Otter Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Otter Creek 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	13% 8% 3 7% 5% 4 4 4 6% 7% 39%	101083
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 41%	97940
Transparency	Day	23% 47% 5% 15% 9% 1	104767
	Night	23% 46% 5% 14% 10% 1	102371
Seeing	Day	17% 11% 26% 24% 15% 7%	15350
	Night	18% 9% 26% 29% 17% 2	25095

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	13% 13% 8% 9% 4 4 4 3 6% 5% 30%	2527
	11th to 20th	Day	17% 9% 4 13% 7% 5% 5% 3 4 4 30%	2538
	21st to end	Day	26% 13% 8% 6% 4 3 3 2 4 6% 24%	3220
February	1st to 10th	Day	18% 12% 4 9% 4 4 3 2 4 6% 34%	1900
	11th to 20th	Day	17% 9% 4 8% 5% 4 4 3 5% 6% 36%	1848
	21st to end	Day	19% 11% 4 8% 5% 4 3 4 5% 5% 32%	1570
March	1st to 10th	Day	26% 14% 3 6% 4 3 3 3 3 5% 32%	3120
	11th to 20th	Day	13% 7% 2 6% 4 3 4 3 5% 7% 46%	3379
	21st to end	Day	13% 8% 2 7% 5% 5% 4 4 6% 7% 38%	3941
April	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 6% 8% 39%	2280
	11th to 20th	Day	15% 9% 2 7% 4 4 4 3 4 6% 41%	2254
	21st to end	Day	18% 6% 2 6% 5% 5% 4 3 6% 6% 38%	2408
May	1st to 10th	Day	18% 9% 3 7% 5% 5% 5% 4 7% 8% 30%	4082
	11th to 20th	Day	18% 7% 3 6% 4 5% 4 4 5% 6% 38%	4081
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 4 7% 8% 38%	4476
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 4 6% 7% 44%	2553
	11th to 20th	Day	5% 5% 2 7% 5% 5% 5% 5% 6% 11% 45%	2660
	21st to end	Day	7% 6% 2 5% 6% 5% 5% 5% 7% 9% 44%	2660
July	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 7% 9% 39%	4440
	11th to 20th	Day	6% 5% 2 5% 4 5% 5% 5% 8% 10% 45%	4440
	21st to end	Day	12% 10% 3 10% 6% 7% 5% 5% 7% 7% 26%	4466
August	1st to 10th	Day	6% 5% 2 5% 3 3 4 4 7% 10% 49%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 9% 41%	3767
	21st to end	Day	5% 4 1 4 4 5% 4 3 5% 9% 55%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 3 5% 8% 44%	2229
	11th to 20th	Day	10% 6% 1 6% 4 4 5% 3 5% 9% 45%	2090
	21st to end	Day	13% 6% 2 5% 5% 4 4 3 5% 6% 48%	2090
October	1st to 10th	Day	10% 5% 2 4 4 3 3 3 4 7% 55%	2090
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 5% 5% 50%	2008
	21st to end	Day	18% 7% 3 5% 3 4 4 2 5% 6% 43%	1881
November	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 4 5% 54%	1708
	11th to 20th	Day	16% 9% 2 5% 3 3 4 3 5% 6% 44%	1710
	21st to end	Day	17% 9% 3 6% 4 3 4 3 4 5% 42%	1710
December	1st to 10th	Day	19% 13% 3 8% 4 4 3 4 4 6% 33%	1710
	11th to 20th	Day	14% 13% 6% 9% 5% 4 4 3 5% 5% 33%	2153
	21st to end	Day	19% 17% 4 8% 4 4 5% 3 5% 6% 25%	2810
January	1st to 10th	Night	16% 15% 4 9% 6% 4 4 3 4 6% 29%	4428
	11th to 20th	Night	16% 13% 5% 11% 6% 5% 4 3 4 4 28%	4427
	21st to end	Night	23% 16% 4 6% 4 3 3 3 4 5% 28%	4432
February	1st to 10th	Night	20% 12% 5% 7% 5% 4 5% 4 5% 6% 29%	2280
	11th to 20th	Night	18% 10% 4 9% 5% 4 3 3 4 6% 36%	2218
