Hillsdale Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hillsdale Lake clear sky chart from 2005-11-06 to 2025-03-12.

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	11% 7% 3 6% 4 4 4 3 5% 7% 46%	108864
	Night	11% 7% 2 6% 4 4 4 3 5% 6% 48%	110343
Transparency	Day	36% 6% 12% 26% 17% 3	112514
	Night	35% 5% 11% 26% 19% 4	114820
Seeing	Day	14% 10% 28% 28% 16% 4	16029
	Night	14% 9% 32% 33% 12% 1	26067

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	15% 9% 3 10% 4 4 4 3 4 5% 37%	4077
	11th to 20th	Day	7% 8% 4 10% 6% 7% 5% 2 5% 5% 41%	4080
	21st to end	Day	12% 12% 4 8% 4 3 4 3 4 5% 39%	4488
February	1st to 10th	Day	15% 11% 4 7% 4 3 4 3 4 6% 39%	1800
	11th to 20th	Day	13% 9% 3 6% 6% 4 4 4 4 5% 42%	1759
	21st to end	Day	10% 9% 3 7% 4 4 3 3 6% 6% 45%	1715
March	1st to 10th	Day	12% 9% 3 6% 3 3 3 3 3 5% 48%	3546
	11th to 20th	Day	11% 6% 2 4 3 3 3 2 5% 6% 54%	3491
	21st to end	Day	14% 11% 5% 8% 5% 4 4 3 5% 6% 37%	3814
April	1st to 10th	Day	13% 7% 3 7% 5% 3 3 3 5% 6% 46%	2180
	11th to 20th	Day	15% 8% 2 6% 5% 4 4 3 5% 6% 42%	2254
	21st to end	Day	18% 8% 3 8% 4 5% 4 3 4 5% 37%	2422
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 3 5% 7% 38%	4082
	11th to 20th	Day	15% 8% 2 7% 5% 4 4 3 5% 8% 40%	4082
	21st to end	Day	13% 5% 2 6% 4 4 4 4 5% 8% 44%	4477
June	1st to 10th	Day	7% 4 2 5% 4 4 5% 5% 8% 9% 48%	2636
	11th to 20th	Day	7% 5% 2 5% 5% 4 4 4 7% 10% 47%	2660
	21st to end	Day	6% 4 1 5% 4 4 5% 3 6% 9% 52%	2563
July	1st to 10th	Day	11% 7% 2 6% 5% 5% 5% 4 6% 8% 42%	4120
	11th to 20th	Day	5% 4 1 5% 3 3 4 4 7% 10% 55%	4120
	21st to end	Day	7% 3 2 5% 5% 5% 6% 5% 8% 11% 44%	4465
August	1st to 10th	Day	5% 4 2 5% 4 4 5% 3 6% 8% 54%	4104
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 6% 8% 47%	4041
	21st to end	Day	5% 4 2 4 3 3 4 3 6% 8% 57%	4281
September	1st to 10th	Day	13% 4 1 5% 3 3 3 3 4 7% 54%	2274
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	2090
	21st to end	Day	10% 4 2 5% 3 3 4 4 5% 6% 55%	2090
October	1st to 10th	Day	11% 6% 2 4 3 3 3 3 5% 6% 54%	1900
	11th to 20th	Day	13% 6% 2 4 2 2 2 2 4 5% 57%	1900
	21st to end	Day	15% 7% 2 5% 3 4 3 2 3 5% 49%	2090
November	1st to 10th	Day	10% 6% 1 5% 3 3 3 3 4 6% 55%	1953
	11th to 20th	Day	15% 6% 2 4 3 2 3 2 4 7% 52%	1774
	21st to end	Day	15% 6% 3 6% 3 3 3 3 4 6% 49%	1600
December	1st to 10th	Day	7% 6% 2 6% 4 3 3 3 5% 6% 56%	2610
	11th to 20th	Day	10% 7% 3 7% 4 3 3 3 5% 5% 50%	3008
	21st to end	Day	18% 17% 8% 10% 4 4 3 2 4 4 26%	4318
January	1st to 10th	Night	12% 10% 3 14% 5% 4 4 2 4 5% 37%	5888
	11th to 20th	Night	9% 8% 3 8% 5% 7% 4 3 4 5% 43%	5900
	21st to end	Night	14% 9% 4 9% 4 3 3 3 4 6% 42%	6490
February	1st to 10th	Night	11% 11% 2 7% 5% 4 5% 3 5% 6% 40%	2600
	11th to 20th	Night	12% 9% 3 7% 4 3 3 3 4 7% 43%	2533
	21st to end	Night	12% 7% 3 5% 5% 4 4 3 4 6% 48%	1928
