Millard Oakley STEM Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Millard Oakley STEM Center 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	15% 8% 3 7% 5% 4 4 4 6% 7% 38%	100907
	Night	15% 8% 3 6% 4 4 4 3 5% 7% 41%	98064
Transparency	Day	43% 7% 11% 21% 15% 3	104661
	Night	41% 6% 11% 21% 17% 4	102448
Seeing	Day	19% 12% 24% 22% 16% 7%	14637
	Night	18% 10% 24% 28% 17% 3	24647

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	16% 15% 5% 10% 5% 4 4 4 5% 4 27%	2836
	11th to 20th	Day	21% 11% 4 13% 4 3 4 2 3 4 29%	2840
	21st to end	Day	25% 12% 7% 6% 3 3 3 3 4 5% 29%	3261
February	1st to 10th	Day	20% 12% 4 8% 4 4 4 3 4 5% 33%	1900
	11th to 20th	Day	22% 11% 5% 7% 6% 3 4 3 4 5% 31%	1848
	21st to end	Day	22% 10% 3 7% 4 4 3 3 5% 6% 33%	1570
March	1st to 10th	Day	24% 10% 3 6% 5% 4 3 3 4 6% 31%	3120
	11th to 20th	Day	15% 8% 2 6% 4 3 3 3 4 5% 46%	3439
	21st to end	Day	15% 8% 3 6% 4 4 5% 3 5% 6% 39%	3841
April	1st to 10th	Day	14% 7% 2 6% 5% 4 4 3 6% 6% 42%	2280
	11th to 20th	Day	15% 8% 2 5% 4 4 5% 4 5% 6% 42%	2254
	21st to end	Day	15% 7% 3 6% 5% 4 5% 4 5% 7% 39%	2400
May	1st to 10th	Day	21% 7% 2 6% 4 3 5% 4 6% 7% 34%	4082
	11th to 20th	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 35%	4081
	21st to end	Day	13% 5% 3 7% 5% 5% 5% 4 6% 7% 40%	4476
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 40%	2470
	11th to 20th	Day	6% 5% 2 5% 4 6% 5% 4 7% 11% 45%	2470
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 6% 8% 11% 38%	2470
July	1st to 10th	Day	8% 5% 2 7% 5% 6% 6% 6% 8% 11% 36%	4120
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 4 8% 9% 37%	4120
	21st to end	Day	18% 10% 4 9% 7% 6% 6% 5% 6% 7% 21%	4466
August	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 7% 11% 45%	4104
	11th to 20th	Day	7% 5% 2 6% 6% 6% 5% 6% 9% 10% 38%	3736
	21st to end	Day	7% 4 1 5% 4 5% 5% 5% 7% 8% 49%	4180
September	1st to 10th	Day	14% 5% 2 6% 6% 5% 6% 4 6% 6% 39%	2187
	11th to 20th	Day	13% 7% 3 7% 4 4 3 4 5% 7% 42%	2090
	21st to end	Day	14% 5% 2 5% 3 3 3 4 5% 7% 48%	2090
October	1st to 10th	Day	10% 5% 1 5% 3 4 3 3 4 6% 55%	2090
	11th to 20th	Day	14% 5% 2 5% 3 3 4 2 4 7% 52%	2028
	21st to end	Day	16% 6% 2 5% 3 3 3 3 6% 6% 46%	1943
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 6% 55%	1708
	11th to 20th	Day	15% 7% 2 4 3 3 4 4 4 5% 48%	1710
	21st to end	Day	16% 9% 3 5% 4 3 3 3 5% 5% 44%	1710
December	1st to 10th	Day	22% 12% 3 7% 4 4 3 3 5% 5% 31%	1710
	11th to 20th	Day	17% 13% 3 8% 5% 4 4 4 5% 4 33%	2153
	21st to end	Day	19% 14% 4 7% 4 4 4 3 5% 8% 28%	3124
January	1st to 10th	Night	20% 14% 4 7% 3 3 3 2 4 5% 33%	4109
	11th to 20th	Night	20% 13% 4 7% 6% 5% 3 2 3 4 33%	4120
	21st to end	Night	23% 13% 4 7% 4 3 3 2 4 5% 33%	4391
February	1st to 10th	Night	21% 9% 4 8% 5% 4 4 4 5% 5% 31%	2280
	11th to 20th	Night	23% 10% 5% 8% 4 4 3 2 4 5% 33%	2218
	21st to end	Night	24% 13% 3 7% 3 4 3 3 5% 6% 29%	1884
