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 2024-12-24.

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% 31%	101870
	Night	18% 10% 3 8% 5% 4 4 4 5% 6% 32%	98304
Transparency	Day	52% 6% 11% 21% 10% 1	105371
	Night	51% 6% 12% 20% 10% 1	102893
Seeing	Day	26% 13% 30% 21% 8% 2	16162
	Night	25% 13% 30% 25% 7%	24276

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	14% 14% 5% 9% 6% 5% 4 3 5% 6% 29%	2269
	11th to 20th	Day	15% 11% 6% 11% 7% 4 4 3 4 6% 29%	2520
	21st to end	Day	11% 10% 4 11% 6% 6% 6% 4 6% 6% 31%	2808
February	1st to 10th	Day	13% 13% 4 9% 8% 6% 4 4 6% 5% 27%	1710
	11th to 20th	Day	14% 12% 4 10% 7% 6% 6% 3 4 5% 27%	1682
	21st to end	Day	12% 13% 4 9% 7% 5% 4 3 5% 6% 33%	1570
March	1st to 10th	Day	22% 14% 4 8% 4 4 4 2 4 5% 28%	3196
	11th to 20th	Day	18% 19% 6% 10% 6% 5% 4 4 5% 4 20%	3480
	21st to end	Day	25% 13% 5% 9% 5% 3 3 3 4 6% 25%	3816
April	1st to 10th	Day	21% 13% 3 9% 5% 4 4 4 5% 6% 26%	2255
	11th to 20th	Day	20% 11% 3 7% 5% 4 4 3 5% 7% 32%	2442
	21st to end	Day	25% 10% 3 7% 5% 4 3 2 4 4 32%	2470
May	1st to 10th	Day	18% 10% 3 9% 6% 5% 4 4 5% 6% 29%	4106
	11th to 20th	Day	21% 9% 3 9% 6% 4 4 4 5% 7% 29%	4194
	21st to end	Day	16% 8% 3 8% 6% 6% 6% 5% 6% 8% 30%	5180
June	1st to 10th	Day	24% 9% 3 7% 4 5% 5% 4 5% 7% 27%	2850
	11th to 20th	Day	20% 7% 3 6% 4 4 5% 4 6% 8% 34%	2850
	21st to end	Day	26% 10% 3 6% 6% 4 5% 4 5% 8% 24%	2850
July	1st to 10th	Day	14% 6% 3 8% 6% 5% 5% 5% 7% 9% 32%	4760
	11th to 20th	Day	16% 6% 2 6% 5% 5% 6% 5% 7% 8% 35%	4612
	21st to end	Day	15% 7% 2 7% 5% 5% 5% 3 6% 8% 37%	4759
August	1st to 10th	Day	18% 7% 3 7% 5% 6% 6% 5% 7% 7% 31%	4105
	11th to 20th	Day	15% 8% 3 9% 5% 5% 6% 5% 7% 8% 30%	4045
	21st to end	Day	15% 6% 2 7% 4 5% 4 4 6% 9% 37%	4532
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 6% 43%	2241
	11th to 20th	Day	17% 6% 2 5% 4 4 3 3 4 5% 47%	2090
	21st to end	Day	19% 6% 2 6% 4 3 4 3 4 9% 40%	2090
October	1st to 10th	Day	17% 9% 3 7% 5% 3 4 4 5% 6% 38%	1986
	11th to 20th	Day	21% 10% 3 8% 3 3 4 3 4 5% 35%	1900
	21st to end	Day	22% 12% 3 7% 5% 4 4 3 5% 6% 30%	1888
November	1st to 10th	Day	19% 10% 2 8% 5% 4 5% 4 5% 5% 33%	1761
	11th to 20th	Day	19% 10% 3 7% 4 4 5% 3 6% 6% 32%	1607
	21st to end	Day	20% 11% 3 7% 6% 5% 4 3 5% 7% 28%	1600
December	1st to 10th	Day	21% 12% 4 9% 6% 5% 5% 3 5% 6% 25%	1456
	11th to 20th	Day	21% 12% 4 9% 6% 4 5% 3 4 4 27%	1738
	21st to end	Day	21% 12% 4 11% 5% 5% 4 3 4 4 27%	2452
January	1st to 10th	Night	11% 13% 5% 11% 6% 6% 5% 4 5% 6% 27%	4683
	11th to 20th	Night	15% 10% 4 10% 7% 6% 6% 4 6% 6% 27%	4440
	21st to end	Night	11% 12% 5% 10% 5% 5% 5% 4 7% 8% 29%	4845
February	1st to 10th	Night	12% 13% 4 9% 6% 5% 5% 4 6% 6% 30%	2470
	11th to 20th	Night	14% 13% 5% 11% 7% 6% 5% 3 4 6% 27%	2380
	21st to end	Night	14% 12% 3 8% 6% 5% 5% 4 5% 6% 32%	1884