March	1st to 10th	Night	13% 8% 2 4 3 2 3 3 5% 5% 51%	3529
	11th to 20th	Night	10% 6% 2 4 2 3 2 3 5% 7% 56%	3497
	21st to end	Night	15% 9% 3 7% 4 4 3 3 5% 6% 39%	3817
April	1st to 10th	Night	11% 6% 2 6% 4 3 3 3 6% 6% 50%	2000
	11th to 20th	Night	13% 7% 3 6% 4 4 3 3 3 7% 47%	1875
	21st to end	Night	16% 6% 3 6% 4 4 4 4 4 6% 43%	1753
May	1st to 10th	Night	16% 7% 2 6% 4 4 5% 4 5% 6% 41%	2823
	11th to 20th	Night	15% 7% 3 6% 4 3 3 2 5% 7% 44%	2823
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 7% 54%	3090
June	1st to 10th	Night	6% 2 1 4 3 4 5% 4 7% 10% 54%	1534
	11th to 20th	Night	4 3 1 5% 3 4 5% 4 7% 10% 52%	1520
	21st to end	Night	5% 2 1 4 3 3 3 4 6% 9% 60%	1607
July	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 6% 6% 48%	2850
	11th to 20th	Night	3 2 1 4 3 3 4 4 6% 10% 60%	2850
	21st to end	Night	6% 4 2 4 3 5% 6% 5% 8% 11% 47%	3098
August	1st to 10th	Night	3 1 1 3 3 4 5% 4 7% 9% 60%	2836
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 5% 7% 51%	2798
	21st to end	Night	4 3 1 6% 4 4 4 3 5% 7% 60%	3376
September	1st to 10th	Night	10% 4 2 5% 3 3 3 3 4 6% 58%	1902
	11th to 20th	Night	9% 5% 1 4 3 3 4 4 5% 7% 54%	2090
	21st to end	Night	7% 4 2 5% 3 3 4 3 4 6% 58%	2090
October	1st to 10th	Night	10% 4 2 3 3 3 4 3 4 5% 58%	2261
	11th to 20th	Night	12% 5% 2 4 3 2 3 2 3 5% 58%	2280
	21st to end	Night	15% 7% 2 5% 3 3 3 2 3 5% 52%	2508
November	1st to 10th	Night	9% 6% 2 4 3 3 3 2 4 5% 61%	2341
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 5% 7% 54%	2624
	21st to end	Night	15% 7% 2 5% 3 3 2 3 4 4 54%	2800
December	1st to 10th	Night	7% 5% 2 4 3 3 3 4 5% 6% 57%	4580
	11th to 20th	Night	12% 7% 3 6% 4 3 4 3 5% 6% 46%	5199
	21st to end	Night	19% 15% 5% 9% 5% 4 3 3 3 4 30%	6653

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	49% 4 10% 24% 12% 1	4078
	11th to 20th	Day	46% 4 9% 22% 16% 3	4080
	21st to end	Day	47% 4 11% 17% 18% 4	4488
February	1st to 10th	Day	48% 5% 12% 23% 10% 3	1800
	11th to 20th	Day	45% 5% 12% 22% 14% 3	1768
	21st to end	Day	40% 4 11% 25% 17% 4	1715
March	1st to 10th	Day	39% 4 9% 21% 23% 4	3546
	11th to 20th	Day	31% 7% 13% 27% 20% 3	3491
	21st to end	Day	46% 8% 15% 24% 6% 1	3814
April	1st to 10th	Day	40% 5% 11% 23% 18% 2	2180
	11th to 20th	Day	42% 6% 12% 22% 17% 1	2254
	21st to end	Day	49% 6% 11% 23% 11% 1	2422
May	1st to 10th	Day	45% 8% 10% 21% 14% 2	4120
	11th to 20th	Day	40% 9% 14% 22% 14%	4086
	21st to end	Day	37% 9% 13% 27% 12% 2	4489
June	1st to 10th	Day	28% 10% 18% 27% 15% 2	2636
	11th to 20th	Day	30% 9% 14% 29% 16% 2	2660
	21st to end	Day	28% 7% 15% 29% 17% 4	2563
July	1st to 10th	Day	39% 6% 14% 21% 18% 3	4056
	11th to 20th	Day	25% 6% 14% 36% 17% 2	4051
	21st to end	Day	30% 8% 18% 32% 12% 1	4325
August	1st to 10th	Day	27% 7% 14% 28% 22% 3	4090
	11th to 20th	Day	36% 5% 18% 25% 15% 1	4080
	21st to end	Day	25% 5% 15% 35% 15% 4	4280