March	1st to 10th	Night	22% 12% 3 6% 5% 4 4 4 5% 5% 31%	3733
	11th to 20th	Night	15% 6% 2 5% 4 4 4 3 4 6% 48%	3520
	21st to end	Night	16% 8% 3 7% 5% 4 5% 3 5% 6% 38%	3817
April	1st to 10th	Night	13% 6% 2 6% 5% 5% 5% 3 5% 7% 43%	1900
	11th to 20th	Night	16% 7% 2 4 4 3 4 3 5% 6% 47%	1875
	21st to end	Night	15% 7% 2 6% 5% 4 4 3 5% 7% 43%	1777
May	1st to 10th	Night	16% 6% 2 7% 5% 5% 5% 4 6% 7% 37%	2813
	11th to 20th	Night	16% 7% 2 7% 5% 5% 5% 3 5% 7% 37%	2812
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 4 7% 9% 44%	3079
June	1st to 10th	Night	7% 6% 2 7% 5% 5% 5% 4 6% 9% 44%	1710
	11th to 20th	Night	4 4 1 5% 4 4 5% 4 8% 11% 51%	1710
	21st to end	Night	6% 5% 1 5% 5% 5% 5% 6% 7% 12% 42%	1663
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 5% 8% 11% 38%	2836
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 7% 9% 45%	2840
	21st to end	Night	12% 9% 4 11% 7% 6% 7% 4 7% 8% 24%	3087
August	1st to 10th	Night	6% 4 2 5% 4 4 4 3 6% 10% 53%	2825
	11th to 20th	Night	7% 5% 2 6% 4 5% 5% 3 7% 10% 46%	3091
	21st to end	Night	5% 3 1 3 3 4 4 4 5% 9% 58%	3476
September	1st to 10th	Night	11% 6% 3 6% 4 3 5% 3 6% 7% 46%	1972
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 3 5% 7% 45%	2090
	21st to end	Night	12% 5% 2 4 3 3 4 3 5% 7% 52%	2090
October	1st to 10th	Night	10% 5% 2 4 2 2 2 3 4 6% 60%	2090
	11th to 20th	Night	17% 5% 1 5% 3 3 3 3 4 5% 51%	2152
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 6% 49%	2650
November	1st to 10th	Night	11% 7% 2 4 3 3 4 2 4 6% 52%	2470
	11th to 20th	Night	14% 9% 2 4 3 3 3 3 4 7% 48%	2470
	21st to end	Night	17% 9% 3 5% 3 3 3 3 4 6% 43%	2470
December	1st to 10th	Night	22% 13% 4 7% 4 4 4 2 4 5% 31%	2470
	11th to 20th	Night	17% 12% 4 8% 3 3 3 3 4 5% 38%	3042
	21st to end	Night	16% 14% 4 9% 5% 6% 5% 3 5% 6% 26%	4532

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	58% 6% 7% 15% 12% 2	2837
	11th to 20th	Day	61% 5% 6% 13% 14% 1	2840
	21st to end	Day	57% 5% 8% 19% 11% 1	3261
February	1st to 10th	Day	55% 5% 7% 15% 16% 2	1900
	11th to 20th	Day	56% 4 7% 17% 13% 3	1858
	21st to end	Day	53% 5% 10% 13% 15% 5%	1570
March	1st to 10th	Day	54% 6% 7% 15% 13% 6%	3120
	11th to 20th	Day	40% 5% 10% 24% 16% 6%	3439
	21st to end	Day	43% 8% 9% 25% 14% 1	3841
April	1st to 10th	Day	41% 7% 11% 22% 16% 3	2280
	11th to 20th	Day	41% 6% 7% 20% 23% 3	2254
	21st to end	Day	43% 7% 10% 25% 13% 2	2400
May	1st to 10th	Day	46% 9% 12% 22% 10% 1	4120
	11th to 20th	Day	48% 8% 12% 23% 10%	4085
	21st to end	Day	40% 10% 12% 19% 17% 2	4489
June	1st to 10th	Day	40% 9% 14% 21% 14% 2	2470
	11th to 20th	Day	32% 10% 19% 21% 16% 2	2470
	21st to end	Day	36% 11% 16% 18% 14% 4	2470
July	1st to 10th	Day	37% 11% 20% 22% 8% 2	4055
	11th to 20th	Day	41% 8% 16% 26% 7% 2	4051
	21st to end	Day	59% 8% 12% 14% 5% 1	4324
August	1st to 10th	Day	31% 9% 15% 30% 14% 1	4091
