Houghton Lake Observatory Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Houghton Lake Observatory Site 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% 11% 4 9% 6% 5% 5% 4 5% 7% 32%	101051
	Night	14% 12% 5% 10% 5% 5% 4 3 5% 6% 31%	98004
Transparency	Day	50% 7% 11% 20% 12% 1	104608
	Night	51% 7% 12% 20% 10% 1	102588
Seeing	Day	20% 16% 30% 21% 10% 3	15643
	Night	19% 12% 32% 26% 10% 1	25376

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	14% 20% 10% 15% 6% 5% 5% 2 4 5% 14%	2527
	11th to 20th	Day	14% 17% 7% 18% 12% 11% 7% 3 3 3 6%	2530
	21st to end	Day	18% 21% 11% 13% 6% 4 4 3 4 5% 10%	2783
February	1st to 10th	Day	10% 17% 6% 13% 12% 6% 6% 3 4 5% 18%	1687
	11th to 20th	Day	11% 15% 7% 14% 10% 5% 6% 4 3 4 20%	1824
	21st to end	Day	12% 17% 6% 14% 8% 4 5% 4 4 4 22%	1570
March	1st to 10th	Day	13% 14% 5% 8% 7% 5% 5% 3 5% 6% 30%	3120
	11th to 20th	Day	12% 10% 7% 15% 6% 4 4 3 5% 6% 28%	3439
	21st to end	Day	19% 12% 6% 9% 6% 5% 5% 3 4 4 25%	3876
April	1st to 10th	Day	17% 17% 4 9% 5% 4 3 3 4 6% 29%	2280
	11th to 20th	Day	18% 13% 3 7% 4 4 3 3 4 5% 35%	2371
	21st to end	Day	15% 11% 3 9% 5% 4 5% 4 5% 7% 32%	2470
May	1st to 10th	Day	14% 9% 3 8% 5% 4 5% 4 5% 7% 35%	4082
	11th to 20th	Day	12% 7% 2 6% 5% 4 5% 4 6% 8% 42%	4102
	21st to end	Day	11% 6% 3 6% 4 4 4 4 5% 8% 45%	4824
June	1st to 10th	Day	12% 6% 3 7% 4 5% 4 4 6% 8% 40%	2755
	11th to 20th	Day	12% 7% 2 5% 4 4 5% 4 6% 8% 40%	2850
	21st to end	Day	13% 7% 2 7% 5% 4 6% 3 6% 8% 38%	2736
July	1st to 10th	Day	13% 7% 2 9% 5% 6% 5% 4 6% 8% 35%	4440
	11th to 20th	Day	7% 6% 2 6% 4 4 6% 4 7% 10% 44%	4440
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 10% 41%	4813
August	1st to 10th	Day	10% 5% 2 7% 6% 5% 6% 5% 8% 9% 38%	4142
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 5% 7% 43%	4044
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 5% 5% 8% 41%	4387
September	1st to 10th	Day	12% 7% 2 6% 5% 5% 5% 4 7% 8% 40%	2223
	11th to 20th	Day	12% 5% 3 6% 4 4 4 3 5% 9% 46%	2090
	21st to end	Day	14% 8% 2 7% 5% 4 5% 4 6% 9% 35%	2090
October	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 4 6% 40%	2081
	11th to 20th	Day	22% 13% 3 10% 6% 5% 4 3 5% 6% 23%	1834
	21st to end	Day	21% 15% 4 10% 5% 5% 5% 4 5% 6% 20%	1881
November	1st to 10th	Day	14% 15% 5% 7% 4 4 5% 4 5% 6% 30%	1708
	11th to 20th	Day	13% 17% 6% 12% 5% 5% 5% 4 5% 6% 21%	1710
	21st to end	Day	21% 18% 8% 11% 6% 4 3 2 4 5% 19%	1612
December	1st to 10th	Day	14% 20% 10% 14% 7% 4 4 4 5% 4 13%	1364
	11th to 20th	Day	16% 19% 5% 14% 7% 6% 4 3 4 4 16%	1675
	21st to end	Day	22% 26% 8% 14% 6% 4 3 2 3 3 8%	2691
January	1st to 10th	Night	14% 17% 9% 16% 6% 5% 4 3 3 4 17%	4428
	11th to 20th	Night	12% 17% 7% 16% 11% 10% 6% 4 4 4 10%	4440
	21st to end	Night	16% 20% 9% 17% 6% 5% 5% 3 5% 4 10%	4884
February	1st to 10th	Night	10% 15% 6% 13% 10% 8% 5% 4 6% 5% 17%	2491
