Rothney Astrophysical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rothney Astrophysical Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	8% 8% 3 8% 5% 5% 5% 4 7% 8% 39%	105585
	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 41%	101967
Transparency	Day	39% 8% 16% 24% 11% 2	105332
	Night	39% 7% 15% 24% 13% 2	101866
Seeing	Day	12% 10% 28% 30% 15% 4	15340
	Night	10% 7% 31% 36% 14% 2	24364

By Month

Percentage Cloud Cover NW (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	2 6% 6% 14% 5% 5% 5% 5% 7% 9% 35%	2219
	11th to 20th	Day	2 9% 3 11% 5% 6% 6% 5% 8% 8% 38%	2277
	21st to end	Day	2 8% 3 9% 5% 5% 5% 4 6% 9% 42%	2794
February	1st to 10th	Day	2 9% 4 12% 8% 6% 6% 5% 7% 8% 33%	1520
	11th to 20th	Day	2 11% 4 9% 8% 7% 6% 5% 7% 8% 32%	1646
	21st to end	Day	1 10% 6% 12% 8% 6% 5% 4 8% 8% 32%	1546
March	1st to 10th	Day	2 8% 4 12% 7% 8% 7% 5% 6% 7% 35%	3138
	11th to 20th	Day	5% 10% 2 6% 5% 4 4 4 7% 8% 47%	3442
	21st to end	Day	5% 19% 7% 13% 6% 5% 5% 4 5% 6% 24%	3906
April	1st to 10th	Day	8% 14% 4 10% 6% 5% 5% 4 7% 8% 29%	2318
	11th to 20th	Day	9% 13% 4 9% 6% 5% 5% 5% 6% 8% 31%	2440
	21st to end	Day	10% 12% 3 8% 6% 4 5% 5% 6% 8% 32%	2470
May	1st to 10th	Day	16% 17% 4 8% 4 4 4 4 5% 6% 28%	4308
	11th to 20th	Day	9% 8% 3 9% 6% 6% 6% 5% 8% 8% 31%	4694
	21st to end	Day	17% 10% 4 9% 7% 7% 5% 4 6% 7% 24%	5161
June	1st to 10th	Day	17% 7% 3 8% 6% 6% 6% 5% 8% 7% 28%	2850
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 4 7% 7% 26%	2850
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 10% 41%	2850
July	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 7% 8% 49%	4740
	11th to 20th	Day	6% 3 1 4 3 3 5% 4 8% 10% 52%	4740
	21st to end	Day	3 3 1 4 3 4 4 4 7% 9% 57%	4966
August	1st to 10th	Day	10% 5% 2 6% 3 4 5% 5% 7% 10% 42%	4401
	11th to 20th	Day	8% 5% 2 6% 4 4 6% 5% 7% 10% 44%	4074
	21st to end	Day	9% 4 2 4 4 4 4 4 6% 7% 53%	4521
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 50%	2346
	11th to 20th	Day	12% 7% 2 5% 4 4 4 3 6% 6% 45%	2090
	21st to end	Day	8% 8% 2 6% 3 4 5% 3 6% 8% 46%	2090
October	1st to 10th	Day	6% 7% 3 6% 4 4 4 4 6% 9% 46%	3370
	11th to 20th	Day	5% 6% 3 7% 4 4 5% 5% 7% 11% 42%	2888
	21st to end	Day	6% 7% 2 6% 5% 5% 4 4 6% 6% 48%	3101
November	1st to 10th	Day	6% 14% 5% 9% 6% 5% 4 4 6% 7% 35%	1602
	11th to 20th	Day	5% 11% 3 8% 5% 4 3 5% 7% 8% 43%	1443
	21st to end	Day	3 11% 5% 9% 5% 4 5% 5% 5% 10% 40%	1330
December	1st to 10th	Day	3 8% 5% 12% 7% 5% 6% 4 7% 8% 37%	1330
	11th to 20th	Day	2 8% 5% 13% 6% 6% 7% 5% 8% 9% 32%	1682
	21st to end	Day	3 9% 3 8% 5% 4 4 4 6% 10% 45%	2442
January	1st to 10th	Night	2 10% 4 11% 8% 6% 7% 6% 7% 8% 30%	4726
	11th to 20th	Night	2 6% 4 12% 7% 6% 7% 6% 6% 8% 35%	4636
	21st to end	Night	3 10% 4 10% 6% 6% 5% 4 6% 8% 39%	4862
February	1st to 10th	Night	3 10% 4 10% 7% 6% 5% 5% 7% 9% 34%	2660
	11th to 20th	Night	3 12% 6% 10% 6% 5% 5% 5% 7% 9% 33%	2419
