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 2024-04-25.

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	14% 11% 5% 8% 7% 4 5% 5% 5% 7% 30%	82896
	Night	14% 12% 5% 9% 7% 3 5% 4 5% 6% 30%	86241
Transparency	Day	53% 7% 11% 18% 10% 1	82596
	Night	53% 7% 12% 18% 9% 1	86062
Seeing	Day	20% 15% 30% 21% 10% 3	14813
	Night	19% 12% 32% 26% 10% 1	24756

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% 19% 11% 15% 7% 4 4 4 4 5% 14%	2527
	11th to 20th	Day	14% 16% 7% 15% 15% 9% 7% 4 3 3 6%	2530
	21st to end	Day	19% 20% 12% 12% 7% 4 4 4 4 5% 10%	2783
February	1st to 10th	Day	11% 15% 7% 12% 13% 5% 7% 4 4 5% 18%	1687
	11th to 20th	Day	11% 14% 8% 13% 11% 4 6% 5% 4 4 20%	1824
	21st to end	Day	12% 15% 7% 12% 10% 3 5% 5% 4 4 22%	1570
March	1st to 10th	Day	13% 13% 6% 7% 7% 4 5% 4 5% 6% 30%	3120
	11th to 20th	Day	12% 10% 7% 14% 7% 3 4 5% 5% 5% 28%	3439
	21st to end	Day	19% 11% 7% 8% 7% 4 5% 4 4 5% 25%	3876
April	1st to 10th	Day	17% 15% 5% 8% 6% 3 3 3 4 6% 29%	2280
	11th to 20th	Day	19% 12% 4 6% 5% 3 4 4 4 5% 36%	2371
	21st to end	Day	15% 11% 3 8% 6% 3 5% 5% 5% 7% 32%	2394
May	1st to 10th	Day	16% 9% 4 7% 6% 3 5% 5% 5% 6% 34%	2340
	11th to 20th	Day	16% 8% 3 6% 6% 4 5% 5% 6% 6% 37%	2308
	21st to end	Day	11% 6% 3 6% 5% 4 5% 5% 5% 9% 42%	2725
June	1st to 10th	Day	13% 6% 3 6% 5% 4 4 5% 6% 8% 41%	2610
	11th to 20th	Day	12% 7% 2 5% 5% 3 5% 6% 6% 9% 41%	2700
	21st to end	Day	12% 6% 3 6% 6% 3 5% 5% 6% 9% 38%	2593
July	1st to 10th	Day	7% 4 2 5% 5% 4 6% 5% 6% 9% 47%	2520
	11th to 20th	Day	9% 6% 3 6% 5% 3 6% 5% 6% 10% 41%	2520
	21st to end	Day	9% 4 2 6% 6% 4 7% 6% 7% 9% 41%	2743
August	1st to 10th	Day	9% 5% 3 5% 7% 3 6% 6% 7% 10% 39%	2352
	11th to 20th	Day	10% 6% 2 5% 6% 4 5% 6% 6% 8% 42%	2303
	21st to end	Day	12% 7% 3 6% 5% 3 4 5% 4 9% 42%	2499
September	1st to 10th	Day	13% 7% 2 5% 6% 4 5% 5% 7% 8% 39%	2106
	11th to 20th	Day	13% 5% 3 5% 5% 3 5% 4 5% 9% 44%	1980
	21st to end	Day	15% 7% 3 6% 6% 3 5% 6% 6% 9% 34%	1980
October	1st to 10th	Day	17% 10% 3 6% 5% 3 5% 4 5% 6% 37%	1972
	11th to 20th	Day	24% 12% 3 9% 7% 4 5% 4 5% 6% 22%	1738
	21st to end	Day	22% 15% 4 9% 6% 4 5% 5% 4 5% 21%	1782
November	1st to 10th	Day	14% 14% 5% 6% 5% 3 5% 5% 5% 7% 30%	1672
	11th to 20th	Day	14% 16% 6% 11% 6% 4 5% 5% 5% 6% 21%	1710
	21st to end	Day	21% 17% 8% 11% 7% 3 3 3 3 5% 19%	1612
December	1st to 10th	Day	14% 19% 11% 13% 8% 3 5% 5% 4 5% 13%	1364
	11th to 20th	Day	16% 18% 6% 13% 8% 5% 5% 4 4 5% 16%	1675
	21st to end	Day	23% 25% 8% 13% 7% 3 4 3 3 3 8%	2691
January	1st to 10th	Night	15% 17% 9% 14% 8% 4 5% 4 3 4 17%	4428
	11th to 20th	Night	12% 15% 8% 14% 13% 8% 7% 5% 4 4 10%	4440
	21st to end	Night	16% 19% 10% 16% 8% 3 5% 4 5% 4 10%	4884
February	1st to 10th	Night	11% 14% 7% 11% 11% 6% 6% 6% 5% 5% 17%	2491
	11th to 20th	Night	13% 12% 7% 12% 8% 5% 6% 5% 5% 6% 21%	2240
	21st to end	Night	15% 13% 6% 11% 8% 4 5% 4 4 5% 24%	1884
