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 2026-04-17.

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%	140301
	Night	5% 6% 3 7% 5% 5% 5% 5% 7% 9% 43%	139138
Transparency	Day	37% 6% 16% 26% 12% 2	134925
	Night	36% 6% 17% 25% 13% 2	135523
Seeing	Day	11% 12% 31% 28% 14% 3	17429
	Night	9% 12% 33% 31% 12% 1	26884

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 10% 4 11% 6% 6% 5% 4 7% 10% 34%	4124
	11th to 20th	Day	3 3 9% 7% 6% 7% 6% 10% 11% 37%	4140
	21st to end	Day	1 5% 3 8% 5% 6% 7% 4 6% 8% 48%	5045
February	1st to 10th	Day	5% 9% 4 9% 6% 6% 7% 6% 9% 9% 31%	1890
	11th to 20th	Day	3 8% 4 8% 7% 6% 8% 6% 9% 10% 31%	1845
	21st to end	Day	4 9% 4 11% 6% 7% 7% 5% 7% 10% 30%	1557
March	1st to 10th	Day	4 5% 3 9% 6% 6% 5% 4 7% 8% 43%	4833
	11th to 20th	Day	4 7% 3 8% 5% 5% 6% 4 8% 11% 39%	5110
	21st to end	Day	5% 14% 7% 13% 9% 5% 5% 4 7% 7% 22%	5607
April	1st to 10th	Day	6% 10% 3 9% 6% 5% 5% 5% 6% 8% 36%	2519
	11th to 20th	Day	8% 13% 5% 9% 6% 5% 5% 4 6% 7% 31%	2646
	21st to end	Day	10% 12% 3 9% 5% 4 5% 5% 6% 8% 34%	2600
May	1st to 10th	Day	11% 11% 4 7% 4 4 4 4 5% 6% 40%	6294
	11th to 20th	Day	11% 10% 3 10% 7% 6% 6% 5% 7% 7% 28%	6298
	21st to end	Day	11% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	7397
June	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 5% 6% 7% 37%	3000
	11th to 20th	Day	15% 8% 3 7% 6% 5% 5% 5% 6% 8% 33%	3000
	21st to end	Day	8% 4 2 5% 5% 5% 5% 5% 7% 8% 45%	3000
July	1st to 10th	Day	5% 4 2 5% 4 5% 5% 4 7% 8% 52%	6779
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 6% 8% 51%	6780
	21st to end	Day	5% 4 1 4 3 3 4 3 5% 8% 58%	7326
August	1st to 10th	Day	7% 5% 2 6% 4 6% 6% 5% 7% 9% 44%	5966
	11th to 20th	Day	3 2 1 4 3 4 5% 5% 8% 10% 53%	5798
	21st to end	Day	7% 4 1 3 2 3 3 3 5% 7% 63%	6468
September	1st to 10th	Day	10% 5% 1 5% 4 3 4 4 5% 7% 52%	2419
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 3 5% 8% 46%	2295
	21st to end	Day	9% 6% 2 4 3 3 4 3 5% 7% 54%	2175
October	1st to 10th	Day	5% 5% 2 5% 3 4 4 4 6% 9% 51%	3270
	11th to 20th	Day	3 5% 2 6% 4 4 4 4 6% 9% 53%	3250
	21st to end	Day	4 6% 3 6% 4 3 4 4 7% 8% 50%	3192
November	1st to 10th	Day	7% 11% 5% 9% 5% 5% 5% 4 6% 7% 35%	1648
	11th to 20th	Day	3 7% 2 7% 7% 6% 6% 5% 8% 9% 41%	1680
	21st to end	Day	4 9% 4 9% 5% 6% 8% 6% 6% 9% 35%	1680
December	1st to 10th	Day	2 8% 4 11% 10% 7% 6% 5% 7% 9% 31%	2380
	11th to 20th	Day	4 9% 4 10% 8% 6% 7% 5% 7% 7% 33%	2715
	21st to end	Day	2 6% 3 7% 5% 6% 6% 5% 8% 8% 44%	3575
January	1st to 10th	Night	2 7% 3 8% 6% 7% 6% 5% 8% 11% 37%	8768
	11th to 20th	Night	1 3 3 10% 8% 7% 7% 6% 7% 10% 38%	8820
	21st to end	Night	1 4 2 8% 7% 6% 6% 5% 8% 10% 41%	9186
February	1st to 10th	Night	4 9% 3 10% 7% 6% 6% 5% 8% 10% 32%	2730
	11th to 20th	Night	2 8% 4 8% 7% 6% 7% 6% 9% 10% 34%	2662
	21st to end	Night	3 8% 4 9% 7% 6% 6% 4 7% 11% 34%	2249
