Frog Hollow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Frog Hollow Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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% 7% 2 6% 4 4 4 4 5% 7% 45%	101330
	Night	13% 6% 2 5% 3 3 3 3 5% 7% 50%	98349
Transparency	Day	38% 3 9% 23% 20% 6%	104977
	Night	34% 3 9% 22% 23% 9%	102842
Seeing	Day	15% 9% 23% 26% 21% 6%	15341
	Night	15% 8% 25% 31% 18% 2	25151

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	20% 11% 3 5% 3 2 3 2 3 4 43%	2847
	11th to 20th	Day	17% 9% 2 4 3 3 3 2 4 4 49%	2850
	21st to end	Day	25% 7% 2 4 3 2 2 2 3 4 45%	3135
February	1st to 10th	Day	23% 8% 2 6% 3 3 4 3 4 4 39%	1710
	11th to 20th	Day	20% 9% 3 6% 3 4 4 2 3 5% 41%	1744
	21st to end	Day	25% 7% 3 7% 4 2 2 2 4 4 39%	1727
March	1st to 10th	Day	21% 11% 3 6% 4 2 3 2 4 6% 37%	3436
	11th to 20th	Day	16% 7% 3 7% 5% 5% 4 4 5% 7% 38%	3480
	21st to end	Day	15% 9% 3 7% 4 3 3 3 4 5% 42%	3814
April	1st to 10th	Day	14% 6% 2 6% 6% 3 4 4 5% 6% 44%	2209
	11th to 20th	Day	17% 7% 2 5% 4 5% 4 3 4 5% 44%	2254
	21st to end	Day	12% 8% 3 7% 5% 4 4 3 5% 6% 43%	2280
May	1st to 10th	Day	19% 9% 3 7% 5% 3 4 3 4 7% 37%	3816
	11th to 20th	Day	13% 7% 2 6% 5% 5% 4 3 6% 8% 42%	4082
	21st to end	Day	14% 7% 3 7% 5% 6% 5% 4 5% 8% 34%	4477
June	1st to 10th	Day	7% 5% 3 6% 6% 5% 5% 5% 7% 9% 42%	2470
	11th to 20th	Day	7% 5% 2 6% 6% 6% 6% 5% 7% 8% 44%	2470
	21st to end	Day	4 4 2 5% 5% 4 5% 4 7% 10% 49%	2470
July	1st to 10th	Day	8% 5% 3 6% 5% 5% 6% 4 8% 11% 39%	4120
	11th to 20th	Day	6% 4 1 4 4 4 4 4 6% 10% 53%	4120
	21st to end	Day	13% 9% 3 8% 6% 5% 5% 5% 7% 9% 32%	4465
August	1st to 10th	Day	2 2 1 3 3 3 4 4 6% 9% 63%	4104
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 5% 7% 9% 49%	3823
	21st to end	Day	5% 4 2 6% 5% 5% 6% 5% 8% 10% 46%	4180
September	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 7% 48%	2280
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 4 5% 7% 44%	2168
	21st to end	Day	9% 5% 2 5% 3 4 4 3 4 7% 53%	2034
October	1st to 10th	Day	9% 4 1 5% 3 3 4 2 5% 5% 59%	1900
	11th to 20th	Day	13% 6% 1 4 2 3 2 2 4 5% 58%	1900
	21st to end	Day	16% 6% 2 5% 3 3 2 3 4 4 53%	2090
November	1st to 10th	Day	15% 6% 3 4 2 3 3 3 4 6% 51%	1958
	11th to 20th	Day	11% 6% 2 5% 4 2 3 3 4 6% 54%	2000
	21st to end	Day	20% 7% 2 5% 3 3 3 2 3 4 47%	1911
December	1st to 10th	Day	18% 7% 3 5% 3 3 2 2 4 4 47%	1710
	11th to 20th	Day	14% 8% 3 8% 5% 5% 4 4 3 4 43%	2161
	21st to end	Day	17% 9% 3 8% 4 4 4 4 4 6% 39%	3135
January	1st to 10th	Night	17% 8% 2 5% 4 3 3 2 3 5% 48%	4108
	11th to 20th	Night	18% 6% 1 4 3 2 3 1 3 4 55%	4120
	21st to end	Night	24% 8% 2 4 2 2 2 2 3 4 46%	4532
February	1st to 10th	Night	19% 8% 2 4 3 3 3 3 4 5% 45%	2470
	11th to 20th	Night	20% 8% 3 5% 3 3 3 2 4 5% 44%	2324
	21st to end	Night	20% 7% 2 5% 3 3 3 2 4 4 47%	1739