March	1st to 10th	Night	15% 8% 5% 7% 5% 3 4 4 4 6% 38%	3733
	11th to 20th	Night	10% 11% 6% 8% 5% 3 4 4 6% 7% 37%	3521
	21st to end	Night	14% 12% 7% 8% 7% 3 4 5% 5% 5% 30%	3772
April	1st to 10th	Night	15% 14% 5% 7% 5% 3 4 4 5% 7% 32%	1900
	11th to 20th	Night	19% 11% 3 5% 5% 2 4 4 4 6% 36%	1756
	21st to end	Night	15% 10% 3 6% 5% 3 4 4 5% 5% 39%	1665
May	1st to 10th	Night	14% 7% 3 7% 7% 4 5% 5% 5% 7% 36%	1620
	11th to 20th	Night	13% 7% 4 6% 7% 3 5% 5% 5% 7% 37%	1582
	21st to end	Night	13% 5% 2 5% 4 2 5% 5% 4 9% 46%	1551
June	1st to 10th	Night	14% 5% 3 4 5% 3 5% 4 5% 9% 44%	1342
	11th to 20th	Night	9% 4 2 5% 4 4 6% 5% 7% 9% 45%	1260
	21st to end	Night	9% 7% 2 6% 6% 2 5% 5% 7% 7% 46%	1359
July	1st to 10th	Night	6% 3 2 3 4 3 4 5% 7% 9% 53%	1440
	11th to 20th	Night	5% 4 3 5% 5% 3 4 5% 6% 9% 51%	1440
	21st to end	Night	8% 5% 2 5% 5% 3 5% 4 6% 7% 49%	1575
August	1st to 10th	Night	7% 5% 2 4 5% 3 5% 5% 6% 9% 49%	1583
	11th to 20th	Night	8% 4 1 4 4 2 5% 4 6% 10% 52%	1598
	21st to end	Night	10% 7% 2 5% 4 3 4 5% 5% 8% 47%	1854
September	1st to 10th	Night	11% 5% 2 5% 3 3 4 5% 5% 7% 50%	1836
	11th to 20th	Night	12% 6% 2 4 3 2 4 5% 5% 7% 51%	1980
	21st to end	Night	15% 6% 3 7% 6% 3 3 5% 6% 7% 40%	1980
October	1st to 10th	Night	16% 10% 4 5% 4 2 3 3 4 6% 43%	1988
	11th to 20th	Night	20% 11% 4 8% 6% 4 3 3 4 7% 30%	2218
	21st to end	Night	24% 14% 3 6% 6% 2 3 4 4 7% 26%	2574
November	1st to 10th	Night	11% 13% 4 7% 5% 3 5% 5% 5% 8% 34%	2406
	11th to 20th	Night	14% 14% 5% 10% 8% 4 5% 5% 5% 5% 24%	2470
	21st to end	Night	17% 16% 8% 10% 7% 3 4 4 5% 5% 20%	2565
December	1st to 10th	Night	15% 16% 7% 13% 8% 4 6% 5% 4 5% 16%	2813
	11th to 20th	Night	15% 18% 7% 14% 8% 4 5% 5% 5% 5% 15%	3522
	21st to end	Night	25% 24% 8% 11% 6% 3 4 3 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	50% 7% 12% 15% 13% 3	2394
May	1st to 10th	Day	49% 7% 9% 22% 11% 2	2340
	11th to 20th	Day	45% 7% 11% 21% 13% 2	2312
	21st to end	Day	39% 8% 14% 24% 13% 1	2725
June	1st to 10th	Day	40% 7% 12% 25% 14% 2	2610
	11th to 20th	Day	39% 8% 13% 22% 17% 2	2700
	21st to end	Day	41% 7% 14% 23% 14% 1	2593
July	1st to 10th	Day	31% 8% 14% 26% 18% 2	2451
	11th to 20th	Day	37% 8% 13% 24% 17% 1	2445
	21st to end	Day	36% 9% 15% 22% 17% 2	2591
August	1st to 10th	Day	38% 10% 15% 24% 12% 1	2337
	11th to 20th	Day	38% 8% 15% 25% 13% 1	2303
	21st to end	Day	40% 7% 13% 24% 15% 2	2499
September	1st to 10th	Day	40% 9% 13% 23% 14% 2	2106
	11th to 20th	Day	37% 7% 15% 28% 12% 1	1980
	21st to end	Day	45% 7% 15% 25% 8%	1980
October	1st to 10th	Day	47% 7% 10% 24% 11% 1	1972
	11th to 20th	Day	62% 7% 10% 16% 5%	1738
	21st to end	Day	64% 8% 11% 11% 6%	1782
November	1st to 10th	Day	52% 8% 12% 19% 9%	1672
	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% 3	1665
May	1st to 10th	Night	45% 8% 13% 20% 12% 3	1620
