The Rezervatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Rezervatory clear sky chart from 2005-11-06 to 2024-01-17.

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	11% 7% 3 6% 5% 3 4 4 5% 7% 44%	74649
	Night	11% 7% 3 5% 4 2 4 4 5% 7% 48%	75195
Transparency	Day	39% 5% 14% 26% 14% 2	74372
	Night	36% 5% 13% 27% 17% 3	74992
Seeing	Day	14% 9% 29% 30% 15% 3	14639
	Night	13% 8% 33% 34% 11% 1	24665

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	10% 10% 4 6% 7% 4 4 4 4 8% 38%	1707
	11th to 20th	Day	11% 9% 4 10% 5% 3 4 5% 4 6% 39%	1674
	21st to end	Day	10% 10% 5% 10% 7% 4 5% 5% 4 6% 34%	1782
February	1st to 10th	Day	11% 10% 5% 9% 7% 4 4 4 5% 7% 33%	1620
	11th to 20th	Day	10% 11% 4 7% 6% 3 5% 4 5% 7% 38%	1611
	21st to end	Day	11% 8% 4 6% 6% 4 4 4 6% 7% 41%	1480
March	1st to 10th	Day	11% 9% 5% 6% 5% 3 3 4 4 7% 43%	1943
	11th to 20th	Day	15% 10% 3 6% 5% 2 4 4 5% 5% 41%	1980
	21st to end	Day	20% 12% 4 5% 5% 3 4 4 6% 6% 30%	2178
April	1st to 10th	Day	16% 8% 3 5% 5% 3 4 3 5% 6% 43%	2024
	11th to 20th	Day	16% 8% 2 6% 5% 3 5% 4 6% 6% 39%	2248
	21st to end	Day	20% 7% 2 5% 5% 3 4 4 4 7% 39%	2340
May	1st to 10th	Day	15% 7% 3 6% 6% 4 6% 4 5% 6% 37%	2340
	11th to 20th	Day	14% 7% 3 6% 6% 3 4 4 5% 7% 41%	2302
	21st to end	Day	16% 6% 3 6% 5% 3 6% 5% 7% 8% 34%	2586
June	1st to 10th	Day	8% 4 2 5% 4 3 5% 5% 7% 9% 50%	2520
	11th to 20th	Day	10% 4 3 4 5% 3 4 5% 5% 9% 48%	2520
	21st to end	Day	7% 5% 2 5% 4 3 6% 4 5% 8% 51%	2520
July	1st to 10th	Day	8% 4 1 3 4 3 4 4 7% 10% 52%	2356
	11th to 20th	Day	6% 4 2 3 4 3 4 5% 6% 7% 55%	2340
	21st to end	Day	6% 3 2 4 5% 3 4 5% 6% 10% 51%	2546
August	1st to 10th	Day	7% 5% 3 5% 6% 4 5% 6% 7% 10% 42%	2328
	11th to 20th	Day	8% 4 2 4 4 3 5% 6% 6% 8% 50%	2301
	21st to end	Day	8% 4 2 4 4 2 4 5% 4 7% 54%	2540
September	1st to 10th	Day	12% 5% 2 4 4 2 3 4 5% 5% 53%	2081
	11th to 20th	Day	10% 5% 2 4 4 3 3 4 4 7% 53%	1980
	21st to end	Day	10% 5% 1 4 4 2 4 3 4 6% 57%	1980
October	1st to 10th	Day	15% 6% 2 4 4 3 3 4 4 5% 50%	1850
	11th to 20th	Day	12% 6% 2 4 4 2 3 3 3 5% 55%	1800
	21st to end	Day	13% 8% 2 5% 5% 3 4 4 4 6% 47%	1980
November	1st to 10th	Day	9% 5% 3 4 3 2 4 4 5% 6% 56%	1683
	11th to 20th	Day	10% 6% 2 7% 7% 3 5% 4 4 6% 47%	1663
	21st to end	Day	14% 8% 3 4 4 3 3 5% 4 8% 44%	1520
December	1st to 10th	Day	9% 8% 4 6% 5% 2 3 5% 5% 7% 46%	1520
	11th to 20th	Day	8% 10% 5% 8% 6% 3 5% 5% 5% 7% 38%	1918
	21st to end	Day	16% 10% 5% 14% 7% 4 4 5% 4 5% 27%	2888
January	1st to 10th	Night	7% 9% 4 8% 7% 4 4 4 5% 7% 42%	2458
	11th to 20th	Night	10% 10% 5% 7% 5% 3 4 4 5% 7% 40%	2431
	21st to end	Night	12% 10% 4 8% 4 2 3 4 4 7% 42%	2574
February	1st to 10th	Night	12% 10% 4 7% 7% 3 4 5% 4 6% 38%	2340
	11th to 20th	Night	9% 8% 4 6% 5% 3 5% 5% 5% 7% 42%	2251
	21st to end	Night	10% 8% 3 5% 5% 2 4 4 4 6% 49%	1776
