Cedar Drive Observatory
Clear Sky Chart
History

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

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	12% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	101482
	Night	13% 10% 3 8% 5% 4 4 3 5% 6% 38%	97650
Transparency	Day	43% 4 12% 26% 13% 1	104989
	Night	45% 4 12% 25% 13% 2	102271
Seeing	Day	16% 9% 29% 27% 14% 5%	15989
	Night	17% 8% 31% 32% 12% 1	25850

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	12% 11% 4 11% 7% 6% 5% 3 5% 6% 31%	2527
	11th to 20th	Day	10% 13% 4 10% 7% 7% 7% 5% 6% 7% 24%	2530
	21st to end	Day	15% 15% 5% 12% 7% 6% 5% 4 5% 5% 22%	2783
February	1st to 10th	Day	9% 11% 4 10% 7% 4 4 4 6% 7% 35%	1678
	11th to 20th	Day	10% 10% 4 8% 4 5% 5% 4 6% 7% 38%	1799
	21st to end	Day	12% 12% 3 7% 6% 4 4 5% 6% 8% 35%	1570
March	1st to 10th	Day	11% 9% 2 6% 3 3 3 4 5% 6% 47%	3120
	11th to 20th	Day	8% 7% 3 8% 4 4 4 4 6% 9% 42%	3272
	21st to end	Day	20% 12% 3 9% 5% 4 4 3 4 5% 30%	4165
April	1st to 10th	Day	15% 12% 4 7% 5% 4 5% 4 5% 6% 32%	2280
	11th to 20th	Day	20% 9% 3 6% 5% 4 4 4 5% 5% 36%	2254
	21st to end	Day	17% 10% 4 7% 5% 5% 5% 4 5% 6% 34%	2432
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 4 3 5% 8% 40%	4209
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 6% 7% 46%	4399
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	4824
June	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 3 6% 7% 44%	2660
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 4 6% 8% 40%	2660
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 42%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 7% 10% 38%	4440
	11th to 20th	Day	5% 3 1 4 4 4 5% 4 7% 11% 52%	4440
	21st to end	Day	7% 6% 2 6% 5% 5% 4 4 6% 7% 48%	4813
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 9% 42%	4423
	11th to 20th	Day	11% 5% 2 5% 3 4 4 4 6% 9% 47%	3936
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 4 6% 8% 40%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 6% 7% 43%	2280
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 3 6% 8% 47%	2180
	21st to end	Day	12% 7% 3 8% 4 5% 4 4 5% 7% 41%	2090
October	1st to 10th	Day	13% 8% 3 6% 3 4 4 4 5% 6% 45%	1991
	11th to 20th	Day	18% 10% 3 8% 5% 5% 5% 4 6% 6% 32%	1855
	21st to end	Day	18% 8% 3 9% 5% 4 4 3 4 6% 36%	1881
November	1st to 10th	Day	14% 8% 3 6% 4 4 4 3 6% 8% 41%	1717
	11th to 20th	Day	12% 9% 4 9% 7% 5% 5% 3 6% 7% 32%	1693
	21st to end	Day	15% 10% 3 6% 5% 4 4 5% 5% 7% 35%	1520
December	1st to 10th	Day	13% 11% 3 8% 6% 4 5% 5% 7% 6% 32%	1520
	11th to 20th	Day	14% 14% 4 8% 5% 5% 5% 5% 6% 6% 28%	1918
	21st to end	Day	19% 18% 5% 12% 7% 6% 4 3 4 4 18%	2783
January	1st to 10th	Night	13% 14% 6% 10% 5% 4 4 3 4 5% 34%	4428
	11th to 20th	Night	12% 12% 5% 13% 7% 6% 5% 3 5% 5% 27%	4440
	21st to end	Night	13% 18% 7% 11% 6% 4 4 3 4 5% 24%	4884
February	1st to 10th	Night	9% 12% 5% 9% 7% 5% 5% 4 5% 5% 35%	2499
