Hillsdale Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hillsdale Lake clear sky chart from 2005-11-05 to 2024-10-14.

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%	100728
	Night	11% 7% 2 6% 4 4 4 3 5% 6% 49%	97904
Transparency	Day	37% 6% 13% 25% 16% 2	100540
	Night	36% 6% 12% 25% 18% 3	97768
Seeing	Day	14% 10% 28% 28% 17% 4	15582
	Night	14% 9% 32% 33% 12% 1	25384

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% 10% 3 10% 5% 4 4 4 5% 6% 37%	2847
	11th to 20th	Day	10% 9% 4 9% 6% 7% 6% 2 5% 4 39%	2850
	21st to end	Day	13% 15% 6% 9% 4 3 3 3 4 5% 36%	3135
February	1st to 10th	Day	15% 11% 5% 7% 4 3 4 3 4 6% 39%	1710
	11th to 20th	Day	12% 9% 3 6% 5% 4 4 4 4 5% 42%	1668
	21st to end	Day	11% 9% 3 7% 4 4 4 3 6% 6% 44%	1632
March	1st to 10th	Day	13% 9% 3 6% 3 3 3 3 3 5% 48%	3436
	11th to 20th	Day	11% 6% 2 4 3 3 3 2 5% 6% 53%	3480
	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 5% 2 2 3 2 4 5% 56%	1830
	21st to end	Day	16% 7% 2 5% 3 3 3 2 3 5% 48%	1980
November	1st to 10th	Day	10% 6% 1 5% 3 3 4 3 4 6% 56%	1854
	11th to 20th	Day	15% 6% 2 4 3 2 3 2 4 7% 52%	1686
	21st to end	Day	15% 7% 3 6% 3 3 3 2 4 5% 49%	1520
December	1st to 10th	Day	11% 8% 3 6% 5% 3 3 3 5% 7% 47%	1520
	11th to 20th	Day	12% 9% 4 9% 4 4 4 3 5% 5% 42%	1918
	21st to end	Day	16% 14% 8% 11% 4 4 4 3 4 5% 26%	3007
January	1st to 10th	Night	9% 9% 3 14% 5% 4 4 3 4 5% 41%	4108
	11th to 20th	Night	10% 9% 3 8% 6% 8% 5% 4 4 5% 38%	4120
	21st to end	Night	16% 12% 5% 9% 4 3 3 3 4 5% 37%	4532
February	1st to 10th	Night	11% 11% 2 7% 5% 4 5% 3 5% 5% 40%	2470
	11th to 20th	Night	12% 9% 3 7% 4 3 3 3 4 7% 44%	2403
	21st to end	Night	12% 7% 3 5% 5% 4 4 3 4 6% 47%	1836
March	1st to 10th	Night	13% 8% 2 4 3 2 3 3 5% 5% 51%	3419
	11th to 20th	Night	10% 6% 2 4 2 3 2 3 5% 7% 55%	3480
	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	13% 5% 2 5% 3 2 3 2 3 5% 57%	2203
	21st to end	Night	15% 7% 3 5% 3 3 3 2 3 4 52%	2376
November	1st to 10th	Night	8% 5% 2 4 3 3 3 2 4 5% 61%	2220
	11th to 20th	Night	10% 6% 2 4 3 3 3 3 5% 7% 53%	2492
	21st to end	Night	15% 7% 2 5% 2 3 3 3 4 4 53%	2660
December	1st to 10th	Night	11% 8% 3 5% 4 3 4 4 5% 6% 47%	2660
	11th to 20th	Night	12% 8% 3 7% 4 3 4 3 5% 6% 45%	3279
	21st to end	Night	19% 15% 5% 9% 4 4 3 2 3 4 31%	4653