	21st to end	Night	2 8% 5% 14% 8% 5% 5% 5% 5% 7% 37%	1907
March	1st to 10th	Night	1 7% 4 13% 9% 7% 7% 5% 7% 8% 32%	3736
	11th to 20th	Night	4 8% 3 6% 5% 4 5% 4 7% 8% 48%	3537
	21st to end	Night	8% 21% 6% 12% 6% 5% 4 4 6% 6% 22%	3746
April	1st to 10th	Night	6% 15% 4 9% 6% 5% 5% 4 6% 8% 33%	1861
	11th to 20th	Night	10% 13% 6% 10% 5% 4 4 4 5% 6% 34%	1691
	21st to end	Night	9% 12% 4 9% 4 5% 4 4 7% 7% 36%	1710
May	1st to 10th	Night	16% 15% 3 7% 5% 3 4 3 4 7% 31%	2651
	11th to 20th	Night	10% 8% 3 9% 5% 4 6% 5% 6% 9% 35%	2199
	21st to end	Night	14% 9% 4 8% 6% 5% 5% 5% 7% 8% 29%	2414
June	1st to 10th	Night	15% 9% 2 7% 5% 4 4 4 7% 8% 36%	1330
	11th to 20th	Night	18% 8% 3 6% 5% 4 5% 4 7% 9% 31%	1330
	21st to end	Night	8% 5% 2 3 5% 4 4 5% 7% 10% 47%	1330
July	1st to 10th	Night	7% 4 1 7% 5% 5% 4 4 6% 6% 51%	2220
	11th to 20th	Night	5% 3 1 4 3 4 5% 5% 7% 9% 56%	2220
	21st to end	Night	5% 4 2 4 3 3 3 3 4 6% 63%	2570
August	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 7% 9% 45%	2529
	11th to 20th	Night	7% 4 1 5% 5% 4 5% 5% 7% 10% 47%	2751
	21st to end	Night	9% 3 1 4 3 3 3 3 6% 8% 55%	3146
September	1st to 10th	Night	9% 6% 2 5% 4 4 4 3 5% 8% 51%	1830
	11th to 20th	Night	13% 7% 2 4 3 3 4 3 5% 7% 49%	2090
	21st to end	Night	9% 8% 2 6% 3 3 3 3 7% 8% 48%	2090
October	1st to 10th	Night	6% 6% 2 5% 4 3 4 4 6% 7% 52%	3605
	11th to 20th	Night	5% 7% 2 5% 4 3 4 4 6% 9% 51%	4024
	21st to end	Night	5% 8% 3 7% 4 4 5% 4 5% 7% 47%	4457
November	1st to 10th	Night	5% 13% 5% 7% 5% 5% 6% 4 5% 7% 37%	2530
	11th to 20th	Night	3 9% 3 8% 5% 5% 5% 4 6% 8% 43%	2736
	21st to end	Night	3 10% 4 9% 6% 4 5% 4 7% 8% 41%	2850
December	1st to 10th	Night	3 10% 4 9% 7% 5% 6% 4 7% 9% 35%	2850
	11th to 20th	Night	1 8% 4 11% 7% 6% 7% 5% 8% 9% 34%	3510
	21st to end	Night	2 8% 3 9% 5% 5% 5% 5% 6% 7% 44%	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% 8% 15% 25% 11% 3	2219
	11th to 20th	Day	42% 6% 11% 19% 20% 4	2298
	21st to end	Day	34% 9% 17% 30% 9% 1	2794
February	1st to 10th	Day	46% 8% 16% 19% 8% 3	1520
	11th to 20th	Day	45% 7% 16% 21% 9% 2	1655
	21st to end	Day	48% 7% 14% 18% 13% 1	1546
March	1st to 10th	Day	44% 8% 17% 16% 14% 1	3138
	11th to 20th	Day	32% 7% 20% 26% 14% 1	3443
	21st to end	Day	57% 10% 13% 15% 4 1	3906
April	1st to 10th	Day	49% 9% 15% 19% 7% 1	2318
	11th to 20th	Day	48% 9% 13% 19% 9% 1	2440
	21st to end	Day	47% 9% 15% 20% 8% 1	2470
May	1st to 10th	Day	54% 7% 11% 22% 5%	4308
	11th to 20th	Day	42% 12% 14% 23% 9%	4698
	21st to end	Day	52% 11% 15% 14% 8% 1	5162
June	1st to 10th	Day	50% 9% 16% 15% 9% 1	2850
	11th to 20th	Day	54% 8% 14% 15% 8% 2	2850
	21st to end	Day	34% 11% 19% 23% 11% 2	2850
July	1st to 10th	Day	31% 7% 14% 27% 16% 5%	4666
	11th to 20th	Day	25% 7% 19% 33% 14% 2	4659
	21st to end	Day	21% 6% 11% 29% 24% 9%	4809
August	1st to 10th	Day	35% 7% 15% 36% 7% 1	4384
	11th to 20th	Day	32% 7% 26% 26% 7% 1	4113
