Hunt Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hunt Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	13% 7% 2 6% 4 4 5% 4 6% 8% 42%	132318
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 45%	129530
Transparency	Day	38% 7% 11% 21% 18% 5%	136074
	Night	37% 6% 10% 20% 20% 7%	133849
Seeing	Day	17% 9% 23% 25% 18% 8%	16680
	Night	16% 8% 23% 29% 20% 4	26226

By Month

Percentage Cloud Cover SE (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	20% 11% 4 6% 3 2 3 2 4 5% 40%	5258
	11th to 20th	Day	12% 5% 3 6% 2 2 2 2 3 6% 56%	5714
	21st to end	Day	23% 10% 2 8% 4 3 3 3 3 5% 37%	6436
February	1st to 10th	Day	18% 10% 3 6% 4 3 3 3 3 6% 41%	2100
	11th to 20th	Day	21% 8% 2 6% 4 4 3 3 4 5% 39%	2048
	21st to end	Day	19% 8% 3 8% 4 3 3 3 4 5% 41%	1730
March	1st to 10th	Day	21% 8% 3 7% 4 4 4 3 5% 5% 35%	4580
	11th to 20th	Day	12% 7% 2 6% 4 4 4 4 6% 7% 44%	4756
	21st to end	Day	14% 7% 2 7% 4 4 4 3 5% 7% 42%	6092
April	1st to 10th	Day	12% 5% 2 5% 5% 3 4 4 5% 7% 46%	2412
	11th to 20th	Day	13% 6% 2 5% 4 4 3 4 5% 6% 48%	2374
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 5% 8% 47%	2400
May	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 5% 7% 8% 34%	5630
	11th to 20th	Day	15% 8% 3 8% 5% 5% 7% 5% 7% 8% 30%	5861
	21st to end	Day	13% 7% 3 6% 5% 4 5% 4 6% 8% 39%	6433
June	1st to 10th	Day	10% 6% 2 6% 5% 6% 5% 5% 6% 10% 37%	2600
	11th to 20th	Day	5% 5% 2 6% 5% 5% 6% 5% 9% 10% 43%	2674
	21st to end	Day	7% 5% 2 6% 5% 6% 5% 4 7% 10% 42%	2800
July	1st to 10th	Day	5% 5% 2 7% 6% 7% 6% 5% 8% 11% 36%	6360
	11th to 20th	Day	7% 4 2 6% 5% 6% 6% 6% 10% 13% 34%	6001
	21st to end	Day	9% 7% 2 8% 7% 6% 7% 7% 9% 12% 27%	6073
August	1st to 10th	Day	4 3 1 5% 4 4 5% 4 8% 9% 54%	3905
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 4 7% 10% 46%	3849
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 6% 8% 50%	4312
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 7% 45%	2400
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 5% 7% 45%	2205
	21st to end	Day	11% 5% 2 5% 4 4 5% 3 5% 6% 51%	2200
October	1st to 10th	Day	9% 4 2 5% 3 3 4 3 5% 7% 55%	2200
	11th to 20th	Day	9% 4 2 5% 3 3 3 3 5% 6% 57%	2128
	21st to end	Day	15% 5% 2 4 3 4 3 2 4 5% 53%	2107
November	1st to 10th	Day	11% 5% 2 6% 3 3 4 3 4 7% 53%	1852
	11th to 20th	Day	12% 5% 2 5% 2 3 3 2 4 7% 53%	1890
	21st to end	Day	15% 7% 2 6% 3 3 4 4 5% 7% 45%	1890
December	1st to 10th	Day	18% 10% 2 5% 3 3 4 3 4 5% 42%	3020
	11th to 20th	Day	19% 9% 3 7% 4 4 3 3 3 4 42%	3463
	21st to end	Day	19% 9% 3 6% 4 3 3 3 4 6% 41%	4565
January	1st to 10th	Night	18% 9% 3 7% 3 4 3 3 4 6% 41%	7635
	11th to 20th	Night	15% 8% 3 6% 3 2 3 2 4 5% 49%	7242
	21st to end	Night	21% 10% 2 7% 4 3 3 2 3 4 41%	7745
February	1st to 10th	Night	18% 8% 2 6% 4 3 3 3 4 6% 43%	2520
	11th to 20th	Night	22% 8% 3 6% 4 4 3 2 4 4 41%	2458
	21st to end	Night	19% 7% 2 6% 4 4 4 3 5% 6% 39%	2076
