Houlton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Houlton clear sky chart from 2005-11-06 to 2026-04-17.

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	18% 10% 3 8% 5% 5% 5% 4 5% 7% 30%	131092
	Night	17% 10% 4 8% 5% 4 5% 4 5% 6% 32%	131156
Transparency	Day	53% 5% 11% 20% 10% 1	134575
	Night	52% 6% 11% 20% 10% 1	135761
Seeing	Day	27% 14% 30% 20% 8% 2	17848
	Night	25% 13% 31% 24% 7%	26037

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	13% 16% 6% 11% 7% 5% 4 3 4 5% 24%	4207
	11th to 20th	Day	15% 14% 7% 14% 7% 4 4 3 4 5% 22%	4650
	21st to end	Day	7% 9% 4 10% 8% 7% 6% 4 6% 7% 32%	5216
February	1st to 10th	Day	12% 12% 4 11% 8% 5% 4 4 6% 5% 27%	1890
	11th to 20th	Day	14% 12% 4 11% 7% 6% 6% 3 4 5% 27%	1865
	21st to end	Day	12% 13% 4 9% 7% 5% 4 3 4 6% 33%	1730
March	1st to 10th	Day	23% 14% 4 10% 5% 4 4 3 4 4 26%	4686
	11th to 20th	Day	18% 16% 5% 10% 6% 5% 4 4 5% 5% 24%	5090
	21st to end	Day	24% 13% 4 9% 5% 4 4 3 4 6% 23%	5587
April	1st to 10th	Day	21% 14% 3 9% 5% 4 3 4 5% 6% 26%	2493
	11th to 20th	Day	21% 11% 3 7% 5% 4 4 3 5% 7% 30%	2650
	21st to end	Day	25% 10% 3 7% 5% 4 3 2 4 4 33%	2600
May	1st to 10th	Day	24% 11% 3 9% 6% 5% 4 4 5% 6% 24%	5886
	11th to 20th	Day	25% 9% 3 8% 5% 4 4 4 5% 6% 27%	6016
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	7446
June	1st to 10th	Day	24% 9% 3 7% 4 5% 5% 4 6% 7% 27%	3000
	11th to 20th	Day	20% 7% 3 6% 4 4 5% 4 6% 8% 33%	3000
	21st to end	Day	25% 10% 3 6% 6% 4 5% 4 5% 8% 25%	3000
July	1st to 10th	Day	16% 6% 3 8% 6% 6% 6% 5% 8% 10% 27%	6820
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 4 6% 8% 36%	6602
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	6843
August	1st to 10th	Day	18% 7% 3 7% 5% 5% 6% 4 7% 7% 33%	4235
	11th to 20th	Day	15% 8% 3 8% 5% 5% 6% 5% 7% 8% 31%	4175
	21st to end	Day	15% 6% 2 7% 4 5% 5% 4 6% 9% 37%	4675
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 6% 44%	2359
	11th to 20th	Day	17% 6% 2 5% 4 4 3 3 4 5% 48%	2200
	21st to end	Day	18% 6% 2 6% 4 3 4 3 4 9% 41%	2200
October	1st to 10th	Day	17% 8% 3 7% 4 3 4 4 5% 6% 40%	2090
	11th to 20th	Day	21% 10% 2 8% 4 3 4 3 5% 5% 35%	2000
	21st to end	Day	21% 12% 3 7% 5% 4 4 3 5% 6% 29%	1987
November	1st to 10th	Day	19% 10% 2 9% 5% 4 5% 4 5% 5% 32%	1851
	11th to 20th	Day	19% 10% 4 7% 4 4 5% 3 6% 6% 32%	1687
	21st to end	Day	20% 11% 4 8% 6% 5% 4 3 5% 7% 28%	1680
December	1st to 10th	Day	19% 12% 3 8% 5% 5% 5% 4 5% 7% 28%	2435
	11th to 20th	Day	19% 11% 3 8% 5% 4 4 3 4 5% 34%	2688
	21st to end	Day	18% 12% 5% 10% 5% 5% 4 3 5% 5% 29%	3553
January	1st to 10th	Night	12% 16% 6% 12% 7% 5% 5% 3 4 5% 24%	8696
	11th to 20th	Night	15% 14% 6% 12% 7% 5% 5% 4 5% 5% 21%	8235
	21st to end	Night	6% 10% 4 9% 6% 6% 6% 5% 7% 7% 34%	8962
February	1st to 10th	Night	12% 13% 4 10% 6% 5% 5% 4 6% 6% 30%	2730
	11th to 20th	Night	13% 13% 5% 11% 6% 5% 5% 3 4 6% 28%	2637