September	1st to 10th	Day	31% 5% 13% 26% 19% 7%	2274
	11th to 20th	Day	31% 7% 11% 25% 23% 2	2090
	21st to end	Day	29% 6% 9% 27% 25% 3	2090
October	1st to 10th	Day	19% 3 7% 23% 41% 8%	3160
	11th to 20th	Day	19% 2 5% 26% 38% 10%	3140
	21st to end	Day	32% 4 10% 25% 26% 4	3428
November	1st to 10th	Day	31% 5% 11% 29% 19% 5%	1953
	11th to 20th	Day	34% 3 11% 26% 22% 4	1774
	21st to end	Day	39% 3 10% 27% 20% 1	1600
December	1st to 10th	Day	30% 3 12% 38% 17% 1	2610
	11th to 20th	Day	36% 4 11% 32% 15% 1	3005
	21st to end	Day	62% 4 10% 17% 6% 1	4318
January	1st to 10th	Night	50% 5% 12% 22% 11% 1	5888
	11th to 20th	Night	44% 5% 9% 22% 17% 4	5900
	21st to end	Night	45% 4 10% 19% 17% 6%	6490
February	1st to 10th	Night	44% 5% 12% 21% 15% 3	2600
	11th to 20th	Night	42% 5% 11% 23% 16% 3	2534
	21st to end	Night	38% 5% 9% 22% 20% 7%	1928
March	1st to 10th	Night	34% 5% 11% 24% 22% 3	3529
	11th to 20th	Night	28% 6% 10% 26% 27% 4	3497
	21st to end	Night	43% 9% 17% 21% 9% 1	3817
April	1st to 10th	Night	34% 6% 10% 24% 22% 4	2000
	11th to 20th	Night	38% 4 9% 27% 18% 3	1875
	21st to end	Night	41% 6% 12% 25% 14% 2	1753
May	1st to 10th	Night	41% 9% 15% 18% 15% 2	2850
	11th to 20th	Night	39% 7% 14% 27% 13% 1	2824
	21st to end	Night	29% 7% 12% 29% 20% 2	3099
June	1st to 10th	Night	22% 10% 18% 31% 16% 4	1534
	11th to 20th	Night	24% 8% 15% 31% 20% 2	1520
	21st to end	Night	21% 5% 14% 33% 23% 4	1607
July	1st to 10th	Night	34% 7% 12% 24% 19% 4	2805
	11th to 20th	Night	19% 5% 15% 36% 21% 3	2796
	21st to end	Night	28% 7% 19% 31% 14% 1	2999
August	1st to 10th	Night	18% 7% 19% 28% 21% 7%	2826
	11th to 20th	Night	34% 4 14% 27% 19% 2	2825
	21st to end	Night	24% 5% 12% 37% 18% 4	3376
September	1st to 10th	Night	28% 5% 10% 27% 21% 9%	1902
	11th to 20th	Night	29% 6% 11% 24% 25% 4	2090
	21st to end	Night	27% 6% 8% 25% 30% 5%	2090
October	1st to 10th	Night	18% 3 5% 19% 46% 8%	3768
	11th to 20th	Night	22% 3 6% 25% 31% 14%	3779
	21st to end	Night	33% 3 7% 30% 25% 3	4120
November	1st to 10th	Night	28% 3 12% 27% 24% 6%	2341
	11th to 20th	Night	31% 4 8% 26% 25% 5%	2624
	21st to end	Night	36% 3 9% 29% 20% 3	2800
December	1st to 10th	Night	28% 4 14% 33% 19% 1	4580
	11th to 20th	Night	38% 4 11% 27% 17% 2	5201
	21st to end	Night	58% 5% 9% 20% 7% 1	6653

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	19% 15% 35% 25% 5%	300
	11th to 20th	Day	20% 19% 39% 19% 2	300
	21st to end	Day	14% 10% 50% 22% 3	330
February	1st to 10th	Day	24% 16% 38% 20% 2	300
	11th to 20th	Day	21% 17% 41% 16% 5%	300
	21st to end	Day	15% 23% 44% 14% 4	249
March	1st to 10th	Day	17% 18% 42% 19% 4	300
	11th to 20th	Day	23% 17% 34% 20% 5%	273
	21st to end	Day	25% 24% 35% 13% 2 1	297
April	1st to 10th	Day	20% 18% 38% 18% 6% 1	360
	11th to 20th	Day	18% 17% 38% 20% 6%	452
	21st to end	Day	21% 17% 33% 21% 7% 1	602