	11th to 20th	Day	36% 8% 18% 24% 14% 1	3772
	21st to end	Day	30% 8% 12% 34% 14% 1	4179
September	1st to 10th	Day	42% 10% 12% 17% 16% 4	2187
	11th to 20th	Day	41% 8% 13% 20% 16% 2	2090
	21st to end	Day	36% 7% 11% 23% 19% 4	2090
October	1st to 10th	Day	24% 4 7% 18% 36% 10%	3480
	11th to 20th	Day	24% 4 9% 22% 31% 11%	3346
	21st to end	Day	30% 4 9% 25% 23% 9%	3180
November	1st to 10th	Day	32% 4 9% 23% 27% 5%	1708
	11th to 20th	Day	38% 5% 7% 23% 22% 5%	1710
	21st to end	Day	42% 5% 7% 21% 21% 4	1710
December	1st to 10th	Day	54% 5% 6% 20% 12% 2	1710
	11th to 20th	Day	52% 5% 8% 17% 15% 2	2150
	21st to end	Day	54% 6% 10% 19% 9% 2	3124
January	1st to 10th	Night	52% 6% 9% 18% 14% 1	4109
	11th to 20th	Night	56% 4 6% 12% 16% 5%	4120
	21st to end	Night	56% 4 7% 15% 16% 1	4391
February	1st to 10th	Night	54% 4 9% 17% 14% 2	2280
	11th to 20th	Night	55% 4 6% 18% 12% 4	2219
	21st to end	Night	56% 5% 6% 13% 14% 4	1884
March	1st to 10th	Night	54% 6% 10% 11% 14% 4	3733
	11th to 20th	Night	37% 6% 9% 25% 13% 10%	3520
	21st to end	Night	45% 7% 9% 23% 15% 1	3817
April	1st to 10th	Night	39% 6% 9% 23% 20% 3	1900
	11th to 20th	Night	38% 6% 9% 20% 22% 6%	1875
	21st to end	Night	41% 6% 10% 28% 14% 1	1777
May	1st to 10th	Night	44% 9% 14% 22% 10% 1	2840
	11th to 20th	Night	44% 9% 14% 20% 13% 1	2813
	21st to end	Night	32% 12% 16% 22% 16% 2	3087
June	1st to 10th	Night	35% 9% 13% 28% 13% 2	1710
	11th to 20th	Night	24% 9% 21% 26% 17% 2	1710
	21st to end	Night	31% 12% 17% 24% 13% 4	1663
July	1st to 10th	Night	36% 11% 20% 24% 9% 1	2791
	11th to 20th	Night	32% 8% 17% 31% 9% 3	2786
	21st to end	Night	55% 11% 12% 14% 7% 1	2988
August	1st to 10th	Night	27% 6% 14% 36% 16% 1	2814
	11th to 20th	Night	32% 8% 21% 26% 13% 1	3121
	21st to end	Night	22% 7% 13% 38% 18% 2	3476
September	1st to 10th	Night	36% 9% 13% 20% 18% 5%	1972
	11th to 20th	Night	38% 7% 11% 21% 22% 2	2090
	21st to end	Night	32% 7% 11% 23% 23% 5%	2090
October	1st to 10th	Night	23% 3 7% 22% 34% 11%	3480
	11th to 20th	Night	23% 3 6% 24% 28% 15%	3573
	21st to end	Night	25% 3 8% 24% 29% 12%	4363
November	1st to 10th	Night	34% 4 7% 23% 24% 7%	2470
	11th to 20th	Night	36% 4 8% 20% 24% 8%	2470
	21st to end	Night	43% 4 7% 23% 19% 4	2470
December	1st to 10th	Night	56% 5% 7% 17% 12% 2	2470
	11th to 20th	Night	49% 5% 8% 18% 18% 3	3044
	21st to end	Night	56% 7% 11% 15% 10% 1	4532

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% 27% 35% 10% 3 1	270
	11th to 20th	Day	39% 26% 23% 9% 3	270
	21st to end	Day	27% 26% 37% 7% 2	297
February	1st to 10th	Day	32% 26% 26% 13% 2	270
	11th to 20th	Day	39% 25% 30% 4 2	270
	21st to end	Day	40% 26% 28% 4 1	225
March	1st to 10th	Day	31% 22% 30% 15% 1	270
	11th to 20th	Day	27% 21% 31% 15% 4 1	432
	21st to end	Day	29% 19% 32% 15% 5%	506
April	1st to 10th	Day	25% 20% 27% 18% 9% 1	460
	11th to 20th	Day	21% 16% 33% 20% 8% 1	452
	21st to end	Day	24% 13% 32% 20% 10% 2	460