March	1st to 10th	Night	19% 9% 3 6% 4 3 3 2 4 6% 41%	3419
	11th to 20th	Night	16% 7% 2 6% 3 4 3 3 5% 8% 44%	3480
	21st to end	Night	14% 7% 3 7% 4 3 4 4 5% 7% 43%	3817
April	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 5% 5% 50%	1969
	11th to 20th	Night	13% 5% 3 5% 4 3 4 3 5% 7% 49%	1875
	21st to end	Night	12% 6% 2 5% 4 3 3 3 5% 6% 51%	1900
May	1st to 10th	Night	18% 7% 3 6% 4 4 4 3 6% 7% 38%	3077
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 4 8% 44%	2823
	21st to end	Night	15% 7% 2 5% 4 4 4 3 5% 8% 42%	3090
June	1st to 10th	Night	4 4 2 5% 4 3 4 5% 6% 11% 52%	1710
	11th to 20th	Night	4 4 1 5% 3 4 4 4 6% 7% 59%	1710
	21st to end	Night	4 3 1 3 3 3 4 4 6% 9% 59%	1710
July	1st to 10th	Night	9% 3 2 6% 4 3 5% 5% 7% 11% 46%	2850
	11th to 20th	Night	5% 3 1 4 2 3 3 3 7% 12% 57%	2850
	21st to end	Night	11% 7% 3 7% 5% 5% 4 4 5% 8% 41%	3098
August	1st to 10th	Night	1 2 1 2 2 2 3 3 4 8% 72%	2836
	11th to 20th	Night	5% 2 1 4 3 3 5% 4 7% 12% 53%	3008
	21st to end	Night	4 3 1 5% 3 4 5% 4 8% 9% 53%	3476
September	1st to 10th	Night	5% 4 2 5% 3 4 5% 3 5% 7% 55%	1900
	11th to 20th	Night	9% 6% 2 4 3 4 4 4 6% 8% 50%	2007
	21st to end	Night	7% 5% 2 4 3 2 4 3 4 7% 60%	2125
October	1st to 10th	Night	7% 4 1 3 3 3 3 3 5% 6% 63%	2280
	11th to 20th	Night	12% 4 2 3 2 2 3 2 5% 5% 60%	2280
	21st to end	Night	15% 5% 2 4 3 3 3 2 3 4 56%	2508
November	1st to 10th	Night	13% 5% 1 5% 4 4 3 2 5% 5% 54%	2340
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 3 5% 57%	2400
	21st to end	Night	16% 6% 3 5% 3 3 3 3 3 4 52%	2480
December	1st to 10th	Night	17% 6% 2 6% 2 3 3 3 4 5% 47%	2470
	11th to 20th	Night	17% 6% 2 5% 4 4 4 3 4 4 47%	3036
	21st to end	Night	17% 8% 3 6% 3 3 2 3 4 4 47%	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	47% 1 4 21% 22% 5%	2848
	11th to 20th	Day	41% 1 8% 25% 21% 3	2850
	21st to end	Day	46% 1 4 18% 24% 8%	3135
February	1st to 10th	Day	50% 2 5% 19% 18% 6%	1710
	11th to 20th	Day	47% 2 5% 20% 19% 6%	1753
	21st to end	Day	50% 2 6% 13% 21% 8%	1727
March	1st to 10th	Day	50% 2 5% 13% 21% 8%	3436
	11th to 20th	Day	46% 2 8% 21% 18% 6%	3480
	21st to end	Day	46% 2 7% 20% 23% 2	3814
April	1st to 10th	Day	41% 3 8% 22% 19% 7%	2209
	11th to 20th	Day	43% 3 7% 21% 19% 7%	2254
	21st to end	Day	41% 3 9% 22% 20% 4	2280
May	1st to 10th	Day	49% 2 8% 27% 12% 2	3851
	11th to 20th	Day	42% 3 9% 25% 20% 1	4086
	21st to end	Day	49% 3 12% 22% 10% 3	4489
June	1st to 10th	Day	38% 5% 13% 28% 15% 2	2470
	11th to 20th	Day	35% 5% 12% 27% 18% 3	2470
	21st to end	Day	29% 5% 12% 32% 19% 2	2470
July	1st to 10th	Day	36% 7% 20% 28% 9% 1	4056
	11th to 20th	Day	26% 5% 14% 34% 21% 1	4051
	21st to end	Day	47% 5% 13% 24% 9%	4325
August	1st to 10th	Day	18% 4 16% 29% 27% 7%	4090
	11th to 20th	Day	31% 5% 19% 33% 11% 1	3861
	21st to end	Day	31% 7% 14% 28% 18% 2	4179