	21st to end	Night	14% 12% 4 8% 5% 5% 5% 3 5% 6% 33%	2076
March	1st to 10th	Night	24% 11% 5% 10% 5% 4 5% 3 4 4 24%	5373
	11th to 20th	Night	18% 14% 4 8% 5% 4 5% 3 5% 7% 27%	5089
	21st to end	Night	27% 13% 3 5% 4 3 3 3 5% 7% 26%	5587
April	1st to 10th	Night	21% 14% 4 7% 5% 3 4 2 5% 5% 30%	2123
	11th to 20th	Night	21% 9% 3 7% 4 3 4 3 5% 6% 34%	1833
	21st to end	Night	25% 9% 3 7% 4 4 4 3 4 5% 31%	1800
May	1st to 10th	Night	23% 10% 2 7% 5% 4 4 4 5% 6% 28%	4054
	11th to 20th	Night	24% 8% 2 7% 5% 4 5% 3 5% 7% 29%	3885
	21st to end	Night	18% 8% 2 6% 4 4 5% 4 5% 7% 37%	3493
June	1st to 10th	Night	23% 7% 3 8% 5% 5% 5% 4 6% 7% 28%	1400
	11th to 20th	Night	16% 6% 3 8% 5% 4 5% 4 6% 8% 35%	1400
	21st to end	Night	25% 9% 3 7% 4 3 4 3 5% 7% 29%	1400
July	1st to 10th	Night	16% 7% 3 6% 5% 5% 5% 4 6% 8% 34%	3160
	11th to 20th	Night	16% 6% 2 7% 4 4 4 4 6% 8% 37%	3352
	21st to end	Night	9% 7% 2 7% 4 5% 5% 5% 6% 9% 41%	3961
August	1st to 10th	Night	18% 6% 2 9% 5% 5% 5% 4 6% 7% 32%	2915
	11th to 20th	Night	12% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	2872
	21st to end	Night	14% 5% 2 7% 4 3 4 3 5% 6% 45%	3223
September	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 5% 7% 48%	2038
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 6% 50%	2200
	21st to end	Night	17% 6% 2 5% 3 4 4 3 5% 6% 45%	2200
October	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 5% 7% 43%	2309
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 6% 5% 37%	2400
	21st to end	Night	21% 11% 3 7% 4 4 4 3 4 6% 32%	2850
November	1st to 10th	Night	20% 10% 3 8% 4 4 5% 3 4 6% 33%	2667
	11th to 20th	Night	19% 9% 3 7% 5% 4 3 3 4 6% 36%	2930
	21st to end	Night	19% 10% 3 7% 5% 4 5% 4 5% 7% 30%	2940
December	1st to 10th	Night	16% 12% 4 10% 6% 4 5% 5% 6% 6% 28%	4958
	11th to 20th	Night	23% 9% 3 7% 4 4 3 3 5% 6% 33%	5741
	21st to end	Night	19% 12% 4 10% 5% 4 4 3 4 5% 29%	7667

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	65% 5% 9% 16% 6%	4208
	11th to 20th	Day	63% 5% 8% 16% 7%	4680
	21st to end	Day	50% 5% 10% 18% 15% 1	5216
February	1st to 10th	Day	58% 4 11% 17% 8% 2	1890
	11th to 20th	Day	61% 4 8% 17% 9% 1	1873
	21st to end	Day	53% 4 10% 21% 10% 2	1730
March	1st to 10th	Day	63% 3 7% 10% 13% 3	4690
	11th to 20th	Day	62% 6% 11% 13% 7% 1	5090
	21st to end	Day	62% 5% 5% 17% 10% 2	5587
April	1st to 10th	Day	59% 4 9% 17% 10% 2	2493
	11th to 20th	Day	53% 4 9% 20% 11% 2	2650
	21st to end	Day	55% 4 7% 18% 12% 4	2600
May	1st to 10th	Day	59% 7% 7% 19% 8% 1	5897
	11th to 20th	Day	57% 6% 10% 18% 7% 2	6020
	21st to end	Day	52% 7% 10% 18% 12% 1	7446
June	1st to 10th	Day	55% 6% 11% 17% 10% 1	3000
	11th to 20th	Day	48% 5% 12% 20% 13% 2	3000
	21st to end	Day	57% 6% 11% 16% 9% 1	3000
July	1st to 10th	Day	50% 7% 17% 19% 7%	6745
	11th to 20th	Day	44% 7% 15% 28% 7%	6521
	21st to end	Day	41% 5% 15% 30% 8%	6646
