Quartzsite
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Quartzsite clear sky chart from 2005-11-06 to 2025-12-18.

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	2 2 1 2 2 2 2 2 4 5% 77%	135933
	Night	2 2 1 2 2 2 2 2 4 5% 76%	132660
Transparency	Day	12% 2 3 10% 25% 48%	130895
	Night	12% 2 3 10% 25% 48%	128695
Seeing	Day	3 4 16% 33% 31% 12%	16791
	Night	3 3 15% 40% 34% 6%	27064

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	2 4 2 3 2 3 3 2 4 5% 70%	4098
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 4 77%	4100
	21st to end	Day	5% 3 1 4 3 3 3 3 5% 8% 63%	4671
February	1st to 10th	Day	3 3 1 4 2 2 3 2 4 6% 70%	2000
	11th to 20th	Day	3 2 1 4 3 3 3 3 5% 6% 67%	1950
	21st to end	Day	3 2 1 3 3 3 3 2 4 5% 70%	1650
March	1st to 10th	Day	2 1 2 2 2 2 2 4 6% 76%	4667
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 6% 64%	5000
	21st to end	Day	1 1 1 2 2 2 2 3 4 6% 76%	5486
April	1st to 10th	Day	1 2 2 2 3 2 3 4 7% 73%	2226
	11th to 20th	Day	1 2 2 1 1 2 2 3 4 81%	2369
	21st to end	Day	1 1 1 1 1 1 1 2 3 5% 83%	2556
May	1st to 10th	Day	1 1 1 2 1 2 2 2 3 4 82%	5880
	11th to 20th	Day	1 1 1 1 1 1 1 3 3 86%	5841
	21st to end	Day	1 1 1 2 1 1 1 1 2 3 86%	6423
June	1st to 10th	Day	1 1 1 2 1 1 2 1 2 4 83%	2600
	11th to 20th	Day	1 1 1 1 1 1 1 3 91%	2600
	21st to end	Day	1 1 1 1 1 2 1 2 2 3 85%	2600
July	1st to 10th	Day	1 1 1 1 1 2 1 3 3 85%	5879
	11th to 20th	Day	1 1 2 2 2 3 2 4 6% 77%	5880
	21st to end	Day	2 2 1 2 2 2 2 2 4 5% 76%	6401
August	1st to 10th	Day	2 1 1 3 2 3 3 3 4 8% 70%	5779
	11th to 20th	Day	1 1 2 1 1 2 2 2 4 84%	5416
	21st to end	Day	3 2 1 3 2 2 3 3 4 5% 72%	5984
September	1st to 10th	Day	3 3 1 4 3 3 3 2 3 6% 69%	2218
	11th to 20th	Day	1 1 2 1 1 1 1 2 3 86%	2200
	21st to end	Day	2 2 1 2 1 2 3 2 3 5% 79%	2200
October	1st to 10th	Day	2 1 1 1 1 1 2 2 2 3 85%	3600
	11th to 20th	Day	1 1 1 1 1 1 3 90%	3425
	21st to end	Day	1 1 1 1 2 2 4 4 82%	3548
November	1st to 10th	Day	1 1 2 2 2 2 2 3 4 80%	1884
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 5% 75%	1890
	21st to end	Day	4 3 1 4 2 2 2 2 5% 7% 69%	1890
December	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 77%	3040
	11th to 20th	Day	2 1 1 4 3 3 4 5% 8% 7% 63%	3472
	21st to end	Day	4 3 1 3 2 2 4 4 7% 9% 61%	4510
January	1st to 10th	Night	2 3 1 3 3 3 2 3 4 6% 72%	5867
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 5% 77%	5880
	21st to end	Night	7% 3 1 3 2 2 4 3 5% 6% 64%	6310
February	1st to 10th	Night	3 3 1 3 2 3 3 3 4 6% 68%	2400
	11th to 20th	Night	4 3 1 4 3 2 3 3 4 5% 68%	2338
	21st to end	Night	4 3 1 4 2 3 4 3 4 6% 68%	1980
March	1st to 10th	Night	4 2 1 2 2 2 2 2 4 6% 73%	5214
