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 2024-01-16.

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	7% 7% 3 6% 6% 4 5% 6% 6% 8% 41%	74716
	Night	5% 7% 3 6% 6% 4 6% 6% 7% 9% 42%	75099
Transparency	Day	38% 8% 17% 23% 11% 2	74399
	Night	36% 9% 18% 23% 12% 2	74939
Seeing	Day	10% 11% 30% 30% 16% 3	14438
	Night	9% 12% 33% 32% 13% 2	23904

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	3 8% 5% 7% 7% 5% 5% 4 6% 11% 39%	1329
	11th to 20th	Day	2 7% 5% 8% 7% 5% 6% 7% 8% 11% 34%	1298
	21st to end	Day	2 7% 4 9% 8% 6% 8% 9% 7% 10% 30%	1538
February	1st to 10th	Day	5% 8% 4 8% 8% 4 8% 8% 9% 9% 31%	1620
	11th to 20th	Day	3 8% 5% 7% 9% 5% 8% 9% 9% 10% 28%	1575
	21st to end	Day	5% 8% 6% 11% 7% 5% 8% 6% 7% 9% 29%	1332
March	1st to 10th	Day	4 7% 3 9% 7% 5% 7% 6% 8% 9% 35%	1880
	11th to 20th	Day	5% 7% 4 7% 7% 4 6% 5% 7% 10% 37%	1980
	21st to end	Day	6% 9% 4 10% 8% 4 7% 6% 7% 8% 29%	2178
April	1st to 10th	Day	6% 9% 4 8% 8% 4 6% 6% 7% 9% 34%	2158
	11th to 20th	Day	9% 13% 6% 8% 7% 4 5% 5% 6% 7% 30%	2307
	21st to end	Day	11% 11% 4 7% 6% 3 5% 6% 6% 8% 33%	2340
May	1st to 10th	Day	11% 11% 5% 7% 6% 4 6% 5% 5% 6% 34%	2502
	11th to 20th	Day	9% 7% 3 6% 7% 4 6% 6% 6% 8% 38%	2478
	21st to end	Day	20% 9% 4 6% 6% 4 4 4 5% 6% 31%	2910
June	1st to 10th	Day	14% 6% 3 6% 6% 4 5% 6% 6% 8% 35%	2700
	11th to 20th	Day	16% 7% 3 6% 6% 4 6% 6% 6% 8% 32%	2700
	21st to end	Day	8% 4 2 4 6% 4 5% 7% 7% 8% 45%	2700
July	1st to 10th	Day	3 3 2 4 6% 3 5% 6% 8% 10% 50%	2700
	11th to 20th	Day	5% 3 1 4 5% 3 5% 5% 6% 9% 53%	2700
	21st to end	Day	4 2 1 3 4 3 4 5% 6% 9% 60%	2919
August	1st to 10th	Day	6% 3 2 4 4 3 4 5% 5% 9% 55%	2405
	11th to 20th	Day	6% 4 2 4 3 3 4 5% 7% 9% 51%	2299
	21st to end	Day	7% 3 2 3 4 2 4 4 6% 9% 55%	2574
September	1st to 10th	Day	11% 5% 2 5% 4 2 4 4 5% 7% 51%	2178
	11th to 20th	Day	12% 5% 2 5% 4 3 5% 4 5% 8% 47%	2066
	21st to end	Day	10% 6% 2 3 4 2 4 4 5% 8% 52%	1958
October	1st to 10th	Day	8% 9% 4 7% 5% 3 4 5% 7% 9% 40%	1800
	11th to 20th	Day	6% 7% 3 7% 6% 3 5% 5% 5% 8% 44%	1800
	21st to end	Day	6% 7% 4 8% 7% 3 5% 5% 6% 9% 40%	1788
November	1st to 10th	Day	9% 10% 5% 8% 6% 4 5% 5% 6% 7% 35%	1488
	11th to 20th	Day	3 7% 3 6% 7% 4 7% 5% 7% 9% 42%	1520
	21st to end	Day	4 7% 5% 8% 6% 5% 7% 7% 6% 9% 37%	1520
December	1st to 10th	Day	3 10% 4 7% 9% 5% 8% 7% 6% 8% 33%	1349
	11th to 20th	Day	3 7% 3 7% 9% 5% 7% 6% 7% 8% 37%	1685
	21st to end	Day	2 7% 3 6% 5% 4 6% 5% 7% 7% 49%	2442
January	1st to 10th	Night	3 7% 5% 7% 6% 4 5% 6% 8% 12% 36%	2836
	11th to 20th	Night	3 6% 4 7% 8% 4 7% 6% 7% 11% 37%	2790
	21st to end	Night	2 7% 4 6% 7% 5% 8% 7% 10% 10% 34%	2832
February	1st to 10th	Night	3 8% 4 9% 7% 6% 7% 7% 8% 10% 32%	2340
	11th to 20th	Night	2 8% 5% 7% 7% 5% 8% 8% 8% 10% 32%	2272
	21st to end	Night	3 7% 5% 9% 9% 5% 7% 5% 7% 11% 32%	1924
