R2 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the R2 Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	14% 10% 4 8% 7% 4 5% 5% 6% 7% 31%	75075
	Night	14% 10% 4 8% 6% 4 5% 5% 5% 7% 32%	74662
Transparency	Day	53% 4 11% 20% 10% 1	74788
	Night	52% 4 12% 21% 10% 1	74484
Seeing	Day	21% 17% 31% 19% 9% 3	13681
	Night	20% 16% 30% 23% 9% 1	22816

By Month

Percentage Cloud Cover NE (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	13% 15% 8% 13% 10% 5% 6% 5% 6% 4 16%	1517
	11th to 20th	Day	14% 17% 7% 11% 10% 5% 6% 4 5% 6% 15%	1609
	21st to end	Day	11% 17% 8% 12% 10% 4 6% 5% 5% 6% 16%	1782
February	1st to 10th	Day	14% 16% 6% 12% 11% 5% 6% 6% 5% 4 16%	1620
	11th to 20th	Day	11% 13% 8% 12% 9% 5% 5% 5% 5% 6% 21%	1573
	21st to end	Day	17% 16% 6% 10% 6% 3 4 4 4 4 24%	1383
March	1st to 10th	Day	11% 13% 5% 10% 9% 4 4 5% 4 5% 28%	1974
	11th to 20th	Day	11% 12% 6% 10% 8% 3 6% 4 3 5% 31%	1980
	21st to end	Day	16% 13% 4 7% 7% 3 5% 4 4 5% 32%	2178
April	1st to 10th	Day	15% 14% 5% 7% 6% 3 5% 5% 5% 6% 29%	2111
	11th to 20th	Day	18% 10% 3 5% 5% 3 3 5% 4 7% 35%	2230
	21st to end	Day	20% 10% 4 7% 5% 3 3 4 5% 6% 33%	2340
May	1st to 10th	Day	16% 8% 4 7% 5% 3 4 5% 5% 7% 35%	2340
	11th to 20th	Day	16% 8% 3 6% 5% 3 5% 5% 5% 7% 38%	2450
	21st to end	Day	12% 5% 2 4 7% 3 6% 5% 6% 8% 42%	2725
June	1st to 10th	Day	16% 5% 2 5% 5% 3 5% 6% 6% 8% 37%	2520
	11th to 20th	Day	13% 5% 2 5% 6% 3 5% 5% 7% 9% 41%	2607
	21st to end	Day	14% 5% 2 5% 6% 4 5% 5% 6% 10% 39%	2700
July	1st to 10th	Day	9% 4 2 5% 5% 4 5% 6% 7% 9% 44%	2669
	11th to 20th	Day	11% 5% 2 5% 7% 3 6% 6% 6% 10% 39%	2520
	21st to end	Day	10% 5% 3 6% 7% 4 7% 6% 8% 9% 34%	2561
August	1st to 10th	Day	10% 5% 2 6% 7% 4 5% 7% 8% 9% 38%	2327
	11th to 20th	Day	7% 5% 3 6% 7% 5% 6% 7% 8% 9% 36%	2303
	21st to end	Day	13% 6% 2 6% 5% 4 6% 6% 6% 8% 38%	2498
September	1st to 10th	Day	14% 6% 3 7% 6% 4 4 5% 6% 7% 39%	2160
	11th to 20th	Day	13% 5% 2 5% 6% 4 5% 4 5% 8% 41%	2032
	21st to end	Day	14% 6% 3 7% 8% 5% 6% 5% 6% 7% 34%	1958
October	1st to 10th	Day	20% 8% 3 7% 6% 3 5% 4 5% 7% 32%	1800
	11th to 20th	Day	20% 10% 4 8% 8% 4 5% 4 6% 6% 26%	1800
	21st to end	Day	26% 17% 4 7% 5% 3 4 4 5% 5% 20%	1980
November	1st to 10th	Day	13% 12% 5% 8% 7% 3 6% 4 7% 7% 29%	1590
	11th to 20th	Day	12% 15% 5% 9% 8% 4 6% 5% 7% 7% 23%	1520
	21st to end	Day	16% 16% 7% 11% 8% 4 5% 5% 5% 6% 18%	1520
December	1st to 10th	Day	15% 17% 9% 14% 8% 4 5% 5% 5% 5% 13%	1520
	11th to 20th	Day	17% 15% 7% 13% 7% 3 6% 4 5% 6% 17%	1906
	21st to end	Day	25% 19% 8% 14% 8% 3 4 4 3 3 9%	2772
January	1st to 10th	Night	14% 15% 7% 11% 9% 4 6% 6% 5% 5% 18%	2649
	11th to 20th	Night	16% 14% 6% 12% 10% 5% 6% 6% 5% 5% 15%	2422
	21st to end	Night	10% 12% 6% 12% 10% 5% 7% 5% 6% 7% 19%	2574
February	1st to 10th	Night	13% 14% 6% 10% 10% 4 5% 5% 5% 7% 21%	2340