May	1st to 10th	Day	22% 14% 31% 21% 9% 4	463
	11th to 20th	Day	15% 11% 29% 25% 13% 7%	487
	21st to end	Day	15% 8% 23% 25% 18% 11%	529
June	1st to 10th	Day	13% 7% 23% 27% 19% 11%	490
	11th to 20th	Day	6% 4 18% 32% 27% 13%	490
	21st to end	Day	11% 4 22% 30% 20% 13%	490
July	1st to 10th	Day	13% 3 14% 28% 26% 17%	485
	11th to 20th	Day	14% 3 13% 26% 28% 16%	484
	21st to end	Day	15% 3 11% 28% 29% 14%	532
August	1st to 10th	Day	12% 2 17% 26% 30% 13%	486
	11th to 20th	Day	11% 3 18% 34% 27% 7%	479
	21st to end	Day	13% 2 11% 27% 31% 17%	539
September	1st to 10th	Day	13% 3 14% 26% 32% 12%	490
	11th to 20th	Day	14% 4 14% 28% 28% 12%	490
	21st to end	Day	16% 5% 19% 29% 24% 7%	490
October	1st to 10th	Day	12% 5% 22% 32% 21% 8%	490
	11th to 20th	Day	15% 12% 29% 24% 17% 3	490
	21st to end	Day	22% 11% 29% 26% 10% 2	392
November	1st to 10th	Day	20% 10% 34% 26% 8% 2	282
	11th to 20th	Day	19% 17% 35% 25% 4	270
	21st to end	Day	21% 20% 34% 15% 9% 1	270
December	1st to 10th	Day	33% 20% 30% 13% 4	270
	11th to 20th	Day	30% 20% 29% 14% 7%	270
	21st to end	Day	31% 23% 31% 13% 2	297
January	1st to 10th	Night	26% 19% 31% 20% 4	760
	11th to 20th	Night	30% 21% 28% 17% 4	760
	21st to end	Night	23% 19% 37% 19% 2	836
February	1st to 10th	Night	25% 17% 34% 21% 3	760
	11th to 20th	Night	30% 19% 34% 16% 1	743
	21st to end	Night	32% 22% 30% 15% 1	628
March	1st to 10th	Night	24% 16% 33% 24% 3	760
	11th to 20th	Night	26% 17% 31% 20% 6% 1	760
	21st to end	Night	23% 16% 31% 24% 7%	836
April	1st to 10th	Night	17% 13% 32% 28% 8%	570
	11th to 20th	Night	21% 11% 33% 24% 11%	563
	21st to end	Night	18% 10% 31% 31% 9% 1	570
May	1st to 10th	Night	15% 9% 31% 28% 15% 2	570
	11th to 20th	Night	13% 6% 24% 34% 20% 3	561
	21st to end	Night	8% 3 21% 35% 27% 5%	617
June	1st to 10th	Night	9% 5% 16% 37% 29% 4	570
	11th to 20th	Night	5% 1 14% 38% 34% 7%	570
	21st to end	Night	6% 1 15% 40% 32% 6%	570
July	1st to 10th	Night	11% 2 10% 30% 38% 10%	555
	11th to 20th	Night	9% 3 9% 28% 42% 9%	552
	21st to end	Night	8% 2 9% 34% 39% 8%	624
August	1st to 10th	Night	10% 2 7% 31% 44% 7%	567
	11th to 20th	Night	8% 1 10% 40% 35% 5%	564
	21st to end	Night	9% 2 7% 32% 41% 9%	627
September	1st to 10th	Night	10% 3 11% 34% 37% 6%	642
	11th to 20th	Night	12% 3 14% 32% 33% 6%	760
	21st to end	Night	14% 2 19% 32% 29% 5%	760
October	1st to 10th	Night	10% 6% 21% 30% 28% 6%	760
	11th to 20th	Night	19% 8% 22% 33% 16% 2	760
	21st to end	Night	19% 9% 27% 28% 15% 2	836
November	1st to 10th	Night	15% 10% 24% 32% 17% 2	760
	11th to 20th	Night	17% 14% 32% 26% 10% 1	760
	21st to end	Night	23% 13% 27% 27% 9% 1	760
December	1st to 10th	Night	29% 16% 26% 23% 5%	760
	11th to 20th	Night	24% 15% 29% 25% 6% 1	760
	21st to end	Night	27% 18% 28% 23% 4	836

Page generated at 2024-11-03 01:11:12. Version ac07

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