March	1st to 10th	Night	10% 7% 4 5% 5% 3 3 3 4 6% 49%	2016
	11th to 20th	Night	15% 9% 3 5% 4 2 3 3 4 7% 45%	1980
	21st to end	Night	16% 10% 4 7% 6% 3 4 5% 6% 7% 33%	2178
April	1st to 10th	Night	12% 7% 3 5% 4 3 4 4 5% 6% 47%	1934
	11th to 20th	Night	13% 7% 3 5% 5% 2 4 4 4 6% 47%	1659
	21st to end	Night	16% 7% 3 4 5% 3 3 3 4 6% 45%	1620
May	1st to 10th	Night	15% 6% 3 6% 4 3 5% 5% 6% 9% 39%	1620
	11th to 20th	Night	13% 6% 3 4 5% 2 5% 4 5% 8% 45%	1593
	21st to end	Night	13% 8% 2 5% 5% 3 5% 5% 4 8% 42%	1687
June	1st to 10th	Night	5% 4 1 4 5% 2 5% 5% 5% 9% 54%	1440
	11th to 20th	Night	7% 5% 1 4 3 3 5% 6% 5% 10% 51%	1440
	21st to end	Night	4 3 1 3 4 3 5% 4 7% 8% 57%	1440
July	1st to 10th	Night	6% 4 2 4 3 3 3 4 6% 8% 57%	1598
	11th to 20th	Night	3 2 1 2 3 3 3 5% 7% 10% 61%	1620
	21st to end	Night	3 2 2 3 4 2 4 4 6% 10% 59%	1772
August	1st to 10th	Night	5% 3 2 4 5% 3 5% 5% 6% 9% 53%	1611
	11th to 20th	Night	6% 4 2 4 4 2 4 4 5% 10% 57%	1600
	21st to end	Night	8% 4 2 4 4 2 4 4 6% 7% 57%	1814
September	1st to 10th	Night	9% 3 1 3 4 2 3 4 5% 7% 60%	1876
	11th to 20th	Night	10% 3 1 3 3 2 3 4 6% 8% 59%	1980
	21st to end	Night	10% 4 2 3 3 2 4 3 4 6% 60%	1980
October	1st to 10th	Night	14% 4 2 3 3 3 5% 5% 5% 6% 50%	2092
	11th to 20th	Night	14% 5% 2 4 4 2 3 3 4 6% 55%	2160
	21st to end	Night	14% 6% 2 5% 3 2 3 3 4 6% 52%	2376
November	1st to 10th	Night	7% 5% 1 3 3 2 4 4 5% 6% 58%	2391
	11th to 20th	Night	9% 6% 3 5% 4 2 3 3 5% 6% 53%	2515
	21st to end	Night	12% 7% 2 4 4 2 3 4 4 6% 51%	2660
December	1st to 10th	Night	9% 8% 3 5% 6% 4 4 5% 5% 6% 45%	2660
	11th to 20th	Night	9% 8% 3 6% 4 2 4 3 4 8% 48%	3279
	21st to end	Night	18% 13% 5% 10% 5% 2 3 3 3 5% 32%	4774

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	46% 4 17% 22% 11% 1	1708
	11th to 20th	Day	45% 4 16% 23% 12%	1674
	21st to end	Day	51% 4 17% 20% 8% 1	1782
February	1st to 10th	Day	50% 5% 15% 18% 11% 1	1620
	11th to 20th	Day	45% 6% 12% 22% 13% 3	1620
	21st to end	Day	43% 4 14% 23% 13% 3	1480
March	1st to 10th	Day	42% 4 13% 25% 13% 2	1943
	11th to 20th	Day	45% 4 11% 24% 13% 2	1980
	21st to end	Day	53% 6% 15% 18% 7% 1	2178
April	1st to 10th	Day	43% 5% 13% 25% 13% 1	2024
	11th to 20th	Day	45% 5% 13% 23% 13% 3	2248
	21st to end	Day	46% 4 11% 25% 13% 1	2340
May	1st to 10th	Day	47% 5% 13% 20% 14% 1	2340
	11th to 20th	Day	41% 6% 15% 25% 12%	2306
	21st to end	Day	45% 8% 16% 20% 10% 1	2586
June	1st to 10th	Day	30% 7% 18% 30% 13% 2	2520
	11th to 20th	Day	33% 6% 13% 30% 16% 2	2520
	21st to end	Day	31% 6% 16% 29% 15% 4	2520
July	1st to 10th	Day	28% 5% 16% 32% 16% 2	2292
	11th to 20th	Day	27% 5% 14% 28% 20% 6%	2271
	21st to end	Day	27% 7% 17% 30% 18% 1	2405
August	1st to 10th	Day	34% 10% 18% 26% 11% 2	2314
	11th to 20th	Day	30% 7% 14% 31% 17% 1	2301
	21st to end	Day	29% 6% 11% 28% 19% 6%	2540