March	1st to 10th	Night	21% 9% 3 7% 4 4 4 3 4 6% 34%	5493
	11th to 20th	Night	12% 7% 2 4 3 3 3 3 5% 7% 50%	5424
	21st to end	Night	18% 7% 3 6% 4 4 3 3 3 4 44%	5121
April	1st to 10th	Night	13% 5% 2 4 4 4 4 4 6% 6% 47%	2010
	11th to 20th	Night	13% 6% 1 5% 3 3 4 3 5% 7% 49%	1975
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 7% 49%	2000
May	1st to 10th	Night	13% 8% 3 7% 4 4 5% 3 5% 8% 39%	4262
	11th to 20th	Night	18% 9% 3 8% 4 4 4 4 5% 7% 34%	4032
	21st to end	Night	10% 6% 3 6% 4 5% 5% 4 7% 10% 39%	4421
June	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 6% 7% 11% 42%	1800
	11th to 20th	Night	5% 4 2 5% 4 5% 4 4 7% 9% 52%	1715
	21st to end	Night	4 5% 2 5% 5% 4 4 5% 7% 10% 48%	1600
July	1st to 10th	Night	5% 5% 2 6% 6% 5% 6% 5% 8% 12% 39%	3618
	11th to 20th	Night	6% 5% 2 6% 4 5% 6% 6% 8% 14% 39%	3942
	21st to end	Night	7% 7% 3 9% 5% 5% 7% 6% 10% 12% 28%	4746
August	1st to 10th	Night	3 2 1 3 3 3 4 4 7% 10% 60%	3244
	11th to 20th	Night	4 3 1 5% 4 4 5% 4 6% 11% 53%	3200
	21st to end	Night	6% 4 2 4 3 4 4 3 6% 9% 55%	3586
September	1st to 10th	Night	9% 5% 3 7% 4 5% 5% 3 5% 9% 47%	2000
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 7% 47%	2175
	21st to end	Night	8% 4 1 5% 4 5% 4 4 6% 7% 52%	2200
October	1st to 10th	Night	9% 4 2 5% 3 3 3 2 4 6% 61%	2200
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 4 5% 56%	2269
	21st to end	Night	15% 6% 2 4 2 2 2 3 3 4 55%	2730
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 4 5% 56%	2666
	11th to 20th	Night	12% 5% 2 4 3 3 3 2 5% 6% 54%	2730
	21st to end	Night	15% 6% 2 5% 4 4 3 4 4 5% 49%	2730
December	1st to 10th	Night	21% 6% 2 4 3 2 3 3 5% 5% 46%	4380
	11th to 20th	Night	20% 9% 3 5% 3 3 3 3 3 5% 44%	4952
	21st to end	Night	20% 8% 3 6% 3 3 4 3 5% 6% 38%	6633

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	47% 4 6% 26% 15% 2	5259
	11th to 20th	Day	32% 3 5% 22% 33% 5%	5714
	21st to end	Day	52% 2 5% 16% 18% 7%	6436
February	1st to 10th	Day	46% 3 7% 20% 20% 4	2100
	11th to 20th	Day	48% 4 5% 19% 19% 6%	2058
	21st to end	Day	47% 3 6% 13% 23% 7%	1730
March	1st to 10th	Day	50% 5% 7% 13% 17% 8%	4580
	11th to 20th	Day	38% 5% 7% 17% 20% 13%	4756
	21st to end	Day	41% 5% 9% 22% 19% 4	6094
April	1st to 10th	Day	36% 6% 11% 22% 19% 7%	2412
	11th to 20th	Day	37% 5% 7% 23% 22% 7%	2374
	21st to end	Day	35% 5% 11% 26% 21% 3	2400
May	1st to 10th	Day	43% 9% 13% 23% 11% 2	5665
	11th to 20th	Day	47% 9% 15% 19% 9% 1	5865
	21st to end	Day	40% 8% 12% 23% 15% 2	6447
June	1st to 10th	Day	40% 9% 13% 20% 16% 2	2600
	11th to 20th	Day	32% 9% 15% 25% 17% 2	2674
	21st to end	Day	35% 8% 18% 21% 14% 4	2800
July	1st to 10th	Day	37% 12% 18% 23% 10% 1	6291
	11th to 20th	Day	33% 15% 27% 21% 4 1	5929
	21st to end	Day	43% 13% 23% 16% 4	5899
August	1st to 10th	Day	23% 9% 14% 32% 21% 1	3893
	11th to 20th	Day	31% 8% 16% 27% 15% 3	3885