September	1st to 10th	Day	35% 6% 11% 19% 20% 9%	2280
	11th to 20th	Day	39% 5% 9% 21% 20% 6%	2168
	21st to end	Day	31% 3 10% 22% 25% 10%	2034
October	1st to 10th	Day	16% 2 6% 12% 27% 37%	3160
	11th to 20th	Day	20% 1 3 18% 35% 23%	3140
	21st to end	Day	30% 2 5% 24% 31% 8%	3428
November	1st to 10th	Day	36% 2 6% 22% 25% 9%	1958
	11th to 20th	Day	34% 2 5% 18% 29% 12%	2000
	21st to end	Day	42% 2 6% 18% 25% 7%	1911
December	1st to 10th	Day	42% 2 9% 21% 19% 7%	1710
	11th to 20th	Day	46% 2 4 16% 24% 8%	2159
	21st to end	Day	48% 2 5% 19% 21% 6%	3135
January	1st to 10th	Night	41% 1 4 19% 30% 5%	4108
	11th to 20th	Night	38% 2 6% 23% 25% 6%	4120
	21st to end	Night	45% 1 7% 16% 23% 8%	4532
February	1st to 10th	Night	43% 2 6% 19% 21% 8%	2470
	11th to 20th	Night	45% 2 6% 19% 20% 8%	2325
	21st to end	Night	43% 2 6% 16% 23% 11%	1739
March	1st to 10th	Night	46% 1 6% 17% 18% 11%	3419
	11th to 20th	Night	41% 2 9% 21% 17% 10%	3480
	21st to end	Night	43% 2 7% 20% 26% 3	3817
April	1st to 10th	Night	37% 2 9% 21% 18% 12%	1969
	11th to 20th	Night	36% 3 7% 21% 21% 11%	1875
	21st to end	Night	35% 2 10% 25% 24% 4	1900
May	1st to 10th	Night	47% 3 9% 24% 13% 4	3107
	11th to 20th	Night	42% 2 9% 27% 19% 2	2824
	21st to end	Night	42% 4 14% 24% 13% 3	3099
June	1st to 10th	Night	27% 5% 14% 32% 18% 3	1710
	11th to 20th	Night	24% 4 11% 33% 24% 4	1710
	21st to end	Night	21% 5% 13% 30% 26% 4	1710
July	1st to 10th	Night	30% 7% 21% 29% 13% 1	2805
	11th to 20th	Night	21% 4 15% 37% 21% 3	2796
	21st to end	Night	41% 5% 13% 27% 14% 1	2999
August	1st to 10th	Night	12% 2 17% 29% 34% 6%	2826
	11th to 20th	Night	23% 5% 20% 32% 18% 3	3036
	21st to end	Night	25% 6% 14% 24% 28% 2	3476
September	1st to 10th	Night	28% 6% 12% 21% 23% 10%	1900
	11th to 20th	Night	32% 4 10% 22% 23% 8%	2007
	21st to end	Night	26% 4 9% 23% 27% 13%	2125
October	1st to 10th	Night	15% 2 7% 14% 24% 38%	3800
	11th to 20th	Night	17% 2 3 15% 35% 28%	3779
	21st to end	Night	26% 2 5% 20% 31% 15%	4120
November	1st to 10th	Night	34% 3 7% 19% 26% 11%	2340
	11th to 20th	Night	31% 2 6% 19% 28% 13%	2400
	21st to end	Night	37% 2 5% 19% 27% 9%	2480
December	1st to 10th	Night	40% 3 8% 20% 21% 8%	2470
	11th to 20th	Night	41% 2 5% 17% 24% 10%	3037
	21st to end	Night	42% 2 6% 21% 25% 5%	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	30% 13% 34% 19% 4	270
	11th to 20th	Day	23% 20% 37% 16% 3 1	270
	21st to end	Day	24% 24% 34% 13% 5%	297
February	1st to 10th	Day	29% 17% 35% 15% 5%	270
	11th to 20th	Day	34% 20% 31% 13% 1	270
	21st to end	Day	39% 26% 28% 6% 2	225
March	1st to 10th	Day	27% 19% 33% 17% 4	270
	11th to 20th	Day	27% 23% 33% 14% 4	270
	21st to end	Day	24% 21% 37% 16% 2	297
April	1st to 10th	Day	23% 17% 35% 17% 8% 1	389
	11th to 20th	Day	26% 14% 31% 20% 7% 1	452
	21st to end	Day	16% 17% 32% 23% 8% 2	460