	21st to end	Day	29% 5% 18% 34% 13% 1	4520
September	1st to 10th	Day	32% 6% 16% 24% 17% 4	2346
	11th to 20th	Day	37% 7% 16% 25% 13% 2	2090
	21st to end	Day	35% 7% 16% 27% 13% 3	2090
October	1st to 10th	Day	35% 4 17% 35% 8% 1	3370
	11th to 20th	Day	34% 6% 20% 25% 12% 3	2888
	21st to end	Day	35% 6% 12% 32% 14% 2	3101
November	1st to 10th	Day	47% 7% 13% 20% 12% 1	1602
	11th to 20th	Day	37% 7% 17% 25% 11% 2	1443
	21st to end	Day	39% 8% 17% 24% 9% 4	1330
December	1st to 10th	Day	44% 7% 15% 18% 12% 4	1330
	11th to 20th	Day	45% 8% 18% 19% 9% 1	1684
	21st to end	Day	34% 6% 11% 25% 19% 5%	2442
January	1st to 10th	Night	45% 10% 15% 21% 8% 2	4726
	11th to 20th	Night	44% 8% 12% 17% 14% 6%	4677
	21st to end	Night	40% 8% 15% 24% 12% 1	4862
February	1st to 10th	Night	44% 7% 14% 20% 12% 3	2660
	11th to 20th	Night	44% 7% 15% 19% 12% 2	2420
	21st to end	Night	45% 5% 12% 23% 13% 3	1907
March	1st to 10th	Night	44% 9% 13% 22% 11% 1	3736
	11th to 20th	Night	30% 9% 19% 26% 15% 1	3537
	21st to end	Night	58% 9% 12% 14% 6% 1	3746
April	1st to 10th	Night	47% 7% 15% 20% 11% 1	1861
	11th to 20th	Night	49% 6% 14% 21% 9% 1	1691
	21st to end	Night	45% 7% 16% 21% 9% 2	1710
May	1st to 10th	Night	53% 6% 11% 23% 6%	2651
	11th to 20th	Night	39% 10% 13% 29% 8% 1	2199
	21st to end	Night	46% 11% 15% 19% 9%	2414
June	1st to 10th	Night	44% 8% 16% 22% 10% 1	1330
	11th to 20th	Night	47% 8% 16% 18% 9% 2	1330
	21st to end	Night	30% 10% 20% 26% 13% 1	1330
July	1st to 10th	Night	33% 6% 15% 23% 18% 5%	2185
	11th to 20th	Night	23% 6% 24% 33% 10% 4	2178
	21st to end	Night	23% 4 9% 32% 24% 8%	2489
August	1st to 10th	Night	35% 6% 16% 29% 13% 1	2521
	11th to 20th	Night	30% 6% 27% 26% 10% 1	2777
	21st to end	Night	26% 5% 19% 34% 14% 2	3146
September	1st to 10th	Night	32% 5% 18% 25% 16% 4	1830
	11th to 20th	Night	35% 6% 15% 28% 13% 4	2090
	21st to end	Night	32% 5% 18% 26% 14% 4	2090
October	1st to 10th	Night	30% 5% 15% 26% 21% 2	3605
	11th to 20th	Night	30% 4 20% 25% 18% 2	4024
	21st to end	Night	36% 5% 12% 32% 15% 1	4457
November	1st to 10th	Night	44% 7% 14% 20% 13% 2	2530
	11th to 20th	Night	37% 7% 17% 22% 16% 2	2736
	21st to end	Night	38% 7% 18% 22% 12% 4	2850
December	1st to 10th	Night	43% 8% 14% 21% 11% 4	2850
	11th to 20th	Night	41% 11% 18% 21% 8% 1	3507
	21st to end	Night	36% 6% 12% 25% 14% 6%	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	4 6% 24% 38% 16% 12%	180
	11th to 20th	Day	8% 6% 29% 37% 16% 3	180
	21st to end	Day	7% 8% 22% 44% 15% 4	198
February	1st to 10th	Day	7% 13% 36% 30% 9% 5%	180
	11th to 20th	Day	7% 10% 30% 38% 14% 2	261
	21st to end	Day	4 14% 30% 34% 15% 2	358
March	1st to 10th	Day	6% 13% 41% 27% 11% 2	460
	11th to 20th	Day	8% 13% 34% 29% 13% 3	460
	21st to end	Day	10% 15% 35% 25% 11% 4	506
April	1st to 10th	Day	13% 16% 35% 27% 8% 1	460
	11th to 20th	Day	15% 15% 26% 28% 14% 2	452
	21st to end	Day	14% 18% 30% 23% 11% 3	460
