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 2024-01-14.

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	21% 8% 3 6% 6% 3 4 4 5% 6% 34%	74751
	Night	23% 9% 3 6% 5% 3 4 4 4 5% 33%	75022
Transparency	Day	51% 6% 12% 17% 11% 3	74454
	Night	52% 6% 12% 16% 10% 3	74840
Seeing	Day	23% 9% 21% 27% 16% 4	13516
	Night	27% 7% 15% 30% 19% 2	22607

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% 12% 4 8% 7% 3 4 4 3 4 13%	1519
	11th to 20th	Day	36% 11% 4 6% 6% 3 4 3 3 4 20%	1464
	21st to end	Day	28% 10% 4 6% 7% 3 5% 4 4 5% 24%	1728
February	1st to 10th	Day	31% 13% 4 6% 6% 3 5% 5% 5% 6% 17%	1620
	11th to 20th	Day	29% 12% 4 9% 7% 4 4 4 4 4 19%	1575
	21st to end	Day	30% 13% 4 7% 8% 3 4 3 3 4 20%	1412
March	1st to 10th	Day	27% 10% 4 7% 7% 4 7% 4 5% 6% 18%	1876
	11th to 20th	Day	29% 11% 5% 8% 6% 3 5% 4 4 6% 20%	1980
	21st to end	Day	29% 13% 4 9% 7% 4 5% 5% 5% 5% 14%	2229
April	1st to 10th	Day	30% 10% 4 8% 8% 4 5% 3 4 5% 18%	2160
	11th to 20th	Day	25% 11% 5% 7% 6% 4 4 4 5% 5% 24%	2129
	21st to end	Day	24% 8% 4 7% 7% 3 5% 5% 5% 6% 25%	2322
May	1st to 10th	Day	20% 8% 5% 7% 6% 4 4 4 4 4 34%	2484
	11th to 20th	Day	21% 8% 4 6% 7% 3 4 5% 5% 8% 30%	2477
	21st to end	Day	26% 8% 3 6% 6% 4 4 6% 5% 6% 27%	2723
June	1st to 10th	Day	23% 7% 4 6% 6% 3 4 4 5% 6% 31%	2520
	11th to 20th	Day	22% 8% 4 6% 7% 4 5% 6% 6% 6% 26%	2520
	21st to end	Day	9% 5% 2 5% 4 3 5% 4 4 5% 52%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 4 5% 4 7% 57%	2520
	11th to 20th	Day	7% 3 1 3 3 2 4 4 4 6% 63%	2520
	21st to end	Day	6% 3 1 3 2 1 2 2 3 5% 71%	2741
August	1st to 10th	Day	5% 4 1 3 4 3 5% 4 4 7% 61%	2359
	11th to 20th	Day	5% 3 2 3 3 2 3 4 4 6% 65%	2298
	21st to end	Day	7% 4 2 4 4 3 4 4 5% 7% 56%	2440
September	1st to 10th	Day	9% 4 2 3 3 2 3 4 4 7% 61%	2160
	11th to 20th	Day	11% 7% 3 6% 5% 3 4 5% 5% 7% 43%	2160
	21st to end	Day	16% 5% 2 5% 5% 3 5% 4 4 6% 43%	1897
October	1st to 10th	Day	20% 9% 2 5% 5% 2 5% 4 5% 6% 37%	1800
	11th to 20th	Day	20% 7% 4 7% 5% 4 4 4 5% 7% 33%	1800
	21st to end	Day	29% 8% 3 7% 6% 3 4 4 4 5% 28%	1932
November	1st to 10th	Day	31% 9% 4 9% 5% 4 5% 5% 5% 5% 17%	1584
	11th to 20th	Day	32% 8% 4 7% 8% 3 4 3 6% 5% 20%	1520
	21st to end	Day	28% 9% 5% 6% 7% 4 6% 3 4 5% 22%	1520
December	1st to 10th	Day	28% 11% 4 8% 6% 4 4 3 4 4 25%	1520
	11th to 20th	Day	29% 10% 4 8% 7% 4 5% 5% 6% 7% 16%	1928
	21st to end	Day	31% 15% 5% 9% 8% 4 4 5% 5% 4 11%	2794
January	1st to 10th	Night	36% 12% 4 7% 5% 4 5% 3 3 4 17%	2646
	11th to 20th	Night	34% 10% 4 7% 5% 3 4 4 4 5% 20%	2568
	21st to end	Night	28% 11% 4 8% 6% 3 4 3 4 5% 25%	2625
February	1st to 10th	Night	29% 12% 3 7% 7% 3 5% 4 5% 5% 18%	2340
	11th to 20th	Night	32% 10% 4 6% 5% 3 4 3 4 5% 24%	2272
	21st to end	Night	29% 14% 4 8% 5% 3 3 4 4 5% 21%	1844
