Dirt Hills and Cactus Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dirt Hills and Cactus Hills clear sky chart from 2005-11-06 to 2025-07-21.

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	8% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	123662
	Night	7% 8% 3 9% 6% 5% 5% 4 6% 8% 38%	124241
Transparency	Day	42% 6% 15% 25% 11% 1	123396
	Night	43% 6% 15% 24% 11% 1	124097
Seeing	Day	13% 10% 31% 29% 14% 3	16935
	Night	12% 9% 34% 33% 11% 1	26364

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	5% 13% 6% 14% 10% 8% 7% 5% 5% 6% 20%	3179
	11th to 20th	Day	3 7% 4 11% 8% 7% 9% 9% 8% 9% 24%	3526
	21st to end	Day	5% 9% 4 14% 6% 5% 4 5% 5% 7% 35%	4004
February	1st to 10th	Day	7% 13% 6% 13% 9% 7% 7% 5% 7% 5% 23%	1705
	11th to 20th	Day	6% 10% 5% 11% 9% 7% 7% 5% 6% 6% 27%	1755
	21st to end	Day	4 11% 5% 11% 10% 7% 7% 5% 8% 8% 25%	1590
March	1st to 10th	Day	5% 12% 6% 15% 8% 5% 4 3 5% 7% 31%	4500
	11th to 20th	Day	4 12% 5% 14% 7% 5% 5% 4 6% 7% 28%	4857
	21st to end	Day	7% 14% 6% 14% 7% 6% 5% 4 6% 7% 24%	5832
April	1st to 10th	Day	6% 11% 4 8% 6% 6% 6% 4 6% 7% 37%	2400
	11th to 20th	Day	13% 13% 5% 8% 6% 5% 5% 5% 6% 8% 26%	2371
	21st to end	Day	15% 9% 3 7% 5% 4 4 4 6% 7% 36%	2768
May	1st to 10th	Day	13% 9% 3 7% 4 4 3 4 6% 7% 40%	6340
	11th to 20th	Day	14% 9% 3 7% 5% 6% 6% 5% 7% 9% 28%	6298
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 7% 43%	6925
June	1st to 10th	Day	15% 6% 2 6% 4 4 5% 5% 7% 8% 37%	3005
	11th to 20th	Day	17% 7% 3 7% 6% 5% 5% 4 6% 8% 32%	3200
	21st to end	Day	10% 5% 2 5% 4 5% 5% 5% 6% 8% 45%	3118
July	1st to 10th	Day	5% 4 2 6% 5% 6% 6% 5% 7% 9% 46%	4890
	11th to 20th	Day	5% 3 1 4 3 3 5% 4 8% 11% 53%	4764
	21st to end	Day	4 3 1 3 3 3 3 3 6% 7% 63%	4803
August	1st to 10th	Day	8% 4 2 6% 4 4 4 4 5% 7% 51%	4411
	11th to 20th	Day	6% 4 2 5% 3 4 4 5% 6% 9% 53%	4247
	21st to end	Day	9% 4 2 5% 3 3 3 3 5% 7% 56%	4284
September	1st to 10th	Day	12% 4 2 5% 4 4 4 3 5% 8% 49%	2280
	11th to 20th	Day	12% 8% 2 6% 4 4 4 3 5% 7% 45%	2280
	21st to end	Day	13% 7% 1 6% 4 3 3 3 6% 8% 46%	2039
October	1st to 10th	Day	8% 7% 2 5% 4 3 4 3 5% 7% 51%	3170
	11th to 20th	Day	7% 6% 3 6% 3 2 3 3 7% 12% 48%	3088
	21st to end	Day	6% 10% 3 8% 4 5% 5% 4 7% 8% 40%	3091
November	1st to 10th	Day	11% 12% 6% 10% 5% 4 5% 4 4 6% 33%	1625
	11th to 20th	Day	6% 12% 5% 12% 8% 6% 6% 5% 5% 6% 32%	1600
	21st to end	Day	9% 11% 4 10% 8% 7% 6% 4 4 8% 29%	1579
December	1st to 10th	Day	4 11% 4 13% 8% 7% 7% 5% 7% 6% 27%	2290
	11th to 20th	Day	7% 14% 5% 13% 9% 7% 7% 5% 6% 6% 20%	2506
	21st to end	Day	6% 7% 2 10% 9% 5% 4 3 6% 7% 42%	3342
January	1st to 10th	Night	2 11% 5% 13% 9% 7% 8% 6% 7% 7% 24%	6766
	11th to 20th	Night	3 7% 4 12% 9% 9% 10% 5% 10% 8% 23%	6445
	21st to end	Night	3 9% 4 13% 8% 5% 5% 5% 7% 7% 34%	6974
February	1st to 10th	Night	6% 13% 4 12% 8% 7% 7% 6% 8% 8% 22%	2715
	11th to 20th	Night	6% 11% 3 11% 7% 6% 5% 5% 7% 8% 29%	2532