May	1st to 10th	Day	19% 13% 31% 27% 9% 1	488
	11th to 20th	Day	14% 8% 31% 29% 15% 3	675
	21st to end	Day	11% 7% 25% 34% 18% 4	734
June	1st to 10th	Day	10% 4 16% 32% 28% 9%	680
	11th to 20th	Day	7% 2 17% 38% 29% 8%	680
	21st to end	Day	4 2 19% 34% 30% 10%	680
July	1st to 10th	Day	6% 2 13% 33% 36% 9%	671
	11th to 20th	Day	5% 2 9% 32% 40% 12%	668
	21st to end	Day	8% 1 8% 32% 38% 13%	739
August	1st to 10th	Day	5% 1 11% 32% 41% 11%	676
	11th to 20th	Day	11% 2 7% 33% 36% 11%	537
	21st to end	Day	10% 1 6% 22% 42% 19%	539
September	1st to 10th	Day	8% 2 9% 28% 39% 13%	490
	11th to 20th	Day	11% 3 14% 27% 32% 13%	378
	21st to end	Day	15% 6% 13% 34% 23% 9%	300
October	1st to 10th	Day	6% 2 27% 39% 22% 3	300
	11th to 20th	Day	11% 10% 35% 28% 13% 3	300
	21st to end	Day	24% 9% 28% 27% 10% 2	330
November	1st to 10th	Day	20% 13% 29% 24% 12% 2	300
	11th to 20th	Day	16% 12% 37% 25% 8%	300
	21st to end	Day	23% 16% 31% 18% 10% 2	299
December	1st to 10th	Day	22% 19% 34% 17% 6% 2	270
	11th to 20th	Day	25% 15% 35% 17% 6% 1	270
	21st to end	Day	23% 20% 40% 12% 3 1	297
January	1st to 10th	Night	23% 13% 31% 27% 5%	950
	11th to 20th	Night	24% 15% 31% 24% 5%	950
	21st to end	Night	22% 13% 34% 28% 4	1045
February	1st to 10th	Night	24% 15% 32% 25% 5%	950
	11th to 20th	Night	25% 15% 35% 22% 3	850
	21st to end	Night	24% 18% 34% 21% 4	483
March	1st to 10th	Night	21% 12% 34% 26% 6%	570
	11th to 20th	Night	19% 14% 34% 27% 5% 1	570
	21st to end	Night	19% 13% 37% 26% 6%	627
April	1st to 10th	Night	17% 14% 36% 26% 7%	570
	11th to 20th	Night	13% 14% 36% 26% 10% 1	563
	21st to end	Night	12% 12% 36% 28% 11%	570
May	1st to 10th	Night	12% 8% 33% 36% 10% 1	570
	11th to 20th	Night	14% 5% 32% 31% 17% 2	561
	21st to end	Night	9% 4 25% 36% 22% 3	617
June	1st to 10th	Night	5% 2 13% 41% 36% 3	570
	11th to 20th	Night	4 1 12% 46% 34% 2	570
	21st to end	Night	4 2 10% 39% 38% 7%	570
July	1st to 10th	Night	6% 1 9% 34% 44% 7%	555
	11th to 20th	Night	5% 1 5% 34% 45% 9%	552
	21st to end	Night	5% 1 6% 38% 41% 8%	624
August	1st to 10th	Night	3 1 7% 36% 45% 8%	567
	11th to 20th	Night	7% 9% 38% 37% 8%	564
	21st to end	Night	7% 1 7% 33% 45% 7%	627
September	1st to 10th	Night	7% 1 11% 36% 41% 6%	570
	11th to 20th	Night	12% 1 13% 31% 38% 5%	570
	21st to end	Night	9% 2 13% 38% 35% 4	605
October	1st to 10th	Night	8% 3 13% 39% 33% 3	760
	11th to 20th	Night	13% 5% 24% 37% 19% 1	760
	21st to end	Night	18% 8% 27% 29% 17% 2	836
November	1st to 10th	Night	14% 7% 28% 36% 15% 1	780
	11th to 20th	Night	12% 10% 29% 38% 12%	800
	21st to end	Night	19% 12% 29% 28% 11%	880
December	1st to 10th	Night	22% 9% 31% 30% 8%	950
	11th to 20th	Night	24% 11% 28% 30% 7%	950
	21st to end	Night	22% 13% 31% 27% 6%	1045

Page generated at 2024-11-27 16:30:48. Version ac07

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