Brodie Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brodie Road Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	17% 10% 3 8% 5% 5% 4 4 5% 7% 32%	101575
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 31%	97520
Transparency	Day	28% 46% 7% 13% 5%	105023
	Night	30% 46% 7% 12% 5%	102161
Seeing	Day	24% 16% 30% 19% 8% 2	14548
	Night	24% 14% 29% 24% 9% 1	23549

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	18% 16% 6% 13% 6% 4 4 3 4 4 23%	2517
	11th to 20th	Day	14% 15% 6% 11% 7% 6% 5% 4 5% 5% 23%	2520
	21st to end	Day	15% 19% 6% 9% 6% 5% 5% 4 6% 6% 19%	2776
February	1st to 10th	Day	15% 17% 4 11% 7% 4 4 4 4 5% 25%	1710
	11th to 20th	Day	14% 14% 5% 11% 7% 5% 4 3 4 6% 26%	1724
	21st to end	Day	20% 14% 5% 9% 5% 5% 4 3 4 5% 26%	1570
March	1st to 10th	Day	21% 13% 4 10% 6% 5% 4 3 4 5% 26%	3116
	11th to 20th	Day	13% 18% 5% 10% 6% 5% 4 3 4 5% 26%	3352
	21st to end	Day	16% 8% 3 8% 6% 4 4 3 4 6% 38%	4118
April	1st to 10th	Day	21% 12% 4 7% 5% 4 3 2 4 5% 32%	2280
	11th to 20th	Day	21% 10% 3 7% 5% 3 3 3 5% 5% 34%	2254
	21st to end	Day	23% 10% 3 8% 4 4 4 4 4 4 31%	2401
May	1st to 10th	Day	21% 9% 3 8% 5% 5% 5% 4 5% 7% 29%	4426
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 3 5% 7% 33%	4398
	21st to end	Day	17% 6% 2 7% 5% 4 5% 4 6% 8% 36%	4837
June	1st to 10th	Day	23% 8% 2 7% 5% 4 4 4 5% 8% 29%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	2660
	21st to end	Day	20% 7% 3 6% 5% 5% 5% 4 6% 7% 30%	2660
July	1st to 10th	Day	12% 7% 3 7% 6% 6% 5% 4 7% 9% 34%	4440
	11th to 20th	Day	14% 6% 3 6% 5% 5% 5% 5% 8% 8% 36%	4440
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 7% 9% 44%	4814
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 9% 33%	4423
	11th to 20th	Day	14% 7% 3 6% 4 4 5% 4 7% 8% 38%	3961
	21st to end	Day	16% 4 2 6% 4 5% 5% 4 7% 9% 38%	4180
September	1st to 10th	Day	13% 7% 2 5% 4 4 4 4 6% 8% 42%	2280
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 49%	2233
	21st to end	Day	17% 7% 2 5% 4 4 4 3 5% 7% 41%	2090
October	1st to 10th	Day	20% 7% 3 7% 4 4 4 4 4 6% 36%	1914
	11th to 20th	Day	20% 11% 3 9% 6% 5% 4 3 4 6% 30%	1895
	21st to end	Day	24% 11% 3 7% 4 4 5% 4 6% 6% 27%	1881
November	1st to 10th	Day	17% 9% 4 7% 5% 5% 5% 4 4 6% 33%	1734
	11th to 20th	Day	18% 12% 3 9% 6% 5% 5% 3 5% 6% 28%	1593
	21st to end	Day	21% 13% 4 9% 6% 6% 5% 3 6% 6% 22%	1520
December	1st to 10th	Day	24% 15% 4 11% 6% 5% 4 3 6% 4 17%	1520
	11th to 20th	Day	21% 15% 5% 10% 4 3 4 3 4 5% 24%	1906
	21st to end	Day	28% 18% 4 11% 4 3 3 2 3 3 20%	2772
January	1st to 10th	Night	17% 17% 6% 11% 5% 5% 4 3 4 5% 21%	4429
	11th to 20th	Night	13% 15% 5% 14% 7% 6% 6% 4 5% 5% 20%	4440
	21st to end	Night	16% 19% 6% 11% 6% 5% 4 3 4 5% 22%	4879
February	1st to 10th	Night	16% 13% 5% 11% 8% 6% 5% 4 6% 5% 23%	2470
	11th to 20th	Night	14% 12% 6% 11% 6% 6% 5% 4 5% 5% 27%	2340