March	1st to 10th	Night	25% 12% 4 7% 5% 4 4 5% 4 6% 24%	2080
	11th to 20th	Night	26% 9% 3 6% 5% 4 6% 4 5% 7% 24%	1980
	21st to end	Night	28% 12% 5% 8% 7% 3 5% 4 4 5% 18%	2126
April	1st to 10th	Night	27% 13% 4 8% 7% 3 5% 3 4 5% 21%	1800
	11th to 20th	Night	22% 10% 4 8% 6% 2 4 5% 5% 7% 28%	1779
	21st to end	Night	26% 9% 4 6% 4 3 5% 4 5% 5% 28%	1637
May	1st to 10th	Night	19% 9% 3 6% 5% 3 4 4 5% 5% 38%	1476
	11th to 20th	Night	20% 7% 4 5% 6% 4 5% 4 5% 8% 32%	1416
	21st to end	Night	20% 9% 3 7% 6% 3 5% 5% 5% 8% 29%	1552
June	1st to 10th	Night	19% 8% 4 6% 5% 3 4 4 4 6% 37%	1440
	11th to 20th	Night	19% 10% 5% 7% 6% 3 4 3 4 6% 33%	1440
	21st to end	Night	11% 5% 3 3 4 2 4 4 4 5% 56%	1440
July	1st to 10th	Night	8% 3 1 4 3 3 3 3 3 6% 64%	1440
	11th to 20th	Night	6% 2 1 3 3 2 4 3 3 5% 68%	1440
	21st to end	Night	3 1 1 2 2 1 2 2 3 5% 77%	1576
August	1st to 10th	Night	4 3 1 3 3 2 2 3 5% 7% 68%	1578
	11th to 20th	Night	4 3 1 3 3 2 3 4 3 5% 70%	1602
	21st to end	Night	6% 4 2 3 3 2 3 4 3 6% 64%	1916
September	1st to 10th	Night	8% 3 2 3 3 1 3 3 4 6% 66%	1800
	11th to 20th	Night	12% 5% 3 5% 5% 3 4 5% 4 6% 49%	1800
	21st to end	Night	14% 6% 2 3 4 3 4 4 5% 7% 49%	2057
October	1st to 10th	Night	19% 6% 3 4 5% 2 4 4 4 5% 44%	2160
	11th to 20th	Night	19% 6% 3 5% 4 3 3 5% 5% 7% 39%	2160
	21st to end	Night	25% 8% 3 6% 5% 3 3 3 4 5% 35%	2422
November	1st to 10th	Night	32% 8% 3 6% 6% 3 5% 4 5% 5% 22%	2492
	11th to 20th	Night	36% 8% 3 7% 5% 3 3 4 4 4 22%	2660
	21st to end	Night	27% 8% 4 6% 6% 3 5% 4 5% 4 27%	2660
December	1st to 10th	Night	30% 9% 4 6% 5% 2 5% 4 4 6% 25%	2660
	11th to 20th	Night	30% 11% 4 8% 6% 3 4 4 5% 6% 18%	3276
	21st to end	Night	28% 14% 5% 10% 9% 4 5% 4 5% 4 13%	4862

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% 7% 7% 7% 3 1	1519
	11th to 20th	Day	69% 4 8% 9% 6% 4	1464
	21st to end	Day	63% 6% 9% 12% 10% 1	1728
February	1st to 10th	Day	66% 7% 12% 9% 6%	1620
	11th to 20th	Day	67% 8% 9% 10% 4 2	1584
	21st to end	Day	69% 5% 9% 9% 6% 2	1412
March	1st to 10th	Day	65% 7% 12% 10% 5%	1876
	11th to 20th	Day	66% 6% 8% 12% 6% 1	1980
	21st to end	Day	71% 8% 10% 9% 1	2229
April	1st to 10th	Day	67% 7% 11% 11% 3	2160
	11th to 20th	Day	63% 6% 10% 12% 7% 3	2132
	21st to end	Day	60% 8% 12% 12% 8% 2	2322
May	1st to 10th	Day	52% 5% 15% 19% 9% 1	2484
	11th to 20th	Day	52% 8% 14% 18% 6% 1	2480
	21st to end	Day	57% 8% 15% 17% 3	2724
June	1st to 10th	Day	53% 7% 17% 17% 5%	2520
	11th to 20th	Day	56% 8% 18% 13% 5%	2520
	21st to end	Day	34% 5% 18% 28% 10% 4	2520
July	1st to 10th	Day	26% 6% 16% 25% 22% 5%	2451
	11th to 20th	Day	22% 6% 11% 25% 30% 6%	2445
	21st to end	Day	16% 2 9% 30% 36% 6%	2589
August	1st to 10th	Day	21% 6% 15% 32% 20% 5%	2342
	11th to 20th	Day	20% 5% 14% 32% 21% 8%	2298
	21st to end	Day	27% 6% 12% 29% 23% 4	2440
September	1st to 10th	Day	23% 4 13% 27% 20% 12%	2160