	11th to 20th	Night	9% 11% 4 8% 5% 5% 5% 3 5% 7% 38%	2266
	21st to end	Night	15% 12% 3 8% 5% 5% 4 3 5% 5% 35%	1884
March	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 5% 6% 44%	3733
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 4 6% 7% 40%	3716
	21st to end	Night	19% 9% 3 10% 5% 5% 5% 4 4 6% 31%	3466
April	1st to 10th	Night	18% 11% 2 7% 5% 4 4 4 5% 6% 34%	1900
	11th to 20th	Night	21% 6% 3 5% 4 4 4 3 5% 7% 38%	1875
	21st to end	Night	16% 9% 3 6% 5% 4 5% 3 6% 7% 36%	1748
May	1st to 10th	Night	15% 8% 3 7% 4 4 5% 4 6% 8% 37%	2675
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 6% 8% 42%	2506
	21st to end	Night	16% 6% 2 7% 5% 4 5% 4 5% 6% 39%	2743
June	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 4 6% 7% 46%	1520
	11th to 20th	Night	12% 6% 2 7% 4 5% 4 4 7% 8% 41%	1520
	21st to end	Night	8% 6% 2 6% 4 3 4 5% 7% 8% 47%	1520
July	1st to 10th	Night	13% 6% 2 6% 5% 5% 5% 4 5% 7% 43%	2530
	11th to 20th	Night	4 3 1 4 3 3 4 4 7% 9% 57%	2530
	21st to end	Night	7% 5% 2 7% 5% 4 4 4 5% 8% 49%	2750
August	1st to 10th	Night	10% 5% 2 7% 4 4 4 3 7% 8% 45%	2517
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 6% 47%	2878
	21st to end	Night	9% 6% 2 7% 5% 5% 4 3 6% 7% 47%	3476
September	1st to 10th	Night	8% 4 2 6% 4 4 3 3 5% 7% 53%	1900
	11th to 20th	Night	12% 4 2 4 3 3 2 3 5% 7% 55%	1981
	21st to end	Night	12% 6% 2 6% 4 4 5% 3 5% 7% 47%	2090
October	1st to 10th	Night	12% 7% 3 5% 3 3 4 4 5% 7% 48%	2185
	11th to 20th	Night	15% 7% 3 6% 4 5% 5% 4 6% 6% 38%	2323
	21st to end	Night	18% 10% 3 7% 4 4 4 4 5% 7% 34%	2717
November	1st to 10th	Night	13% 9% 2 6% 4 4 3 3 6% 8% 42%	2483
	11th to 20th	Night	13% 11% 4 9% 5% 5% 4 3 5% 6% 35%	2484
	21st to end	Night	14% 11% 3 7% 5% 3 4 3 5% 7% 38%	2660
December	1st to 10th	Night	13% 12% 4 9% 5% 5% 4 4 5% 6% 33%	2660
	11th to 20th	Night	12% 15% 4 10% 6% 5% 4 3 4 5% 32%	3279
	21st to end	Night	22% 18% 5% 9% 5% 4 4 3 4 4 22%	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	56% 3 16% 17% 7% 1	2528
	11th to 20th	Day	60% 3 12% 20% 5% 1	2530
	21st to end	Day	65% 3 11% 16% 5%	2783
February	1st to 10th	Day	49% 4 12% 22% 12% 1	1678
	11th to 20th	Day	46% 4 12% 25% 12% 2	1809
	21st to end	Day	47% 5% 14% 23% 9% 2	1570
March	1st to 10th	Day	39% 3 13% 26% 17% 3	3120
	11th to 20th	Day	40% 3 12% 26% 17% 2	3272
	21st to end	Day	58% 3 10% 21% 8% 1	4165
April	1st to 10th	Day	52% 4 11% 21% 12%	2280
	11th to 20th	Day	50% 3 9% 22% 14% 2	2254
	21st to end	Day	51% 4 10% 21% 12% 2	2432
May	1st to 10th	Day	44% 3 10% 26% 17% 1	4247
	11th to 20th	Day	37% 4 9% 33% 16% 1	4403
	21st to end	Day	43% 4 10% 24% 17% 2	4837
June	1st to 10th	Day	38% 4 12% 29% 15% 2	2660
	11th to 20th	Day	40% 5% 14% 25% 15% 1	2660
	21st to end	Day	37% 6% 14% 27% 13% 2	2660
July	1st to 10th	Day	41% 5% 15% 27% 11% 2	4371
	11th to 20th	Day	23% 6% 16% 37% 16% 2	4365
	21st to end	Day	33% 5% 13% 26% 22% 2	4662