	11th to 20th	Night	2 3 1 4 3 3 4 3 4 5% 68%	5000
	21st to end	Night	2 2 1 3 2 2 3 3 5% 8% 70%	5489
April	1st to 10th	Night	2 3 1 2 2 2 3 2 5% 5% 74%	2170
	11th to 20th	Night	1 2 1 2 2 2 2 1 3 3 81%	1979
	21st to end	Night	1 1 1 1 1 2 2 3 4 85%	1841
May	1st to 10th	Night	3 2 1 2 2 2 2 2 3 4 79%	4100
	11th to 20th	Night	1 1 1 1 1 1 1 3 4 86%	4074
	21st to end	Night	1 2 1 1 2 2 2 3 86%	4474
June	1st to 10th	Night	1 2 1 2 1 1 2 1 3 4 83%	1800
	11th to 20th	Night	1 1 1 1 1 1 2 3 90%	1800
	21st to end	Night	1 1 1 1 1 2 1 2 3 4 84%	1800
July	1st to 10th	Night	1 1 1 1 2 2 3 3 86%	4100
	11th to 20th	Night	1 1 2 2 2 2 2 4 5% 78%	4100
	21st to end	Night	1 1 1 1 2 2 2 4 6% 79%	4472
August	1st to 10th	Night	1 2 2 2 2 2 2 4 7% 75%	4033
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 84%	4434
	21st to end	Night	2 1 1 2 2 2 3 2 4 7% 74%	5015
September	1st to 10th	Night	1 2 1 2 2 2 3 3 4 6% 74%	2180
	11th to 20th	Night	1 1 1 1 1 1 1 2 4 86%	2200
	21st to end	Night	1 1 1 2 2 2 2 2 3 4 83%	2200
October	1st to 10th	Night	1 1 1 1 1 2 2 3 4 83%	3600
	11th to 20th	Night	1 1 1 1 1 1 2 3 90%	3728
	21st to end	Night	1 2 1 1 2 1 3 5% 83%	4252
November	1st to 10th	Night	1 2 1 2 2 2 2 2 3 4 79%	2630
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 74%	2730
	21st to end	Night	4 3 1 3 3 2 2 2 4 5% 71%	2730
December	1st to 10th	Night	2 2 1 2 1 2 2 2 4 5% 76%	4370
	11th to 20th	Night	3 3 1 4 3 3 3 3 4 8% 65%	4902
	21st to end	Night	4 2 1 2 2 3 3 3 4 7% 69%	6468

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	18% 3 2 10% 39% 28%	4099
	11th to 20th	Day	13% 2 3 16% 26% 40%	4100
	21st to end	Day	21% 3 5% 10% 36% 25%	4671
February	1st to 10th	Day	17% 2 3 14% 27% 37%	2000
	11th to 20th	Day	18% 2 3 13% 31% 32%	1960
	21st to end	Day	18% 3 4 13% 28% 34%	1650
March	1st to 10th	Day	12% 2 2 13% 34% 38%	4667
	11th to 20th	Day	20% 3 3 19% 28% 27%	5000
	21st to end	Day	11% 2 2 16% 40% 29%	5486
April	1st to 10th	Day	13% 2 2 11% 28% 44%	2226
	11th to 20th	Day	10% 1 2 7% 27% 54%	2372
	21st to end	Day	7% 1 2 7% 30% 53%	2556
May	1st to 10th	Day	9% 2 4 7% 27% 52%	5880
	11th to 20th	Day	6% 1 2 3 21% 67%	5844
	21st to end	Day	8% 1 1 3 15% 72%	6424
June	1st to 10th	Day	8% 1 1 4 18% 68%	2600
	11th to 20th	Day	4 1 2 11% 82%	2600
	21st to end	Day	8% 1 2 5% 9% 75%	2600
July	1st to 10th	Day	7% 1 2 4 14% 73%	5816
	11th to 20th	Day	10% 3 3 10% 30% 44%	5811
	21st to end	Day	12% 3 3 10% 18% 54%	6217
August	1st to 10th	Day	19% 3 5% 23% 24% 25%	4208
	11th to 20th	Day	10% 3 3 9% 29% 45%	3921
	21st to end	Day	10% 2 3 7% 24% 55%	4311
September	1st to 10th	Day	19% 3 4 11% 21% 42%	2218
	11th to 20th	Day	8% 1 2 6% 20% 63%	2200
	21st to end	Day	10% 3 3 7% 17% 60%	2200
