
	11th to 20th	Night	3 7% 3 7% 7% 6% 6% 5% 9% 9% 39%	2800
	21st to end	Night	4 9% 3 8% 6% 5% 6% 6% 7% 9% 38%	2800
December	1st to 10th	Night	2 8% 3 7% 6% 7% 6% 6% 9% 9% 36%	2980
	11th to 20th	Night	2 7% 4 9% 6% 6% 6% 5% 8% 9% 37%	3656
	21st to end	Night	3 6% 2 6% 4 4 4 4 7% 8% 52%	5266

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	40% 11% 22% 23% 5% 1	2219
	11th to 20th	Day	42% 10% 15% 19% 12% 1	2220
	21st to end	Day	32% 11% 24% 26% 6%	2706
February	1st to 10th	Day	47% 10% 18% 16% 9% 1	1710
	11th to 20th	Day	43% 10% 20% 18% 7% 1	1674
	21st to end	Day	47% 10% 15% 17% 9% 1	1413
March	1st to 10th	Day	35% 11% 21% 25% 7%	3285
	11th to 20th	Day	34% 10% 23% 23% 9%	3490
	21st to end	Day	54% 13% 17% 12% 4 1	3825
April	1st to 10th	Day	43% 9% 17% 22% 8%	2279
	11th to 20th	Day	50% 7% 14% 22% 6% 1	2440
	21st to end	Day	44% 9% 16% 24% 6% 1	2470
May	1st to 10th	Day	53% 7% 14% 21% 5%	4398
	11th to 20th	Day	37% 11% 16% 28% 8%	4392
	21st to end	Day	46% 9% 16% 21% 7%	5155
June	1st to 10th	Day	44% 8% 17% 20% 10% 1	2850
	11th to 20th	Day	47% 7% 14% 20% 11% 1	2850
	21st to end	Day	32% 8% 18% 28% 12% 1	2850
July	1st to 10th	Day	30% 4 17% 26% 18% 5%	4666
	11th to 20th	Day	23% 4 12% 34% 20% 7%	4659
	21st to end	Day	16% 4 9% 28% 32% 12%	4934
August	1st to 10th	Day	29% 4 11% 34% 20% 3	4210
	11th to 20th	Day	26% 5% 16% 37% 15% 1	4067
	21st to end	Day	22% 3 13% 40% 19% 2	4520
September	1st to 10th	Day	31% 5% 15% 24% 19% 7%	2298
	11th to 20th	Day	36% 6% 15% 27% 13% 3	2180
	21st to end	Day	30% 6% 15% 31% 16% 2	2066
October	1st to 10th	Day	30% 4 14% 34% 15% 3	3170
	11th to 20th	Day	28% 4 18% 34% 14% 2	3150
	21st to end	Day	32% 5% 12% 38% 13%	3093
November	1st to 10th	Day	47% 8% 15% 20% 9% 1	1568
	11th to 20th	Day	35% 10% 21% 25% 9% 1	1600
	21st to end	Day	43% 9% 19% 20% 8% 1	1600
December	1st to 10th	Day	46% 9% 18% 19% 6% 2	1419
	11th to 20th	Day	42% 10% 21% 22% 5% 1	1754
	21st to end	Day	33% 7% 15% 25% 13% 7%	2463
January	1st to 10th	Night	35% 13% 23% 23% 6% 1	4726
	11th to 20th	Night	43% 8% 16% 18% 12% 3	4740
	21st to end	Night	32% 10% 22% 28% 7% 1	4980
February	1st to 10th	Night	43% 8% 19% 17% 11% 2	2470
	11th to 20th	Night	40% 10% 20% 18% 11% 1	2403
	21st to end	Night	43% 8% 14% 23% 9% 3	2041
March	1st to 10th	Night	40% 10% 21% 18% 9% 1	3583
	11th to 20th	Night	30% 7% 24% 27% 11%	3490
	21st to end	Night	56% 14% 14% 11% 4 1	3828
April	1st to 10th	Night	44% 8% 18% 22% 8%	1898
	11th to 20th	Night	43% 7% 15% 21% 12% 1	1691
	21st to end	Night	43% 7% 15% 26% 8% 1	1710
May	1st to 10th	Night	47% 9% 11% 23% 9%	2558
	11th to 20th	Night	32% 10% 19% 28% 11% 1	2518
	21st to end	Night	42% 11% 19% 20% 8%	2418
June	1st to 10th	Night	39% 8% 19% 24% 10% 1	1330
	11th to 20th	Night	39% 6% 14% 24% 16% 2	1330
	21st to end	Night	24% 7% 18% 34% 14% 2	1330
July	1st to 10th	Night	22% 4 16% 35% 22% 2	2185
	11th to 20th	Night	20% 5% 10% 35% 23% 7%	2178
	21st to end	Night	13% 3 9% 31% 31% 13%	2367
August	1st to 10th	Night	27% 3 11% 35% 20% 4	2703
	11th to 20th	Night	28% 4 15% 35% 15% 3	2838
	21st to end	Night	29% 3 12% 33% 20% 3	3146
September	1st to 10th	Night	29% 4 13% 27% 18% 9%	1881
	11th to 20th	Night	35% 5% 14% 28% 13% 4	1998
	21st to end	Night	29% 4 16% 30% 18% 2	2114
October	1st to 10th	Night	29% 5% 11% 37% 17% 1	3800
	11th to 20th	Night	30% 4 15% 31% 18% 2	3778
	21st to end	Night	31% 6% 11% 37% 14%	4416
November	1st to 10th	Night	41% 10% 15% 22% 10% 2	2730
	11th to 20th	Night	34% 11% 23% 20% 11%	2800
	21st to end	Night	40% 9% 24% 18% 8% 1	2800
December	1st to 10th	Night	37% 12% 21% 20% 9% 1	2980
	11th to 20th	Night	37% 10% 26% 21% 5% 1	3657
	21st to end	Night	28% 7% 16% 26% 15% 8%	5266