	11th to 20th	Night	11% 13% 6% 10% 9% 5% 6% 5% 5% 6% 23%	2273
	21st to end	Night	12% 12% 5% 11% 8% 4 5% 5% 5% 7% 26%	1870
March	1st to 10th	Night	12% 9% 5% 10% 7% 4 6% 4 4 5% 33%	1971
	11th to 20th	Night	14% 10% 5% 9% 6% 4 4 4 4 6% 35%	1979
	21st to end	Night	15% 10% 3 7% 5% 3 4 4 5% 5% 39%	2178
April	1st to 10th	Night	17% 12% 4 8% 6% 3 5% 4 5% 6% 31%	1847
	11th to 20th	Night	16% 9% 2 5% 6% 3 5% 4 5% 6% 39%	1693
	21st to end	Night	14% 10% 4 7% 5% 4 4 5% 5% 6% 35%	1620
May	1st to 10th	Night	16% 7% 2 6% 5% 3 5% 5% 5% 8% 39%	1620
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 5% 8% 46%	1443
	21st to end	Night	9% 4 2 4 4 3 4 4 5% 9% 52%	1550
June	1st to 10th	Night	13% 4 2 5% 5% 4 6% 5% 6% 9% 42%	1440
	11th to 20th	Night	9% 3 3 6% 4 2 5% 6% 8% 9% 44%	1346
	21st to end	Night	11% 4 3 5% 5% 2 3 5% 7% 7% 48%	1260
July	1st to 10th	Night	5% 3 2 5% 5% 2 4 4 3 6% 59%	1286
	11th to 20th	Night	8% 4 3 4 5% 3 5% 4 7% 6% 51%	1440
	21st to end	Night	8% 3 2 4 4 3 4 6% 6% 8% 51%	1754
August	1st to 10th	Night	8% 4 2 5% 4 2 5% 5% 6% 8% 52%	1611
	11th to 20th	Night	6% 4 2 5% 4 2 4 5% 6% 10% 50%	1598
	21st to end	Night	11% 5% 2 4 4 3 4 5% 5% 8% 48%	1839
September	1st to 10th	Night	9% 5% 2 5% 5% 3 4 5% 7% 8% 47%	1800
	11th to 20th	Night	11% 5% 1 4 3 2 4 4 5% 7% 53%	1926
	21st to end	Night	14% 8% 3 6% 6% 3 4 3 4 7% 42%	2002
October	1st to 10th	Night	18% 7% 3 6% 6% 4 5% 4 5% 6% 37%	2160
	11th to 20th	Night	19% 9% 3 7% 6% 3 5% 6% 5% 6% 32%	2160
	21st to end	Night	22% 13% 3 7% 7% 4 5% 5% 5% 6% 24%	2376
November	1st to 10th	Night	15% 9% 3 7% 6% 3 5% 5% 6% 7% 34%	2483
	11th to 20th	Night	15% 13% 5% 7% 6% 4 5% 6% 6% 8% 27%	2660
	21st to end	Night	16% 14% 6% 8% 7% 4 6% 5% 5% 7% 22%	2660
December	1st to 10th	Night	18% 14% 6% 10% 8% 4 6% 6% 5% 7% 17%	2660
	11th to 20th	Night	14% 16% 7% 12% 7% 4 5% 5% 6% 6% 18%	3288
	21st to end	Night	26% 18% 9% 13% 6% 4 4 4 4 4 9%	4884

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	69% 5% 11% 12% 4	1518
	11th to 20th	Day	70% 4 9% 12% 4 1	1609
	21st to end	Day	69% 5% 7% 12% 7% 1	1782
February	1st to 10th	Day	70% 4 7% 15% 3	1620
	11th to 20th	Day	65% 4 8% 15% 6% 1	1582
	21st to end	Day	64% 4 7% 16% 8% 1	1383
March	1st to 10th	Day	58% 5% 11% 16% 10% 1	1977
	11th to 20th	Day	57% 4 8% 18% 11% 2	1980
	21st to end	Day	56% 3 9% 17% 14% 2	2178
April	1st to 10th	Day	57% 5% 9% 19% 10% 1	2111
	11th to 20th	Day	49% 4 8% 23% 15% 1	2230
	21st to end	Day	52% 4 11% 19% 12% 2	2340
May	1st to 10th	Day	49% 4 9% 22% 15% 1	2340
	11th to 20th	Day	45% 4 9% 26% 13% 1	2454
	21st to end	Day	40% 5% 16% 23% 14% 2	2725
June	1st to 10th	Day	42% 6% 12% 23% 16% 1	2520
	11th to 20th	Day	39% 5% 13% 25% 17% 1	2607
	21st to end	Day	41% 5% 14% 26% 14% 1	2700
July	1st to 10th	Day	35% 6% 14% 25% 18% 2	2596
	11th to 20th	Day	40% 4 13% 30% 11% 1	2445
	21st to end	Day	44% 6% 14% 22% 13% 1	2418