October	1st to 10th	Day	8% 2 2 6% 13% 70%	3600
	11th to 20th	Day	4 1 1 9% 23% 62%	3425
	21st to end	Day	7% 2 2 5% 22% 63%	3548
November	1st to 10th	Day	10% 1 2 10% 29% 47%	1884
	11th to 20th	Day	14% 2 2 12% 25% 45%	1890
	21st to end	Day	17% 2 4 12% 30% 34%	1890
December	1st to 10th	Day	13% 1 2 10% 37% 36%	3040
	11th to 20th	Day	18% 3 4 18% 30% 26%	3471
	21st to end	Day	19% 3 5% 27% 34% 12%	4510
January	1st to 10th	Night	14% 3 2 11% 34% 35%	5867
	11th to 20th	Night	12% 2 2 17% 27% 40%	5880
	21st to end	Night	20% 3 5% 12% 27% 33%	6310
February	1st to 10th	Night	18% 3 3 12% 26% 38%	2400
	11th to 20th	Night	20% 2 3 14% 23% 37%	2339
	21st to end	Night	19% 3 4 11% 25% 39%	1980
March	1st to 10th	Night	13% 2 2 14% 32% 36%	5214
	11th to 20th	Night	19% 3 4 17% 30% 29%	5000
	21st to end	Night	14% 2 2 14% 34% 33%	5489
April	1st to 10th	Night	14% 2 3 10% 28% 43%	2170
	11th to 20th	Night	11% 1 2 7% 25% 54%	1979
	21st to end	Night	6% 2 2 9% 25% 57%	1841
May	1st to 10th	Night	12% 2 2 6% 26% 53%	4097
	11th to 20th	Night	6% 1 1 3 20% 68%	4075
	21st to end	Night	7% 1 3 14% 74%	4474
June	1st to 10th	Night	9% 2 1 4 18% 67%	1800
	11th to 20th	Night	4 1 1 2 12% 81%	1800
	21st to end	Night	8% 1 2 4 8% 77%	1800
July	1st to 10th	Night	6% 2 1 3 12% 76%	4055
	11th to 20th	Night	9% 3 3 8% 31% 47%	4046
	21st to end	Night	8% 3 4 12% 18% 55%	4344
August	1st to 10th	Night	13% 3 4 22% 29% 29%	2928
	11th to 20th	Night	11% 3 2 10% 27% 47%	3209
	21st to end	Night	8% 2 3 7% 24% 57%	3608
September	1st to 10th	Night	12% 3 5% 12% 22% 45%	2180
	11th to 20th	Night	6% 2 2 6% 18% 66%	2200
	21st to end	Night	7% 3 3 8% 17% 62%	2200
October	1st to 10th	Night	8% 1 2 5% 12% 72%	3600
	11th to 20th	Night	4 1 1 7% 21% 66%	3728
	21st to end	Night	7% 1 2 4 18% 68%	4252
November	1st to 10th	Night	11% 2 1 8% 25% 53%	2630
	11th to 20th	Night	14% 1 2 9% 24% 49%	2730
	21st to end	Night	17% 2 3 12% 27% 39%	2730
December	1st to 10th	Night	12% 2 2 10% 28% 46%	4370
	11th to 20th	Night	20% 2 3 11% 29% 35%	4902
	21st to end	Night	17% 2 4 20% 39% 18%	6468

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	6% 5% 23% 37% 25% 4	300
	11th to 20th	Day	7% 3 15% 39% 29% 6%	300
	21st to end	Day	3 7% 23% 33% 26% 8%	400
February	1st to 10th	Day	6% 7% 25% 29% 25% 8%	500
	11th to 20th	Day	5% 9% 25% 36% 21% 3	495
	21st to end	Day	4 12% 28% 35% 18% 3	414
March	1st to 10th	Day	4 13% 26% 37% 19% 3	500
	11th to 20th	Day	6% 8% 22% 32% 27% 5%	500
	21st to end	Day	4 12% 28% 33% 19% 5%	550
April	1st to 10th	Day	4 7% 21% 34% 25% 9%	500
	11th to 20th	Day	2 10% 30% 32% 19% 7%	492
	21st to end	Day	2 8% 28% 30% 22% 11%	500
May	1st to 10th	Day	2 5% 20% 35% 27% 10%	503
	11th to 20th	Day	2 4 24% 35% 24% 11%	528