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% 16% 36% 26% 12% 6%	180
	11th to 20th	Day	6% 14% 33% 28% 14% 4	180
	21st to end	Day	4 18% 36% 33% 8% 1	220
February	1st to 10th	Day	11% 16% 37% 26% 8% 1	270
	11th to 20th	Day	7% 13% 37% 29% 11% 3	270
	21st to end	Day	4 9% 39% 32% 13% 3	225
March	1st to 10th	Day	8% 13% 36% 30% 11% 1	417
	11th to 20th	Day	9% 11% 38% 25% 13% 4	460
	21st to end	Day	9% 13% 33% 28% 14% 3	506
April	1st to 10th	Day	8% 17% 34% 31% 9% 1	460
	11th to 20th	Day	11% 16% 35% 27% 9% 1	452
	21st to end	Day	17% 12% 28% 30% 13% 1	460
May	1st to 10th	Day	15% 9% 22% 31% 18% 4	634
	11th to 20th	Day	13% 9% 25% 31% 19% 4	675
	21st to end	Day	16% 11% 24% 23% 20% 6%	734
June	1st to 10th	Day	15% 12% 26% 27% 17% 3	680
	11th to 20th	Day	18% 15% 31% 23% 12% 1	680
	21st to end	Day	12% 7% 27% 28% 22% 4	680
July	1st to 10th	Day	4 4 28% 40% 21% 3	671
	11th to 20th	Day	6% 7% 31% 36% 18% 3	668
	21st to end	Day	6% 5% 26% 36% 22% 5%	739
August	1st to 10th	Day	8% 7% 24% 39% 19% 3	568
	11th to 20th	Day	6% 6% 26% 38% 20% 4	477
	21st to end	Day	7% 8% 29% 33% 19% 4	539
September	1st to 10th	Day	12% 10% 31% 31% 14% 2	490
	11th to 20th	Day	12% 11% 30% 30% 15% 3	490
	21st to end	Day	15% 13% 34% 24% 11% 3	466
October	1st to 10th	Day	15% 12% 28% 22% 19% 4	300
	11th to 20th	Day	6% 19% 33% 30% 10% 2	300
	21st to end	Day	14% 19% 38% 21% 7% 1	330
November	1st to 10th	Day	14% 20% 35% 21% 10%	300
	11th to 20th	Day	10% 24% 37% 20% 8% 1	300
	21st to end	Day	7% 17% 41% 21% 11% 3	300
December	1st to 10th	Day	11% 19% 37% 23% 8% 2	209
	11th to 20th	Day	10% 18% 41% 25% 6% 1	200
	21st to end	Day	8% 10% 30% 35% 15% 2	204
January	1st to 10th	Night	7% 18% 39% 26% 9% 1	950
	11th to 20th	Night	4 18% 39% 28% 9% 1	950
	21st to end	Night	6% 19% 37% 27% 9% 2	947
February	1st to 10th	Night	8% 14% 32% 31% 14% 2	760
	11th to 20th	Night	5% 14% 42% 28% 10% 1	744
	21st to end	Night	5% 11% 32% 32% 15% 4	628
March	1st to 10th	Night	6% 11% 39% 32% 11% 1	760
	11th to 20th	Night	8% 11% 34% 34% 10% 3	760
	21st to end	Night	11% 9% 35% 29% 13% 2	836
April	1st to 10th	Night	8% 12% 36% 32% 11% 1	580
	11th to 20th	Night	12% 9% 35% 33% 11% 1	563
	21st to end	Night	13% 10% 31% 34% 12% 1	570
May	1st to 10th	Night	13% 9% 22% 34% 21% 1	570
	11th to 20th	Night	11% 6% 25% 37% 18% 2	561
	21st to end	Night	15% 10% 22% 30% 20% 3	415
June	1st to 10th	Night	17% 8% 26% 29% 18% 2	380
	11th to 20th	Night	12% 10% 36% 30% 11%	380
	21st to end	Night	9% 5% 23% 38% 21% 3	380
July	1st to 10th	Night	5% 5% 24% 44% 19% 1	370
	11th to 20th	Night	6% 5% 31% 43% 14% 1	368
	21st to end	Night	4 6% 21% 41% 26% 2	435
August	1st to 10th	Night	8% 4 25% 42% 20% 2	567
	11th to 20th	Night	7% 5% 19% 42% 26% 1	564
	21st to end	Night	11% 6% 25% 37% 21% 1	627
September	1st to 10th	Night	12% 4 28% 37% 16% 3	570
	11th to 20th	Night	12% 9% 26% 35% 18% 1	668
	21st to end	Night	10% 8% 32% 32% 15% 3	760
October	1st to 10th	Night	12% 10% 28% 31% 18% 1	760
	11th to 20th	Night	10% 11% 35% 28% 14% 2	760
	21st to end	Night	8% 18% 36% 29% 8% 1	882
November	1st to 10th	Night	13% 14% 38% 29% 7%	975
	11th to 20th	Night	10% 17% 41% 24% 7% 1	1000
	21st to end	Night	7% 14% 42% 30% 6%	1000
December	1st to 10th	Night	7% 15% 37% 28% 11% 2	1000
	11th to 20th	Night	6% 17% 37% 30% 9% 2	1000
	21st to end	Night	9% 13% 35% 30% 10% 2	1063

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