March	1st to 10th	Night	2 7% 3 7% 6% 7% 6% 6% 8% 11% 37%	5273
	11th to 20th	Night	5% 6% 2 6% 5% 5% 6% 5% 7% 10% 43%	5110
	21st to end	Night	7% 15% 5% 14% 9% 6% 6% 4 6% 7% 21%	5610
April	1st to 10th	Night	5% 10% 4 9% 6% 6% 5% 5% 6% 9% 35%	2096
	11th to 20th	Night	8% 9% 4 8% 5% 5% 5% 5% 7% 9% 33%	1835
	21st to end	Night	8% 9% 4 10% 5% 5% 5% 4 6% 8% 37%	1800
May	1st to 10th	Night	12% 9% 2 6% 4 4 4 3 5% 6% 46%	3672
	11th to 20th	Night	11% 8% 3 8% 6% 6% 6% 5% 7% 8% 31%	3617
	21st to end	Night	10% 6% 3 6% 5% 5% 5% 4 6% 8% 43%	3474
June	1st to 10th	Night	13% 6% 2 6% 4 5% 5% 4 6% 7% 42%	1400
	11th to 20th	Night	8% 7% 2 8% 5% 5% 5% 4 5% 7% 43%	1400
	21st to end	Night	6% 4 2 4 3 3 5% 4 6% 10% 54%	1400
July	1st to 10th	Night	5% 3 1 4 3 3 4 3 6% 8% 60%	3180
	11th to 20th	Night	6% 4 2 5% 3 4 4 4 6% 8% 55%	3180
	21st to end	Night	5% 3 1 4 3 3 4 3 6% 8% 60%	3513
August	1st to 10th	Night	8% 6% 3 6% 4 4 4 4 6% 7% 49%	3843
	11th to 20th	Night	3 3 1 5% 4 4 5% 5% 8% 10% 53%	4051
	21st to end	Night	10% 4 2 4 3 3 3 2 3 5% 61%	4509
September	1st to 10th	Night	9% 5% 1 6% 3 4 4 3 5% 7% 54%	1980
	11th to 20th	Night	9% 7% 2 5% 4 4 4 4 5% 8% 48%	2103
	21st to end	Night	6% 5% 2 5% 4 3 3 3 6% 8% 54%	2225
October	1st to 10th	Night	5% 5% 2 5% 3 4 5% 5% 6% 8% 53%	3920
	11th to 20th	Night	5% 6% 2 6% 4 4 5% 4 6% 9% 50%	3898
	21st to end	Night	3 6% 3 6% 4 4 5% 4 6% 8% 51%	4558
November	1st to 10th	Night	8% 9% 3 8% 5% 6% 6% 5% 7% 8% 36%	2870
	11th to 20th	Night	3 7% 2 7% 7% 6% 6% 5% 8% 9% 39%	2940
	21st to end	Night	4 9% 3 8% 6% 5% 6% 5% 7% 9% 38%	2940
December	1st to 10th	Night	1 7% 3 10% 8% 6% 6% 5% 8% 10% 35%	5007
	11th to 20th	Night	3 7% 4 12% 7% 7% 7% 5% 7% 8% 32%	5696
	21st to end	Night	3 6% 3 7% 4 4 5% 4 7% 9% 48%	7623

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	45% 6% 20% 22% 7%	4125
	11th to 20th	Day	38% 6% 18% 20% 12% 5%	4140
	21st to end	Day	34% 6% 22% 28% 9% 1	5045
February	1st to 10th	Day	45% 9% 18% 16% 10% 1	1890
	11th to 20th	Day	42% 9% 19% 19% 9% 3	1854
	21st to end	Day	46% 9% 15% 20% 9% 1	1557
March	1st to 10th	Day	34% 8% 20% 24% 12% 2	4833
	11th to 20th	Day	36% 7% 17% 26% 13%	5110
	21st to end	Day	55% 9% 18% 12% 5%	5607
April	1st to 10th	Day	43% 9% 17% 24% 8%	2519
	11th to 20th	Day	49% 6% 15% 22% 6% 1	2649
	21st to end	Day	44% 8% 15% 25% 6% 1	2600
May	1st to 10th	Day	43% 5% 12% 27% 10% 3	6294
	11th to 20th	Day	49% 7% 13% 24% 6%	6302
	21st to end	Day	41% 7% 14% 27% 12%	7399
June	1st to 10th	Day	44% 8% 16% 21% 10% 1	3000
	11th to 20th	Day	46% 7% 14% 21% 11% 1	3000
	21st to end	Day	33% 8% 17% 29% 12% 1	3000
July	1st to 10th	Day	30% 3 16% 25% 21% 5%	6706
	11th to 20th	Day	31% 3 16% 30% 16% 5%	6699
	21st to end	Day	25% 3 13% 29% 23% 8%	7114
August	1st to 10th	Day	30% 4 12% 33% 19% 2	4344
	11th to 20th	Day	26% 5% 16% 37% 15% 1	4197
	21st to end	Day	22% 3 13% 40% 20% 2	4663
