RJM Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the RJM Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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% 9% 3 8% 5% 5% 4 4 5% 7% 36%	101587
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 37%	97548
Transparency	Day	45% 6% 12% 24% 12% 1	105105
	Night	45% 6% 11% 24% 13% 1	102170
Seeing	Day	17% 10% 30% 26% 14% 4	16008
	Night	17% 9% 32% 31% 11% 1	25865

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	11% 17% 7% 16% 6% 4 5% 3 4 5% 23%	2527
	11th to 20th	Day	8% 13% 5% 16% 7% 7% 8% 8% 6% 5% 17%	2530
	21st to end	Day	13% 16% 9% 15% 6% 5% 4 3 5% 6% 18%	2893
February	1st to 10th	Day	8% 12% 5% 11% 5% 6% 6% 4 6% 7% 32%	1710
	11th to 20th	Day	9% 12% 4 9% 5% 5% 5% 5% 6% 6% 35%	1703
	21st to end	Day	12% 11% 5% 11% 7% 5% 5% 3 6% 6% 29%	1570
March	1st to 10th	Day	13% 9% 3 5% 4 3 3 3 3 6% 48%	3120
	11th to 20th	Day	9% 8% 4 10% 6% 4 4 3 6% 8% 38%	3442
	21st to end	Day	20% 12% 4 12% 5% 4 3 3 4 5% 27%	4059
April	1st to 10th	Day	16% 12% 3 8% 5% 4 5% 3 4 6% 32%	2280
	11th to 20th	Day	20% 12% 4 7% 5% 4 3 3 5% 6% 31%	2254
	21st to end	Day	20% 11% 3 8% 6% 5% 4 3 5% 6% 30%	2351
May	1st to 10th	Day	17% 6% 3 6% 5% 5% 4 3 5% 6% 39%	4399
	11th to 20th	Day	16% 6% 2 6% 4 4 4 3 5% 7% 43%	4399
	21st to end	Day	17% 7% 2 7% 5% 5% 4 4 6% 6% 37%	4824
June	1st to 10th	Day	14% 5% 2 5% 5% 4 4 3 5% 8% 44%	2660
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	11% 6% 2 6% 6% 5% 5% 5% 7% 8% 39%	2660
July	1st to 10th	Day	13% 5% 2 6% 5% 5% 6% 5% 7% 10% 37%	4440
	11th to 20th	Day	5% 3 2 5% 4 5% 5% 4 7% 10% 49%	4440
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 6% 8% 45%	4813
August	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 5% 8% 41%	4365
	11th to 20th	Day	14% 5% 1 5% 4 4 5% 4 6% 7% 44%	3957
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 3 6% 8% 41%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 4 8% 45%	2280
	11th to 20th	Day	12% 6% 2 5% 3 3 4 5% 6% 8% 46%	2261
	21st to end	Day	14% 6% 3 7% 4 4 4 4 6% 9% 40%	2057
October	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 6% 7% 42%	1900
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 3 5% 7% 33%	1900
	21st to end	Day	18% 11% 3 7% 4 4 4 3 4 6% 35%	1927
November	1st to 10th	Day	14% 8% 3 7% 4 5% 4 4 5% 6% 40%	1708
	11th to 20th	Day	15% 13% 5% 10% 6% 4 5% 3 5% 7% 27%	1577
	21st to end	Day	13% 12% 4 8% 6% 4 5% 3 5% 6% 35%	1520
December	1st to 10th	Day	11% 13% 5% 12% 8% 7% 5% 3 4 6% 26%	1520
	11th to 20th	Day	13% 13% 6% 10% 8% 6% 5% 4 4 6% 24%	1918
	21st to end	Day	20% 21% 6% 12% 6% 4 3 3 3 4 17%	2783
January	1st to 10th	Night	11% 15% 6% 15% 5% 5% 3 3 4 5% 29%	4428
	11th to 20th	Night	8% 13% 5% 14% 9% 6% 8% 7% 7% 5% 19%	4440
	21st to end	Night	13% 17% 8% 14% 5% 5% 4 3 4 5% 22%	4757
February	1st to 10th	Night	8% 12% 6% 10% 6% 5% 5% 3 5% 5% 34%	2470