May	1st to 10th	Day	19% 12% 26% 27% 12% 5%	480
	11th to 20th	Day	17% 9% 22% 27% 20% 4	675
	21st to end	Day	19% 8% 22% 28% 19% 4	734
June	1st to 10th	Day	17% 11% 28% 31% 11% 3	680
	11th to 20th	Day	22% 10% 28% 25% 12% 3	680
	21st to end	Day	10% 6% 26% 31% 21% 5%	680
July	1st to 10th	Day	11% 5% 23% 32% 23% 5%	671
	11th to 20th	Day	12% 5% 25% 31% 22% 4	668
	21st to end	Day	4 7% 28% 35% 19% 6%	642
August	1st to 10th	Day	12% 4 26% 31% 20% 6%	487
	11th to 20th	Day	10% 5% 26% 33% 18% 8%	477
	21st to end	Day	10% 10% 26% 31% 14% 8%	539
September	1st to 10th	Day	12% 9% 28% 28% 16% 6%	490
	11th to 20th	Day	17% 8% 24% 32% 16% 4	490
	21st to end	Day	13% 15% 28% 30% 11% 3	490
October	1st to 10th	Day	12% 10% 29% 28% 17% 3	422
	11th to 20th	Day	13% 10% 27% 31% 14% 5%	300
	21st to end	Day	12% 14% 34% 25% 11% 4	330
November	1st to 10th	Day	15% 11% 30% 30% 10% 3	279
	11th to 20th	Day	13% 12% 28% 34% 9% 3	233
	21st to end	Day	7% 10% 32% 31% 11% 10%	180
December	1st to 10th	Day	6% 6% 31% 39% 12% 6%	180
	11th to 20th	Day	3 11% 33% 39% 9% 5%	180
	21st to end	Day	5% 9% 23% 34% 22% 7%	198
January	1st to 10th	Night	7% 11% 36% 34% 10% 1	950
	11th to 20th	Night	6% 7% 39% 37% 9% 1	913
	21st to end	Night	7% 12% 36% 35% 9% 1	836
February	1st to 10th	Night	6% 12% 33% 31% 13% 5%	760
	11th to 20th	Night	8% 8% 32% 37% 13% 1	744
	21st to end	Night	5% 6% 34% 33% 18% 4	628
March	1st to 10th	Night	5% 6% 39% 34% 12% 4	760
	11th to 20th	Night	7% 7% 36% 36% 11% 2	760
	21st to end	Night	10% 8% 30% 36% 12% 3	836
April	1st to 10th	Night	13% 7% 34% 31% 13% 2	721
	11th to 20th	Night	16% 8% 32% 34% 10%	563
	21st to end	Night	16% 8% 32% 34% 10% 1	570
May	1st to 10th	Night	16% 8% 24% 35% 15% 1	471
	11th to 20th	Night	13% 6% 26% 34% 20% 1	374
	21st to end	Night	19% 5% 22% 35% 18% 1	411
June	1st to 10th	Night	17% 7% 24% 36% 14% 1	380
	11th to 20th	Night	19% 5% 29% 31% 15% 1	380
	21st to end	Night	10% 2 21% 39% 26% 2	380
July	1st to 10th	Night	9% 4 15% 45% 26% 1	370
	11th to 20th	Night	10% 2 18% 48% 19% 2	368
	21st to end	Night	6% 3 18% 44% 27% 2	416
August	1st to 10th	Night	13% 2 12% 42% 29% 3	378
	11th to 20th	Night	10% 2 16% 44% 25% 3	528
	21st to end	Night	9% 4 21% 43% 22% 2	627
September	1st to 10th	Night	13% 4 23% 36% 21% 4	685
	11th to 20th	Night	18% 4 16% 39% 19% 4	760
	21st to end	Night	13% 5% 29% 37% 11% 4	760
October	1st to 10th	Night	14% 3 27% 39% 14% 3	760
	11th to 20th	Night	11% 6% 32% 34% 14% 3	760
	21st to end	Night	9% 8% 34% 36% 11% 2	836
November	1st to 10th	Night	12% 9% 37% 32% 9% 1	834
	11th to 20th	Night	8% 12% 41% 32% 6% 1	950
	21st to end	Night	6% 8% 44% 31% 9% 2	950
December	1st to 10th	Night	7% 8% 37% 33% 12% 2	950
	11th to 20th	Night	4 8% 39% 38% 9% 1	950
	21st to end	Night	7% 8% 36% 35% 12% 2	1045

Page generated at 2024-11-01 20:47:44. Version ac07

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