March	1st to 10th	Night	4 7% 4 8% 7% 5% 7% 7% 7% 10% 34%	2076
	11th to 20th	Night	5% 9% 4 7% 6% 4 7% 6% 8% 9% 36%	1980
	21st to end	Night	7% 8% 4 9% 8% 3 7% 6% 8% 8% 31%	2178
April	1st to 10th	Night	5% 8% 5% 8% 8% 5% 6% 5% 6% 9% 35%	1799
	11th to 20th	Night	9% 9% 4 7% 6% 5% 6% 5% 7% 9% 34%	1601
	21st to end	Night	9% 8% 4 8% 6% 3 6% 6% 6% 9% 36%	1620
May	1st to 10th	Night	9% 9% 3 5% 5% 4 6% 5% 6% 7% 41%	1458
	11th to 20th	Night	8% 6% 3 5% 6% 3 5% 6% 7% 7% 44%	1417
	21st to end	Night	16% 6% 4 6% 8% 4 5% 5% 6% 6% 33%	1362
June	1st to 10th	Night	15% 6% 2 4 5% 4 5% 5% 5% 7% 42%	1260
	11th to 20th	Night	8% 6% 3 8% 5% 3 5% 5% 5% 7% 44%	1260
	21st to end	Night	6% 3 2 3 4 2 4 5% 6% 10% 54%	1260
July	1st to 10th	Night	4 3 2 4 3 3 5% 6% 5% 8% 57%	1260
	11th to 20th	Night	4 3 1 4 3 2 4 5% 7% 9% 59%	1260
	21st to end	Night	3 2 1 3 2 2 3 5% 6% 9% 64%	1397
August	1st to 10th	Night	5% 4 2 4 4 3 4 4 5% 8% 57%	1531
	11th to 20th	Night	5% 4 2 4 4 2 4 5% 8% 9% 53%	1602
	21st to end	Night	8% 4 2 4 4 2 4 5% 5% 7% 54%	1782
September	1st to 10th	Night	9% 5% 1 5% 4 3 4 4 5% 7% 53%	1782
	11th to 20th	Night	9% 7% 3 5% 4 3 4 4 5% 8% 49%	1892
	21st to end	Night	7% 5% 2 5% 5% 2 4 4 6% 8% 52%	2002
October	1st to 10th	Night	9% 7% 3 6% 4 3 4 5% 6% 8% 44%	2160
	11th to 20th	Night	5% 7% 3 6% 5% 4 5% 5% 6% 9% 45%	2160
	21st to end	Night	5% 8% 4 7% 7% 3 5% 5% 7% 8% 40%	2545
November	1st to 10th	Night	9% 8% 3 6% 6% 3 7% 6% 7% 8% 36%	2590
	11th to 20th	Night	3 7% 2 5% 7% 4 7% 6% 8% 10% 40%	2660
	21st to end	Night	4 8% 3 7% 6% 4 6% 7% 7% 9% 39%	2660
December	1st to 10th	Night	2 8% 4 7% 6% 5% 7% 7% 8% 9% 37%	2831
	11th to 20th	Night	2 7% 4 7% 7% 4 7% 6% 8% 9% 38%	3506
	21st to end	Night	3 6% 3 5% 5% 3 5% 5% 6% 8% 52%	5214

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	39% 11% 21% 22% 5% 1	1329
	11th to 20th	Day	40% 13% 18% 20% 8% 1	1298
	21st to end	Day	42% 13% 21% 18% 5% 1	1538
February	1st to 10th	Day	46% 10% 19% 17% 8%	1620
	11th to 20th	Day	45% 10% 20% 18% 6% 1	1584
	21st to end	Day	49% 9% 14% 17% 10% 1	1332
March	1st to 10th	Day	40% 13% 19% 21% 7%	1880
	11th to 20th	Day	39% 11% 19% 22% 8% 1	1980
	21st to end	Day	48% 10% 18% 16% 7% 1	2178
April	1st to 10th	Day	43% 9% 17% 23% 7%	2158
	11th to 20th	Day	50% 7% 14% 21% 6% 1	2310
	21st to end	Day	45% 9% 16% 24% 6% 1	2340
May	1st to 10th	Day	48% 7% 16% 20% 9%	2502
	11th to 20th	Day	40% 9% 16% 27% 8% 1	2482
	21st to end	Day	51% 7% 14% 20% 7%	2911
June	1st to 10th	Day	45% 8% 17% 20% 9% 1	2700
	11th to 20th	Day	47% 8% 15% 20% 10% 1	2700
	21st to end	Day	32% 9% 19% 28% 11% 1	2700
July	1st to 10th	Day	25% 8% 20% 29% 15% 3	2626
	11th to 20th	Day	26% 7% 14% 27% 22% 4	2619
	21st to end	Day	18% 7% 14% 29% 26% 5%	2757
August	1st to 10th	Day	25% 7% 16% 29% 19% 4	2389
	11th to 20th	Day	27% 8% 17% 30% 16% 2	2299
	21st to end	Day	24% 6% 15% 27% 25% 3	2574