	11th to 20th	Night	9% 9% 3 8% 4 4 6% 5% 6% 6% 39%	2363
	21st to end	Night	14% 11% 3 9% 6% 5% 5% 3 6% 6% 32%	1884
March	1st to 10th	Night	10% 8% 3 6% 4 4 4 3 6% 8% 45%	3733
	11th to 20th	Night	8% 8% 3 9% 5% 5% 6% 4 6% 7% 39%	3548
	21st to end	Night	23% 10% 4 13% 5% 4 3 2 3 4 28%	3572
April	1st to 10th	Night	18% 11% 2 7% 4 4 4 3 5% 7% 34%	1900
	11th to 20th	Night	21% 8% 2 6% 4 3 4 3 5% 6% 38%	1875
	21st to end	Night	19% 8% 3 6% 5% 4 3 3 6% 7% 36%	1824
May	1st to 10th	Night	16% 8% 3 8% 5% 5% 4 3 5% 7% 36%	2506
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 48%	2506
	21st to end	Night	14% 7% 3 7% 4 4 4 3 5% 7% 41%	2743
June	1st to 10th	Night	12% 7% 2 4 4 4 5% 4 6% 7% 46%	1520
	11th to 20th	Night	12% 5% 3 7% 5% 4 5% 5% 6% 8% 41%	1520
	21st to end	Night	10% 6% 2 5% 4 4 5% 3 6% 8% 47%	1520
July	1st to 10th	Night	14% 4 2 5% 4 5% 4 4 5% 8% 45%	2530
	11th to 20th	Night	5% 3 2 4 3 4 4 4 6% 7% 57%	2530
	21st to end	Night	7% 5% 2 6% 4 4 4 3 5% 7% 54%	2750
August	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 5% 6% 47%	2572
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 5% 6% 50%	2877
	21st to end	Night	13% 6% 2 6% 4 4 4 3 6% 7% 46%	3476
September	1st to 10th	Night	10% 5% 2 5% 4 4 3 3 5% 8% 51%	1900
	11th to 20th	Night	11% 6% 1 5% 4 3 3 3 5% 7% 51%	1900
	21st to end	Night	11% 7% 2 6% 3 4 4 3 5% 6% 49%	2118
October	1st to 10th	Night	12% 6% 2 6% 3 4 5% 3 4 6% 49%	2280
	11th to 20th	Night	15% 10% 3 7% 4 4 4 4 6% 7% 38%	2280
	21st to end	Night	17% 12% 3 7% 4 4 5% 3 5% 6% 34%	2670
November	1st to 10th	Night	15% 9% 3 7% 5% 3 4 3 3 7% 40%	2470
	11th to 20th	Night	13% 13% 5% 10% 5% 5% 4 4 5% 5% 33%	2603
	21st to end	Night	13% 11% 4 9% 5% 4 4 3 6% 6% 34%	2660
December	1st to 10th	Night	11% 12% 5% 10% 6% 6% 5% 4 6% 7% 29%	2660
	11th to 20th	Night	12% 15% 5% 12% 7% 5% 5% 4 5% 5% 25%	3279
	21st to end	Night	22% 17% 6% 11% 5% 4 3 3 4 4 21%	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	63% 6% 10% 15% 5% 1	2528
	11th to 20th	Day	64% 7% 9% 13% 6% 1	2530
	21st to end	Day	66% 5% 12% 13% 4	2893
February	1st to 10th	Day	51% 6% 12% 20% 10% 1	1710
	11th to 20th	Day	47% 8% 12% 23% 9% 1	1712
	21st to end	Day	55% 6% 11% 17% 10% 2	1570
March	1st to 10th	Day	39% 4 12% 23% 19% 2	3120
	11th to 20th	Day	41% 6% 12% 26% 14% 1	3442
	21st to end	Day	59% 5% 8% 19% 7% 1	4059
April	1st to 10th	Day	53% 6% 10% 19% 11% 1	2280
	11th to 20th	Day	53% 5% 8% 20% 11% 2	2254
	21st to end	Day	54% 7% 10% 18% 11% 1	2351
May	1st to 10th	Day	43% 7% 10% 27% 13%	4440
	11th to 20th	Day	39% 7% 11% 31% 12% 1	4403
	21st to end	Day	46% 7% 10% 22% 14% 1	4837
June	1st to 10th	Day	37% 8% 13% 28% 13% 1	2660
	11th to 20th	Day	42% 8% 13% 24% 13% 1	2660
	21st to end	Day	40% 7% 15% 25% 10% 2	2660
July	1st to 10th	Day	40% 8% 16% 27% 8% 1	4371
	11th to 20th	Day	27% 8% 16% 33% 15% 1	4365
	21st to end	Day	36% 7% 13% 26% 18% 1	4662
August	1st to 10th	Day	40% 6% 13% 27% 13% 1	4350