	21st to end	Night	3 9% 4 10% 7% 7% 7% 4 7% 8% 34%	2040
March	1st to 10th	Night	4 9% 4 11% 7% 5% 6% 5% 7% 9% 32%	5374
	11th to 20th	Night	6% 10% 4 10% 6% 7% 6% 4 6% 8% 32%	5133
	21st to end	Night	7% 11% 6% 16% 8% 5% 5% 4 6% 8% 23%	5127
April	1st to 10th	Night	7% 9% 3 7% 5% 4 5% 5% 7% 9% 41%	2000
	11th to 20th	Night	11% 12% 5% 8% 5% 4 5% 4 7% 8% 33%	1977
	21st to end	Night	12% 10% 4 7% 4 5% 5% 4 6% 7% 37%	1630
May	1st to 10th	Night	13% 9% 3 6% 3 4 4 3 6% 7% 43%	3640
	11th to 20th	Night	17% 9% 2 6% 5% 4 6% 5% 6% 8% 33%	3617
	21st to end	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	3972
June	1st to 10th	Night	11% 5% 3 4 4 4 4 4 6% 10% 45%	1385
	11th to 20th	Night	14% 5% 2 4 5% 5% 5% 3 6% 9% 42%	1200
	21st to end	Night	9% 5% 1 5% 3 4 3 4 6% 10% 51%	1273
July	1st to 10th	Night	6% 4 2 5% 3 3 4 5% 8% 10% 51%	2290
	11th to 20th	Night	5% 3 1 4 3 4 4 4 6% 9% 57%	2417
	21st to end	Night	3 2 1 4 3 3 3 4 6% 8% 64%	2761
August	1st to 10th	Night	7% 5% 2 5% 3 3 3 2 5% 6% 58%	2528
	11th to 20th	Night	4 3 2 5% 4 4 4 4 6% 9% 56%	2589
	21st to end	Night	7% 4 2 4 3 3 4 4 5% 8% 57%	3382
September	1st to 10th	Night	9% 4 1 5% 3 4 4 3 5% 7% 55%	1900
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 5% 8% 49%	1900
	21st to end	Night	9% 6% 1 5% 4 4 4 3 5% 7% 51%	2138
October	1st to 10th	Night	9% 5% 2 6% 3 4 4 3 5% 7% 51%	3800
	11th to 20th	Night	5% 5% 2 5% 3 4 4 3 7% 12% 51%	3809
	21st to end	Night	7% 8% 3 7% 4 5% 5% 4 6% 8% 43%	4467
November	1st to 10th	Night	12% 14% 4 8% 6% 4 4 3 4 6% 34%	2668
	11th to 20th	Night	7% 10% 4 12% 8% 6% 5% 4 5% 8% 31%	2800
	21st to end	Night	7% 11% 5% 11% 7% 6% 6% 4 5% 7% 30%	2817
December	1st to 10th	Night	6% 13% 6% 15% 9% 8% 6% 4 5% 7% 22%	4900
	11th to 20th	Night	5% 14% 6% 14% 9% 8% 6% 5% 6% 5% 21%	5679
	21st to end	Night	3 7% 3 11% 7% 5% 4 4 5% 5% 44%	7596

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	63% 6% 11% 15% 5%	3179
	11th to 20th	Day	52% 7% 14% 16% 11% 1	3526
	21st to end	Day	47% 6% 21% 22% 3	4004
February	1st to 10th	Day	60% 5% 9% 15% 10%	1705
	11th to 20th	Day	55% 7% 12% 12% 13% 1	1764
	21st to end	Day	52% 7% 15% 16% 9% 1	1590
March	1st to 10th	Day	53% 4 16% 19% 7%	4500
	11th to 20th	Day	52% 7% 17% 19% 4	4857
	21st to end	Day	57% 8% 13% 14% 7%	5832
April	1st to 10th	Day	44% 7% 15% 21% 12% 1	2400
	11th to 20th	Day	54% 6% 13% 19% 6% 1	2374
	21st to end	Day	47% 6% 15% 22% 9% 1	2768
May	1st to 10th	Day	42% 6% 11% 27% 13% 1	6340
	11th to 20th	Day	48% 8% 15% 21% 8%	6302
	21st to end	Day	38% 7% 12% 29% 14% 1	6926
June	1st to 10th	Day	42% 7% 16% 24% 9% 2	3005
	11th to 20th	Day	49% 8% 13% 19% 10% 1	3200
	21st to end	Day	34% 8% 17% 31% 9% 1	3118
July	1st to 10th	Day	31% 10% 20% 26% 12% 1	4816
	11th to 20th	Day	22% 7% 17% 35% 16% 1	4683
	21st to end	Day	19% 4 12% 38% 20% 6%	4652
August	1st to 10th	Day	31% 6% 16% 28% 18% 1	4396