	11th to 20th	Night	13% 13% 6% 13% 7% 6% 5% 4 6% 6% 21%	2240
	21st to end	Night	15% 14% 6% 13% 7% 5% 4 3 5% 5% 24%	1884
March	1st to 10th	Night	15% 9% 5% 8% 4 4 4 3 4 6% 38%	3733
	11th to 20th	Night	9% 12% 5% 9% 4 4 4 3 5% 7% 37%	3521
	21st to end	Night	14% 13% 6% 11% 5% 4 4 4 5% 5% 30%	3772
April	1st to 10th	Night	15% 15% 4 8% 5% 4 4 3 5% 6% 32%	1900
	11th to 20th	Night	18% 12% 3 5% 4 3 4 3 5% 6% 36%	1756
	21st to end	Night	16% 11% 3 7% 4 3 4 3 5% 5% 38%	1710
May	1st to 10th	Night	13% 8% 2 7% 5% 5% 4 4 5% 6% 41%	2813
	11th to 20th	Night	12% 7% 3 6% 5% 4 5% 4 5% 8% 40%	2789
	21st to end	Night	16% 6% 2 5% 3 3 4 3 5% 7% 45%	2743
June	1st to 10th	Night	14% 6% 2 5% 5% 4 4 3 6% 8% 42%	1416
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 7% 9% 45%	1330
	21st to end	Night	9% 7% 2 7% 6% 3 5% 3 7% 6% 45%	1435
July	1st to 10th	Night	9% 7% 2 7% 5% 5% 5% 5% 7% 8% 40%	2530
	11th to 20th	Night	6% 4 2 5% 3 3 4 4 5% 8% 55%	2530
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 7% 7% 49%	2750
August	1st to 10th	Night	10% 5% 2 5% 4 5% 5% 4 6% 8% 45%	2785
	11th to 20th	Night	13% 6% 2 4 3 3 4 2 5% 8% 50%	2785
	21st to end	Night	9% 7% 2 6% 4 4 4 4 6% 7% 47%	3252
September	1st to 10th	Night	10% 6% 2 5% 3 3 4 4 5% 7% 51%	1938
	11th to 20th	Night	11% 6% 2 4 3 3 4 4 5% 7% 52%	2090
	21st to end	Night	15% 7% 2 8% 4 3 4 4 6% 6% 41%	2090
October	1st to 10th	Night	15% 10% 3 6% 3 3 3 2 4 6% 44%	2099
	11th to 20th	Night	19% 12% 4 9% 4 4 3 3 4 6% 32%	2342
	21st to end	Night	22% 15% 3 8% 4 3 4 3 5% 7% 27%	2717
November	1st to 10th	Night	11% 14% 3 7% 4 4 5% 3 5% 8% 34%	2470
	11th to 20th	Night	14% 16% 4 11% 7% 5% 5% 4 5% 5% 23%	2470
	21st to end	Night	17% 18% 7% 11% 5% 4 4 3 5% 5% 20%	2565
December	1st to 10th	Night	14% 18% 6% 13% 7% 6% 6% 4 5% 5% 16%	2813
	11th to 20th	Night	14% 19% 6% 15% 7% 5% 5% 3 5% 5% 15%	3522
	21st to end	Night	24% 25% 7% 12% 5% 4 3 2 3 3 11%	4971

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	72% 9% 10% 6% 3	2528
	11th to 20th	Day	82% 6% 5% 5% 1	2530
	21st to end	Day	75% 7% 12% 4 2	2783
February	1st to 10th	Day	69% 6% 7% 14% 4 1	1687
	11th to 20th	Day	66% 6% 10% 12% 6% 1	1834
	21st to end	Day	64% 5% 11% 16% 4 1	1570
March	1st to 10th	Day	53% 8% 11% 19% 8% 1	3120
	11th to 20th	Day	53% 8% 13% 18% 7% 2	3439
	21st to end	Day	59% 7% 8% 16% 9% 1	3876
April	1st to 10th	Day	57% 5% 10% 16% 11% 1	2280
	11th to 20th	Day	51% 5% 10% 19% 15% 1	2371
	21st to end	Day	51% 6% 12% 15% 13% 2	2470
May	1st to 10th	Day	44% 9% 10% 18% 17% 2	4120
	11th to 20th	Day	37% 9% 14% 25% 14% 1	4106
	21st to end	Day	36% 8% 13% 21% 20% 3	4837
June	1st to 10th	Day	40% 7% 12% 25% 14% 2	2755
	11th to 20th	Day	39% 8% 12% 22% 17% 2	2850
	21st to end	Day	42% 7% 13% 23% 14% 1	2736
July	1st to 10th	Day	46% 6% 13% 20% 14% 2	4371
	11th to 20th	Day	33% 7% 14% 30% 16% 1	4365