	11th to 20th	Day	37% 6% 11% 33% 12%	3996
	21st to end	Day	40% 6% 13% 28% 12% 1	4179
September	1st to 10th	Day	38% 7% 12% 28% 15%	2280
	11th to 20th	Day	35% 8% 18% 31% 8% 1	2261
	21st to end	Day	41% 7% 12% 29% 11%	2057
October	1st to 10th	Day	28% 3 9% 38% 22%	3160
	11th to 20th	Day	43% 5% 11% 24% 16% 1	3140
	21st to end	Day	44% 4 15% 28% 9%	3152
November	1st to 10th	Day	44% 6% 12% 22% 13% 2	1708
	11th to 20th	Day	56% 6% 12% 19% 7% 1	1577
	21st to end	Day	50% 5% 15% 22% 7% 1	1520
December	1st to 10th	Day	59% 6% 12% 17% 5%	1520
	11th to 20th	Day	60% 6% 12% 13% 7% 2	1915
	21st to end	Day	72% 4 6% 13% 5%	2783
January	1st to 10th	Night	57% 6% 9% 20% 7% 1	4428
	11th to 20th	Night	62% 7% 10% 14% 6%	4440
	21st to end	Night	65% 6% 8% 16% 5% 1	4757
February	1st to 10th	Night	51% 4 11% 21% 11% 2	2470
	11th to 20th	Night	43% 7% 12% 26% 10% 2	2364
	21st to end	Night	51% 5% 12% 20% 10% 2	1884
March	1st to 10th	Night	37% 6% 13% 28% 12% 3	3733
	11th to 20th	Night	41% 7% 10% 25% 15% 2	3548
	21st to end	Night	61% 4 7% 19% 8% 1	3572
April	1st to 10th	Night	50% 6% 7% 18% 17% 2	1900
	11th to 20th	Night	47% 5% 8% 22% 15% 3	1875
	21st to end	Night	45% 8% 10% 22% 13% 2	1824
May	1st to 10th	Night	46% 8% 13% 15% 17% 1	2530
	11th to 20th	Night	35% 6% 9% 32% 16% 3	2507
	21st to end	Night	39% 8% 13% 21% 17% 1	2751
June	1st to 10th	Night	34% 8% 13% 28% 16% 1	1520
	11th to 20th	Night	38% 8% 12% 25% 14% 2	1520
	21st to end	Night	34% 8% 13% 29% 13% 3	1520
July	1st to 10th	Night	37% 7% 17% 24% 14% 2	2490
	11th to 20th	Night	24% 7% 14% 35% 19% 2	2482
	21st to end	Night	30% 6% 12% 30% 19% 2	2662
August	1st to 10th	Night	37% 6% 14% 26% 15% 2	2563
	11th to 20th	Night	34% 7% 14% 30% 15% 1	2904
	21st to end	Night	37% 6% 15% 25% 15% 2	3476
September	1st to 10th	Night	31% 6% 13% 31% 18% 1	1900
	11th to 20th	Night	32% 6% 13% 33% 15%	1900
	21st to end	Night	35% 6% 12% 32% 14% 1	2118
October	1st to 10th	Night	27% 5% 6% 36% 23% 3	3800
	11th to 20th	Night	34% 5% 10% 31% 19%	3779
	21st to end	Night	50% 4 9% 23% 14%	4395
November	1st to 10th	Night	45% 4 12% 23% 14% 1	2470
	11th to 20th	Night	53% 6% 13% 16% 11% 1	2603
	21st to end	Night	50% 6% 14% 23% 7% 1	2660
December	1st to 10th	Night	53% 8% 13% 20% 5%	2660
	11th to 20th	Night	60% 6% 11% 17% 6% 1	3281
	21st to end	Night	67% 5% 7% 16% 4	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	19% 11% 31% 25% 12% 3	270
	11th to 20th	Day	17% 11% 40% 25% 6% 1	270
	21st to end	Day	18% 9% 35% 28% 9% 1	297
February	1st to 10th	Day	14% 14% 46% 16% 8% 3	270
	11th to 20th	Day	16% 17% 40% 18% 9%	270
	21st to end	Day	16% 12% 45% 25% 2	225
March	1st to 10th	Day	17% 13% 41% 18% 11% 1	270
	11th to 20th	Day	19% 13% 34% 21% 11% 2	270
	21st to end	Day	23% 13% 33% 20% 9% 3	439
April	1st to 10th	Day	25% 14% 32% 23% 6% 1	460
	11th to 20th	Day	28% 13% 28% 21% 8% 2	452