May	1st to 10th	Day	19% 13% 36% 22% 8% 1	653
	11th to 20th	Day	19% 11% 29% 26% 13% 3	675
	21st to end	Day	15% 10% 30% 25% 16% 4	734
June	1st to 10th	Day	6% 4 21% 36% 25% 8%	680
	11th to 20th	Day	6% 4 27% 37% 21% 4	680
	21st to end	Day	6% 7% 32% 36% 17% 2	680
July	1st to 10th	Day	10% 4 15% 31% 29% 12%	671
	11th to 20th	Day	4 3 16% 39% 30% 7%	668
	21st to end	Day	8% 2 16% 34% 31% 8%	739
August	1st to 10th	Day	7% 3 13% 39% 31% 7%	676
	11th to 20th	Day	9% 3 17% 38% 29% 5%	665
	21st to end	Day	8% 2 13% 30% 36% 10%	601
September	1st to 10th	Day	14% 2 14% 34% 29% 8%	484
	11th to 20th	Day	6% 2 19% 38% 28% 7%	300
	21st to end	Day	13% 6% 23% 38% 14% 6%	300
October	1st to 10th	Day	13% 5% 29% 26% 19% 9%	300
	11th to 20th	Day	12% 15% 37% 24% 10% 1	300
	21st to end	Day	21% 14% 37% 22% 6% 1	330
November	1st to 10th	Day	18% 10% 35% 28% 7% 3	300
	11th to 20th	Day	17% 17% 32% 23% 10% 1	300
	21st to end	Day	20% 12% 37% 22% 8%	300
December	1st to 10th	Day	8% 15% 42% 26% 6% 3	300
	11th to 20th	Day	17% 16% 36% 22% 8% 1	300
	21st to end	Day	23% 21% 37% 18% 2	330
January	1st to 10th	Night	13% 13% 39% 29% 6%	1000
	11th to 20th	Night	15% 14% 40% 27% 5% 1	1000
	21st to end	Night	13% 13% 42% 29% 3	1100
February	1st to 10th	Night	18% 11% 43% 25% 3	1000
	11th to 20th	Night	18% 15% 40% 25% 3	979
	21st to end	Night	17% 13% 43% 23% 3	608
March	1st to 10th	Night	15% 11% 44% 25% 5%	600
	11th to 20th	Night	19% 11% 37% 29% 4	575
	21st to end	Night	24% 13% 34% 25% 4	627
April	1st to 10th	Night	14% 12% 42% 28% 5%	570
	11th to 20th	Night	17% 14% 34% 29% 6%	563
	21st to end	Night	18% 11% 37% 27% 6%	570
May	1st to 10th	Night	18% 7% 35% 32% 8% 1	570
	11th to 20th	Night	15% 7% 30% 34% 13%	561
	21st to end	Night	12% 6% 29% 35% 15% 2	617
June	1st to 10th	Night	6% 4 19% 45% 25% 1	570
	11th to 20th	Night	4 3 28% 45% 19% 1	570
	21st to end	Night	6% 2 30% 47% 13% 1	570
July	1st to 10th	Night	8% 2 13% 44% 30% 2	555
	11th to 20th	Night	3 1 16% 47% 29% 3	552
	21st to end	Night	8% 1 13% 43% 33% 2	624
August	1st to 10th	Night	5% 1 15% 47% 31% 2	567
	11th to 20th	Night	8% 2 12% 46% 30% 2	564
	21st to end	Night	6% 1 13% 40% 38% 2	627
September	1st to 10th	Night	11% 1 19% 41% 25% 2	570
	11th to 20th	Night	10% 2 21% 38% 25% 4	570
	21st to end	Night	7% 5% 22% 44% 19% 3	570
October	1st to 10th	Night	13% 4 27% 35% 20% 2	741
	11th to 20th	Night	16% 7% 40% 29% 8% 1	760
	21st to end	Night	18% 11% 34% 29% 8%	836
November	1st to 10th	Night	11% 8% 37% 31% 11% 1	781
	11th to 20th	Night	12% 14% 37% 29% 8%	1000
	21st to end	Night	19% 11% 35% 30% 6%	1000
December	1st to 10th	Night	16% 10% 38% 29% 6% 1	1000
	11th to 20th	Night	18% 11% 39% 27% 5%	1000
	21st to end	Night	19% 14% 36% 27% 4	1100

Page generated at 2025-03-09 07:08:47. Version ac07

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