March	1st to 10th	Night	22% 13% 4 8% 5% 4 6% 3 4 4 26%	3643
	11th to 20th	Night	17% 18% 4 9% 5% 4 5% 4 5% 6% 24%	3479
	21st to end	Night	27% 13% 3 6% 4 3 3 3 5% 7% 26%	3816
April	1st to 10th	Night	21% 14% 4 7% 5% 3 4 2 4 5% 31%	1921
	11th to 20th	Night	20% 8% 3 7% 4 4 4 3 5% 6% 36%	1688
	21st to end	Night	25% 9% 3 7% 4 4 4 3 4 5% 31%	1710
May	1st to 10th	Night	21% 8% 2 6% 4 4 4 4 6% 7% 35%	2834
	11th to 20th	Night	19% 9% 3 8% 6% 5% 6% 4 5% 7% 29%	2704
	21st to end	Night	15% 7% 3 6% 4 4 5% 4 6% 8% 38%	2434
June	1st to 10th	Night	23% 7% 3 8% 5% 5% 5% 3 5% 7% 28%	1330
	11th to 20th	Night	16% 6% 3 8% 5% 4 5% 4 6% 8% 35%	1330
	21st to end	Night	25% 9% 3 7% 4 3 4 3 4 7% 29%	1330
July	1st to 10th	Night	13% 7% 2 6% 5% 5% 5% 5% 7% 9% 37%	2210
	11th to 20th	Night	18% 6% 2 6% 4 4 4 4 6% 8% 38%	2350
	21st to end	Night	12% 8% 2 7% 4 5% 4 4 6% 8% 39%	2760
August	1st to 10th	Night	19% 6% 2 9% 6% 5% 5% 4 7% 8% 30%	2825
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 4 7% 9% 33%	2782
	21st to end	Night	14% 6% 2 7% 4 3 4 3 5% 6% 45%	3124
September	1st to 10th	Night	13% 5% 2 5% 3 4 4 3 5% 7% 47%	1936
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 4 7% 49%	2090
	21st to end	Night	17% 6% 2 5% 3 4 4 3 5% 6% 45%	2090
October	1st to 10th	Night	19% 6% 2 5% 4 3 4 3 5% 7% 42%	2193
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 6% 5% 37%	2280
	21st to end	Night	21% 11% 3 7% 4 4 4 3 4 6% 33%	2707
November	1st to 10th	Night	19% 9% 3 8% 4 4 5% 3 5% 6% 34%	2537
	11th to 20th	Night	19% 9% 3 7% 5% 4 3 3 4 6% 36%	2790
	21st to end	Night	20% 10% 3 7% 5% 4 5% 4 5% 7% 31%	2800
December	1st to 10th	Night	22% 13% 4 8% 6% 4 4 3 4 5% 27%	2940
	11th to 20th	Night	25% 10% 3 7% 4 5% 4 3 5% 6% 28%	3681
	21st to end	Night	21% 13% 5% 9% 5% 4 4 3 4 5% 30%	5288

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	56% 6% 13% 18% 6%	2270
	11th to 20th	Day	57% 6% 6% 21% 9% 1	2520
	21st to end	Day	51% 7% 12% 17% 12% 1	2808
February	1st to 10th	Day	58% 4 11% 17% 8% 2	1710
	11th to 20th	Day	61% 5% 9% 16% 9% 1	1690
	21st to end	Day	53% 5% 10% 20% 10% 2	1570
March	1st to 10th	Day	59% 4 8% 14% 10% 4	3200
	11th to 20th	Day	66% 7% 8% 11% 7% 1	3480
	21st to end	Day	62% 5% 5% 16% 11% 2	3816
April	1st to 10th	Day	60% 4 9% 16% 10% 2	2255
	11th to 20th	Day	51% 4 10% 21% 12% 2	2442
	21st to end	Day	56% 4 7% 18% 12% 4	2470
May	1st to 10th	Day	52% 8% 8% 23% 8% 1	4120
	11th to 20th	Day	53% 6% 12% 20% 9% 1	4198
	21st to end	Day	48% 9% 11% 19% 13% 1	5180
June	1st to 10th	Day	56% 6% 11% 17% 9% 1	2850
	11th to 20th	Day	48% 5% 12% 20% 13% 2	2850
	21st to end	Day	58% 6% 11% 16% 8% 1	2850
July	1st to 10th	Day	46% 7% 17% 20% 10%	4685
	11th to 20th	Day	44% 7% 15% 27% 6%	4531
	21st to end	Day	45% 6% 14% 27% 8%	4607
August	1st to 10th	Day	50% 6% 14% 24% 5%	4092