	11th to 20th	Night	45% 7% 11% 21% 15% 2	1583
	21st to end	Night	36% 7% 14% 26% 14% 3	1552
June	1st to 10th	Night	37% 6% 12% 25% 19% 1	1342
	11th to 20th	Night	33% 8% 15% 24% 18% 2	1260
	21st to end	Night	35% 7% 12% 27% 16% 2	1359
July	1st to 10th	Night	24% 7% 14% 32% 20% 3	1400
	11th to 20th	Night	28% 8% 15% 30% 19% 1	1392
	21st to end	Night	32% 8% 14% 26% 17% 2	1487
August	1st to 10th	Night	30% 9% 19% 29% 13% 1	1574
	11th to 20th	Night	27% 8% 16% 32% 16% 1	1598
	21st to end	Night	34% 7% 14% 26% 17% 2	1854
September	1st to 10th	Night	32% 8% 13% 27% 18% 2	1836
	11th to 20th	Night	31% 6% 16% 34% 13%	1980
	21st to end	Night	42% 7% 14% 29% 7% 1	1980
October	1st to 10th	Night	42% 6% 12% 25% 13% 1	1988
	11th to 20th	Night	55% 5% 12% 21% 7% 1	2218
	21st to end	Night	58% 6% 12% 17% 7%	2574
November	1st to 10th	Night	46% 7% 13% 22% 10% 1	2406
	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% 8% 2	437
May	1st to 10th	Day	24% 21% 29% 17% 5% 3	423
	11th to 20th	Day	19% 14% 31% 24% 7% 4	454
	21st to end	Day	15% 12% 33% 24% 13% 4	679
June	1st to 10th	Day	15% 15% 32% 27% 9% 3	630
	11th to 20th	Day	16% 14% 32% 25% 11% 3	630
	21st to end	Day	15% 11% 33% 28% 12% 3	630
July	1st to 10th	Day	7% 8% 30% 29% 18% 7%	621
	11th to 20th	Day	10% 10% 29% 30% 15% 6%	618
	21st to end	Day	10% 8% 32% 30% 14% 6%	684
August	1st to 10th	Day	10% 5% 25% 30% 19% 10%	471
	11th to 20th	Day	10% 7% 22% 31% 19% 10%	439
	21st to end	Day	18% 8% 24% 27% 18% 6%	495
September	1st to 10th	Day	16% 10% 26% 24% 16% 8%	450
	11th to 20th	Day	10% 10% 25% 28% 19% 8%	450
	21st to end	Day	20% 12% 22% 27% 14% 6%	450
October	1st to 10th	Day	26% 14% 25% 20% 14% 2	450
	11th to 20th	Day	31% 17% 33% 16% 3	388
	21st to end	Day	31% 24% 30% 9% 5% 1	297
November	1st to 10th	Day	24% 20% 37% 15% 4 1	270
	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	21% 10% 32% 31% 6% 1	555
May	1st to 10th	Night	16% 10% 36% 29% 9%	540
	11th to 20th	Night	17% 9% 33% 29% 11%	531
	21st to end	Night	15% 6% 31% 32% 16% 1	584
June	1st to 10th	Night	15% 7% 31% 36% 11%	442
	11th to 20th	Night	11% 7% 31% 39% 12%	360
	21st to end	Night	11% 5% 29% 36% 17% 1	459
July	1st to 10th	Night	7% 2 21% 45% 23% 2	525
	11th to 20th	Night	7% 4 24% 40% 22% 3	522
	21st to end	Night	11% 3 25% 39% 21% 1	591
August	1st to 10th	Night	10% 2 23% 41% 23% 2	537
	11th to 20th	Night	8% 4 21% 35% 29% 3	534
	21st to end	Night	13% 5% 23% 39% 20% 1	594
September	1st to 10th	Night	12% 5% 25% 33% 21% 4	576
	11th to 20th	Night	13% 7% 23% 33% 20% 4	720
	21st to end	Night	18% 8% 26% 29% 16% 3	720
October	1st to 10th	Night	21% 10% 26% 28% 14% 1	720
	11th to 20th	Night	24% 15% 30% 25% 6% 1	720
	21st to end	Night	33% 13% 28% 21% 5% 1	792
November	1st to 10th	Night	19% 13% 37% 22% 9% 1	740
	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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