	11th to 20th	Day	39% 7% 13% 20% 14% 7%	2160
	21st to end	Day	40% 7% 13% 18% 15% 6%	1897
October	1st to 10th	Day	46% 7% 10% 19% 15% 4	1800
	11th to 20th	Day	50% 6% 15% 14% 12% 3	1800
	21st to end	Day	58% 5% 9% 13% 13% 1	1932
November	1st to 10th	Day	67% 7% 10% 11% 4 1	1584
	11th to 20th	Day	66% 5% 12% 9% 6% 2	1520
	21st to end	Day	64% 5% 7% 10% 12% 1	1520
December	1st to 10th	Day	63% 5% 10% 10% 10% 2	1520
	11th to 20th	Day	66% 8% 11% 11% 4	1928
	21st to end	Day	74% 8% 9% 6% 3	2794
January	1st to 10th	Night	72% 5% 8% 7% 5% 2	2646
	11th to 20th	Night	66% 5% 9% 10% 7% 3	2568
	21st to end	Night	63% 5% 9% 12% 10% 2	2625
February	1st to 10th	Night	67% 7% 10% 10% 5% 1	2340
	11th to 20th	Night	63% 6% 12% 10% 6% 2	2274
	21st to end	Night	66% 5% 10% 10% 6% 2	1844
March	1st to 10th	Night	61% 6% 11% 16% 6%	2080
	11th to 20th	Night	58% 8% 12% 13% 6% 2	1980
	21st to end	Night	67% 9% 12% 11% 1	2126
April	1st to 10th	Night	65% 6% 12% 12% 5%	1800
	11th to 20th	Night	56% 8% 14% 13% 6% 3	1779
	21st to end	Night	57% 6% 14% 14% 6% 3	1637
May	1st to 10th	Night	46% 8% 15% 21% 8% 2	1476
	11th to 20th	Night	50% 8% 17% 17% 5% 4	1416
	21st to end	Night	51% 9% 17% 17% 5%	1552
June	1st to 10th	Night	49% 7% 17% 21% 5%	1440
	11th to 20th	Night	53% 6% 18% 19% 4	1440
	21st to end	Night	31% 6% 18% 29% 11% 5%	1440
July	1st to 10th	Night	24% 5% 13% 29% 22% 7%	1400
	11th to 20th	Night	20% 5% 12% 26% 30% 7%	1392
	21st to end	Night	10% 4 10% 35% 32% 9%	1488
August	1st to 10th	Night	16% 5% 16% 37% 20% 6%	1570
	11th to 20th	Night	18% 5% 14% 37% 18% 8%	1602
	21st to end	Night	22% 6% 12% 36% 19% 5%	1916
September	1st to 10th	Night	21% 6% 14% 29% 20% 12%	1800
	11th to 20th	Night	35% 6% 12% 24% 13% 10%	1800
	21st to end	Night	34% 6% 16% 20% 16% 8%	2057
October	1st to 10th	Night	43% 5% 9% 22% 17% 4	2160
	11th to 20th	Night	44% 7% 12% 18% 16% 4	2160
	21st to end	Night	52% 6% 9% 14% 16% 3	2422
November	1st to 10th	Night	62% 7% 9% 14% 8%	2492
	11th to 20th	Night	65% 6% 9% 9% 8% 3	2660
	21st to end	Night	59% 6% 9% 11% 13% 3	2660
December	1st to 10th	Night	60% 6% 11% 11% 10% 2	2660
	11th to 20th	Night	65% 7% 10% 10% 7%	3276
	21st to end	Night	68% 9% 12% 8% 2 1	4862

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	42% 13% 18% 15% 11% 1	180
	11th to 20th	Day	43% 7% 17% 20% 10% 2	166
	21st to end	Day	37% 8% 16% 22% 16% 2	320
February	1st to 10th	Day	39% 11% 17% 23% 8% 2	340
	11th to 20th	Day	35% 13% 25% 19% 7% 1	335
	21st to end	Day	38% 13% 23% 16% 10%	316
March	1st to 10th	Day	35% 12% 25% 20% 7% 1	420
	11th to 20th	Day	30% 13% 25% 20% 10% 1	420
	21st to end	Day	35% 13% 25% 19% 8%	462
April	1st to 10th	Day	36% 14% 20% 20% 7% 3	420
	11th to 20th	Day	30% 15% 26% 16% 8% 4	412
	21st to end	Day	26% 12% 27% 22% 11% 1	420