	11th to 20th	Day	26% 7% 18% 36% 13% 1	4289
	21st to end	Day	28% 5% 14% 38% 14% 1	4283
September	1st to 10th	Day	33% 5% 15% 27% 17% 3	2280
	11th to 20th	Day	39% 5% 15% 27% 12% 2	2280
	21st to end	Day	36% 5% 12% 30% 15% 2	2039
October	1st to 10th	Day	34% 5% 11% 35% 13% 2	3170
	11th to 20th	Day	30% 3 15% 36% 13% 2	3088
	21st to end	Day	40% 5% 16% 32% 7%	3091
November	1st to 10th	Day	52% 6% 13% 20% 8% 1	1625
	11th to 20th	Day	53% 7% 13% 20% 7% 1	1600
	21st to end	Day	54% 7% 18% 15% 5%	1579
December	1st to 10th	Day	54% 9% 20% 14% 4	2290
	11th to 20th	Day	62% 6% 20% 8% 4	2503
	21st to end	Day	42% 4 9% 26% 13% 6%	3342
January	1st to 10th	Night	56% 5% 15% 18% 6%	6766
	11th to 20th	Night	54% 6% 14% 14% 11% 1	6445
	21st to end	Night	47% 7% 21% 21% 3	6974
February	1st to 10th	Night	57% 6% 12% 16% 9% 1	2715
	11th to 20th	Night	51% 6% 14% 17% 12% 1	2533
	21st to end	Night	47% 6% 13% 23% 11%	2040
March	1st to 10th	Night	44% 7% 21% 20% 8%	5374
	11th to 20th	Night	47% 7% 18% 23% 5%	5133
	21st to end	Night	58% 7% 13% 16% 6%	5127
April	1st to 10th	Night	38% 7% 14% 25% 16% 1	2000
	11th to 20th	Night	47% 6% 11% 22% 12% 2	1977
	21st to end	Night	45% 7% 12% 24% 11%	1630
May	1st to 10th	Night	39% 5% 10% 28% 17% 1	3640
	11th to 20th	Night	47% 7% 15% 19% 11% 1	3618
	21st to end	Night	37% 7% 11% 29% 15% 1	3972
June	1st to 10th	Night	34% 6% 16% 29% 13% 2	1385
	11th to 20th	Night	38% 7% 17% 25% 13% 1	1200
	21st to end	Night	29% 7% 19% 33% 12% 1	1273
July	1st to 10th	Night	25% 9% 27% 28% 10% 1	2255
	11th to 20th	Night	22% 7% 16% 32% 21% 2	2375
	21st to end	Night	17% 5% 12% 40% 19% 7%	2674
August	1st to 10th	Night	27% 5% 14% 33% 20% 1	2520
	11th to 20th	Night	24% 6% 15% 37% 17% 1	2613
	21st to end	Night	25% 5% 15% 36% 17% 2	3382
September	1st to 10th	Night	28% 6% 10% 30% 21% 5%	1900
	11th to 20th	Night	33% 6% 13% 28% 18% 3	1900
	21st to end	Night	32% 6% 12% 31% 17% 2	2138
October	1st to 10th	Night	33% 5% 14% 32% 15% 2	3800
	11th to 20th	Night	27% 4 14% 41% 13% 1	3809
	21st to end	Night	39% 5% 11% 33% 12% 1	4467
November	1st to 10th	Night	52% 6% 12% 19% 8% 2	2668
	11th to 20th	Night	52% 6% 16% 18% 7% 1	2800
	21st to end	Night	53% 6% 17% 19% 5%	2817
December	1st to 10th	Night	62% 5% 18% 10% 4	4900
	11th to 20th	Night	63% 6% 15% 12% 3	5681
	21st to end	Night	42% 4 10% 24% 15% 5%	7596

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	13% 13% 34% 29% 11% 2	200
	11th to 20th	Day	10% 15% 33% 30% 11% 1	276
	21st to end	Day	10% 14% 39% 29% 8%	330
February	1st to 10th	Day	16% 10% 42% 25% 7% 1	300
	11th to 20th	Day	10% 9% 38% 28% 12% 3	300
	21st to end	Day	4 10% 33% 39% 12% 2	249
March	1st to 10th	Day	15% 10% 38% 25% 9% 3	300
	11th to 20th	Day	13% 12% 36% 26% 10% 3	435
	21st to end	Day	15% 11% 34% 24% 13% 3	550
April	1st to 10th	Day	11% 17% 34% 30% 6% 1	500
	11th to 20th	Day	20% 14% 32% 26% 7% 1	492
	21st to end	Day	19% 10% 29% 28% 13% 1	680
