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 2024-11-12.

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% 11% 4 9% 6% 5% 5% 4 6% 7% 31%	102054
	Night	14% 10% 4 9% 6% 5% 5% 4 5% 6% 33%	97129
Transparency	Day	51% 5% 12% 21% 10% 1	105656
	Night	50% 5% 12% 22% 11% 1	101616
Seeing	Day	21% 17% 31% 19% 9% 3	14851
	Night	20% 16% 30% 23% 9% 1	23822

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	15% 15% 6% 13% 6% 5% 5% 3 5% 5% 21%	2517
	11th to 20th	Day	11% 18% 8% 17% 11% 7% 5% 3 4 5% 12%	2776
	21st to end	Day	20% 22% 7% 12% 6% 4 4 3 4 4 15%	3124
February	1st to 10th	Day	13% 17% 5% 14% 9% 6% 6% 4 4 5% 17%	1710
	11th to 20th	Day	10% 14% 8% 14% 8% 6% 5% 4 5% 6% 20%	1663
	21st to end	Day	16% 17% 5% 11% 6% 5% 4 3 4 5% 24%	1467
March	1st to 10th	Day	15% 14% 6% 10% 6% 4 4 3 4 5% 29%	3429
	11th to 20th	Day	10% 18% 6% 11% 6% 5% 5% 3 4 5% 28%	3480
	21st to end	Day	14% 12% 4 8% 6% 4 4 3 4 5% 35%	3815
April	1st to 10th	Day	15% 15% 4 8% 5% 4 5% 3 5% 6% 29%	2229
	11th to 20th	Day	18% 11% 3 7% 4 4 3 4 5% 7% 35%	2356
	21st to end	Day	20% 10% 4 8% 4 4 3 3 6% 6% 33%	2470
May	1st to 10th	Day	16% 9% 3 7% 4 4 4 4 6% 8% 35%	4108
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 6% 7% 31%	4356
	21st to end	Day	11% 6% 2 6% 5% 4 4 3 6% 8% 45%	4837
June	1st to 10th	Day	16% 6% 2 6% 5% 4 5% 5% 6% 8% 36%	2660
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 7% 9% 40%	2752
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 9% 38%	2850
July	1st to 10th	Day	11% 5% 2 7% 6% 6% 6% 5% 7% 10% 36%	4701
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 10% 42%	4440
	21st to end	Day	9% 5% 2 7% 6% 5% 6% 5% 7% 8% 41%	4480
August	1st to 10th	Day	13% 8% 3 7% 5% 4 5% 5% 7% 8% 36%	4104
	11th to 20th	Day	10% 7% 3 8% 6% 5% 6% 5% 8% 9% 32%	4044
	21st to end	Day	11% 5% 2 7% 4 5% 5% 4 6% 9% 42%	4386
September	1st to 10th	Day	14% 6% 2 8% 5% 5% 4 4 6% 7% 40%	2280
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 3 6% 8% 42%	2144
	21st to end	Day	15% 6% 2 9% 6% 6% 6% 4 6% 7% 34%	2066
October	1st to 10th	Day	19% 8% 3 9% 5% 5% 4 4 5% 7% 32%	1900
	11th to 20th	Day	18% 10% 4 10% 6% 5% 5% 3 6% 5% 28%	1900
	21st to end	Day	24% 17% 4 9% 4 4 4 3 5% 5% 20%	2090
November	1st to 10th	Day	13% 13% 5% 9% 7% 5% 5% 3 7% 7% 28%	1674
	11th to 20th	Day	11% 17% 4 11% 6% 6% 7% 4 7% 6% 22%	1528
	21st to end	Day	16% 18% 6% 11% 7% 5% 5% 4 5% 6% 17%	1520
December	1st to 10th	Day	14% 20% 7% 15% 7% 6% 5% 3 6% 5% 12%	1520
	11th to 20th	Day	17% 16% 6% 14% 6% 5% 5% 3 5% 5% 17%	1906
	21st to end	Day	25% 20% 8% 15% 6% 4 4 3 3 3 9%	2772
January	1st to 10th	Night	15% 15% 7% 13% 7% 6% 5% 3 4 6% 18%	4429
	11th to 20th	Night	12% 14% 7% 15% 12% 9% 6% 5% 4 5% 11%	4182