September	1st to 10th	Day	31% 4 15% 25% 18% 7%	2419
	11th to 20th	Day	36% 6% 15% 27% 14% 3	2295
	21st to end	Day	29% 5% 15% 31% 17% 2	2175
October	1st to 10th	Day	30% 4 14% 34% 15% 3	3270
	11th to 20th	Day	28% 3 18% 34% 14% 2	3250
	21st to end	Day	31% 5% 12% 38% 14%	3192
November	1st to 10th	Day	47% 7% 15% 20% 9% 1	1648
	11th to 20th	Day	35% 10% 22% 24% 8% 1	1680
	21st to end	Day	43% 9% 19% 20% 8% 1	1680
December	1st to 10th	Day	47% 6% 21% 20% 4 1	2380
	11th to 20th	Day	48% 7% 19% 23% 4	2714
	21st to end	Day	36% 5% 13% 28% 14% 5%	3575
January	1st to 10th	Night	39% 7% 18% 24% 12% 1	8769
	11th to 20th	Night	39% 4 19% 20% 13% 4	8820
	21st to end	Night	36% 6% 21% 26% 10% 2	9186
February	1st to 10th	Night	43% 7% 18% 17% 13% 2	2730
	11th to 20th	Night	39% 9% 18% 19% 14% 2	2663
	21st to end	Night	42% 8% 14% 24% 10% 3	2249
March	1st to 10th	Night	36% 7% 23% 19% 14% 2	5273
	11th to 20th	Night	34% 5% 18% 28% 14% 1	5110
	21st to end	Night	56% 10% 16% 11% 6% 1	5610
April	1st to 10th	Night	43% 7% 18% 23% 9% 1	2096
	11th to 20th	Night	43% 7% 15% 21% 12% 1	1835
	21st to end	Night	43% 7% 15% 27% 8% 1	1800
May	1st to 10th	Night	37% 6% 9% 29% 16% 2	3671
	11th to 20th	Night	45% 7% 18% 22% 8%	3618
	21st to end	Night	36% 8% 19% 27% 10%	3474
June	1st to 10th	Night	39% 7% 18% 25% 11% 1	1400
	11th to 20th	Night	39% 6% 14% 24% 16% 2	1400
	21st to end	Night	24% 7% 18% 36% 13% 2	1400
July	1st to 10th	Night	23% 3 15% 31% 25% 4	3145
	11th to 20th	Night	29% 3 12% 32% 19% 5%	3138
	21st to end	Night	23% 3 13% 32% 22% 9%	3413
August	1st to 10th	Night	28% 3 11% 35% 20% 4	2789
	11th to 20th	Night	28% 4 16% 35% 15% 2	2928
	21st to end	Night	29% 3 12% 33% 21% 3	3245
September	1st to 10th	Night	29% 4 12% 29% 17% 9%	1980
	11th to 20th	Night	34% 5% 15% 29% 13% 4	2103
	21st to end	Night	28% 4 16% 31% 18% 2	2225
October	1st to 10th	Night	29% 4 11% 38% 16% 1	3920
	11th to 20th	Night	31% 4 15% 30% 18% 2	3898
	21st to end	Night	31% 5% 11% 38% 15%	4558
November	1st to 10th	Night	42% 10% 15% 22% 10% 2	2870
	11th to 20th	Night	35% 10% 24% 20% 11%	2940
	21st to end	Night	39% 8% 24% 19% 9% 1	2940
December	1st to 10th	Night	41% 8% 23% 20% 7% 1	5007
	11th to 20th	Night	46% 7% 23% 18% 5%	5697
	21st to end	Night	32% 5% 13% 29% 16% 6%	7623

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	9% 18% 35% 24% 10% 5%	220
	11th to 20th	Day	11% 18% 32% 23% 12% 4	220
	21st to end	Day	7% 21% 36% 29% 7% 1	270
February	1st to 10th	Day	12% 18% 38% 23% 7% 1	330
	11th to 20th	Day	8% 14% 40% 26% 10% 2	330
	21st to end	Day	7% 15% 37% 27% 11% 2	273
March	1st to 10th	Day	10% 15% 36% 27% 11% 2	493
	11th to 20th	Day	12% 14% 37% 22% 11% 4	540
	21st to end	Day	12% 14% 34% 25% 12% 3	594
April	1st to 10th	Day	9% 16% 35% 28% 9% 1	540
	11th to 20th	Day	11% 17% 36% 26% 8% 2	517
	21st to end	Day	17% 12% 29% 29% 12% 1	500
May	1st to 10th	Day	14% 11% 23% 31% 18% 4	683