	11th to 20th	Day	49% 8% 15% 23% 6%	4084
	21st to end	Day	42% 7% 15% 24% 13%	4532
September	1st to 10th	Day	40% 6% 13% 27% 14%	2241
	11th to 20th	Day	40% 3 11% 30% 15% 1	2090
	21st to end	Day	43% 5% 9% 28% 14% 1	2090
October	1st to 10th	Day	50% 5% 12% 27% 6%	3298
	11th to 20th	Day	48% 4 11% 28% 9%	3140
	21st to end	Day	42% 3 16% 23% 15%	3088
November	1st to 10th	Day	53% 5% 12% 19% 10% 1	1761
	11th to 20th	Day	52% 6% 11% 19% 10% 2	1607
	21st to end	Day	57% 6% 15% 17% 5%	1600
December	1st to 10th	Day	62% 5% 11% 14% 7%	1456
	11th to 20th	Day	61% 4 8% 16% 9% 1	1738
	21st to end	Day	61% 6% 10% 13% 8% 1	2452
January	1st to 10th	Night	55% 8% 15% 15% 6%	4683
	11th to 20th	Night	54% 9% 8% 20% 8% 1	4440
	21st to end	Night	52% 7% 11% 18% 11% 1	4845
February	1st to 10th	Night	55% 6% 10% 18% 10% 1	2470
	11th to 20th	Night	59% 6% 7% 16% 10% 1	2383
	21st to end	Night	53% 5% 9% 19% 11% 2	1884
March	1st to 10th	Night	61% 5% 7% 18% 8% 1	3652
	11th to 20th	Night	61% 8% 9% 14% 8% 1	3480
	21st to end	Night	59% 3 6% 19% 11% 2	3816
April	1st to 10th	Night	56% 4 7% 16% 14% 3	1921
	11th to 20th	Night	50% 4 9% 19% 15% 2	1688
	21st to end	Night	54% 4 8% 17% 14% 2	1710
May	1st to 10th	Night	46% 8% 14% 22% 9% 1	2840
	11th to 20th	Night	51% 8% 12% 21% 7% 1	2705
	21st to end	Night	41% 8% 16% 22% 12% 1	2435
June	1st to 10th	Night	56% 5% 9% 21% 10% 1	1330
	11th to 20th	Night	46% 7% 13% 22% 12% 1	1330
	21st to end	Night	56% 6% 12% 17% 9% 2	1330
July	1st to 10th	Night	41% 7% 19% 23% 10%	2175
	11th to 20th	Night	44% 6% 15% 28% 6%	2308
	21st to end	Night	42% 6% 15% 28% 9%	2672
August	1st to 10th	Night	52% 7% 14% 22% 5%	2813
	11th to 20th	Night	45% 7% 19% 21% 8%	2809
	21st to end	Night	40% 6% 15% 22% 16%	3124
September	1st to 10th	Night	37% 6% 12% 30% 13% 1	1936
	11th to 20th	Night	37% 4 13% 31% 14% 1	2090
	21st to end	Night	41% 5% 11% 28% 13% 1	2090
October	1st to 10th	Night	48% 5% 13% 24% 10%	3661
	11th to 20th	Night	44% 5% 12% 28% 10%	3779
	21st to end	Night	43% 5% 18% 21% 13%	4457
November	1st to 10th	Night	51% 5% 13% 21% 9% 1	2537
	11th to 20th	Night	51% 6% 12% 19% 11% 1	2790
	21st to end	Night	54% 8% 13% 16% 8% 1	2800
December	1st to 10th	Night	61% 5% 10% 18% 6%	2940
	11th to 20th	Night	57% 6% 8% 18% 10%	3682
	21st to end	Night	59% 5% 9% 16% 8% 2	5288

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	28% 15% 34% 18% 5%	180
	11th to 20th	Day	33% 21% 31% 10% 5% 1	180
	21st to end	Day	24% 14% 37% 15% 10%	221
February	1st to 10th	Day	28% 16% 32% 16% 6% 1	370
	11th to 20th	Day	23% 20% 37% 17% 3 1	375
	21st to end	Day	23% 18% 34% 22% 4	382
March	1st to 10th	Day	30% 17% 33% 17% 3	460
	11th to 20th	Day	27% 17% 32% 16% 7% 1	460
	21st to end	Day	31% 17% 28% 16% 6% 2	506
April	1st to 10th	Day	36% 19% 23% 16% 5% 2	460
	11th to 20th	Day	31% 17% 29% 17% 6% 1	452
