Houghton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Houghton clear sky chart from 2005-11-06 to 2026-03-03.

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	12% 10% 4 11% 7% 5% 4 3 5% 6% 32%	131317
	Night	12% 12% 5% 13% 8% 6% 5% 3 4 5% 26%	130141
Transparency	Day	53% 3 12% 21% 9% 1	134735
	Night	60% 4 11% 17% 7% 1	134796
Seeing	Day	19% 12% 32% 24% 10% 3	17874
	Night	19% 11% 28% 29% 12% 1	27930

By Month

Percentage Cloud Cover NE (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	6% 15% 10% 28% 17% 6% 4 1 3 3 7%	4691
	11th to 20th	Day	6% 15% 9% 19% 22% 11% 9% 2 2 1 3	4679
	21st to end	Day	6% 12% 10% 16% 11% 14% 8% 6% 4 3 10%	5156
February	1st to 10th	Day	8% 13% 6% 16% 14% 12% 7% 4 5% 4 12%	1780
	11th to 20th	Day	8% 13% 6% 16% 10% 11% 6% 3 4 4 19%	1926
	21st to end	Day	8% 16% 5% 14% 11% 8% 6% 4 5% 6% 16%	1730
March	1st to 10th	Day	10% 9% 4 13% 7% 6% 5% 4 6% 6% 30%	4498
	11th to 20th	Day	9% 13% 5% 15% 9% 5% 4 4 5% 6% 25%	4676
	21st to end	Day	20% 14% 6% 15% 6% 4 3 3 3 4 23%	5969
April	1st to 10th	Day	14% 13% 5% 8% 5% 4 6% 5% 5% 6% 29%	2400
	11th to 20th	Day	18% 11% 4 9% 6% 5% 4 3 5% 6% 28%	2379
	21st to end	Day	18% 10% 4 7% 5% 4 4 3 6% 6% 34%	2600
May	1st to 10th	Day	14% 8% 2 5% 3 3 3 3 4 6% 49%	6338
	11th to 20th	Day	11% 8% 2 7% 4 4 5% 3 6% 7% 42%	6319
	21st to end	Day	9% 8% 3 8% 5% 5% 4 4 5% 7% 42%	6949
June	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 6% 7% 44%	2800
	11th to 20th	Day	12% 6% 3 7% 5% 4 5% 4 6% 7% 41%	2800
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 7% 43%	2800
July	1st to 10th	Day	12% 5% 2 5% 3 3 4 3 5% 7% 51%	6359
	11th to 20th	Day	11% 4 2 5% 4 3 4 3 5% 8% 51%	6360
	21st to end	Day	9% 5% 2 5% 3 3 3 3 5% 8% 55%	6926
August	1st to 10th	Day	9% 5% 2 8% 5% 4 4 4 6% 8% 44%	4563
	11th to 20th	Day	13% 6% 2 4 3 3 3 4 5% 7% 50%	4311
	21st to end	Day	13% 5% 2 5% 3 4 4 3 4 8% 48%	4312
September	1st to 10th	Day	15% 6% 2 6% 4 5% 4 3 6% 8% 42%	2400
	11th to 20th	Day	13% 8% 3 7% 4 4 4 3 6% 9% 39%	2314
	21st to end	Day	19% 9% 3 7% 5% 4 3 3 6% 7% 36%	2200
October	1st to 10th	Day	15% 12% 3 9% 5% 4 4 3 5% 7% 33%	2059
	11th to 20th	Day	20% 19% 4 9% 4 5% 5% 4 4 6% 20%	1923
	21st to end	Day	20% 22% 6% 9% 6% 4 4 3 4 4 18%	1980
November	1st to 10th	Day	16% 20% 6% 12% 5% 5% 4 3 3 4 21%	1852
	11th to 20th	Day	15% 21% 8% 16% 8% 5% 4 3 3 4 14%	1744
	21st to end	Day	13% 21% 9% 21% 9% 4 4 4 3 3 9%	1680