	21st to end	Day	36% 8% 14% 23% 18% 1	4662
August	1st to 10th	Day	39% 8% 12% 26% 14% 1	4127
	11th to 20th	Day	39% 6% 12% 28% 14% 1	4083
	21st to end	Day	41% 6% 12% 26% 14% 1	4386
September	1st to 10th	Day	39% 8% 13% 24% 14% 2	2223
	11th to 20th	Day	36% 7% 15% 27% 15% 1	2090
	21st to end	Day	44% 7% 14% 25% 10%	2090
October	1st to 10th	Day	34% 5% 8% 32% 18% 3	3458
	11th to 20th	Day	51% 4 9% 22% 14%	3024
	21st to end	Day	61% 6% 11% 17% 6%	3081
November	1st to 10th	Day	52% 8% 12% 19% 8%	1708
	11th to 20th	Day	62% 8% 13% 11% 5%	1710
	21st to end	Day	69% 6% 12% 10% 3	1612
December	1st to 10th	Day	72% 7% 9% 10% 2	1364
	11th to 20th	Day	69% 7% 10% 11% 2	1671
	21st to end	Day	81% 5% 7% 5% 2	2691
January	1st to 10th	Night	68% 7% 10% 13% 3	4428
	11th to 20th	Night	77% 7% 7% 7% 2	4440
	21st to end	Night	74% 8% 9% 6% 2	4884
February	1st to 10th	Night	65% 6% 9% 12% 6% 1	2491
	11th to 20th	Night	61% 7% 11% 16% 6%	2241
	21st to end	Night	62% 5% 11% 14% 7%	1884
March	1st to 10th	Night	46% 7% 15% 23% 9% 1	3733
	11th to 20th	Night	42% 8% 14% 23% 11% 1	3521
	21st to end	Night	52% 9% 12% 18% 8% 1	3772
April	1st to 10th	Night	52% 5% 10% 19% 13% 1	1900
	11th to 20th	Night	48% 5% 9% 19% 16% 2	1756
	21st to end	Night	45% 7% 11% 19% 16% 2	1710
May	1st to 10th	Night	40% 9% 12% 17% 18% 3	2840
	11th to 20th	Night	38% 8% 10% 29% 13% 1	2790
	21st to end	Night	38% 7% 13% 21% 16% 5%	2751
June	1st to 10th	Night	38% 7% 11% 24% 19% 1	1416
	11th to 20th	Night	33% 8% 15% 24% 18% 2	1330
	21st to end	Night	36% 7% 12% 27% 16% 2	1435
July	1st to 10th	Night	40% 5% 13% 24% 13% 5%	2490
	11th to 20th	Night	26% 6% 13% 37% 17% 1	2482
	21st to end	Night	32% 7% 16% 25% 19% 1	2662
August	1st to 10th	Night	35% 7% 15% 28% 14% 1	2776
	11th to 20th	Night	32% 5% 16% 32% 15%	2812
	21st to end	Night	35% 6% 14% 27% 18% 1	3252
September	1st to 10th	Night	31% 7% 13% 29% 18% 2	1938
	11th to 20th	Night	30% 6% 15% 34% 15%	2090
	21st to end	Night	42% 7% 13% 29% 8% 1	2090
October	1st to 10th	Night	33% 4 12% 33% 17% 1	3502
	11th to 20th	Night	45% 4 11% 25% 15%	3891
	21st to end	Night	51% 4 12% 26% 7%	4467
November	1st to 10th	Night	47% 7% 13% 22% 10% 1	2470
	11th to 20th	Night	59% 8% 13% 14% 6% 1	2470
	21st to end	Night	66% 6% 14% 12% 2 1	2565
December	1st to 10th	Night	68% 8% 9% 12% 3	2813
	11th to 20th	Night	68% 8% 12% 9% 3	3525
	21st to end	Night	78% 6% 7% 5% 3	4971

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	26% 19% 37% 13% 5%	270
	11th to 20th	Day	26% 18% 42% 11% 3	270
	21st to end	Day	30% 16% 35% 15% 4 1	297
February	1st to 10th	Day	21% 29% 36% 11% 3 1	270
	11th to 20th	Day	23% 30% 36% 10% 1	270
	21st to end	Day	29% 30% 35% 5% 1	225
March	1st to 10th	Day	29% 26% 36% 9% 1	270
	11th to 20th	Day	23% 19% 35% 16% 5% 1	432
	21st to end	Day	30% 16% 28% 19% 5% 1	506
April	1st to 10th	Day	26% 20% 33% 15% 5% 1	460