	21st to end	Day	24% 13% 29% 22% 10% 2	474
May	1st to 10th	Day	20% 14% 31% 25% 8% 1	653
	11th to 20th	Day	19% 12% 27% 26% 12% 4	675
	21st to end	Day	18% 9% 27% 26% 14% 6%	734
June	1st to 10th	Day	12% 8% 29% 28% 18% 5%	680
	11th to 20th	Day	16% 8% 32% 25% 14% 4	680
	21st to end	Day	14% 7% 28% 29% 15% 6%	680
July	1st to 10th	Day	10% 3 19% 30% 27% 11%	671
	11th to 20th	Day	9% 6% 27% 32% 18% 9%	668
	21st to end	Day	6% 3 26% 34% 23% 8%	739
August	1st to 10th	Day	10% 5% 24% 31% 22% 8%	676
	11th to 20th	Day	15% 5% 19% 25% 27% 8%	620
	21st to end	Day	14% 6% 23% 31% 19% 6%	539
September	1st to 10th	Day	17% 7% 22% 27% 20% 7%	490
	11th to 20th	Day	12% 6% 24% 34% 20% 4	490
	21st to end	Day	15% 10% 25% 32% 14% 4	457
October	1st to 10th	Day	16% 12% 27% 26% 14% 5%	300
	11th to 20th	Day	22% 15% 35% 19% 7% 1	300
	21st to end	Day	26% 13% 38% 19% 4 1	330
November	1st to 10th	Day	20% 11% 32% 26% 10% 2	282
	11th to 20th	Day	18% 16% 38% 21% 6% 1	270
	21st to end	Day	21% 12% 42% 16% 9%	270
December	1st to 10th	Day	15% 14% 42% 22% 5% 1	270
	11th to 20th	Day	20% 14% 37% 22% 6%	270
	21st to end	Day	29% 14% 35% 18% 4	297
January	1st to 10th	Night	15% 11% 36% 29% 8% 1	950
	11th to 20th	Night	16% 10% 37% 29% 6% 1	950
	21st to end	Night	18% 9% 36% 30% 7%	1045
February	1st to 10th	Night	13% 12% 37% 30% 7% 1	950
	11th to 20th	Night	15% 12% 40% 25% 8% 1	889
	21st to end	Night	20% 12% 37% 27% 4	628
March	1st to 10th	Night	16% 12% 35% 28% 7% 1	760
	11th to 20th	Night	16% 11% 36% 28% 8% 1	612
	21st to end	Night	22% 9% 30% 27% 9% 2	627
April	1st to 10th	Night	22% 11% 38% 23% 5% 1	570
	11th to 20th	Night	25% 9% 30% 29% 7%	563
	21st to end	Night	23% 7% 33% 29% 6% 1	570
May	1st to 10th	Night	22% 7% 35% 30% 6% 1	570
	11th to 20th	Night	20% 7% 30% 32% 9% 1	561
	21st to end	Night	15% 5% 26% 38% 15%	617
June	1st to 10th	Night	14% 7% 27% 39% 12% 1	570
	11th to 20th	Night	15% 5% 31% 39% 10%	570
	21st to end	Night	11% 6% 22% 43% 17% 2	570
July	1st to 10th	Night	8% 2 21% 38% 30% 2	555
	11th to 20th	Night	9% 4 21% 39% 25% 3	552
	21st to end	Night	5% 2 18% 50% 23% 3	624
August	1st to 10th	Night	8% 2 17% 46% 24% 2	567
	11th to 20th	Night	12% 3 20% 34% 29% 3	564
	21st to end	Night	15% 4 19% 38% 22% 3	627
September	1st to 10th	Night	12% 4 22% 39% 18% 4	570
	11th to 20th	Night	12% 4 26% 36% 20% 3	570
	21st to end	Night	13% 7% 29% 35% 15% 1	760
October	1st to 10th	Night	15% 8% 29% 30% 17% 1	760
	11th to 20th	Night	18% 9% 35% 30% 8%	760
	21st to end	Night	23% 8% 33% 27% 8% 1	836
November	1st to 10th	Night	20% 10% 32% 28% 9% 1	760
	11th to 20th	Night	18% 12% 41% 23% 7%	893
	21st to end	Night	19% 14% 36% 26% 6%	950
December	1st to 10th	Night	17% 11% 39% 25% 7%	950
	11th to 20th	Night	20% 12% 34% 26% 7% 1	950
	21st to end	Night	27% 11% 32% 25% 5%	1045

Page generated at 2024-11-03 01:11:11. Version ac07

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