December	1st to 10th	Day	7% 19% 13% 28% 10% 5% 4 3 4 3 4	2690
	11th to 20th	Day	10% 16% 9% 26% 13% 9% 4 3 3 3 5%	3084
	21st to end	Day	18% 17% 8% 18% 9% 6% 4 2 3 4 11%	4070
January	1st to 10th	Night	6% 16% 9% 25% 15% 8% 4 2 3 2 9%	8233
	11th to 20th	Night	7% 16% 8% 23% 18% 9% 9% 3 3 2 3	8236
	21st to end	Night	5% 12% 7% 14% 13% 13% 11% 6% 5% 5% 9%	9058
February	1st to 10th	Night	9% 14% 5% 14% 13% 12% 6% 4 4 3 16%	2835
	11th to 20th	Night	8% 13% 4 14% 11% 11% 7% 4 4 5% 18%	2580
	21st to end	Night	11% 16% 5% 11% 8% 7% 6% 4 5% 5% 22%	2076
March	1st to 10th	Night	8% 8% 3 11% 6% 6% 6% 5% 7% 8% 31%	5387
	11th to 20th	Night	8% 11% 6% 14% 7% 6% 6% 4 6% 7% 26%	5299
	21st to end	Night	21% 12% 5% 13% 7% 5% 4 3 4 5% 20%	4962
April	1st to 10th	Night	16% 12% 4 8% 6% 7% 6% 4 5% 6% 26%	2000
	11th to 20th	Night	19% 11% 4 8% 4 4 4 3 5% 5% 33%	1970
	21st to end	Night	18% 10% 4 7% 5% 4 4 3 4 6% 35%	1800
May	1st to 10th	Night	13% 6% 3 6% 4 4 4 4 5% 6% 47%	3619
	11th to 20th	Night	13% 8% 3 7% 5% 5% 4 3 5% 6% 41%	3596
	21st to end	Night	12% 8% 3 8% 5% 5% 5% 4 6% 7% 37%	3949
June	1st to 10th	Night	13% 6% 2 6% 5% 5% 6% 4 5% 7% 40%	1600
	11th to 20th	Night	11% 7% 4 7% 6% 5% 6% 5% 7% 7% 36%	1600
	21st to end	Night	14% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	1600
July	1st to 10th	Night	9% 6% 2 5% 5% 4 5% 3 5% 8% 48%	3620
	11th to 20th	Night	13% 4 2 4 3 4 4 4 5% 8% 49%	3620
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 9% 48%	3948
August	1st to 10th	Night	12% 5% 2 6% 5% 5% 4 4 6% 8% 44%	2597
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 4 7% 52%	2739
	21st to end	Night	15% 5% 2 5% 4 3 3 3 4 6% 48%	3586
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 5% 5% 6% 46%	2000
	11th to 20th	Night	12% 7% 3 7% 5% 5% 4 3 5% 7% 41%	2065
	21st to end	Night	17% 9% 3 8% 4 4 4 3 5% 6% 38%	2200
October	1st to 10th	Night	17% 9% 2 7% 5% 4 4 4 5% 6% 36%	2339
	11th to 20th	Night	17% 16% 4 9% 6% 5% 5% 3 5% 5% 27%	2476
	21st to end	Night	20% 18% 4 9% 5% 5% 4 3 4 4 24%	2860
November	1st to 10th	Night	15% 21% 5% 9% 6% 4 4 3 5% 6% 21%	2666
	11th to 20th	Night	15% 18% 8% 15% 7% 5% 5% 2 4 4 17%	2872
	21st to end	Night	14% 19% 9% 19% 7% 5% 4 3 4 4 13%	2940
December	1st to 10th	Night	11% 18% 9% 24% 11% 7% 5% 3 3 3 6%	4720
	11th to 20th	Night	9% 18% 8% 21% 12% 8% 5% 3 3 3 10%	5343
	21st to end	Night	16% 18% 7% 18% 9% 5% 4 2 3 4 15%	7150