May	1st to 10th	Day	22% 13% 23% 25% 13% 4	423
	11th to 20th	Day	28% 12% 15% 26% 18% 2	448
	21st to end	Day	23% 8% 19% 31% 17% 3	485
June	1st to 10th	Day	23% 8% 19% 28% 17% 4	450
	11th to 20th	Day	21% 12% 25% 26% 15% 1	450
	21st to end	Day	9% 6% 23% 35% 22% 4	450
July	1st to 10th	Day	7% 4 19% 41% 25% 4	446
	11th to 20th	Day	4 5% 20% 45% 21% 5%	444
	21st to end	Day	4 3 16% 45% 26% 7%	487
August	1st to 10th	Day	7% 3 14% 40% 28% 9%	447
	11th to 20th	Day	4 3 16% 38% 31% 10%	437
	21st to end	Day	7% 5% 23% 37% 22% 6%	495
September	1st to 10th	Day	9% 5% 25% 34% 22% 5%	450
	11th to 20th	Day	14% 6% 18% 30% 26% 5%	450
	21st to end	Day	16% 9% 23% 32% 17% 3	450
October	1st to 10th	Day	22% 8% 22% 25% 19% 5%	450
	11th to 20th	Day	22% 10% 18% 27% 19% 4	450
	21st to end	Day	32% 11% 21% 19% 13% 4	447
November	1st to 10th	Day	29% 18% 18% 23% 11% 2	228
	11th to 20th	Day	28% 11% 27% 16% 15% 3	180
	21st to end	Day	28% 11% 19% 22% 19% 1	180
December	1st to 10th	Day	37% 13% 16% 21% 10% 4	180
	11th to 20th	Day	42% 10% 22% 17% 8% 1	180
	21st to end	Day	45% 12% 17% 13% 12% 2	198
January	1st to 10th	Night	43% 9% 17% 19% 11% 1	760
	11th to 20th	Night	38% 10% 12% 24% 13% 1	734
	21st to end	Night	33% 7% 15% 30% 13% 2	792
February	1st to 10th	Night	35% 9% 16% 26% 13% 2	720
	11th to 20th	Night	36% 10% 16% 24% 13% 1	704
	21st to end	Night	37% 10% 17% 29% 8%	592
March	1st to 10th	Night	32% 9% 18% 27% 13% 1	720
	11th to 20th	Night	30% 9% 18% 31% 12% 1	720
	21st to end	Night	34% 10% 18% 25% 12% 1	792
April	1st to 10th	Night	33% 7% 18% 26% 16% 1	720
	11th to 20th	Night	27% 9% 18% 29% 14% 2	711
	21st to end	Night	32% 8% 17% 27% 15% 1	557
May	1st to 10th	Night	21% 8% 18% 34% 17% 1	396
	11th to 20th	Night	21% 7% 16% 29% 27% 1	354
	21st to end	Night	26% 5% 16% 32% 20% 2	389
June	1st to 10th	Night	22% 5% 17% 31% 25%	360
	11th to 20th	Night	23% 6% 19% 36% 15% 1	360
	21st to end	Night	11% 4 18% 44% 22% 1	360
July	1st to 10th	Night	7% 3 9% 50% 30%	350
	11th to 20th	Night	6% 3 14% 46% 30% 1	348
	21st to end	Night	3 2 7% 53% 34% 2	394
August	1st to 10th	Night	5% 1 7% 38% 43% 6%	504
	11th to 20th	Night	5% 2 6% 34% 47% 6%	534
	21st to end	Night	8% 3 13% 41% 32% 4	728
September	1st to 10th	Night	9% 3 14% 40% 32% 3	720
	11th to 20th	Night	12% 3 11% 33% 35% 6%	720
	21st to end	Night	16% 4 12% 38% 26% 3	720
October	1st to 10th	Night	22% 4 15% 30% 25% 3	720
	11th to 20th	Night	22% 6% 12% 31% 24% 4	720
	21st to end	Night	28% 9% 17% 26% 16% 4	792
November	1st to 10th	Night	34% 7% 18% 28% 12% 1	740
	11th to 20th	Night	39% 10% 15% 25% 11% 1	760
	21st to end	Night	30% 8% 17% 29% 15% 1	760
December	1st to 10th	Night	34% 7% 17% 27% 13% 1	760
	11th to 20th	Night	40% 9% 16% 23% 11%	760
	21st to end	Night	41% 11% 18% 21% 8% 1	836

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