	11th to 20th	Day	30% 21% 27% 14% 7% 2	452
	21st to end	Day	25% 17% 27% 22% 7% 2	460
May	1st to 10th	Day	24% 20% 30% 18% 5% 3	463
	11th to 20th	Day	19% 14% 31% 25% 7% 4	495
	21st to end	Day	15% 12% 33% 25% 12% 3	734
June	1st to 10th	Day	15% 16% 31% 26% 9% 3	680
	11th to 20th	Day	15% 15% 33% 23% 10% 3	680
	21st to end	Day	16% 12% 32% 26% 11% 3	680
July	1st to 10th	Day	8% 9% 30% 29% 17% 7%	671
	11th to 20th	Day	10% 10% 29% 30% 16% 6%	668
	21st to end	Day	9% 7% 31% 31% 15% 6%	739
August	1st to 10th	Day	10% 7% 26% 30% 18% 10%	512
	11th to 20th	Day	11% 7% 23% 30% 19% 9%	479
	21st to end	Day	17% 8% 24% 27% 18% 6%	539
September	1st to 10th	Day	16% 11% 26% 24% 16% 8%	490
	11th to 20th	Day	10% 9% 24% 28% 21% 8%	490
	21st to end	Day	19% 12% 23% 27% 14% 5%	490
October	1st to 10th	Day	25% 14% 26% 19% 13% 2	490
	11th to 20th	Day	29% 17% 35% 17% 3	424
	21st to end	Day	31% 24% 31% 9% 4 1	330
November	1st to 10th	Day	24% 20% 36% 15% 4 1	282
	11th to 20th	Day	26% 22% 37% 13% 2	270
	21st to end	Day	25% 28% 33% 12% 3	223
December	1st to 10th	Day	32% 21% 32% 7% 7% 1	180
	11th to 20th	Day	32% 23% 32% 11% 2	180
	21st to end	Day	29% 29% 31% 8% 2	272
January	1st to 10th	Night	21% 18% 35% 19% 6%	950
	11th to 20th	Night	24% 16% 33% 21% 5% 1	950
	21st to end	Night	19% 13% 40% 23% 5%	1045
February	1st to 10th	Night	18% 17% 38% 22% 4	781
	11th to 20th	Night	22% 19% 33% 21% 4	743
	21st to end	Night	24% 20% 36% 17% 3	628
March	1st to 10th	Night	19% 16% 36% 21% 8% 1	760
	11th to 20th	Night	20% 18% 34% 22% 6%	760
	21st to end	Night	22% 15% 34% 23% 5% 1	816
April	1st to 10th	Night	20% 15% 36% 23% 5%	570
	11th to 20th	Night	23% 14% 33% 24% 5%	563
	21st to end	Night	22% 10% 31% 30% 6% 1	570
May	1st to 10th	Night	15% 10% 36% 30% 8%	570
	11th to 20th	Night	16% 9% 33% 31% 11% 1	561
	21st to end	Night	15% 7% 30% 32% 16% 1	617
June	1st to 10th	Night	15% 8% 31% 35% 11%	466
	11th to 20th	Night	11% 7% 33% 38% 11%	380
	21st to end	Night	12% 6% 30% 34% 16% 1	485
July	1st to 10th	Night	8% 3 21% 45% 22% 2	555
	11th to 20th	Night	7% 4 25% 39% 22% 3	552
	21st to end	Night	11% 3 24% 40% 21% 1	624
August	1st to 10th	Night	10% 2 23% 40% 22% 2	567
	11th to 20th	Night	8% 4 20% 35% 29% 3	564
	21st to end	Night	13% 5% 22% 40% 19% 1	627
September	1st to 10th	Night	11% 6% 26% 32% 21% 4	608
	11th to 20th	Night	12% 6% 23% 35% 21% 4	760
	21st to end	Night	18% 8% 27% 29% 15% 3	760
October	1st to 10th	Night	20% 11% 27% 28% 14% 1	760
	11th to 20th	Night	24% 14% 30% 25% 6% 1	760
	21st to end	Night	32% 14% 28% 22% 5%	836
November	1st to 10th	Night	20% 12% 36% 22% 8% 1	760
	11th to 20th	Night	23% 17% 36% 20% 4	760
	21st to end	Night	25% 15% 37% 19% 3	760
December	1st to 10th	Night	24% 17% 35% 20% 4	913
	11th to 20th	Night	24% 18% 38% 15% 4 1	950
	21st to end	Night	30% 14% 35% 19% 2	1045

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