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	85% 2 8% 4 1	4692
	11th to 20th	Day	91% 2 3 4	4710
	21st to end	Day	78% 3 9% 7% 2	5156
February	1st to 10th	Day	74% 4 10% 10% 2	1780
	11th to 20th	Day	70% 2 9% 15% 4	1935
	21st to end	Day	67% 5% 7% 13% 7% 1	1730
March	1st to 10th	Day	54% 3 13% 18% 10% 1	4500
	11th to 20th	Day	61% 3 14% 14% 8% 1	4676
	21st to end	Day	68% 2 7% 15% 8%	5969
April	1st to 10th	Day	53% 5% 10% 22% 10%	2400
	11th to 20th	Day	57% 3 8% 22% 9% 1	2379
	21st to end	Day	51% 4 9% 22% 13% 2	2600
May	1st to 10th	Day	38% 3 10% 29% 18% 2	6347
	11th to 20th	Day	42% 3 10% 27% 13% 5%	6323
	21st to end	Day	42% 4 13% 24% 16% 2	6949
June	1st to 10th	Day	39% 3 16% 28% 14% 1	2800
	11th to 20th	Day	41% 4 15% 26% 13% 1	2800
	21st to end	Day	40% 4 15% 28% 11% 1	2800
July	1st to 10th	Day	33% 3 16% 34% 12% 1	6291
	11th to 20th	Day	32% 4 18% 34% 11% 1	6285
	21st to end	Day	28% 3 16% 38% 14%	6728
August	1st to 10th	Day	37% 4 18% 29% 10% 1	4548
	11th to 20th	Day	34% 4 21% 31% 9%	4353
	21st to end	Day	36% 5% 18% 28% 12% 1	4311
September	1st to 10th	Day	40% 4 15% 32% 9%	2400
	11th to 20th	Day	42% 4 22% 25% 5%	2314
	21st to end	Day	48% 3 16% 25% 8%	2200
October	1st to 10th	Day	41% 4 13% 34% 8%	3345
	11th to 20th	Day	60% 3 11% 16% 11%	3113
	21st to end	Day	63% 5% 12% 16% 4	3180
November	1st to 10th	Day	68% 3 10% 14% 5%	1852
	11th to 20th	Day	76% 3 9% 9% 3	1744
	21st to end	Day	82% 3 8% 5% 2	1680
December	1st to 10th	Day	84% 4 7% 4	2690
	11th to 20th	Day	87% 3 5% 3 1	3085
	21st to end	Day	79% 3 6% 12% 1	4070
January	1st to 10th	Night	82% 3 8% 6% 1	8233
	11th to 20th	Night	89% 3 5% 3	8280
	21st to end	Night	75% 4 12% 8% 1	9058
February	1st to 10th	Night	73% 4 9% 11% 3	2835
	11th to 20th	Night	69% 4 9% 14% 4	2581
	21st to end	Night	64% 3 10% 17% 6% 1	2076
March	1st to 10th	Night	49% 4 16% 18% 11% 1	5398
	11th to 20th	Night	58% 3 13% 18% 8% 1	5300
	21st to end	Night	67% 3 6% 17% 7% 1	4962
April	1st to 10th	Night	58% 4 8% 19% 10% 1	2000
	11th to 20th	Night	54% 4 8% 22% 11% 2	1970
	21st to end	Night	51% 3 7% 22% 15% 1	1800
May	1st to 10th	Night	39% 3 12% 28% 14% 4	3626
	11th to 20th	Night	44% 4 9% 23% 15% 5%	3597
	21st to end	Night	45% 4 10% 22% 17% 1	3950
June	1st to 10th	Night	43% 4 11% 27% 14% 2	1600
	11th to 20th	Night	45% 5% 14% 22% 14% 1	1600
	21st to end	Night	43% 4 15% 23% 13% 2	1600
July	1st to 10th	Night	36% 5% 18% 27% 13% 2	3580
	11th to 20th	Night	32% 4 19% 33% 12%	3572
	21st to end	Night	33% 4 15% 30% 17% 1	3832
August	1st to 10th	Night	38% 3 15% 31% 11% 2	2588
	11th to 20th	Night	33% 4 18% 33% 12% 1	2763
	21st to end	Night	37% 5% 15% 28% 13% 1	3586
September	1st to 10th	Night	38% 4 14% 32% 11% 1	2000
	11th to 20th	Night	43% 4 18% 29% 6%	2065
	21st to end	Night	47% 3 16% 26% 7% 1	2200
October	1st to 10th	Night	37% 4 11% 34% 14%	3820
	11th to 20th	Night	51% 3 11% 23% 11%	4025
	21st to end	Night	60% 3 15% 16% 5%	4610
November	1st to 10th	Night	64% 4 10% 16% 5%	2666
	11th to 20th	Night	72% 3 10% 10% 5%	2872
	21st to end	Night	76% 4 10% 8% 2	2940
December	1st to 10th	Night	82% 5% 7% 5% 1	4720
	11th to 20th	Night	81% 3 7% 8% 1	5341
	21st to end	Night	76% 3 7% 10% 3	7150