	21st to end	Night	15% 14% 5% 10% 6% 4 4 4 4 5% 30%	1884
March	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 4 5% 32%	3724
	11th to 20th	Night	19% 17% 5% 10% 6% 4 4 2 4 5% 26%	3589
	21st to end	Night	14% 10% 4 9% 5% 4 4 3 4 4 38%	3512
April	1st to 10th	Night	22% 11% 3 7% 5% 4 3 4 4 6% 31%	1900
	11th to 20th	Night	22% 10% 3 7% 5% 4 4 3 5% 4 35%	1875
	21st to end	Night	22% 9% 2 7% 5% 4 4 3 5% 5% 34%	1786
May	1st to 10th	Night	21% 9% 2 7% 5% 5% 5% 4 5% 7% 31%	2524
	11th to 20th	Night	22% 9% 2 6% 3 3 4 3 5% 6% 37%	2495
	21st to end	Night	15% 7% 2 7% 5% 4 5% 4 5% 9% 37%	2738
June	1st to 10th	Night	20% 7% 2 6% 5% 5% 5% 5% 7% 8% 31%	1520
	11th to 20th	Night	16% 7% 3 5% 4 4 5% 4 5% 7% 40%	1520
	21st to end	Night	19% 6% 3 7% 5% 4 5% 4 5% 8% 34%	1520
July	1st to 10th	Night	13% 8% 3 9% 6% 5% 5% 5% 6% 7% 35%	2520
	11th to 20th	Night	13% 6% 3 6% 3 4 4 4 6% 9% 41%	2520
	21st to end	Night	12% 6% 3 6% 4 4 4 4 6% 8% 43%	2739
August	1st to 10th	Night	15% 7% 3 7% 4 4 4 4 6% 8% 39%	2506
	11th to 20th	Night	15% 7% 3 6% 4 4 5% 3 5% 7% 41%	2832
	21st to end	Night	13% 6% 3 7% 5% 5% 5% 3 5% 8% 40%	3476
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 4 5% 7% 44%	1900
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 7% 49%	1947
	21st to end	Night	17% 5% 2 5% 4 4 4 3 5% 6% 43%	2090
October	1st to 10th	Night	19% 7% 3 7% 4 4 5% 3 6% 6% 37%	2264
	11th to 20th	Night	19% 9% 3 8% 6% 5% 4 4 5% 5% 33%	2283
	21st to end	Night	23% 9% 4 8% 5% 5% 5% 3 4 5% 29%	2717
November	1st to 10th	Night	20% 10% 3 7% 4 4 4 3 4 6% 33%	2505
	11th to 20th	Night	19% 10% 3 8% 5% 5% 5% 4 4 6% 31%	2584
	21st to end	Night	22% 13% 4 10% 6% 5% 5% 3 4 6% 25%	2660
December	1st to 10th	Night	21% 16% 6% 9% 7% 5% 4 4 4 5% 19%	2660
	11th to 20th	Night	22% 16% 4 9% 5% 4 4 3 4 4 25%	3288
	21st to end	Night	31% 17% 4 9% 4 3 3 2 3 4 20%	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	42% 36% 10% 7% 4 1	2518
	11th to 20th	Day	41% 36% 9% 10% 5%	2520
	21st to end	Day	44% 39% 9% 5% 1	2776
February	1st to 10th	Day	23% 64% 3 8% 2 1	1710
	11th to 20th	Day	21% 63% 3 8% 5%	1733
	21st to end	Day	21% 65% 3 4 5% 2	1570
March	1st to 10th	Day	39% 39% 4 12% 5% 1	3119
	11th to 20th	Day	40% 39% 5% 8% 7% 1	3352
	21st to end	Day	29% 38% 4 14% 13% 1	4118
April	1st to 10th	Day	20% 65% 2 7% 5% 1	2280
	11th to 20th	Day	19% 65% 2 8% 6% 1	2254
	21st to end	Day	20% 64% 3 6% 5%	2401
May	1st to 10th	Day	37% 39% 4 16% 4	4440
	11th to 20th	Day	35% 39% 11% 11% 4	4402
	21st to end	Day	30% 39% 6% 18% 7%	4837
June	1st to 10th	Day	19% 64% 2 8% 5% 1	2660
	11th to 20th	Day	16% 65% 4 8% 5% 1	2660
	21st to end	Day	18% 64% 3 9% 5% 1	2660
July	1st to 10th	Day	31% 37% 9% 16% 7%	4370
	11th to 20th	Day	27% 37% 10% 22% 4	4365
	21st to end	Day	22% 37% 9% 26% 5%	4661