August	1st to 10th	Day	49% 6% 15% 24% 6%	4222
	11th to 20th	Day	48% 8% 15% 23% 6%	4214
	21st to end	Day	41% 7% 15% 24% 12%	4675
September	1st to 10th	Day	39% 6% 13% 28% 14%	2359
	11th to 20th	Day	39% 3 11% 30% 15% 1	2200
	21st to end	Day	42% 5% 9% 29% 15% 1	2200
October	1st to 10th	Day	49% 5% 12% 27% 7%	3402
	11th to 20th	Day	48% 4 11% 28% 8%	3240
	21st to end	Day	43% 4 16% 23% 14%	3187
November	1st to 10th	Day	53% 5% 12% 20% 10% 1	1851
	11th to 20th	Day	52% 6% 11% 19% 9% 2	1687
	21st to end	Day	58% 6% 14% 17% 5%	1680
December	1st to 10th	Day	57% 6% 17% 13% 8%	2435
	11th to 20th	Day	54% 4 10% 18% 10% 4	2688
	21st to end	Day	59% 5% 11% 12% 11% 1	3553
January	1st to 10th	Night	62% 6% 11% 13% 7%	8696
	11th to 20th	Night	63% 6% 8% 15% 7% 1	8280
	21st to end	Night	47% 5% 8% 21% 17% 2	8962
February	1st to 10th	Night	54% 6% 9% 19% 10% 1	2730
	11th to 20th	Night	58% 6% 7% 17% 10% 1	2640
	21st to end	Night	53% 5% 8% 20% 12% 2	2076
March	1st to 10th	Night	64% 4 6% 14% 10% 2	5382
	11th to 20th	Night	56% 7% 14% 14% 8%	5090
	21st to end	Night	58% 3 5% 19% 13% 1	5587
April	1st to 10th	Night	57% 4 7% 16% 13% 3	2123
	11th to 20th	Night	51% 4 9% 19% 14% 2	1833
	21st to end	Night	54% 4 8% 17% 14% 2	1800
May	1st to 10th	Night	54% 6% 11% 18% 10% 1	4060
	11th to 20th	Night	53% 8% 10% 22% 6% 1	3886
	21st to end	Night	44% 7% 14% 23% 10% 2	3494
June	1st to 10th	Night	55% 5% 9% 21% 10% 1	1400
	11th to 20th	Night	46% 7% 13% 22% 11% 1	1400
	21st to end	Night	55% 6% 11% 17% 9% 2	1400
July	1st to 10th	Night	46% 7% 17% 22% 8%	3125
	11th to 20th	Night	44% 7% 15% 30% 5%	3310
	21st to end	Night	39% 7% 17% 28% 10%	3844
August	1st to 10th	Night	50% 6% 14% 23% 6%	2903
	11th to 20th	Night	44% 7% 19% 21% 8%	2899
	21st to end	Night	39% 6% 16% 22% 16%	3223
September	1st to 10th	Night	37% 6% 12% 31% 13% 1	2038
	11th to 20th	Night	37% 4 13% 32% 14% 1	2200
	21st to end	Night	41% 5% 11% 28% 14% 1	2200
October	1st to 10th	Night	47% 5% 13% 25% 11%	3777
	11th to 20th	Night	44% 5% 12% 28% 10%	3899
	21st to end	Night	43% 5% 18% 21% 13%	4600
November	1st to 10th	Night	52% 5% 12% 21% 9% 1	2667
	11th to 20th	Night	51% 6% 12% 19% 10% 1	2930
	21st to end	Night	54% 8% 13% 15% 9% 1	2940
December	1st to 10th	Night	56% 6% 11% 20% 6%	4958
	11th to 20th	Night	53% 4 9% 21% 12% 1	5742
	21st to end	Night	59% 5% 9% 16% 11% 2	7667

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	30% 17% 33% 16% 4	220
	11th to 20th	Day	34% 20% 31% 9% 5%	220
	21st to end	Day	23% 19% 36% 14% 8%	269
February	1st to 10th	Day	27% 17% 32% 17% 7% 1	430
	11th to 20th	Day	23% 22% 36% 15% 4	438
	21st to end	Day	23% 19% 34% 20% 3	446
March	1st to 10th	Day	31% 19% 31% 16% 3	540
	11th to 20th	Day	30% 19% 31% 14% 6% 1	540
	21st to end	Day	33% 18% 27% 15% 6% 2	594
April	1st to 10th	Day	37% 20% 24% 14% 4 1	540
	11th to 20th	Day	34% 18% 27% 15% 5% 1	516