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	17% 15% 36% 24% 6% 2	330
	11th to 20th	Day	19% 14% 38% 22% 6% 1	330
	21st to end	Day	19% 17% 40% 21% 3	363
February	1st to 10th	Day	19% 25% 37% 15% 3 1	330
	11th to 20th	Day	16% 27% 33% 17% 7%	330
	21st to end	Day	19% 26% 42% 11% 2	273
March	1st to 10th	Day	15% 20% 42% 19% 3 1	306
	11th to 20th	Day	16% 22% 37% 19% 5% 1	305
	21st to end	Day	24% 15% 31% 21% 7% 2	550
April	1st to 10th	Day	23% 11% 35% 24% 6% 1	500
	11th to 20th	Day	28% 14% 28% 21% 7% 2	492
	21st to end	Day	26% 11% 29% 22% 9% 3	500
May	1st to 10th	Day	18% 13% 35% 23% 8% 2	693
	11th to 20th	Day	16% 11% 37% 24% 9% 3	725
	21st to end	Day	17% 9% 31% 29% 12% 2	789
June	1st to 10th	Day	14% 9% 33% 29% 12% 2	730
	11th to 20th	Day	17% 8% 34% 28% 10% 3	730
	21st to end	Day	17% 10% 29% 27% 13% 4	730
July	1st to 10th	Day	10% 5% 31% 33% 17% 4	721
	11th to 20th	Day	11% 8% 31% 29% 16% 6%	718
	21st to end	Day	8% 6% 31% 33% 17% 5%	794
August	1st to 10th	Day	13% 8% 27% 33% 16% 4	726
	11th to 20th	Day	15% 6% 21% 31% 20% 7%	641
	21st to end	Day	18% 9% 23% 29% 16% 5%	583
September	1st to 10th	Day	18% 6% 28% 26% 16% 5%	530
	11th to 20th	Day	16% 8% 25% 31% 18% 2	530
	21st to end	Day	21% 11% 25% 26% 15% 3	530
October	1st to 10th	Day	22% 15% 26% 24% 11% 3	389
	11th to 20th	Day	30% 18% 32% 18% 2	330
	21st to end	Day	34% 16% 31% 14% 3 1	363
November	1st to 10th	Day	26% 22% 27% 20% 5% 1	330
	11th to 20th	Day	31% 19% 35% 11% 5%	330
	21st to end	Day	25% 21% 35% 14% 4 1	330
December	1st to 10th	Day	21% 16% 37% 20% 5% 1	330
	11th to 20th	Day	25% 21% 35% 14% 4 1	330
	21st to end	Day	26% 15% 38% 17% 4 1	363
January	1st to 10th	Night	17% 17% 36% 24% 5% 1	1050
	11th to 20th	Night	17% 14% 39% 21% 7% 2	1050
	21st to end	Night	17% 15% 35% 26% 7% 1	1155
February	1st to 10th	Night	17% 18% 33% 24% 7% 1	1050
	11th to 20th	Night	16% 17% 32% 24% 10% 1	946
	21st to end	Night	20% 11% 36% 26% 6%	692
March	1st to 10th	Night	14% 12% 30% 32% 10% 2	809
	11th to 20th	Night	17% 14% 31% 29% 8% 1	757
	21st to end	Night	23% 9% 23% 29% 14% 2	660
April	1st to 10th	Night	23% 7% 29% 33% 7% 2	600
	11th to 20th	Night	26% 8% 25% 30% 10% 1	593
	21st to end	Night	23% 6% 24% 32% 13% 2	600
May	1st to 10th	Night	20% 7% 27% 32% 14% 1	600
	11th to 20th	Night	19% 5% 29% 32% 13% 3	591
	21st to end	Night	16% 5% 22% 37% 19% 1	650
June	1st to 10th	Night	16% 6% 20% 42% 15% 2	600
	11th to 20th	Night	15% 5% 22% 44% 14% 1	600
	21st to end	Night	18% 3 22% 38% 17% 2	600
July	1st to 10th	Night	9% 4 20% 42% 22% 3	585
	11th to 20th	Night	13% 6% 25% 31% 23% 2	582
	21st to end	Night	9% 3 21% 42% 22% 3	657
August	1st to 10th	Night	11% 3 21% 40% 24% 2	597
	11th to 20th	Night	12% 3 17% 32% 31% 4	594
	21st to end	Night	16% 5% 22% 31% 24% 2	660
September	1st to 10th	Night	17% 6% 20% 31% 22% 4	600
	11th to 20th	Night	17% 5% 23% 33% 20% 3	665
	21st to end	Night	21% 7% 23% 32% 16% 1	800
October	1st to 10th	Night	23% 11% 26% 26% 14% 1	800
	11th to 20th	Night	26% 12% 28% 25% 9%	800
	21st to end	Night	31% 11% 23% 27% 8% 1	880
November	1st to 10th	Night	27% 14% 27% 27% 6%	820
	11th to 20th	Night	25% 17% 28% 21% 8% 1	982
	21st to end	Night	24% 18% 31% 24% 4	1050
December	1st to 10th	Night	21% 19% 34% 19% 6% 1	1050
	11th to 20th	Night	20% 19% 32% 20% 8% 1	1050
	21st to end	Night	27% 14% 32% 22% 6%	1155

Page generated at 2026-02-28 01:40:20. Version ac07

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