	21st to end	Night	20% 11% 4 8% 5% 4 4 3 5% 5% 32%	1884
March	1st to 10th	Night	22% 13% 3 7% 4 3 4 3 4 4 32%	3733
	11th to 20th	Night	13% 8% 2 6% 4 3 4 3 5% 5% 48%	3581
	21st to end	Night	13% 8% 2 8% 5% 4 4 3 5% 6% 41%	3704
April	1st to 10th	Night	12% 7% 3 5% 4 5% 4 4 6% 8% 43%	1900
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 7% 42%	1875
	21st to end	Night	15% 8% 3 6% 5% 4 4 3 5% 8% 38%	1772
May	1st to 10th	Night	17% 10% 4 8% 5% 5% 4 4 5% 7% 31%	2813
	11th to 20th	Night	15% 7% 3 6% 4 4 4 4 5% 8% 40%	2812
	21st to end	Night	7% 5% 2 7% 6% 5% 5% 5% 7% 10% 41%	3079
June	1st to 10th	Night	9% 5% 2 6% 4 3 4 3 7% 9% 47%	1621
	11th to 20th	Night	5% 4 1 5% 5% 4 5% 5% 6% 10% 50%	1520
	21st to end	Night	4 3 1 5% 5% 4 4 6% 7% 12% 49%	1520
July	1st to 10th	Night	8% 5% 2 6% 4 5% 4 4 5% 9% 48%	2530
	11th to 20th	Night	6% 4 2 4 3 4 4 4 6% 10% 55%	2530
	21st to end	Night	10% 8% 4 10% 7% 6% 6% 5% 7% 8% 30%	3083
August	1st to 10th	Night	5% 4 1 5% 3 4 3 3 6% 9% 56%	2825
	11th to 20th	Night	5% 5% 2 6% 4 4 5% 4 7% 10% 48%	3058
	21st to end	Night	4 2 1 3 3 2 3 3 5% 9% 65%	3476
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 5% 7% 51%	1930
	11th to 20th	Night	8% 6% 2 6% 4 4 4 4 6% 7% 50%	2090
	21st to end	Night	11% 5% 2 5% 4 3 4 3 5% 6% 52%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 2 2 5% 6% 60%	2090
	11th to 20th	Night	14% 5% 2 6% 4 4 4 2 4 6% 50%	2166
	21st to end	Night	16% 7% 2 6% 3 3 3 3 4 5% 47%	2717
November	1st to 10th	Night	12% 6% 2 4 4 4 4 4 4 5% 52%	2470
	11th to 20th	Night	14% 7% 2 7% 4 4 4 3 4 6% 46%	2470
	21st to end	Night	16% 10% 3 4 4 4 4 3 5% 5% 42%	2470
December	1st to 10th	Night	20% 11% 4 6% 5% 3 3 3 5% 6% 33%	2470
	11th to 20th	Night	17% 11% 3 10% 4 4 4 4 4 5% 34%	3042
	21st to end	Night	18% 16% 5% 10% 6% 5% 5% 3 4 5% 23%	4834

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	37% 39% 6% 12% 6% 1	2528
	11th to 20th	Day	38% 37% 5% 14% 5% 1	2538
	21st to end	Day	43% 39% 4 11% 2	3220
February	1st to 10th	Day	18% 64% 3 8% 6% 1	1900
	11th to 20th	Day	18% 64% 3 10% 5%	1858
	21st to end	Day	18% 64% 3 8% 5% 2	1570
March	1st to 10th	Day	40% 40% 2 9% 5% 4	3120
	11th to 20th	Day	17% 41% 6% 21% 14% 1	3379
	21st to end	Day	22% 41% 9% 15% 12%	3941
April	1st to 10th	Day	18% 65% 4 8% 4	2280
	11th to 20th	Day	16% 65% 3 10% 4 1	2254
	21st to end	Day	15% 66% 4 10% 4 2	2408
May	1st to 10th	Day	30% 44% 10% 11% 5%	4120
	11th to 20th	Day	27% 42% 6% 16% 9%	4085
	21st to end	Day	26% 42% 6% 10% 14% 1	4489
June	1st to 10th	Day	14% 66% 3 9% 7% 1	2553
	11th to 20th	Day	13% 66% 5% 8% 7%	2660
	21st to end	Day	14% 64% 6% 9% 6%	2660
July	1st to 10th	Day	28% 36% 8% 16% 12%	4371
	11th to 20th	Day	19% 36% 7% 29% 9% 1	4365
	21st to end	Day	41% 36% 7% 10% 5% 1	4324
August	1st to 10th	Day	18% 37% 9% 27% 9%	4091
	11th to 20th	Day	25% 37% 8% 20% 10%	3804