August	1st to 10th	Day	31% 38% 11% 15% 5%	4409
	11th to 20th	Day	30% 38% 10% 20% 2	4002
	21st to end	Day	26% 38% 12% 16% 8%	4180
September	1st to 10th	Day	15% 60% 7% 12% 6%	2280
	11th to 20th	Day	13% 60% 6% 13% 7% 1	2233
	21st to end	Day	14% 59% 6% 13% 6%	2090
October	1st to 10th	Day	28% 37% 8% 22% 4	3174
	11th to 20th	Day	25% 37% 12% 21% 5%	3123
	21st to end	Day	27% 37% 15% 17% 4	3081
November	1st to 10th	Day	26% 57% 6% 8% 3 1	1734
	11th to 20th	Day	21% 61% 4 10% 5%	1593
	21st to end	Day	26% 61% 6% 4 3	1520
December	1st to 10th	Day	28% 60% 5% 6% 2	1520
	11th to 20th	Day	36% 48% 8% 6% 2	1906
	21st to end	Day	47% 36% 4 10% 3	2772
January	1st to 10th	Night	42% 36% 13% 7% 2	4429
	11th to 20th	Night	43% 36% 9% 9% 3	4440
	21st to end	Night	45% 38% 9% 6% 2	4879
February	1st to 10th	Night	23% 64% 4 7% 2	2470
	11th to 20th	Night	21% 63% 3 8% 5%	2342
	21st to end	Night	19% 64% 3 7% 7% 1	1884
March	1st to 10th	Night	32% 40% 5% 15% 7% 2	3734
	11th to 20th	Night	41% 38% 5% 8% 6% 2	3590
	21st to end	Night	32% 39% 1 16% 11% 1	3512
April	1st to 10th	Night	21% 64% 3 6% 6%	1900
	11th to 20th	Night	20% 65% 2 7% 6% 1	1875
	21st to end	Night	19% 65% 3 6% 5% 1	1786
May	1st to 10th	Night	35% 40% 7% 15% 3	2530
	11th to 20th	Night	34% 38% 9% 12% 6%	2496
	21st to end	Night	29% 39% 6% 14% 11% 1	2739
June	1st to 10th	Night	17% 65% 3 8% 6% 1	1520
	11th to 20th	Night	15% 65% 3 9% 8% 1	1520
	21st to end	Night	18% 63% 4 8% 6% 1	1520
July	1st to 10th	Night	33% 37% 8% 11% 9% 1	2480
	11th to 20th	Night	26% 36% 12% 23% 3	2472
	21st to end	Night	25% 37% 11% 17% 10%	2651
August	1st to 10th	Night	29% 39% 9% 19% 5%	2496
	11th to 20th	Night	31% 39% 11% 17% 2	2857
	21st to end	Night	27% 38% 10% 15% 9% 1	3476
September	1st to 10th	Night	14% 60% 5% 12% 8%	1900
	11th to 20th	Night	13% 60% 6% 15% 5% 1	1947
	21st to end	Night	14% 59% 5% 14% 8%	2090
October	1st to 10th	Night	25% 38% 11% 21% 5%	3784
	11th to 20th	Night	25% 37% 10% 22% 6%	3794
	21st to end	Night	29% 37% 12% 14% 7%	4467
November	1st to 10th	Night	26% 56% 6% 7% 4 1	2505
	11th to 20th	Night	23% 60% 4 8% 4	2584
	21st to end	Night	25% 60% 5% 7% 3	2660
December	1st to 10th	Night	27% 60% 5% 7% 2	2660
	11th to 20th	Night	35% 48% 4 7% 4	3288
	21st to end	Night	47% 36% 4 10% 3	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	31% 16% 32% 18% 3	180
	11th to 20th	Day	32% 26% 27% 9% 4 1	180
	21st to end	Day	20% 21% 39% 18% 4	200
February	1st to 10th	Day	32% 30% 27% 9% 2	270
	11th to 20th	Day	27% 27% 38% 8%	331
	21st to end	Day	31% 20% 33% 15% 2	382
March	1st to 10th	Day	28% 22% 31% 15% 4	460
	11th to 20th	Day	29% 22% 33% 13% 2 1	460
	21st to end	Day	32% 22% 24% 14% 6% 1	506
April	1st to 10th	Day	31% 19% 31% 14% 5%	460
	11th to 20th	Day	34% 19% 26% 13% 6% 1	452
	21st to end	Day	32% 19% 29% 13% 7% 1	460
May	1st to 10th	Day	25% 17% 34% 16% 6% 1	463