September	1st to 10th	Day	33% 5% 11% 29% 17% 6%	2081
	11th to 20th	Day	32% 4 12% 33% 18% 1	1980
	21st to end	Day	29% 4 10% 32% 24% 1	1980
October	1st to 10th	Day	36% 5% 12% 25% 20% 2	1850
	11th to 20th	Day	33% 4 8% 27% 23% 5%	1800
	21st to end	Day	39% 5% 13% 21% 19% 4	1980
November	1st to 10th	Day	30% 4 15% 28% 21% 2	1683
	11th to 20th	Day	38% 4 13% 25% 18% 1	1663
	21st to end	Day	40% 4 11% 30% 14% 1	1520
December	1st to 10th	Day	37% 5% 17% 27% 13% 2	1520
	11th to 20th	Day	45% 4 16% 28% 6%	1915
	21st to end	Day	59% 4 10% 19% 7%	2888
January	1st to 10th	Night	41% 5% 14% 23% 16% 1	2458
	11th to 20th	Night	45% 4 16% 26% 10%	2431
	21st to end	Night	43% 4 15% 25% 11% 1	2574
February	1st to 10th	Night	48% 4 13% 20% 12% 2	2340
	11th to 20th	Night	40% 6% 15% 23% 15% 3	2252
	21st to end	Night	36% 4 12% 25% 18% 4	1776
March	1st to 10th	Night	37% 5% 12% 29% 14% 3	2016
	11th to 20th	Night	42% 4 10% 25% 17% 3	1980
	21st to end	Night	49% 6% 14% 20% 9% 1	2178
April	1st to 10th	Night	37% 6% 11% 26% 17% 3	1934
	11th to 20th	Night	39% 5% 11% 27% 17% 2	1659
	21st to end	Night	40% 5% 12% 23% 18% 1	1620
May	1st to 10th	Night	42% 6% 14% 23% 14% 2	1620
	11th to 20th	Night	38% 6% 15% 24% 17% 1	1594
	21st to end	Night	41% 6% 18% 20% 12% 3	1688
June	1st to 10th	Night	27% 6% 15% 34% 16% 3	1440
	11th to 20th	Night	28% 7% 15% 27% 19% 5%	1440
	21st to end	Night	23% 6% 15% 33% 20% 3	1440
July	1st to 10th	Night	26% 5% 15% 30% 20% 4	1553
	11th to 20th	Night	18% 6% 19% 31% 21% 5%	1566
	21st to end	Night	19% 5% 16% 37% 20% 3	1673
August	1st to 10th	Night	26% 9% 18% 32% 14% 1	1601
	11th to 20th	Night	23% 6% 14% 33% 21% 2	1600
	21st to end	Night	26% 5% 13% 26% 21% 9%	1814
September	1st to 10th	Night	25% 4 12% 29% 23% 7%	1876
	11th to 20th	Night	24% 6% 12% 36% 19% 4	1980
	21st to end	Night	27% 4 8% 29% 27% 4	1980
October	1st to 10th	Night	34% 5% 11% 24% 23% 3	2092
	11th to 20th	Night	32% 3 8% 25% 27% 6%	2160
	21st to end	Night	35% 3 12% 23% 24% 3	2376
November	1st to 10th	Night	25% 4 15% 26% 24% 4	2391
	11th to 20th	Night	33% 3 12% 31% 19% 3	2515
	21st to end	Night	35% 4 12% 28% 19% 2	2660
December	1st to 10th	Night	38% 5% 14% 29% 13% 1	2660
	11th to 20th	Night	36% 4 15% 35% 10%	3281
	21st to end	Night	57% 3 11% 21% 7% 1	4774

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	17% 13% 36% 25% 9% 2	270
	11th to 20th	Day	19% 14% 35% 26% 5% 1	258
	21st to end	Day	16% 10% 45% 21% 6% 1	264
February	1st to 10th	Day	14% 20% 41% 23% 3	240
	11th to 20th	Day	17% 14% 39% 23% 5% 1	240
	21st to end	Day	16% 19% 38% 22% 5%	198
March	1st to 10th	Day	15% 14% 43% 22% 5% 2	240
	11th to 20th	Day	28% 10% 34% 21% 7% 1	240
	21st to end	Day	30% 15% 34% 16% 4 1	264
April	1st to 10th	Day	18% 16% 42% 20% 4	284
	11th to 20th	Day	20% 14% 38% 19% 8%	526
	21st to end	Day	23% 15% 29% 22% 8% 2	600