September	1st to 10th	Day	32% 5% 14% 24% 19% 6%	2178
	11th to 20th	Day	35% 6% 15% 27% 13% 3	2066
	21st to end	Day	30% 6% 15% 31% 15% 2	1958
October	1st to 10th	Day	39% 8% 18% 23% 11% 1	1800
	11th to 20th	Day	37% 6% 19% 25% 11% 2	1800
	21st to end	Day	39% 8% 18% 23% 11%	1788
November	1st to 10th	Day	48% 8% 16% 18% 9% 1	1488
	11th to 20th	Day	35% 11% 22% 24% 8% 1	1520
	21st to end	Day	41% 10% 19% 21% 8% 1	1520
December	1st to 10th	Day	45% 9% 19% 18% 6% 2	1349
	11th to 20th	Day	41% 11% 21% 22% 5% 1	1684
	21st to end	Day	33% 7% 15% 25% 13% 7%	2442
January	1st to 10th	Night	38% 12% 20% 20% 7% 2	2836
	11th to 20th	Night	37% 11% 21% 22% 8% 2	2790
	21st to end	Night	36% 12% 22% 19% 11% 1	2832
February	1st to 10th	Night	42% 8% 20% 17% 10% 2	2340
	11th to 20th	Night	41% 10% 20% 18% 11% 1	2273
	21st to end	Night	44% 8% 13% 22% 10% 3	1924
March	1st to 10th	Night	41% 10% 20% 21% 8%	2076
	11th to 20th	Night	40% 9% 20% 21% 10% 1	1980
	21st to end	Night	46% 10% 17% 19% 7% 2	2178
April	1st to 10th	Night	44% 7% 18% 22% 9%	1799
	11th to 20th	Night	44% 7% 14% 20% 13% 1	1601
	21st to end	Night	43% 7% 15% 26% 7% 1	1620
May	1st to 10th	Night	40% 8% 12% 27% 12% 1	1458
	11th to 20th	Night	35% 7% 15% 27% 15% 1	1418
	21st to end	Night	49% 7% 14% 19% 10%	1362
June	1st to 10th	Night	40% 8% 19% 24% 9% 1	1260
	11th to 20th	Night	39% 6% 15% 24% 15% 1	1260
	21st to end	Night	24% 7% 19% 34% 14% 2	1260
July	1st to 10th	Night	23% 7% 14% 34% 19% 3	1225
	11th to 20th	Night	22% 8% 13% 27% 25% 6%	1218
	21st to end	Night	14% 6% 14% 31% 28% 7%	1319
August	1st to 10th	Night	25% 5% 15% 31% 18% 6%	1523
	11th to 20th	Night	25% 8% 17% 28% 19% 4	1602
	21st to end	Night	28% 5% 12% 23% 28% 5%	1782
September	1st to 10th	Night	30% 4 13% 26% 18% 8%	1782
	11th to 20th	Night	34% 6% 14% 28% 14% 4	1892
	21st to end	Night	30% 5% 16% 31% 17% 2	2002
October	1st to 10th	Night	36% 8% 16% 26% 14% 1	2160
	11th to 20th	Night	33% 7% 18% 27% 13% 2	2160
	21st to end	Night	39% 10% 16% 25% 10% 1	2545
November	1st to 10th	Night	41% 11% 16% 21% 9% 2	2590
	11th to 20th	Night	33% 11% 24% 20% 11%	2660
	21st to end	Night	38% 9% 25% 18% 9% 1	2660
December	1st to 10th	Night	37% 12% 21% 19% 10% 1	2831
	11th to 20th	Night	36% 11% 27% 21% 5% 1	3507
	21st to end	Night	28% 7% 16% 26% 15% 8%	5214

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% 13% 33% 29% 14% 5%	171
	21st to end	Day	4 20% 34% 32% 8% 2	196
February	1st to 10th	Day	11% 18% 38% 24% 8% 1	240
	11th to 20th	Day	8% 14% 38% 28% 10% 3	240
	21st to end	Day	4 10% 38% 33% 13% 3	198
March	1st to 10th	Day	8% 13% 37% 29% 11% 2	379
	11th to 20th	Day	9% 11% 38% 24% 14% 5%	420
	21st to end	Day	9% 12% 34% 28% 13% 3	462
April	1st to 10th	Day	7% 16% 34% 32% 10% 1	420
	11th to 20th	Day	11% 17% 34% 27% 9% 1	412
	21st to end	Day	17% 11% 28% 30% 13% 1	420