	21st to end	Night	18% 14% 7% 12% 10% 6% 5% 4 5% 5% 14%	4532
February	1st to 10th	Night	12% 15% 5% 11% 8% 5% 4 4 6% 7% 22%	2470
	11th to 20th	Night	10% 14% 6% 12% 7% 7% 6% 4 6% 6% 23%	2403
	21st to end	Night	11% 13% 4 12% 7% 5% 5% 5% 5% 7% 27%	1984
March	1st to 10th	Night	16% 11% 5% 10% 6% 5% 4 4 5% 6% 30%	3409
	11th to 20th	Night	11% 12% 4 9% 5% 4 4 3 5% 7% 35%	3479
	21st to end	Night	14% 8% 3 7% 5% 4 4 4 5% 5% 40%	3817
April	1st to 10th	Night	17% 13% 3 9% 6% 4 4 3 5% 6% 31%	1949
	11th to 20th	Night	17% 9% 2 6% 5% 4 5% 4 5% 6% 38%	1788
	21st to end	Night	14% 11% 3 7% 5% 5% 4 4 5% 7% 35%	1710
May	1st to 10th	Night	16% 8% 2 7% 4 4 4 4 5% 6% 40%	2833
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 5% 8% 40%	2537
	21st to end	Night	9% 5% 2 5% 4 4 4 3 6% 8% 52%	2738
June	1st to 10th	Night	14% 5% 2 6% 4 6% 5% 3 6% 8% 42%	1520
	11th to 20th	Night	9% 4 2 7% 4 3 6% 5% 8% 10% 43%	1420
	21st to end	Night	12% 4 2 6% 4 3 4 4 7% 7% 47%	1330
July	1st to 10th	Night	5% 4 2 7% 4 5% 4 4 6% 7% 51%	2262
	11th to 20th	Night	11% 4 1 4 3 4 4 3 5% 6% 53%	2520
	21st to end	Night	7% 4 2 5% 5% 4 5% 5% 6% 8% 50%	3070
August	1st to 10th	Night	10% 5% 3 6% 3 4 4 3 6% 7% 49%	2825
	11th to 20th	Night	12% 5% 2 5% 3 4 3 3 5% 8% 49%	2785
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 8% 48%	3237
September	1st to 10th	Night	9% 5% 2 6% 4 4 4 5% 7% 7% 47%	1900
	11th to 20th	Night	10% 5% 1 4 3 3 3 4 6% 6% 54%	2033
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 4 7% 41%	2114
October	1st to 10th	Night	17% 7% 3 7% 5% 5% 5% 3 5% 6% 38%	2280
	11th to 20th	Night	18% 9% 3 7% 5% 5% 5% 5% 5% 5% 34%	2280
	21st to end	Night	20% 13% 3 8% 5% 5% 5% 4 6% 6% 26%	2508
November	1st to 10th	Night	15% 10% 3 8% 5% 5% 5% 4 6% 6% 34%	2618
	11th to 20th	Night	14% 14% 4 8% 5% 5% 5% 5% 6% 7% 26%	2675
	21st to end	Night	15% 15% 5% 9% 6% 5% 6% 4 5% 7% 22%	2660
December	1st to 10th	Night	18% 15% 5% 11% 7% 5% 5% 5% 5% 7% 17%	2660
	11th to 20th	Night	13% 17% 6% 13% 6% 5% 5% 4 6% 6% 17%	3288
	21st to end	Night	25% 19% 8% 14% 5% 5% 4 3 4 3 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	64% 3 15% 13% 4	2518
	11th to 20th	Day	76% 3 9% 9% 3	2776
	21st to end	Day	74% 3 9% 9% 4	3124
February	1st to 10th	Day	69% 4 7% 16% 4	1710
	11th to 20th	Day	65% 4 8% 15% 6% 1	1672
	21st to end	Day	63% 4 8% 16% 8% 1	1467
March	1st to 10th	Day	59% 3 11% 16% 9%	3432
	11th to 20th	Day	60% 3 8% 20% 8% 1	3480
	21st to end	Day	52% 3 9% 20% 14% 2	3815
April	1st to 10th	Day	57% 4 9% 19% 10% 1	2229
	11th to 20th	Day	50% 4 8% 23% 15% 1	2356
	21st to end	Day	53% 3 11% 19% 12% 2	2470
May	1st to 10th	Day	48% 4 11% 22% 15% 1	4120
