Haggart Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Haggart Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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% 8% 3 7% 4 4 4 3 5% 6% 38%	136598
	Night	22% 9% 3 7% 4 4 4 3 4 5% 35%	132386
Transparency	Day	47% 7% 12% 18% 13% 4	131379
	Night	50% 7% 12% 17% 11% 3	128614
Seeing	Day	22% 10% 21% 27% 16% 4	16051
	Night	26% 7% 15% 30% 19% 2	25108

By Month

Percentage Cloud Cover SW (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	39% 13% 4 10% 5% 4 4 3 4 3 11%	3719
	11th to 20th	Day	28% 11% 3 7% 5% 5% 4 3 4 6% 23%	3688
	21st to end	Day	27% 8% 3 7% 5% 4 4 3 4 4 31%	4372
February	1st to 10th	Day	29% 13% 4 7% 5% 5% 5% 4 6% 6% 16%	1800
	11th to 20th	Day	29% 13% 3 10% 6% 5% 4 3 4 4 19%	1755
	21st to end	Day	30% 14% 4 8% 6% 4 4 2 3 4 20%	1575
March	1st to 10th	Day	18% 11% 4 9% 6% 6% 6% 5% 7% 7% 21%	4711
	11th to 20th	Day	26% 13% 4 9% 5% 4 4 3 4 4 26%	5000
	21st to end	Day	24% 13% 4 11% 7% 6% 6% 4 6% 6% 13%	5614
April	1st to 10th	Day	29% 12% 3 8% 7% 5% 4 3 4 6% 19%	2400
	11th to 20th	Day	23% 13% 4 8% 5% 5% 4 3 5% 5% 26%	2369
	21st to end	Day	23% 10% 4 9% 5% 5% 4 4 5% 6% 25%	2580
May	1st to 10th	Day	17% 7% 3 7% 5% 5% 4 3 5% 5% 40%	6232
	11th to 20th	Day	18% 9% 4 10% 6% 5% 4 4 5% 6% 30%	6277
	21st to end	Day	18% 7% 3 7% 6% 5% 5% 4 6% 8% 32%	6902
June	1st to 10th	Day	21% 8% 3 6% 5% 4 4 3 5% 6% 34%	2800
	11th to 20th	Day	20% 9% 3 7% 6% 5% 5% 4 6% 7% 27%	2800
	21st to end	Day	9% 6% 2 6% 4 4 4 3 5% 6% 51%	2800
July	1st to 10th	Day	5% 3 1 3 2 2 3 2 3 5% 71%	6319
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 3 79%	6320
	21st to end	Day	5% 3 1 2 2 2 2 2 3 5% 73%	6880
August	1st to 10th	Day	5% 4 1 4 3 3 3 3 5% 6% 63%	5834
	11th to 20th	Day	7% 4 2 5% 3 4 4 4 5% 7% 54%	5796
	21st to end	Day	8% 5% 2 4 3 4 4 4 6% 7% 52%	6126
September	1st to 10th	Day	8% 4 2 4 3 3 4 3 5% 7% 58%	2400
	11th to 20th	Day	12% 8% 3 7% 4 4 4 4 5% 7% 43%	2400
	21st to end	Day	16% 5% 2 6% 4 4 5% 3 4 7% 45%	2106
October	1st to 10th	Day	16% 7% 2 5% 4 3 4 3 5% 6% 45%	3280
	11th to 20th	Day	18% 7% 3 8% 5% 5% 5% 4 6% 7% 32%	3261
	21st to end	Day	28% 9% 3 8% 5% 4 5% 4 6% 8% 22%	3468
November	1st to 10th	Day	30% 10% 4 10% 4 5% 5% 4 5% 5% 17%	1754
	11th to 20th	Day	32% 9% 4 8% 7% 4 3 3 6% 5% 19%	1680
	21st to end	Day	28% 11% 4 7% 6% 6% 5% 3 5% 5% 21%	1680
December	1st to 10th	Day	24% 8% 2 7% 4 4 4 4 5% 6% 31%	2700
	11th to 20th	Day	31% 12% 4 11% 6% 6% 5% 4 5% 5% 11%	3108
	21st to end	Day	34% 15% 5% 11% 6% 4 4 3 5% 4 10%	4092
January	1st to 10th	Night	36% 15% 4 10% 5% 5% 4 3 3 4 13%	6446
	11th to 20th	Night	29% 12% 3 7% 4 5% 5% 4 4 5% 23%	6404
	21st to end	Night	28% 9% 3 7% 4 3 3 2 3 5% 33%	6584
February	1st to 10th	Night	28% 13% 3 9% 7% 5% 5% 3 5% 5% 17%	2600
	11th to 20th	Night	32% 11% 3 7% 5% 3 3 2 5% 5% 23%	2532