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% 5% 10% 24% 13% 1	2848
	11th to 20th	Day	49% 4 12% 22% 11% 1	2850
	21st to end	Day	51% 5% 12% 16% 16% 1	3135
February	1st to 10th	Day	47% 5% 12% 23% 10% 3	1710
	11th to 20th	Day	44% 5% 13% 22% 14% 2	1677
	21st to end	Day	41% 4 11% 23% 16% 5%	1632
March	1st to 10th	Day	39% 5% 9% 21% 22% 3	3436
	11th to 20th	Day	31% 7% 13% 27% 19% 3	3480
	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	31% 5% 11% 27% 23% 3	1900
	11th to 20th	Day	31% 4 8% 26% 25% 5%	1830
	21st to end	Day	39% 5% 11% 21% 19% 5%	1980
November	1st to 10th	Day	30% 5% 12% 29% 19% 5%	1854
	11th to 20th	Day	34% 3 11% 27% 22% 4	1686
	21st to end	Day	39% 3 9% 26% 20% 2	1520
December	1st to 10th	Day	37% 4 14% 31% 13% 1	1520
	11th to 20th	Day	43% 6% 12% 25% 12% 2	1915
	21st to end	Day	58% 6% 10% 17% 8% 2	3007
January	1st to 10th	Night	45% 6% 14% 22% 12% 1	4108
	11th to 20th	Night	48% 6% 11% 21% 13% 1	4120
	21st to end	Night	50% 5% 12% 20% 11% 2	4532
February	1st to 10th	Night	45% 6% 11% 21% 15% 3	2470
	11th to 20th	Night	40% 5% 11% 23% 17% 3	2404
	21st to end	Night	38% 5% 9% 22% 19% 7%	1836
March	1st to 10th	Night	34% 6% 12% 23% 22% 3	3419
	11th to 20th	Night	28% 6% 10% 26% 27% 4	3480
	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	28% 5% 8% 25% 28% 6%	2261
	11th to 20th	Night	31% 4 7% 27% 23% 7%	2208
	21st to end	Night	37% 4 8% 23% 24% 4	2376
November	1st to 10th	Night	27% 3 12% 27% 24% 6%	2220
	11th to 20th	Night	31% 5% 9% 26% 25% 4	2492
	21st to end	Night	36% 3 9% 28% 20% 3	2660
December	1st to 10th	Night	37% 6% 13% 26% 17% 1	2660
	11th to 20th	Night	38% 6% 11% 27% 16% 2	3281
	21st to end	Night	57% 6% 8% 19% 9% 2	4653

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% 16% 35% 25% 5%	270
	11th to 20th	Day	23% 19% 37% 19% 2	270
	21st to end	Day	14% 11% 49% 22% 3	297
February	1st to 10th	Day	23% 16% 37% 20% 3	270
	11th to 20th	Day	19% 16% 42% 17% 6%	270
	21st to end	Day	16% 25% 42% 13% 4	225
March	1st to 10th	Day	17% 18% 43% 18% 3	270
	11th to 20th	Day	23% 17% 35% 20% 5%	270
	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	13% 15% 39% 23% 8% 1	279
	21st to end	Day	22% 14% 36% 22% 5% 1	297
November	1st to 10th	Day	17% 10% 34% 29% 8% 3	270
	11th to 20th	Day	16% 17% 33% 23% 10% 1	270
	21st to end	Day	21% 11% 37% 21% 9%	270
December	1st to 10th	Day	9% 16% 41% 26% 6% 3	270
	11th to 20th	Day	18% 16% 34% 23% 9% 1	270
	21st to end	Day	21% 21% 39% 19% 1	297
January	1st to 10th	Night	13% 13% 39% 29% 6%	950
	11th to 20th	Night	15% 14% 39% 27% 5% 1	950
	21st to end	Night	13% 13% 40% 30% 3	1045
February	1st to 10th	Night	18% 11% 43% 24% 3	950
	11th to 20th	Night	17% 14% 40% 26% 3	929
	21st to end	Night	18% 14% 43% 22% 3 1	580
March	1st to 10th	Night	14% 11% 44% 25% 5%	570
	11th to 20th	Night	19% 11% 36% 29% 4	570
	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% 41% 29% 7% 1	735
	21st to end	Night	18% 11% 34% 28% 8%	792
November	1st to 10th	Night	11% 8% 38% 31% 12% 1	740
	11th to 20th	Night	12% 13% 37% 29% 8%	950
	21st to end	Night	19% 11% 34% 30% 5%	950
December	1st to 10th	Night	17% 10% 37% 29% 6% 1	950
	11th to 20th	Night	18% 10% 39% 28% 5%	950
	21st to end	Night	19% 14% 36% 26% 4	1045

Page generated at 2024-10-11 09:50:00. Version ac07

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