August	1st to 10th	Day	37% 7% 16% 26% 13% 1	4408
	11th to 20th	Day	33% 5% 14% 35% 12%	3976
	21st to end	Day	40% 7% 14% 23% 16% 1	4179
September	1st to 10th	Day	39% 5% 13% 27% 15% 1	2280
	11th to 20th	Day	35% 4 18% 32% 11% 1	2180
	21st to end	Day	42% 4 13% 30% 11%	2090
October	1st to 10th	Day	26% 2 11% 35% 25% 1	3303
	11th to 20th	Day	45% 4 9% 28% 14% 1	3058
	21st to end	Day	43% 4 14% 28% 10%	3081
November	1st to 10th	Day	41% 4 13% 27% 13% 1	1717
	11th to 20th	Day	51% 4 14% 20% 9% 1	1693
	21st to end	Day	48% 5% 17% 23% 6% 1	1520
December	1st to 10th	Day	50% 5% 13% 25% 6% 1	1520
	11th to 20th	Day	56% 5% 14% 14% 9% 2	1915
	21st to end	Day	71% 3 7% 14% 5%	2783
January	1st to 10th	Night	55% 2 10% 22% 9% 1	4428
	11th to 20th	Night	60% 3 9% 21% 7%	4440
	21st to end	Night	64% 2 11% 17% 6%	4884
February	1st to 10th	Night	51% 4 9% 23% 11% 2	2499
	11th to 20th	Night	47% 4 11% 24% 12% 2	2267
	21st to end	Night	51% 3 11% 22% 11% 2	1884
March	1st to 10th	Night	41% 3 14% 29% 11% 2	3733
	11th to 20th	Night	43% 3 9% 27% 17% 1	3716
	21st to end	Night	56% 3 9% 21% 10% 2	3466
April	1st to 10th	Night	50% 4 7% 19% 18% 1	1900
	11th to 20th	Night	47% 3 9% 23% 15% 4	1875
	21st to end	Night	47% 3 10% 24% 15% 1	1748
May	1st to 10th	Night	46% 4 14% 19% 17% 1	2702
	11th to 20th	Night	39% 4 11% 30% 15% 1	2507
	21st to end	Night	46% 3 12% 19% 15% 5%	2751
June	1st to 10th	Night	37% 5% 12% 31% 15% 1	1520
	11th to 20th	Night	40% 4 11% 26% 17% 2	1520
	21st to end	Night	33% 7% 16% 26% 15% 3	1520
July	1st to 10th	Night	40% 6% 14% 23% 12% 5%	2490
	11th to 20th	Night	22% 5% 18% 35% 18% 2	2482
	21st to end	Night	32% 5% 13% 24% 23% 2	2662
August	1st to 10th	Night	35% 5% 13% 27% 18% 2	2508
	11th to 20th	Night	35% 6% 13% 29% 16% 1	2904
	21st to end	Night	34% 6% 14% 23% 20% 3	3476
September	1st to 10th	Night	31% 4 12% 32% 21% 1	1900
	11th to 20th	Night	31% 3 14% 36% 15% 1	1981
	21st to end	Night	37% 3 14% 30% 15% 1	2090
October	1st to 10th	Night	28% 3 8% 39% 20% 2	3640
	11th to 20th	Night	35% 5% 12% 29% 16% 2	3859
	21st to end	Night	47% 4 11% 23% 15%	4467
November	1st to 10th	Night	41% 4 12% 26% 16% 2	2483
	11th to 20th	Night	50% 4 13% 20% 13% 1	2484
	21st to end	Night	47% 3 14% 26% 8% 1	2660
December	1st to 10th	Night	52% 3 14% 23% 7% 1	2660
	11th to 20th	Night	57% 3 14% 18% 9% 1	3281
	21st to end	Night	67% 4 8% 16% 5%	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	14% 10% 31% 30% 12% 2	270
	11th to 20th	Day	20% 9% 32% 30% 7% 1	270
	21st to end	Day	21% 7% 27% 35% 9% 1	297
February	1st to 10th	Day	14% 9% 37% 29% 9% 2	270
	11th to 20th	Day	11% 14% 42% 22% 10% 1	270
	21st to end	Day	19% 12% 41% 25% 3	225
March	1st to 10th	Day	16% 14% 36% 24% 10%	270
	11th to 20th	Day	19% 10% 30% 30% 8% 2	283
	21st to end	Day	26% 8% 27% 28% 8% 3	506
April	1st to 10th	Day	23% 13% 31% 24% 8% 1	460
	11th to 20th	Day	27% 14% 27% 19% 10% 2	452