	11th to 20th	Day	21% 16% 33% 20% 9% 2	487
	21st to end	Day	20% 17% 31% 22% 7% 1	529
June	1st to 10th	Day	28% 11% 31% 23% 7% 2	490
	11th to 20th	Day	18% 15% 32% 25% 8% 2	490
	21st to end	Day	25% 11% 33% 18% 10% 3	490
July	1st to 10th	Day	16% 8% 33% 26% 13% 2	485
	11th to 20th	Day	14% 11% 33% 27% 13% 2	484
	21st to end	Day	17% 8% 33% 29% 11% 2	532
August	1st to 10th	Day	17% 8% 28% 31% 14% 3	486
	11th to 20th	Day	16% 6% 27% 31% 13% 6%	479
	21st to end	Day	17% 9% 32% 23% 14% 6%	539
September	1st to 10th	Day	18% 10% 30% 21% 15% 5%	490
	11th to 20th	Day	15% 8% 26% 22% 20% 11%	490
	21st to end	Day	19% 14% 31% 19% 14% 4	490
October	1st to 10th	Day	23% 15% 27% 20% 12% 3	490
	11th to 20th	Day	25% 20% 27% 20% 6% 1	487
	21st to end	Day	33% 14% 30% 18% 5%	429
November	1st to 10th	Day	30% 18% 27% 18% 6% 1	386
	11th to 20th	Day	26% 24% 28% 17% 4	253
	21st to end	Day	28% 22% 28% 17% 6% 1	180
December	1st to 10th	Day	30% 17% 34% 15% 4	180
	11th to 20th	Day	32% 23% 32% 11% 1 1	180
	21st to end	Day	35% 24% 26% 14% 2	198
January	1st to 10th	Night	28% 18% 35% 15% 4	760
	11th to 20th	Night	29% 20% 26% 20% 5% 1	760
	21st to end	Night	21% 18% 34% 21% 5%	836
February	1st to 10th	Night	23% 19% 33% 22% 4	760
	11th to 20th	Night	23% 22% 34% 18% 4	743
	21st to end	Night	26% 18% 31% 23% 2	628
March	1st to 10th	Night	24% 19% 30% 23% 4	760
	11th to 20th	Night	27% 18% 32% 19% 3 1	760
	21st to end	Night	25% 17% 27% 25% 6% 1	836
April	1st to 10th	Night	31% 15% 29% 21% 4	760
	11th to 20th	Night	26% 19% 29% 21% 5%	751
	21st to end	Night	29% 14% 29% 20% 8%	646
May	1st to 10th	Night	26% 11% 30% 24% 7% 2	390
	11th to 20th	Night	24% 10% 29% 26% 9% 1	374
	21st to end	Night	17% 10% 38% 27% 9%	411
June	1st to 10th	Night	22% 8% 28% 32% 10% 1	380
	11th to 20th	Night	21% 8% 27% 31% 12% 1	380
	21st to end	Night	18% 8% 30% 27% 16% 1	380
July	1st to 10th	Night	13% 7% 30% 34% 15% 1	370
	11th to 20th	Night	14% 5% 29% 36% 15%	368
	21st to end	Night	14% 4 31% 37% 14% 1	416
August	1st to 10th	Night	14% 6% 22% 37% 19% 1	378
	11th to 20th	Night	15% 2 26% 34% 22% 2	583
	21st to end	Night	17% 6% 27% 31% 17% 2	836
September	1st to 10th	Night	14% 6% 31% 34% 14% 1	760
	11th to 20th	Night	19% 6% 21% 30% 21% 3	760
	21st to end	Night	19% 10% 28% 24% 18% 2	760
October	1st to 10th	Night	23% 10% 27% 28% 11% 1	760
	11th to 20th	Night	25% 12% 29% 24% 10%	760
	21st to end	Night	28% 16% 28% 24% 4	836
November	1st to 10th	Night	28% 17% 25% 23% 7% 1	771
	11th to 20th	Night	24% 19% 32% 16% 9% 1	760
	21st to end	Night	28% 18% 26% 20% 7%	760
December	1st to 10th	Night	31% 18% 28% 19% 4	760
	11th to 20th	Night	31% 21% 26% 16% 5% 1	760
	21st to end	Night	38% 18% 26% 14% 4	836

Page generated at 2024-11-05 08:15:47. Version ac07

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