	21st to end	Night	29% 14% 4 9% 4 4 3 3 4 5% 21%	2055
March	1st to 10th	Night	18% 12% 4 10% 7% 6% 5% 5% 6% 6% 22%	5166
	11th to 20th	Night	24% 11% 3 8% 4 4 4 3 5% 5% 29%	5000
	21st to end	Night	27% 13% 3 10% 6% 6% 5% 4 5% 6% 14%	5360
April	1st to 10th	Night	26% 14% 4 10% 6% 5% 4 3 5% 5% 21%	2000
	11th to 20th	Night	21% 11% 3 8% 4 3 3 4 5% 7% 31%	1979
	21st to end	Night	24% 10% 4 8% 4 5% 4 3 5% 5% 28%	1818
May	1st to 10th	Night	19% 7% 3 6% 3 3 3 2 4 6% 44%	3718
	11th to 20th	Night	19% 9% 4 8% 4 5% 4 3 4 5% 36%	3616
	21st to end	Night	18% 9% 4 7% 5% 4 4 3 6% 8% 32%	3972
June	1st to 10th	Night	18% 9% 3 6% 5% 4 4 3 4 6% 38%	1600
	11th to 20th	Night	18% 10% 4 7% 5% 4 4 3 4 5% 34%	1600
	21st to end	Night	11% 5% 2 5% 3 3 4 3 4 5% 54%	1600
July	1st to 10th	Night	7% 2 1 3 2 2 2 2 3 4 72%	3640
	11th to 20th	Night	3 2 1 2 2 2 2 1 2 3 81%	3640
	21st to end	Night	4 3 1 3 2 1 2 2 4 5% 74%	3970
August	1st to 10th	Night	6% 3 1 4 3 3 4 3 5% 7% 62%	3960
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 5% 53%	4052
	21st to end	Night	9% 5% 2 5% 3 3 3 3 4 6% 57%	4867
September	1st to 10th	Night	8% 3 2 4 3 2 3 2 4 6% 64%	2000
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 4 6% 48%	2000
	21st to end	Night	13% 6% 2 3 4 4 4 3 5% 7% 50%	2288
October	1st to 10th	Night	15% 5% 2 5% 3 3 4 3 5% 7% 49%	3920
	11th to 20th	Night	17% 6% 3 6% 5% 4 4 4 6% 8% 37%	3897
	21st to end	Night	27% 9% 3 8% 5% 4 4 3 5% 6% 25%	4338
November	1st to 10th	Night	32% 9% 3 7% 5% 5% 5% 3 5% 5% 21%	2762
	11th to 20th	Night	37% 9% 3 8% 4 4 4 3 4 4 21%	2940
	21st to end	Night	27% 10% 3 7% 5% 4 5% 3 5% 5% 25%	2940
December	1st to 10th	Night	22% 8% 3 5% 4 3 4 4 6% 7% 34%	4700
	11th to 20th	Night	35% 13% 4 10% 5% 5% 4 3 4 5% 12%	5316
	21st to end	Night	33% 13% 4 10% 6% 5% 4 3 4 4 13%	7106

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	76% 8% 6% 6% 4 1	3719
	11th to 20th	Day	62% 6% 7% 15% 8% 2	3688
	21st to end	Day	55% 7% 7% 12% 16% 3	4372
February	1st to 10th	Day	66% 8% 11% 10% 5%	1800
	11th to 20th	Day	67% 8% 9% 9% 4 2	1764
	21st to end	Day	68% 5% 10% 8% 7% 2	1575
March	1st to 10th	Day	57% 7% 17% 16% 4	4711
	11th to 20th	Day	60% 7% 8% 16% 9% 1	5000
	21st to end	Day	67% 10% 13% 8% 3	5614
April	1st to 10th	Day	66% 7% 12% 12% 3	2400
	11th to 20th	Day	59% 7% 10% 13% 9% 2	2372
	21st to end	Day	59% 8% 11% 13% 7% 1	2580
May	1st to 10th	Day	42% 8% 10% 23% 16%	6232
	11th to 20th	Day	50% 9% 15% 18% 8% 1	6280
	21st to end	Day	48% 10% 21% 17% 4	6904
June	1st to 10th	Day	51% 7% 16% 18% 7% 1	2800
	11th to 20th	Day	53% 8% 17% 15% 6%	2800
	21st to end	Day	34% 6% 18% 28% 10% 4	2800
July	1st to 10th	Day	16% 4 10% 29% 20% 21%	6251
	11th to 20th	Day	12% 3 7% 21% 39% 19%	6245
	21st to end	Day	14% 3 16% 35% 26% 5%	6681
August	1st to 10th	Day	20% 5% 11% 27% 26% 12%	4250
	11th to 20th	Day	26% 7% 18% 31% 13% 5%	4195
	21st to end	Day	29% 6% 12% 25% 20% 8%	4417