May	1st to 10th	Day	19% 12% 33% 24% 10% 1	603
	11th to 20th	Day	18% 10% 30% 27% 13% 2	625
	21st to end	Day	19% 8% 26% 30% 16% 2	679
June	1st to 10th	Day	8% 5% 22% 34% 25% 6%	630
	11th to 20th	Day	8% 6% 29% 36% 18% 4	630
	21st to end	Day	7% 6% 30% 38% 15% 3	630
July	1st to 10th	Day	9% 3 15% 34% 30% 9%	621
	11th to 20th	Day	6% 4 20% 39% 25% 5%	618
	21st to end	Day	6% 2 18% 42% 28% 2	684
August	1st to 10th	Day	7% 2 19% 44% 24% 4	626
	11th to 20th	Day	7% 3 18% 41% 28% 3	615
	21st to end	Day	9% 3 21% 38% 25% 4	659
September	1st to 10th	Day	13% 6% 24% 34% 18% 4	371
	11th to 20th	Day	7% 3 29% 35% 20% 5%	270
	21st to end	Day	12% 9% 33% 29% 14% 2	270
October	1st to 10th	Day	22% 6% 26% 26% 15% 5%	270
	11th to 20th	Day	12% 16% 40% 22% 9% 1	270
	21st to end	Day	18% 13% 36% 20% 11% 2	297
November	1st to 10th	Day	14% 13% 38% 23% 9% 3	270
	11th to 20th	Day	12% 15% 43% 22% 7% 1	270
	21st to end	Day	22% 11% 30% 26% 9% 1	270
December	1st to 10th	Day	9% 10% 40% 33% 7% 2	270
	11th to 20th	Day	16% 11% 37% 28% 8% 1	270
	21st to end	Day	21% 12% 42% 20% 4	297
January	1st to 10th	Night	13% 11% 35% 34% 7%	950
	11th to 20th	Night	15% 12% 34% 32% 7%	935
	21st to end	Night	18% 7% 40% 29% 5%	990
February	1st to 10th	Night	15% 11% 39% 30% 4	900
	11th to 20th	Night	12% 10% 42% 30% 5%	857
	21st to end	Night	16% 11% 40% 28% 5%	592
March	1st to 10th	Night	15% 14% 37% 26% 8%	576
	11th to 20th	Night	20% 7% 36% 29% 7%	540
	21st to end	Night	20% 12% 38% 24% 6%	594
April	1st to 10th	Night	16% 14% 41% 24% 5%	540
	11th to 20th	Night	15% 13% 38% 28% 4 1	533
	21st to end	Night	19% 11% 34% 28% 8%	540
May	1st to 10th	Night	18% 10% 32% 33% 8%	540
	11th to 20th	Night	15% 10% 31% 32% 11%	531
	21st to end	Night	17% 8% 28% 33% 13% 1	584
June	1st to 10th	Night	7% 4 24% 46% 19%	540
	11th to 20th	Night	9% 4 30% 43% 13% 1	540
	21st to end	Night	4 4 33% 43% 16% 1	540
July	1st to 10th	Night	7% 3 16% 45% 28% 1	525
	11th to 20th	Night	3 2 20% 49% 25% 1	522
	21st to end	Night	3 1 15% 55% 25%	591
August	1st to 10th	Night	5% 2 18% 48% 23% 3	537
	11th to 20th	Night	7% 2 18% 48% 24% 1	534
	21st to end	Night	8% 2 23% 40% 24% 3	594
September	1st to 10th	Night	11% 3 24% 40% 21% 1	540
	11th to 20th	Night	11% 2 29% 40% 17% 1	540
	21st to end	Night	11% 6% 32% 34% 15% 1	540
October	1st to 10th	Night	16% 6% 31% 33% 12% 2	652
	11th to 20th	Night	16% 11% 35% 30% 7%	720
	21st to end	Night	19% 9% 29% 34% 9%	792
November	1st to 10th	Night	9% 10% 34% 37% 9% 1	911
	11th to 20th	Night	13% 11% 40% 31% 6% 1	950
	21st to end	Night	15% 11% 34% 31% 9% 1	950
December	1st to 10th	Night	13% 10% 41% 30% 6%	950
	11th to 20th	Night	15% 9% 34% 35% 7%	950
	21st to end	Night	19% 11% 33% 31% 5%	1045

Page generated at 2024-01-14 08:54:58. Version ac07

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