	21st to end	Day	15% 37% 7% 32% 8% 1	4179
September	1st to 10th	Day	13% 60% 4 12% 9% 2	2229
	11th to 20th	Day	13% 60% 6% 10% 9% 1	2090
	21st to end	Day	16% 60% 3 13% 8%	2090
October	1st to 10th	Day	10% 36% 2 19% 30% 1	3480
	11th to 20th	Day	13% 36% 6% 18% 24% 2	3302
	21st to end	Day	17% 36% 4 20% 17% 6%	3081
November	1st to 10th	Day	18% 58% 4 12% 7% 1	1708
	11th to 20th	Day	16% 59% 3 10% 9% 3	1710
	21st to end	Day	20% 60% 3 11% 6% 1	1710
December	1st to 10th	Day	23% 60% 4 7% 5% 1	1710
	11th to 20th	Day	27% 48% 3 12% 9% 1	2150
	21st to end	Day	40% 39% 6% 10% 5%	2810
January	1st to 10th	Night	37% 38% 6% 11% 6% 1	4428
	11th to 20th	Night	40% 37% 3 13% 5% 1	4427
	21st to end	Night	39% 40% 3 10% 7% 1	4432
February	1st to 10th	Night	20% 64% 3 7% 5% 1	2280
	11th to 20th	Night	19% 64% 3 8% 6%	2219
	21st to end	Night	19% 64% 3 6% 6% 1	1884
March	1st to 10th	Night	39% 41% 4 11% 4 1	3733
	11th to 20th	Night	18% 42% 6% 18% 14% 3	3581
	21st to end	Night	23% 41% 5% 17% 13%	3704
April	1st to 10th	Night	16% 66% 4 8% 6% 1	1900
	11th to 20th	Night	17% 65% 4 8% 5% 1	1875
	21st to end	Night	16% 65% 3 10% 4 2	1772
May	1st to 10th	Night	31% 45% 6% 14% 3 1	2840
	11th to 20th	Night	24% 43% 9% 19% 5%	2813
	21st to end	Night	22% 43% 10% 14% 10% 1	3087
June	1st to 10th	Night	13% 65% 3 11% 5% 2	1621
	11th to 20th	Night	11% 66% 4 9% 8% 2	1520
	21st to end	Night	10% 64% 7% 11% 8%	1520
July	1st to 10th	Night	23% 37% 8% 19% 12% 1	2490
	11th to 20th	Night	17% 35% 7% 29% 12%	2482
	21st to end	Night	39% 37% 8% 10% 6% 1	2985
August	1st to 10th	Night	16% 37% 9% 29% 9%	2814
	11th to 20th	Night	21% 38% 9% 21% 11%	3087
	21st to end	Night	9% 36% 9% 29% 15% 2	3476
September	1st to 10th	Night	10% 60% 4 12% 11% 2	1930
	11th to 20th	Night	11% 60% 4 11% 12% 2	2090
	21st to end	Night	13% 60% 4 14% 9% 1	2090
October	1st to 10th	Night	10% 36% 3 11% 38% 2	3480
	11th to 20th	Night	12% 36% 3 15% 31% 3	3586
	21st to end	Night	17% 36% 4 14% 24% 5%	4467
November	1st to 10th	Night	20% 57% 3 10% 9% 1	2470
	11th to 20th	Night	16% 59% 2 9% 10% 3	2470
	21st to end	Night	20% 59% 3 11% 6%	2470
December	1st to 10th	Night	23% 60% 4 8% 4 1	2470
	11th to 20th	Night	25% 50% 4 11% 8% 1	3044
	21st to end	Night	44% 39% 5% 7% 5% 1	4834

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	25% 16% 37% 16% 5% 1	270
	11th to 20th	Day	29% 27% 27% 15% 2	270
	21st to end	Day	27% 27% 33% 11% 2	297
February	1st to 10th	Day	27% 23% 36% 13% 2	270
	11th to 20th	Day	28% 27% 35% 7% 1 1	270
	21st to end	Day	32% 20% 39% 7% 2	225
March	1st to 10th	Day	28% 20% 38% 12% 3	270
	11th to 20th	Day	26% 17% 37% 11% 8% 1	398
	21st to end	Day	26% 22% 32% 14% 5% 1	506
April	1st to 10th	Day	23% 17% 28% 23% 8% 1	460
	11th to 20th	Day	24% 17% 27% 19% 9% 3	452
	21st to end	Day	21% 16% 34% 19% 8% 2	460