	11th to 20th	Day	52% 4 13% 22% 8% 1	4360
	21st to end	Day	38% 4 14% 23% 19% 3	4837
June	1st to 10th	Day	44% 6% 12% 22% 15% 1	2660
	11th to 20th	Day	38% 5% 13% 25% 17% 1	2752
	21st to end	Day	42% 5% 13% 25% 14% 1	2850
July	1st to 10th	Day	39% 8% 15% 21% 15% 1	4628
	11th to 20th	Day	35% 6% 13% 34% 11% 1	4365
	21st to end	Day	38% 7% 13% 24% 17% 1	4337
August	1st to 10th	Day	44% 6% 14% 24% 11% 1	4091
	11th to 20th	Day	43% 7% 17% 23% 10%	4083
	21st to end	Day	37% 6% 15% 31% 10% 1	4386
September	1st to 10th	Day	43% 5% 11% 28% 10% 2	2280
	11th to 20th	Day	39% 4 12% 30% 14%	2144
	21st to end	Day	49% 5% 13% 25% 9%	2066
October	1st to 10th	Day	43% 7% 13% 26% 11% 1	3160
	11th to 20th	Day	43% 6% 15% 22% 14%	3140
	21st to end	Day	58% 6% 13% 17% 5%	3428
November	1st to 10th	Day	53% 6% 13% 19% 8%	1674
	11th to 20th	Day	60% 4 13% 14% 8% 1	1528
	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% 3 13% 13% 3	4429
	11th to 20th	Night	74% 3 10% 10% 3	4182
	21st to end	Night	72% 4 11% 9% 4 1	4532
February	1st to 10th	Night	62% 4 10% 19% 5%	2470
	11th to 20th	Night	61% 5% 9% 18% 7%	2405
	21st to end	Night	57% 4 13% 18% 8% 1	1984
March	1st to 10th	Night	57% 3 11% 22% 7% 1	3419
	11th to 20th	Night	49% 4 13% 24% 10% 2	3480
	21st to end	Night	45% 3 9% 25% 16% 2	3817
April	1st to 10th	Night	55% 4 9% 20% 12% 1	1949
	11th to 20th	Night	47% 4 10% 21% 16% 2	1788
	21st to end	Night	49% 4 11% 20% 15% 2	1710
May	1st to 10th	Night	45% 3 12% 20% 17% 3	2840
	11th to 20th	Night	45% 3 13% 25% 11% 2	2538
	21st to end	Night	32% 4 14% 27% 21% 2	2739
June	1st to 10th	Night	40% 5% 10% 26% 17% 2	1520
	11th to 20th	Night	35% 6% 13% 25% 19% 1	1420
	21st to end	Night	36% 5% 14% 28% 16% 1	1330
July	1st to 10th	Night	30% 7% 15% 25% 20% 3	2226
	11th to 20th	Night	31% 5% 12% 35% 16% 1	2472
	21st to end	Night	30% 8% 14% 31% 15% 2	2972
August	1st to 10th	Night	35% 4 13% 30% 16% 1	2814
	11th to 20th	Night	34% 5% 16% 31% 13% 1	2812
	21st to end	Night	33% 6% 15% 32% 13% 1	3237
September	1st to 10th	Night	33% 6% 15% 30% 14% 1	1900
	11th to 20th	Night	29% 4 12% 36% 18%	2033
	21st to end	Night	44% 4 13% 28% 10%	2114
October	1st to 10th	Night	35% 5% 10% 29% 20% 1	3800
	11th to 20th	Night	42% 6% 15% 24% 14%	3779
	21st to end	Night	45% 8% 15% 23% 8%	4120
November	1st to 10th	Night	49% 5% 12% 24% 9% 1	2618
	11th to 20th	Night	56% 4 13% 17% 8% 1	2675
	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	25% 29% 29% 12% 3 2	252
	21st to end	Day	27% 27% 31% 13% 2	297
February	1st to 10th	Day	31% 29% 27% 9% 3	270
	11th to 20th	Day	23% 34% 36% 6% 1	270
	21st to end	Day	36% 31% 26% 7%	225
March	1st to 10th	Day	24% 24% 34% 13% 5%	457
	11th to 20th	Day	24% 22% 36% 13% 4	460