	21st to end	Day	34% 15% 30% 16% 5% 1	500
May	1st to 10th	Day	34% 14% 28% 19% 4 1	503
	11th to 20th	Day	31% 15% 28% 20% 6% 1	591
	21st to end	Day	26% 14% 33% 19% 7% 1	790
June	1st to 10th	Day	31% 11% 28% 21% 7% 2	730
	11th to 20th	Day	25% 12% 29% 23% 9% 2	730
	21st to end	Day	29% 10% 29% 21% 10% 1	730
July	1st to 10th	Day	21% 10% 31% 25% 11% 2	720
	11th to 20th	Day	18% 8% 32% 27% 14% 1	630
	21st to end	Day	17% 9% 31% 30% 11% 2	576
August	1st to 10th	Day	15% 7% 33% 27% 13% 4	526
	11th to 20th	Day	19% 9% 22% 33% 13% 4	519
	21st to end	Day	19% 11% 27% 25% 13% 5%	583
September	1st to 10th	Day	16% 10% 32% 24% 14% 4	530
	11th to 20th	Day	20% 10% 26% 24% 15% 5%	530
	21st to end	Day	20% 12% 29% 26% 10% 4	530
October	1st to 10th	Day	23% 13% 25% 22% 15% 4	469
	11th to 20th	Day	30% 12% 29% 16% 10% 4	420
	21st to end	Day	33% 15% 29% 16% 6% 1	462
November	1st to 10th	Day	30% 16% 28% 18% 8%	425
	11th to 20th	Day	29% 17% 32% 16% 7%	430
	21st to end	Day	30% 17% 30% 16% 5%	430
December	1st to 10th	Day	32% 15% 33% 14% 6%	279
	11th to 20th	Day	36% 18% 32% 9% 5%	220
	21st to end	Day	34% 19% 30% 13% 3 1	242
January	1st to 10th	Night	25% 17% 32% 22% 4	926
	11th to 20th	Night	27% 16% 31% 22% 4	840
	21st to end	Night	18% 17% 37% 23% 5%	924
February	1st to 10th	Night	21% 19% 35% 20% 5%	840
	11th to 20th	Night	25% 18% 36% 17% 3	823
	21st to end	Night	23% 18% 33% 22% 3	692
March	1st to 10th	Night	26% 14% 37% 21% 2	840
	11th to 20th	Night	28% 13% 33% 21% 5% 1	840
	21st to end	Night	26% 16% 31% 22% 5% 1	924
April	1st to 10th	Night	33% 16% 31% 17% 4	800
	11th to 20th	Night	29% 16% 32% 17% 6%	613
	21st to end	Night	33% 11% 33% 17% 6%	600
May	1st to 10th	Night	29% 12% 33% 22% 5%	600
	11th to 20th	Night	28% 13% 30% 23% 5%	592
	21st to end	Night	20% 11% 34% 30% 4 1	454
June	1st to 10th	Night	26% 7% 31% 29% 8% 1	400
	11th to 20th	Night	20% 11% 30% 31% 8% 1	400
	21st to end	Night	32% 3 31% 29% 5% 1	400
July	1st to 10th	Night	16% 3 37% 34% 9%	390
	11th to 20th	Night	14% 5% 29% 39% 13%	388
	21st to end	Night	18% 5% 27% 37% 13%	448
August	1st to 10th	Night	16% 4 27% 38% 16%	598
	11th to 20th	Night	16% 3 25% 38% 18% 1	592
	21st to end	Night	16% 6% 25% 37% 15% 1	660
September	1st to 10th	Night	18% 6% 33% 29% 13%	713
	11th to 20th	Night	19% 7% 23% 34% 15% 1	800
	21st to end	Night	21% 9% 28% 29% 13% 1	800
October	1st to 10th	Night	22% 10% 26% 29% 12% 1	800
	11th to 20th	Night	25% 10% 29% 26% 10% 1	800
	21st to end	Night	30% 15% 26% 24% 4	880
November	1st to 10th	Night	30% 15% 29% 21% 5%	820
	11th to 20th	Night	27% 16% 29% 21% 7% 1	945
	21st to end	Night	29% 16% 29% 22% 5%	950
December	1st to 10th	Night	32% 13% 30% 19% 5% 1	950
	11th to 20th	Night	29% 20% 29% 18% 3	950
	21st to end	Night	30% 17% 30% 19% 4 1	1045

Page generated at 2026-04-14 02:44:29. Version ac07

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