	21st to end	Day	29% 9% 14% 21% 23% 4	4311
September	1st to 10th	Day	37% 8% 13% 19% 19% 5%	2400
	11th to 20th	Day	37% 7% 12% 18% 21% 5%	2205
	21st to end	Day	33% 6% 11% 22% 21% 7%	2200
October	1st to 10th	Day	21% 4 6% 14% 30% 26%	3590
	11th to 20th	Day	19% 3 4 17% 31% 26%	3446
	21st to end	Day	25% 3 4 22% 34% 12%	3384
November	1st to 10th	Day	33% 4 8% 18% 28% 9%	1852
	11th to 20th	Day	32% 4 7% 20% 27% 10%	1890
	21st to end	Day	38% 4 6% 20% 24% 7%	1890
December	1st to 10th	Day	45% 4 5% 18% 25% 3	3020
	11th to 20th	Day	47% 4 6% 19% 17% 6%	3460
	21st to end	Day	44% 4 7% 23% 20% 2	4565
January	1st to 10th	Night	46% 3 7% 23% 19% 2	7636
	11th to 20th	Night	39% 3 5% 17% 27% 9%	7242
	21st to end	Night	48% 3 3 17% 21% 8%	7745
February	1st to 10th	Night	43% 4 5% 20% 21% 7%	2520
	11th to 20th	Night	47% 4 6% 17% 18% 7%	2459
	21st to end	Night	45% 4 7% 15% 20% 9%	2076
March	1st to 10th	Night	50% 4 7% 13% 17% 8%	5493
	11th to 20th	Night	34% 4 8% 17% 21% 16%	5424
	21st to end	Night	44% 4 6% 22% 18% 6%	5121
April	1st to 10th	Night	36% 5% 12% 20% 20% 7%	2010
	11th to 20th	Night	34% 5% 6% 22% 22% 11%	1975
	21st to end	Night	33% 6% 11% 24% 22% 5%	2000
May	1st to 10th	Night	40% 9% 14% 21% 15% 2	4292
	11th to 20th	Night	48% 7% 14% 20% 9% 2	4033
	21st to end	Night	36% 9% 14% 22% 17% 2	4429
June	1st to 10th	Night	34% 9% 14% 22% 19% 2	1800
	11th to 20th	Night	26% 9% 16% 26% 20% 4	1715
	21st to end	Night	30% 9% 17% 22% 19% 3	1600
July	1st to 10th	Night	34% 10% 24% 22% 9% 1	3580
	11th to 20th	Night	32% 12% 30% 21% 5% 1	3894
	21st to end	Night	42% 15% 23% 16% 4 1	4606
August	1st to 10th	Night	18% 7% 14% 37% 22% 2	3232
	11th to 20th	Night	24% 9% 19% 30% 15% 3	3230
	21st to end	Night	25% 8% 15% 22% 24% 6%	3586
September	1st to 10th	Night	35% 6% 16% 20% 16% 6%	2000
	11th to 20th	Night	34% 7% 13% 19% 21% 6%	2175
	21st to end	Night	29% 6% 10% 24% 24% 7%	2200
October	1st to 10th	Night	18% 3 6% 17% 31% 25%	3590
	11th to 20th	Night	20% 3 4 15% 32% 27%	3690
	21st to end	Night	23% 3 4 23% 30% 17%	4403
November	1st to 10th	Night	31% 4 7% 18% 26% 13%	2666
	11th to 20th	Night	32% 3 7% 19% 28% 12%	2730
	21st to end	Night	38% 4 6% 21% 23% 9%	2730
December	1st to 10th	Night	40% 3 6% 22% 25% 3	4380
	11th to 20th	Night	45% 4 6% 18% 23% 4	4954
	21st to end	Night	43% 5% 7% 24% 18% 2	6633

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	33% 19% 32% 14% 3	330
	11th to 20th	Day	28% 23% 30% 15% 3 1	330
	21st to end	Day	28% 22% 37% 10% 3 1	363
February	1st to 10th	Day	23% 22% 37% 15% 3	330
	11th to 20th	Day	35% 22% 32% 8% 2 1	330
	21st to end	Day	34% 19% 34% 10% 2	273
March	1st to 10th	Day	26% 21% 35% 14% 4 1	330
	11th to 20th	Day	24% 20% 38% 14% 4 1	388
	21st to end	Day	23% 13% 36% 22% 6%	594
April	1st to 10th	Day	22% 16% 31% 21% 9% 1	504
	11th to 20th	Day	22% 12% 34% 20% 10% 3	492
	21st to end	Day	18% 10% 31% 28% 12% 2	500