May	1st to 10th	Day	22% 13% 30% 22% 8% 4	463
	11th to 20th	Day	19% 10% 29% 25% 13% 5%	487
	21st to end	Day	12% 8% 27% 26% 15% 12%	529
June	1st to 10th	Day	13% 6% 23% 28% 19% 10%	573
	11th to 20th	Day	6% 5% 25% 34% 21% 9%	680
	21st to end	Day	11% 5% 26% 27% 19% 11%	680
July	1st to 10th	Day	12% 5% 15% 27% 24% 17%	671
	11th to 20th	Day	8% 3 18% 34% 23% 14%	668
	21st to end	Day	10% 2 16% 35% 27% 11%	532
August	1st to 10th	Day	9% 4 14% 31% 27% 16%	486
	11th to 20th	Day	12% 5% 18% 31% 25% 10%	479
	21st to end	Day	10% 3 9% 28% 30% 19%	539
September	1st to 10th	Day	13% 2 15% 28% 33% 9%	490
	11th to 20th	Day	11% 3 15% 28% 31% 13%	490
	21st to end	Day	18% 7% 18% 26% 21% 10%	490
October	1st to 10th	Day	11% 6% 21% 34% 21% 6%	490
	11th to 20th	Day	17% 14% 31% 23% 11% 5%	466
	21st to end	Day	25% 13% 37% 18% 7%	330
November	1st to 10th	Day	12% 12% 37% 27% 8% 4	282
	11th to 20th	Day	23% 17% 30% 24% 5% 1	270
	21st to end	Day	26% 11% 37% 18% 8% 1	270
December	1st to 10th	Day	21% 25% 30% 16% 7% 1	270
	11th to 20th	Day	24% 17% 35% 18% 6%	270
	21st to end	Day	31% 21% 31% 14% 3	297
January	1st to 10th	Night	22% 18% 31% 25% 4	950
	11th to 20th	Night	27% 18% 31% 20% 3	937
	21st to end	Night	24% 16% 37% 21% 2	836
February	1st to 10th	Night	28% 14% 34% 22% 2	760
	11th to 20th	Night	25% 17% 36% 20% 2	743
	21st to end	Night	28% 16% 37% 18% 2	628
March	1st to 10th	Night	23% 16% 32% 25% 5%	760
	11th to 20th	Night	23% 13% 35% 23% 6% 1	760
	21st to end	Night	24% 11% 28% 29% 7%	774
April	1st to 10th	Night	16% 12% 35% 29% 8%	570
	11th to 20th	Night	19% 11% 33% 24% 12%	563
	21st to end	Night	20% 9% 34% 27% 8% 1	570
May	1st to 10th	Night	19% 7% 32% 26% 16% 1	570
	11th to 20th	Night	15% 6% 22% 37% 17% 4	561
	21st to end	Night	8% 2 21% 37% 27% 5%	617
June	1st to 10th	Night	11% 3 20% 36% 27% 3	570
	11th to 20th	Night	8% 2 14% 45% 27% 3	570
	21st to end	Night	5% 2 21% 39% 30% 4	570
July	1st to 10th	Night	11% 2 11% 26% 40% 9%	555
	11th to 20th	Night	7% 2 9% 36% 40% 6%	552
	21st to end	Night	10% 2 13% 37% 33% 7%	624
August	1st to 10th	Night	8% 2 9% 34% 42% 6%	567
	11th to 20th	Night	7% 2 10% 39% 36% 6%	564
	21st to end	Night	7% 1 8% 33% 44% 7%	627
September	1st to 10th	Night	13% 2 12% 32% 37% 6%	600
	11th to 20th	Night	11% 2 13% 34% 34% 6%	760
	21st to end	Night	13% 3 20% 31% 29% 4	760
October	1st to 10th	Night	10% 5% 18% 34% 28% 5%	760
	11th to 20th	Night	16% 9% 28% 29% 17% 2	760
	21st to end	Night	20% 9% 33% 25% 12% 1	836
November	1st to 10th	Night	16% 8% 29% 29% 16% 1	760
	11th to 20th	Night	18% 15% 29% 28% 10%	760
	21st to end	Night	23% 13% 25% 28% 11%	760
December	1st to 10th	Night	26% 12% 30% 26% 5% 1	760
	11th to 20th	Night	25% 12% 30% 25% 7% 1	760
	21st to end	Night	29% 15% 30% 22% 4	1021

Page generated at 2024-11-03 02:11:16. Version ac07

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