August	1st to 10th	Day	39% 6% 16% 25% 12% 2	2314
	11th to 20th	Day	41% 5% 17% 26% 11%	2303
	21st to end	Day	43% 5% 14% 26% 12% 1	2498
September	1st to 10th	Day	44% 5% 12% 27% 10% 2	2160
	11th to 20th	Day	41% 4 12% 30% 13%	2032
	21st to end	Day	49% 5% 13% 25% 8% 1	1958
October	1st to 10th	Day	53% 4 12% 19% 11% 1	1800
	11th to 20th	Day	58% 4 12% 19% 6% 1	1800
	21st to end	Day	66% 3 12% 13% 6%	1980
November	1st to 10th	Day	53% 6% 13% 20% 8% 1	1590
	11th to 20th	Day	60% 4 13% 14% 8% 1	1520
	21st to end	Day	69% 4 12% 12% 3	1520
December	1st to 10th	Day	73% 4 11% 9% 2	1520
	11th to 20th	Day	69% 6% 11% 11% 3	1906
	21st to end	Day	81% 2 6% 8% 2	2772
January	1st to 10th	Night	67% 4 10% 13% 6%	2649
	11th to 20th	Night	69% 5% 10% 10% 5%	2422
	21st to end	Night	63% 4 11% 15% 6% 1	2574
February	1st to 10th	Night	63% 4 10% 18% 5%	2340
	11th to 20th	Night	61% 5% 9% 17% 8%	2275
	21st to end	Night	58% 4 13% 17% 8% 1	1870
March	1st to 10th	Night	54% 4 12% 19% 10% 1	1981
	11th to 20th	Night	52% 3 9% 21% 12% 2	1980
	21st to end	Night	48% 4 10% 21% 15% 2	2178
April	1st to 10th	Night	54% 4 9% 19% 13% 1	1847
	11th to 20th	Night	46% 4 10% 21% 17% 2	1693
	21st to end	Night	49% 4 10% 20% 15% 2	1620
May	1st to 10th	Night	44% 4 10% 22% 17% 3	1620
	11th to 20th	Night	39% 4 10% 27% 18% 4	1444
	21st to end	Night	31% 5% 16% 26% 17% 4	1551
June	1st to 10th	Night	39% 5% 11% 26% 17% 2	1440
	11th to 20th	Night	35% 5% 12% 26% 20% 2	1346
	21st to end	Night	36% 5% 14% 29% 16% 1	1260
July	1st to 10th	Night	28% 5% 11% 29% 24% 3	1250
	11th to 20th	Night	32% 4 12% 34% 17% 1	1392
	21st to end	Night	30% 6% 15% 31% 15% 3	1656
August	1st to 10th	Night	31% 4 17% 32% 14% 1	1600
	11th to 20th	Night	29% 6% 15% 34% 15% 1	1598
	21st to end	Night	35% 5% 14% 30% 15% 1	1839
September	1st to 10th	Night	34% 6% 16% 30% 14% 1	1800
	11th to 20th	Night	31% 4 12% 36% 17% 1	1926
	21st to end	Night	44% 3 13% 29% 10%	2002
October	1st to 10th	Night	48% 4 11% 22% 14% 1	2160
	11th to 20th	Night	52% 5% 13% 23% 8%	2160
	21st to end	Night	60% 5% 9% 17% 9%	2376
November	1st to 10th	Night	48% 5% 13% 24% 9% 1	2483
	11th to 20th	Night	56% 4 14% 17% 8% 1	2660
	21st to end	Night	62% 5% 16% 15% 2 1	2660
December	1st to 10th	Night	66% 4 13% 14% 3	2660
	11th to 20th	Night	66% 5% 13% 12% 3	3288
	21st to end	Night	80% 3 9% 7% 2	4884

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	21% 26% 33% 14% 4 1	180
	11th to 20th	Day	27% 26% 29% 13% 3 2	231
	21st to end	Day	23% 30% 31% 13% 3	264
February	1st to 10th	Day	34% 31% 26% 8% 2	240
	11th to 20th	Day	24% 36% 34% 5% 1	240
	21st to end	Day	36% 33% 24% 6%	198
March	1st to 10th	Day	23% 25% 34% 13% 4	417
	11th to 20th	Day	23% 22% 38% 13% 5%	420
	21st to end	Day	30% 21% 29% 14% 5% 1	462
April	1st to 10th	Day	25% 22% 33% 14% 6%	420
	11th to 20th	Day	33% 18% 25% 13% 8% 3	412