May	1st to 10th	Day	19% 6% 28% 28% 14% 4	503
	11th to 20th	Day	15% 6% 30% 25% 16% 9%	527
	21st to end	Day	11% 5% 24% 30% 18% 11%	573
June	1st to 10th	Day	14% 4 15% 33% 24% 10%	530
	11th to 20th	Day	8% 2 15% 34% 25% 16%	604
	21st to end	Day	10% 2 15% 28% 30% 16%	730
July	1st to 10th	Day	8% 1 10% 30% 33% 16%	721
	11th to 20th	Day	9% 1 6% 24% 35% 25%	570
	21st to end	Day	9% 2 8% 23% 38% 20%	576
August	1st to 10th	Day	9% 3 9% 26% 34% 20%	526
	11th to 20th	Day	10% 2 8% 30% 31% 20%	519
	21st to end	Day	14% 1 8% 28% 30% 19%	583
September	1st to 10th	Day	11% 2 10% 37% 28% 11%	530
	11th to 20th	Day	14% 3 11% 26% 32% 15%	530
	21st to end	Day	14% 5% 13% 29% 30% 8%	530
October	1st to 10th	Day	12% 4 23% 33% 20% 8%	530
	11th to 20th	Day	10% 8% 31% 35% 15% 2	458
	21st to end	Day	23% 11% 25% 28% 11% 1	363
November	1st to 10th	Day	19% 8% 30% 29% 12% 2	330
	11th to 20th	Day	15% 16% 39% 23% 6% 1	330
	21st to end	Day	18% 18% 36% 18% 7% 1	330
December	1st to 10th	Day	32% 17% 32% 15% 4	330
	11th to 20th	Day	25% 18% 35% 15% 7%	330
	21st to end	Day	29% 16% 32% 19% 4	363
January	1st to 10th	Night	23% 16% 35% 21% 5%	840
	11th to 20th	Night	23% 15% 32% 23% 7%	840
	21st to end	Night	23% 15% 36% 23% 2	924
February	1st to 10th	Night	24% 12% 31% 28% 5%	840
	11th to 20th	Night	28% 16% 30% 23% 2	823
	21st to end	Night	25% 17% 34% 22% 2	692
March	1st to 10th	Night	22% 14% 31% 28% 5%	840
	11th to 20th	Night	20% 12% 33% 27% 7% 1	840
	21st to end	Night	20% 10% 36% 24% 10%	716
April	1st to 10th	Night	17% 14% 31% 27% 11%	603
	11th to 20th	Night	16% 10% 32% 29% 12% 2	593
	21st to end	Night	13% 10% 29% 31% 15% 2	600
May	1st to 10th	Night	13% 4 27% 33% 22% 2	600
	11th to 20th	Night	14% 3 23% 31% 24% 6%	591
	21st to end	Night	9% 1 15% 37% 31% 7%	650
June	1st to 10th	Night	9% 2 12% 37% 33% 8%	600
	11th to 20th	Night	5% 2 10% 33% 39% 11%	600
	21st to end	Night	6% 2 8% 30% 42% 12%	600
July	1st to 10th	Night	6% 1 6% 26% 47% 14%	585
	11th to 20th	Night	8% 1 6% 25% 40% 20%	582
	21st to end	Night	7% 8% 24% 46% 15%	657
August	1st to 10th	Night	6% 4 29% 45% 15%	597
	11th to 20th	Night	7% 1 6% 33% 41% 13%	594
	21st to end	Night	12% 1 7% 30% 38% 12%	660
September	1st to 10th	Night	12% 1 9% 35% 35% 8%	600
	11th to 20th	Night	13% 2 12% 30% 37% 6%	775
	21st to end	Night	10% 2 14% 33% 36% 5%	800
October	1st to 10th	Night	11% 3 19% 34% 27% 6%	800
	11th to 20th	Night	12% 6% 22% 38% 20% 2	800
	21st to end	Night	19% 6% 19% 35% 18% 3	880
November	1st to 10th	Night	14% 8% 22% 35% 20% 2	820
	11th to 20th	Night	13% 10% 31% 33% 11% 2	840
	21st to end	Night	19% 9% 30% 31% 11% 1	840
December	1st to 10th	Night	23% 11% 28% 30% 8%	840
	11th to 20th	Night	23% 12% 28% 29% 8%	840
	21st to end	Night	27% 12% 29% 27% 6%	924

Page generated at 2026-03-30 01:18:45. Version ac07

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