	11th to 20th	Day	14% 9% 26% 30% 18% 4	725
	21st to end	Day	16% 11% 25% 23% 19% 6%	789
June	1st to 10th	Day	15% 13% 26% 27% 17% 3	730
	11th to 20th	Day	18% 15% 32% 22% 11% 1	730
	21st to end	Day	13% 7% 28% 28% 21% 4	730
July	1st to 10th	Day	5% 5% 28% 39% 20% 3	721
	11th to 20th	Day	7% 8% 31% 34% 17% 3	718
	21st to end	Day	7% 5% 26% 36% 22% 5%	794
August	1st to 10th	Day	8% 7% 25% 38% 18% 4	612
	11th to 20th	Day	6% 7% 28% 36% 19% 4	517
	21st to end	Day	8% 8% 28% 33% 19% 4	583
September	1st to 10th	Day	12% 10% 31% 32% 14% 2	530
	11th to 20th	Day	12% 10% 31% 30% 15% 3	530
	21st to end	Day	14% 14% 35% 24% 10% 3	505
October	1st to 10th	Day	15% 14% 28% 21% 18% 4	330
	11th to 20th	Day	8% 19% 32% 29% 9% 2	330
	21st to end	Day	15% 20% 37% 20% 7% 1	363
November	1st to 10th	Day	16% 22% 33% 20% 9%	330
	11th to 20th	Day	10% 24% 37% 20% 8% 1	330
	21st to end	Day	8% 18% 39% 21% 12% 3	330
December	1st to 10th	Day	12% 20% 37% 21% 7% 2	230
	11th to 20th	Day	14% 18% 40% 23% 5% 1	220
	21st to end	Day	8% 12% 35% 31% 12% 2	242
January	1st to 10th	Night	8% 19% 38% 25% 9% 1	1050
	11th to 20th	Night	8% 19% 38% 26% 9% 1	1050
	21st to end	Night	8% 19% 37% 26% 9% 2	1046
February	1st to 10th	Night	9% 15% 32% 30% 13% 2	840
	11th to 20th	Night	5% 14% 43% 28% 9% 1	824
	21st to end	Night	7% 12% 33% 30% 14% 4	692
March	1st to 10th	Night	7% 11% 38% 32% 11% 1	840
	11th to 20th	Night	9% 12% 35% 32% 9% 3	840
	21st to end	Night	12% 10% 36% 28% 12% 2	924
April	1st to 10th	Night	8% 13% 36% 31% 11% 1	640
	11th to 20th	Night	12% 10% 34% 32% 10% 1	611
	21st to end	Night	12% 10% 31% 34% 12% 1	600
May	1st to 10th	Night	12% 9% 23% 34% 20% 1	600
	11th to 20th	Night	12% 6% 26% 37% 17% 2	591
	21st to end	Night	15% 10% 22% 30% 19% 3	437
June	1st to 10th	Night	17% 8% 27% 29% 18% 2	400
	11th to 20th	Night	13% 10% 37% 30% 11%	400
	21st to end	Night	10% 5% 23% 39% 21% 3	400
July	1st to 10th	Night	5% 5% 26% 44% 19% 1	390
	11th to 20th	Night	6% 5% 31% 42% 14% 1	388
	21st to end	Night	5% 6% 21% 41% 26% 2	458
August	1st to 10th	Night	8% 3 24% 42% 20% 2	597
	11th to 20th	Night	7% 5% 20% 42% 25% 1	594
	21st to end	Night	11% 6% 24% 37% 21% 1	660
September	1st to 10th	Night	12% 4 28% 37% 17% 3	600
	11th to 20th	Night	11% 8% 26% 35% 18% 2	703
	21st to end	Night	10% 8% 33% 32% 14% 3	800
October	1st to 10th	Night	12% 10% 28% 32% 17% 1	800
	11th to 20th	Night	11% 11% 35% 28% 14% 2	800
	21st to end	Night	8% 18% 36% 29% 8% 1	929
November	1st to 10th	Night	13% 15% 37% 28% 6%	1025
	11th to 20th	Night	10% 17% 41% 25% 7% 1	1050
	21st to end	Night	8% 14% 41% 30% 6%	1050
December	1st to 10th	Night	8% 17% 36% 27% 10% 2	1050
	11th to 20th	Night	7% 18% 36% 29% 8% 2	1050
	21st to end	Night	9% 14% 37% 29% 9% 2	1155

Page generated at 2026-04-14 00:44:24. Version ac07

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