	21st to end	Day	27% 19% 33% 14% 5% 2	420
May	1st to 10th	Day	23% 16% 31% 19% 9% 3	423
	11th to 20th	Day	21% 17% 31% 19% 8% 4	447
	21st to end	Day	16% 15% 29% 24% 11% 4	485
June	1st to 10th	Day	17% 15% 35% 24% 8% 2	450
	11th to 20th	Day	17% 14% 31% 24% 12% 2	537
	21st to end	Day	16% 13% 39% 20% 8% 3	630
July	1st to 10th	Day	10% 9% 33% 29% 15% 4	591
	11th to 20th	Day	11% 7% 34% 28% 13% 6%	444
	21st to end	Day	11% 8% 38% 27% 11% 5%	488
August	1st to 10th	Day	10% 7% 29% 29% 15% 10%	446
	11th to 20th	Day	8% 9% 30% 27% 18% 8%	439
	21st to end	Day	16% 10% 31% 22% 15% 7%	495
September	1st to 10th	Day	14% 12% 28% 26% 13% 7%	450
	11th to 20th	Day	12% 10% 28% 23% 17% 10%	450
	21st to end	Day	15% 15% 29% 23% 13% 5%	450
October	1st to 10th	Day	26% 15% 23% 18% 13% 5%	450
	11th to 20th	Day	24% 22% 33% 15% 6% 1	450
	21st to end	Day	35% 20% 27% 14% 3 1	495
November	1st to 10th	Day	24% 23% 31% 18% 3 1	239
	11th to 20th	Day	27% 22% 32% 13% 5% 1	180
	21st to end	Day	29% 23% 38% 8% 1	180
December	1st to 10th	Day	28% 28% 31% 11% 2	180
	11th to 20th	Day	28% 31% 28% 11% 1 1	180
	21st to end	Day	28% 28% 37% 5% 3	198
January	1st to 10th	Night	24% 27% 31% 14% 4	760
	11th to 20th	Night	26% 22% 30% 17% 4	735
	21st to end	Night	18% 19% 35% 21% 6%	792
February	1st to 10th	Night	23% 27% 33% 15% 2	720
	11th to 20th	Night	22% 24% 37% 14% 3	703
	21st to end	Night	22% 26% 33% 17% 2	592
March	1st to 10th	Night	22% 24% 33% 19% 3	720
	11th to 20th	Night	24% 22% 30% 19% 5% 1	720
	21st to end	Night	22% 19% 31% 21% 7%	792
April	1st to 10th	Night	25% 19% 33% 21% 2	720
	11th to 20th	Night	21% 18% 32% 19% 9% 1	629
	21st to end	Night	22% 13% 32% 26% 7%	540
May	1st to 10th	Night	19% 8% 30% 29% 11% 2	540
	11th to 20th	Night	17% 8% 33% 31% 10% 1	382
	21st to end	Night	10% 9% 37% 31% 13%	389
June	1st to 10th	Night	14% 7% 35% 33% 11%	360
	11th to 20th	Night	12% 9% 29% 35% 14%	360
	21st to end	Night	11% 8% 31% 34% 16% 1	360
July	1st to 10th	Night	7% 4 27% 41% 20% 2	350
	11th to 20th	Night	11% 7% 27% 34% 19% 1	348
	21st to end	Night	8% 5% 31% 37% 17% 1	574
August	1st to 10th	Night	10% 3 25% 36% 24% 2	537
	11th to 20th	Night	6% 6% 21% 40% 24% 3	534
	21st to end	Night	14% 5% 28% 30% 22% 2	651
September	1st to 10th	Night	12% 8% 28% 28% 19% 5%	720
	11th to 20th	Night	13% 8% 25% 29% 20% 5%	720
	21st to end	Night	18% 10% 23% 28% 17% 4	720
October	1st to 10th	Night	20% 10% 31% 23% 15% 2	720
	11th to 20th	Night	25% 16% 32% 20% 7% 1	720
	21st to end	Night	29% 18% 30% 19% 4	792
November	1st to 10th	Night	24% 17% 29% 22% 8% 1	740
	11th to 20th	Night	22% 24% 27% 20% 6% 1	760
	21st to end	Night	26% 20% 31% 19% 4	760
December	1st to 10th	Night	28% 23% 33% 13% 3 1	760
	11th to 20th	Night	23% 25% 33% 16% 3	760
	21st to end	Night	32% 21% 29% 16% 2	836

Page generated at 2024-01-11 04:22:43. Version ac07

Copyright 2024 Attilla Danko