September	1st to 10th	Day	25% 5% 14% 26% 19% 12%	2400
	11th to 20th	Day	39% 7% 14% 20% 14% 7%	2400
	21st to end	Day	39% 6% 14% 20% 16% 6%	2106
October	1st to 10th	Day	38% 6% 8% 23% 21% 3	3280
	11th to 20th	Day	48% 7% 17% 16% 10% 2	3261
	21st to end	Day	59% 6% 9% 16% 9% 1	3468
November	1st to 10th	Day	67% 7% 11% 11% 4 1	1754
	11th to 20th	Day	67% 5% 12% 9% 6% 2	1680
	21st to end	Day	64% 6% 8% 10% 11% 1	1680
December	1st to 10th	Day	52% 6% 11% 15% 15% 2	2700
	11th to 20th	Day	73% 7% 10% 8% 2	3108
	21st to end	Day	76% 8% 8% 7% 2	4092
January	1st to 10th	Night	75% 6% 7% 6% 5% 1	6446
	11th to 20th	Night	60% 9% 8% 15% 6% 2	6404
	21st to end	Night	56% 4 6% 13% 16% 4	6584
February	1st to 10th	Night	67% 8% 10% 10% 5% 1	2600
	11th to 20th	Night	64% 6% 12% 10% 7% 2	2534
	21st to end	Night	64% 6% 10% 11% 6% 2	2055
March	1st to 10th	Night	58% 7% 14% 15% 6%	5166
	11th to 20th	Night	55% 8% 12% 14% 11% 1	5000
	21st to end	Night	67% 9% 14% 9% 1	5360
April	1st to 10th	Night	64% 7% 12% 12% 5%	2000
	11th to 20th	Night	53% 8% 14% 15% 7% 3	1979
	21st to end	Night	56% 7% 14% 15% 6% 2	1818
May	1st to 10th	Night	39% 9% 10% 28% 13% 1	3715
	11th to 20th	Night	45% 12% 14% 22% 5% 1	3616
	21st to end	Night	45% 13% 22% 16% 4	3972
June	1st to 10th	Night	48% 7% 16% 22% 7% 1	1600
	11th to 20th	Night	51% 6% 17% 21% 5%	1600
	21st to end	Night	31% 7% 18% 29% 11% 5%	1600
July	1st to 10th	Night	17% 4 10% 27% 24% 19%	3600
	11th to 20th	Night	12% 2 8% 19% 43% 16%	3592
	21st to end	Night	14% 4 20% 32% 26% 4	3857
August	1st to 10th	Night	14% 4 10% 36% 28% 7%	2881
	11th to 20th	Night	30% 7% 20% 27% 10% 5%	2929
	21st to end	Night	29% 5% 12% 27% 18% 8%	3499
September	1st to 10th	Night	22% 6% 15% 27% 19% 11%	2000
	11th to 20th	Night	36% 6% 13% 23% 14% 9%	2000
	21st to end	Night	33% 6% 16% 22% 15% 8%	2288
October	1st to 10th	Night	34% 6% 10% 28% 20% 2	3920
	11th to 20th	Night	43% 7% 17% 18% 12% 2	3897
	21st to end	Night	57% 7% 9% 15% 10% 2	4338
November	1st to 10th	Night	63% 7% 9% 13% 7%	2762
	11th to 20th	Night	67% 6% 8% 9% 7% 2	2940
	21st to end	Night	60% 6% 9% 10% 12% 3	2940
December	1st to 10th	Night	47% 8% 11% 18% 14% 1	4700
	11th to 20th	Night	74% 6% 8% 7% 4	5316
	21st to end	Night	71% 8% 12% 7% 2	7106

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	44% 13% 17% 16% 10%	220
	11th to 20th	Day	37% 7% 18% 24% 10% 4	212
	21st to end	Day	34% 11% 17% 20% 15% 3	380
February	1st to 10th	Day	36% 12% 20% 22% 8% 3	400
	11th to 20th	Day	34% 15% 25% 17% 7% 1	395
	21st to end	Day	38% 13% 21% 17% 10% 1	377
March	1st to 10th	Day	34% 13% 25% 20% 7% 1	500
	11th to 20th	Day	31% 12% 25% 19% 10% 2	500
	21st to end	Day	33% 15% 26% 18% 7%	550
April	1st to 10th	Day	34% 15% 20% 20% 8% 3	500
	11th to 20th	Day	26% 16% 27% 18% 9% 3	492
	21st to end	Day	26% 13% 26% 23% 12% 2	500