	21st to end	Day	31% 21% 30% 14% 5% 1	506
April	1st to 10th	Day	27% 21% 33% 13% 5%	460
	11th to 20th	Day	36% 18% 24% 12% 7% 3	452
	21st to end	Day	28% 18% 33% 14% 5% 2	460
May	1st to 10th	Day	23% 15% 33% 19% 8% 2	463
	11th to 20th	Day	21% 16% 31% 20% 9% 3	487
	21st to end	Day	16% 16% 30% 24% 10% 4	529
June	1st to 10th	Day	19% 14% 34% 23% 7% 2	490
	11th to 20th	Day	16% 13% 33% 25% 11% 2	582
	21st to end	Day	18% 14% 39% 19% 8% 3	680
July	1st to 10th	Day	11% 9% 33% 30% 14% 4	639
	11th to 20th	Day	12% 8% 33% 28% 13% 6%	484
	21st to end	Day	11% 8% 37% 26% 12% 6%	532
August	1st to 10th	Day	11% 8% 30% 28% 14% 10%	486
	11th to 20th	Day	9% 9% 30% 26% 18% 9%	479
	21st to end	Day	15% 9% 30% 23% 16% 7%	539
September	1st to 10th	Day	14% 13% 28% 25% 13% 8%	490
	11th to 20th	Day	11% 9% 26% 23% 19% 12%	490
	21st to end	Day	16% 15% 28% 23% 13% 5%	490
October	1st to 10th	Day	25% 15% 25% 18% 12% 4	490
	11th to 20th	Day	22% 21% 33% 16% 7% 2	490
	21st to end	Day	34% 20% 28% 14% 3 1	539
November	1st to 10th	Day	24% 24% 30% 17% 3 1	263
	11th to 20th	Day	27% 23% 32% 13% 5% 1	182
	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% 31% 17% 4	760
	21st to end	Night	19% 19% 35% 21% 6%	836
February	1st to 10th	Night	23% 26% 34% 17% 2	760
	11th to 20th	Night	23% 23% 37% 14% 3	743
	21st to end	Night	22% 25% 33% 17% 2	628
March	1st to 10th	Night	22% 23% 33% 19% 3	760
	11th to 20th	Night	24% 22% 30% 19% 5% 1	760
	21st to end	Night	23% 19% 31% 20% 6%	836
April	1st to 10th	Night	26% 18% 34% 20% 2	760
	11th to 20th	Night	22% 18% 32% 18% 8% 1	664
	21st to end	Night	22% 13% 32% 25% 7%	570
May	1st to 10th	Night	19% 8% 30% 31% 11% 2	570
	11th to 20th	Night	18% 8% 32% 32% 11%	403
	21st to end	Night	10% 9% 36% 32% 12%	411
June	1st to 10th	Night	15% 7% 34% 33% 11%	380
	11th to 20th	Night	11% 10% 29% 36% 13%	380
	21st to end	Night	12% 8% 31% 33% 16% 1	380
July	1st to 10th	Night	7% 4 28% 40% 19% 2	370
	11th to 20th	Night	11% 8% 26% 34% 19% 1	368
	21st to end	Night	8% 5% 30% 37% 18% 2	607
August	1st to 10th	Night	10% 4 25% 37% 23% 2	567
	11th to 20th	Night	7% 7% 21% 39% 24% 3	564
	21st to end	Night	14% 5% 28% 31% 21% 2	688
September	1st to 10th	Night	12% 8% 28% 28% 19% 4	760
	11th to 20th	Night	13% 7% 23% 29% 22% 6%	760
	21st to end	Night	19% 9% 23% 29% 17% 3	760
October	1st to 10th	Night	20% 10% 31% 23% 14% 2	760
	11th to 20th	Night	24% 16% 31% 21% 8% 1	760
	21st to end	Night	28% 18% 30% 19% 5%	836
November	1st to 10th	Night	24% 18% 29% 22% 8% 1	780
	11th to 20th	Night	22% 24% 27% 20% 6% 1	765
	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 2024-11-08 22:45:37. Version ac07

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