May	1st to 10th	Day	14% 9% 22% 32% 19% 4	585
	11th to 20th	Day	13% 8% 25% 30% 20% 4	625
	21st to end	Day	17% 11% 24% 22% 20% 6%	679
June	1st to 10th	Day	15% 11% 26% 27% 18% 3	630
	11th to 20th	Day	18% 14% 31% 24% 12% 1	630
	21st to end	Day	10% 6% 26% 30% 23% 5%	630
July	1st to 10th	Day	4 4 26% 41% 22% 3	621
	11th to 20th	Day	6% 8% 30% 36% 18% 3	618
	21st to end	Day	6% 4 26% 37% 22% 5%	684
August	1st to 10th	Day	7% 6% 24% 39% 20% 4	524
	11th to 20th	Day	6% 7% 23% 40% 20% 5%	437
	21st to end	Day	6% 7% 28% 34% 20% 5%	495
September	1st to 10th	Day	13% 10% 32% 30% 14% 1	450
	11th to 20th	Day	12% 10% 29% 31% 16% 3	450
	21st to end	Day	14% 12% 33% 26% 11% 3	428
October	1st to 10th	Day	15% 10% 28% 22% 20% 5%	270
	11th to 20th	Day	6% 17% 32% 31% 11% 3	270
	21st to end	Day	13% 19% 37% 23% 8% 1	297
November	1st to 10th	Day	14% 19% 34% 21% 11%	270
	11th to 20th	Day	8% 22% 38% 23% 9% 1	270
	21st to end	Day	6% 18% 40% 21% 12% 3	270
December	1st to 10th	Day	9% 19% 38% 24% 7% 3	189
	11th to 20th	Day	9% 18% 38% 27% 6% 1	180
	21st to end	Day	8% 10% 29% 35% 15% 3	198
January	1st to 10th	Night	7% 18% 39% 26% 9% 1	950
	11th to 20th	Night	5% 18% 39% 28% 10% 1	930
	21st to end	Night	6% 20% 38% 25% 9% 2	897
February	1st to 10th	Night	8% 14% 32% 30% 14% 2	720
	11th to 20th	Night	6% 14% 42% 28% 9% 1	704
	21st to end	Night	6% 9% 32% 32% 16% 4	592
March	1st to 10th	Night	6% 11% 40% 32% 11% 1	720
	11th to 20th	Night	8% 11% 35% 33% 10% 3	720
	21st to end	Night	11% 9% 35% 29% 13% 2	792
April	1st to 10th	Night	7% 11% 35% 33% 12% 1	550
	11th to 20th	Night	13% 8% 34% 33% 11% 1	533
	21st to end	Night	13% 9% 30% 35% 12% 1	540
May	1st to 10th	Night	12% 9% 21% 34% 21% 1	540
	11th to 20th	Night	11% 6% 25% 37% 18% 2	531
	21st to end	Night	16% 10% 22% 30% 20% 3	393
June	1st to 10th	Night	17% 8% 26% 29% 19% 2	360
	11th to 20th	Night	12% 9% 37% 30% 12%	360
	21st to end	Night	9% 5% 23% 38% 22% 3	360
July	1st to 10th	Night	5% 6% 24% 44% 19% 1	350
	11th to 20th	Night	6% 5% 32% 43% 14% 1	348
	21st to end	Night	4 6% 22% 42% 25% 2	412
August	1st to 10th	Night	7% 3 25% 42% 20% 2	537
	11th to 20th	Night	7% 5% 19% 42% 26% 1	534
	21st to end	Night	10% 5% 24% 38% 22% 1	594
September	1st to 10th	Night	13% 4 29% 37% 14% 3	540
	11th to 20th	Night	11% 8% 26% 35% 19% 1	632
	21st to end	Night	10% 7% 31% 33% 15% 3	720
October	1st to 10th	Night	12% 10% 28% 31% 19% 1	720
	11th to 20th	Night	9% 11% 35% 28% 15% 2	720
	21st to end	Night	8% 18% 35% 30% 9% 1	835
November	1st to 10th	Night	13% 14% 38% 28% 7%	925
	11th to 20th	Night	9% 16% 42% 25% 7% 1	950
	21st to end	Night	7% 14% 42% 31% 7%	950
December	1st to 10th	Night	5% 15% 38% 29% 11% 2	950
	11th to 20th	Night	5% 17% 37% 31% 9% 2	950
	21st to end	Night	9% 13% 35% 30% 10% 2	1045

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