	21st to end	Day	33% 13% 30% 17% 5% 1	460
May	1st to 10th	Day	33% 14% 27% 20% 5% 1	463
	11th to 20th	Day	30% 15% 27% 21% 6% 1	548
	21st to end	Day	25% 14% 34% 19% 7% 1	735
June	1st to 10th	Day	32% 11% 28% 20% 7% 2	680
	11th to 20th	Day	25% 11% 29% 24% 9% 2	680
	21st to end	Day	29% 10% 29% 21% 10% 1	680
July	1st to 10th	Day	21% 9% 31% 26% 11% 2	670
	11th to 20th	Day	18% 7% 33% 26% 15% 1	585
	21st to end	Day	17% 7% 31% 31% 11% 3	532
August	1st to 10th	Day	16% 8% 33% 27% 13% 3	486
	11th to 20th	Day	20% 9% 23% 34% 11% 4	479
	21st to end	Day	20% 12% 26% 25% 13% 5%	539
September	1st to 10th	Day	16% 10% 33% 25% 13% 3	490
	11th to 20th	Day	21% 10% 27% 23% 14% 6%	490
	21st to end	Day	20% 11% 29% 25% 10% 4	490
October	1st to 10th	Day	23% 13% 25% 21% 14% 4	435
	11th to 20th	Day	31% 13% 28% 16% 9% 4	390
	21st to end	Day	34% 15% 28% 16% 7% 1	429
November	1st to 10th	Day	29% 15% 28% 19% 8% 1	395
	11th to 20th	Day	29% 17% 31% 15% 7% 1	400
	21st to end	Day	31% 17% 31% 17% 5%	400
December	1st to 10th	Day	32% 14% 32% 15% 7%	256
	11th to 20th	Day	37% 17% 32% 10% 6%	200
	21st to end	Day	33% 20% 29% 14% 2 1	204
January	1st to 10th	Night	24% 17% 32% 23% 4	831
	11th to 20th	Night	27% 17% 32% 21% 3	760
	21st to end	Night	19% 16% 36% 23% 5%	836
February	1st to 10th	Night	22% 19% 35% 20% 4 1	760
	11th to 20th	Night	25% 18% 37% 16% 3 1	743
	21st to end	Night	24% 17% 33% 23% 3	628
March	1st to 10th	Night	25% 13% 38% 22% 2	760
	11th to 20th	Night	26% 13% 33% 22% 5% 1	760
	21st to end	Night	26% 16% 30% 22% 5% 1	836
April	1st to 10th	Night	31% 15% 31% 18% 4	724
	11th to 20th	Night	28% 16% 33% 17% 6%	564
	21st to end	Night	32% 11% 32% 18% 6%	570
May	1st to 10th	Night	29% 12% 32% 22% 5%	570
	11th to 20th	Night	28% 13% 31% 23% 6%	562
	21st to end	Night	20% 11% 35% 29% 4 1	431
June	1st to 10th	Night	26% 7% 31% 29% 8% 1	380
	11th to 20th	Night	20% 9% 31% 32% 8% 1	380
	21st to end	Night	32% 3 30% 29% 6% 1	380
July	1st to 10th	Night	16% 4 36% 35% 9%	370
	11th to 20th	Night	15% 5% 27% 40% 13%	368
	21st to end	Night	19% 4 26% 38% 13%	425
August	1st to 10th	Night	16% 4 27% 37% 15%	568
	11th to 20th	Night	17% 3 25% 38% 17% 1	562
	21st to end	Night	16% 6% 25% 36% 15% 1	627
September	1st to 10th	Night	18% 6% 33% 30% 12%	677
	11th to 20th	Night	20% 8% 23% 34% 15% 1	760
	21st to end	Night	21% 9% 28% 29% 13% 1	760
October	1st to 10th	Night	23% 9% 25% 30% 12% 1	760
	11th to 20th	Night	26% 10% 29% 25% 9% 1	760
	21st to end	Night	31% 16% 26% 23% 4	836
November	1st to 10th	Night	28% 14% 30% 21% 6%	780
	11th to 20th	Night	27% 16% 29% 20% 7% 1	895
	21st to end	Night	29% 16% 28% 22% 5%	900
December	1st to 10th	Night	33% 13% 30% 19% 5% 1	900
	11th to 20th	Night	30% 19% 29% 19% 4	900
	21st to end	Night	31% 17% 30% 18% 4 1	953

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