	21st to end	Day	22% 10% 31% 21% 15% 2	460
May	1st to 10th	Day	18% 10% 33% 27% 9% 3	538
	11th to 20th	Day	17% 10% 31% 28% 11% 4	675
	21st to end	Day	16% 8% 27% 28% 13% 7%	734
June	1st to 10th	Day	10% 8% 33% 30% 15% 4	680
	11th to 20th	Day	16% 8% 30% 27% 14% 4	680
	21st to end	Day	13% 6% 30% 31% 16% 4	680
July	1st to 10th	Day	9% 4 21% 31% 25% 9%	671
	11th to 20th	Day	8% 5% 26% 33% 20% 8%	668
	21st to end	Day	7% 5% 24% 32% 23% 10%	739
August	1st to 10th	Day	8% 5% 22% 33% 23% 8%	676
	11th to 20th	Day	12% 4 17% 29% 26% 12%	523
	21st to end	Day	14% 6% 21% 25% 24% 10%	539
September	1st to 10th	Day	17% 6% 22% 28% 20% 8%	490
	11th to 20th	Day	11% 3 23% 30% 23% 8%	490
	21st to end	Day	15% 9% 29% 23% 20% 6%	490
October	1st to 10th	Day	16% 11% 27% 26% 16% 4	391
	11th to 20th	Day	20% 17% 32% 24% 7%	300
	21st to end	Day	23% 15% 34% 23% 6%	330
November	1st to 10th	Day	17% 13% 35% 25% 9% 1	285
	11th to 20th	Day	15% 16% 39% 20% 9% 1	270
	21st to end	Day	23% 8% 39% 24% 6%	270
December	1st to 10th	Day	15% 13% 42% 23% 6%	270
	11th to 20th	Day	22% 13% 39% 17% 7% 1	270
	21st to end	Day	29% 13% 32% 19% 6%	297
January	1st to 10th	Night	16% 11% 37% 29% 7%	950
	11th to 20th	Night	20% 11% 36% 25% 8% 1	950
	21st to end	Night	19% 7% 36% 30% 8% 1	1045
February	1st to 10th	Night	15% 10% 38% 29% 7% 1	950
	11th to 20th	Night	15% 10% 39% 27% 9%	791
	21st to end	Night	21% 10% 35% 29% 4	628
March	1st to 10th	Night	18% 9% 33% 32% 8% 1	760
	11th to 20th	Night	15% 12% 36% 29% 7% 1	729
	21st to end	Night	22% 7% 31% 31% 9% 1	627
April	1st to 10th	Night	23% 8% 37% 27% 4 1	570
	11th to 20th	Night	26% 7% 30% 30% 8%	563
	21st to end	Night	20% 6% 32% 32% 9% 1	570
May	1st to 10th	Night	23% 6% 33% 31% 7% 1	570
	11th to 20th	Night	18% 6% 33% 34% 9%	561
	21st to end	Night	14% 5% 25% 38% 17% 1	617
June	1st to 10th	Night	11% 7% 26% 40% 14% 1	570
	11th to 20th	Night	15% 6% 26% 40% 12% 1	570
	21st to end	Night	10% 4 25% 43% 17% 1	570
July	1st to 10th	Night	7% 2 19% 47% 23% 2	555
	11th to 20th	Night	8% 3 22% 41% 25% 1	552
	21st to end	Night	6% 2 21% 47% 24% 1	624
August	1st to 10th	Night	10% 2 16% 47% 25% 1	567
	11th to 20th	Night	9% 3 15% 41% 29% 3	564
	21st to end	Night	10% 3 20% 42% 23% 2	627
September	1st to 10th	Night	10% 4 24% 35% 23% 4	570
	11th to 20th	Night	13% 5% 23% 35% 22% 3	651
	21st to end	Night	14% 6% 23% 36% 19% 2	760
October	1st to 10th	Night	15% 9% 26% 31% 18% 1	760
	11th to 20th	Night	18% 10% 34% 29% 9%	760
	21st to end	Night	22% 10% 31% 26% 9% 1	836
November	1st to 10th	Night	17% 9% 38% 27% 8% 1	764
	11th to 20th	Night	17% 14% 39% 23% 6%	774
	21st to end	Night	19% 11% 35% 26% 7%	950
December	1st to 10th	Night	19% 10% 39% 25% 7%	950
	11th to 20th	Night	21% 9% 36% 25% 7% 1	950
	21st to end	Night	27% 11% 33% 25% 4	1045

Page generated at 2024-11-03 12:19:06. Version ac07

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