May	1st to 10th	Day	21% 13% 24% 25% 12% 4	503
	11th to 20th	Day	27% 12% 17% 26% 16% 2	528
	21st to end	Day	21% 8% 19% 29% 18% 3	573
June	1st to 10th	Day	22% 8% 19% 29% 17% 4	530
	11th to 20th	Day	19% 11% 27% 26% 15% 1	530
	21st to end	Day	9% 7% 22% 35% 21% 5%	530
July	1st to 10th	Day	6% 4 21% 41% 24% 4	526
	11th to 20th	Day	4 5% 19% 45% 22% 5%	524
	21st to end	Day	4 2 16% 43% 27% 7%	575
August	1st to 10th	Day	7% 3 13% 41% 27% 8%	527
	11th to 20th	Day	4 3 15% 37% 30% 9%	517
	21st to end	Day	8% 5% 22% 36% 22% 7%	583
September	1st to 10th	Day	8% 5% 23% 35% 25% 5%	530
	11th to 20th	Day	14% 6% 20% 30% 25% 5%	530
	21st to end	Day	16% 8% 23% 32% 17% 4	530
October	1st to 10th	Day	21% 8% 22% 25% 18% 5%	530
	11th to 20th	Day	22% 12% 18% 27% 18% 4	530
	21st to end	Day	31% 11% 22% 21% 11% 4	529
November	1st to 10th	Day	32% 16% 17% 21% 11% 3	278
	11th to 20th	Day	32% 12% 25% 15% 14% 3	220
	21st to end	Day	30% 11% 19% 21% 19%	220
December	1st to 10th	Day	37% 12% 15% 20% 10% 7%	220
	11th to 20th	Day	44% 10% 21% 17% 8%	220
	21st to end	Day	46% 12% 17% 13% 11% 2	242
January	1st to 10th	Night	43% 9% 17% 20% 10% 1	840
	11th to 20th	Night	36% 10% 14% 25% 14% 1	824
	21st to end	Night	33% 7% 16% 29% 13% 2	880
February	1st to 10th	Night	33% 10% 18% 25% 12% 2	800
	11th to 20th	Night	37% 11% 16% 23% 12% 1	784
	21st to end	Night	37% 10% 17% 29% 8%	660
March	1st to 10th	Night	30% 10% 18% 28% 13% 1	800
	11th to 20th	Night	30% 9% 18% 30% 12% 1	800
	21st to end	Night	33% 11% 19% 25% 11% 1	880
April	1st to 10th	Night	32% 8% 18% 26% 16% 1	800
	11th to 20th	Night	26% 10% 19% 30% 14% 2	791
	21st to end	Night	31% 9% 16% 28% 15% 1	618
May	1st to 10th	Night	21% 8% 18% 35% 17% 1	439
	11th to 20th	Night	22% 7% 16% 30% 25% 1	394
	21st to end	Night	25% 5% 16% 33% 19% 1	433
June	1st to 10th	Night	22% 6% 17% 32% 24% 1	400
	11th to 20th	Night	22% 7% 20% 37% 15% 1	400
	21st to end	Night	11% 5% 17% 44% 23% 1	400
July	1st to 10th	Night	7% 3 9% 50% 30%	390
	11th to 20th	Night	6% 3 14% 45% 31% 1	388
	21st to end	Night	3 2 8% 52% 34% 2	438
August	1st to 10th	Night	6% 1 7% 37% 43% 6%	561
	11th to 20th	Night	7% 2 6% 35% 44% 6%	594
	21st to end	Night	8% 4 13% 41% 32% 4	810
September	1st to 10th	Night	8% 4 13% 39% 33% 3	800
	11th to 20th	Night	13% 3 11% 34% 33% 6%	800
	21st to end	Night	15% 5% 13% 38% 27% 3	800
October	1st to 10th	Night	21% 4 16% 32% 24% 3	800
	11th to 20th	Night	22% 7% 13% 31% 24% 4	800
	21st to end	Night	27% 9% 18% 27% 16% 3	880
November	1st to 10th	Night	35% 8% 18% 27% 12%	820
	11th to 20th	Night	40% 10% 15% 24% 10% 1	840
	21st to end	Night	30% 8% 17% 29% 15% 1	840
December	1st to 10th	Night	34% 7% 16% 26% 15% 2	840
	11th to 20th	Night	41% 10% 16% 22% 11%	840
	21st to end	Night	40% 11% 18% 21% 8% 1	924

Page generated at 2026-01-13 22:14:27. Version ac07

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