	21st to end	Day	1 5% 21% 38% 24% 12%	573
June	1st to 10th	Day	2 3 13% 33% 33% 15%	530
	11th to 20th	Day	1 16% 35% 32% 15%	530
	21st to end	Day	2 10% 42% 33% 14%	530
July	1st to 10th	Day	1 6% 35% 40% 17%	526
	11th to 20th	Day	2 1 4 28% 42% 24%	524
	21st to end	Day	3 1 4 24% 43% 25%	575
August	1st to 10th	Day	2 4 29% 42% 23%	527
	11th to 20th	Day	3 1 3 25% 42% 26%	517
	21st to end	Day	2 3 27% 43% 25%	583
September	1st to 10th	Day	2 1 11% 25% 42% 19%	530
	11th to 20th	Day	2 1 10% 35% 40% 12%	530
	21st to end	Day	2 2 13% 33% 35% 15%	530
October	1st to 10th	Day	2 4 15% 33% 33% 13%	530
	11th to 20th	Day	2 2 15% 34% 36% 11%	440
	21st to end	Day	1 2 16% 24% 42% 15%	363
November	1st to 10th	Day	2 4 13% 37% 34% 11%	330
	11th to 20th	Day	3 3 15% 35% 36% 7%	330
	21st to end	Day	2 3 19% 38% 27% 11%	330
December	1st to 10th	Day	6% 2 13% 38% 30% 11%	330
	11th to 20th	Day	1 2 15% 36% 38% 7%	321
	21st to end	Day	7% 6% 20% 38% 23% 6%	330
January	1st to 10th	Night	4 2 16% 43% 30% 6%	800
	11th to 20th	Night	4 3 16% 42% 30% 6%	800
	21st to end	Night	6% 4 18% 43% 26% 3	880
February	1st to 10th	Night	4 5% 17% 42% 27% 5%	800
	11th to 20th	Night	5% 5% 20% 43% 24% 4	784
	21st to end	Night	5% 6% 23% 44% 18% 4	660
March	1st to 10th	Night	4 5% 26% 43% 20% 3	800
	11th to 20th	Night	4 5% 21% 36% 27% 8%	800
	21st to end	Night	3 5% 25% 41% 22% 4	880
April	1st to 10th	Night	3 5% 22% 41% 27% 3	800
	11th to 20th	Night	2 5% 26% 40% 23% 3	791
	21st to end	Night	1 4 26% 40% 26% 3	641
May	1st to 10th	Night	2 5% 21% 44% 25% 3	600
	11th to 20th	Night	2 3 22% 41% 30% 2	591
	21st to end	Night	1 3 19% 47% 26% 4	650
June	1st to 10th	Night	2 1 12% 50% 33% 2	600
	11th to 20th	Night	1 15% 47% 35% 3	600
	21st to end	Night	1 1 10% 44% 40% 4	600
July	1st to 10th	Night	2 4 42% 49% 3	585
	11th to 20th	Night	3 1 2 38% 50% 6%	582
	21st to end	Night	2 4 34% 53% 8%	657
August	1st to 10th	Night	2 1 4 32% 55% 7%	597
	11th to 20th	Night	3 1 4 30% 53% 10%	758
	21st to end	Night	3 1 3 28% 55% 11%	880
September	1st to 10th	Night	2 1 7% 32% 49% 10%	800
	11th to 20th	Night	1 1 8% 36% 44% 10%	800
	21st to end	Night	1 1 10% 39% 42% 8%	800
October	1st to 10th	Night	3 2 13% 43% 36% 4	800
	11th to 20th	Night	1 1 12% 43% 38% 6%	800
	21st to end	Night	1 3 12% 39% 36% 10%	880
November	1st to 10th	Night	2 1 14% 42% 34% 8%	820
	11th to 20th	Night	3 1 11% 41% 35% 9%	840
	21st to end	Night	5% 2 15% 42% 30% 6%	840
December	1st to 10th	Night	5% 2 13% 44% 33% 4	840
	11th to 20th	Night	5% 3 13% 42% 33% 4	828
	21st to end	Night	6% 3 18% 44% 25% 5%	880

Page generated at 2025-12-14 23:13:51. Version ac07

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