May	1st to 10th	Day	13% 7% 26% 32% 17% 4	703
	11th to 20th	Day	14% 11% 25% 28% 15% 7%	725
	21st to end	Day	17% 9% 25% 26% 17% 5%	789
June	1st to 10th	Day	16% 14% 28% 23% 15% 4	730
	11th to 20th	Day	19% 14% 32% 21% 11% 2	730
	21st to end	Day	12% 9% 27% 31% 17% 5%	730
July	1st to 10th	Day	7% 6% 26% 34% 22% 5%	721
	11th to 20th	Day	7% 8% 30% 34% 17% 4	718
	21st to end	Day	6% 6% 26% 34% 21% 7%	740
August	1st to 10th	Day	11% 4 25% 36% 18% 6%	676
	11th to 20th	Day	10% 5% 25% 33% 20% 7%	608
	21st to end	Day	9% 6% 26% 38% 15% 5%	539
September	1st to 10th	Day	12% 10% 33% 27% 13% 4	490
	11th to 20th	Day	16% 10% 27% 33% 14% 1	490
	21st to end	Day	17% 13% 32% 25% 10% 3	314
October	1st to 10th	Day	18% 7% 31% 23% 19% 2	300
	11th to 20th	Day	12% 13% 36% 25% 12% 2	300
	21st to end	Day	14% 17% 38% 22% 7% 2	330
November	1st to 10th	Day	19% 12% 34% 25% 9% 1	300
	11th to 20th	Day	13% 14% 39% 26% 8%	300
	21st to end	Day	12% 12% 43% 24% 8% 1	300
December	1st to 10th	Day	12% 11% 44% 22% 9% 2	300
	11th to 20th	Day	9% 12% 47% 24% 6% 1	270
	21st to end	Day	10% 8% 37% 32% 10% 2	220
January	1st to 10th	Night	8% 13% 40% 31% 8% 1	1000
	11th to 20th	Night	11% 13% 40% 28% 7% 1	1000
	21st to end	Night	12% 12% 41% 25% 9% 1	1100
February	1st to 10th	Night	11% 11% 33% 33% 10% 1	915
	11th to 20th	Night	11% 9% 40% 30% 9% 1	784
	21st to end	Night	7% 9% 30% 35% 16% 3	660
March	1st to 10th	Night	10% 9% 36% 33% 11% 1	800
	11th to 20th	Night	11% 9% 39% 31% 10% 1	800
	21st to end	Night	12% 7% 31% 37% 11% 1	725
April	1st to 10th	Night	11% 10% 33% 34% 12%	600
	11th to 20th	Night	16% 8% 37% 32% 7% 1	593
	21st to end	Night	16% 10% 30% 37% 7%	600
May	1st to 10th	Night	16% 5% 28% 37% 13% 1	600
	11th to 20th	Night	16% 8% 27% 32% 15% 2	591
	21st to end	Night	19% 7% 27% 29% 15% 3	650
June	1st to 10th	Night	13% 6% 31% 33% 15% 1	480
	11th to 20th	Night	16% 7% 28% 36% 13%	400
	21st to end	Night	11% 7% 27% 39% 15% 2	400
July	1st to 10th	Night	7% 4 25% 45% 18% 1	390
	11th to 20th	Night	8% 5% 26% 44% 16% 1	463
	21st to end	Night	4 4 28% 46% 17% 2	624
August	1st to 10th	Night	8% 3 23% 46% 17% 2	567
	11th to 20th	Night	8% 3 23% 41% 23% 2	564
	21st to end	Night	8% 4 27% 40% 20% 1	627
September	1st to 10th	Night	9% 4 24% 45% 16% 1	570
	11th to 20th	Night	12% 6% 23% 44% 14% 2	570
	21st to end	Night	12% 7% 31% 40% 10%	632
October	1st to 10th	Night	18% 7% 27% 35% 12% 1	760
	11th to 20th	Night	12% 9% 32% 35% 11% 1	779
	21st to end	Night	15% 10% 37% 31% 6%	1045
November	1st to 10th	Night	20% 10% 37% 28% 6%	975
	11th to 20th	Night	12% 11% 40% 27% 9% 2	1000
	21st to end	Night	12% 11% 44% 25% 7% 1	1000
December	1st to 10th	Night	12% 8% 40% 27% 11% 3	1000
	11th to 20th	Night	11% 11% 39% 30% 9% 1	1000
	21st to end	Night	13% 8% 38% 28% 11% 2	1100

Page generated at 2025-07-17 23:10:04. Version ac07

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