Chandler
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chandler clear sky chart from 2005-11-06 to 2024-12-06.

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	17% 9% 3 7% 5% 5% 5% 4 6% 7% 34%	102048
	Night	17% 10% 3 7% 5% 4 4 3 5% 6% 35%	97773
Transparency	Day	48% 4 14% 23% 10% 1	105534
	Night	51% 4 12% 22% 10% 1	102380
Seeing	Day	21% 4 18% 33% 19% 5%	16732
	Night	23% 5% 24% 31% 15% 2	24260

By Month

Percentage Cloud Cover NE (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	13% 11% 3 8% 5% 5% 5% 4 5% 6% 35%	2207
	11th to 20th	Day	11% 10% 4 7% 5% 4 6% 5% 10% 7% 31%	2210
	21st to end	Day	6% 7% 3 8% 5% 5% 4 4 6% 7% 43%	2880
February	1st to 10th	Day	10% 12% 5% 9% 5% 5% 4 4 4 6% 35%	1710
	11th to 20th	Day	11% 15% 4 10% 6% 5% 5% 3 6% 5% 30%	1663
	21st to end	Day	9% 11% 5% 7% 5% 6% 5% 5% 5% 6% 35%	1413
March	1st to 10th	Day	13% 13% 4 8% 4 4 5% 4 6% 7% 34%	3335
	11th to 20th	Day	16% 19% 5% 10% 6% 5% 5% 3 4 5% 21%	3480
	21st to end	Day	23% 12% 3 7% 5% 4 5% 3 4 4 30%	3816
April	1st to 10th	Day	21% 11% 3 8% 5% 4 5% 3 5% 6% 30%	2269
	11th to 20th	Day	17% 10% 3 7% 6% 4 5% 3 5% 7% 33%	2432
	21st to end	Day	23% 9% 3 8% 5% 4 3 3 5% 5% 31%	2470
May	1st to 10th	Day	20% 11% 4 11% 6% 5% 5% 3 4 7% 23%	4350
	11th to 20th	Day	17% 9% 3 7% 5% 5% 4 4 5% 6% 35%	4398
	21st to end	Day	23% 9% 3 8% 5% 5% 5% 3 4 6% 28%	5049
June	1st to 10th	Day	23% 9% 3 7% 5% 5% 4 3 6% 6% 28%	2850
	11th to 20th	Day	18% 7% 2 6% 6% 4 4 5% 6% 8% 34%	2850
	21st to end	Day	26% 8% 3 7% 6% 4 5% 4 6% 7% 24%	2850
July	1st to 10th	Day	14% 6% 3 6% 5% 5% 6% 5% 8% 8% 34%	4760
	11th to 20th	Day	12% 6% 2 6% 5% 6% 6% 6% 7% 9% 35%	4760
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 7% 8% 42%	4973
August	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 5% 8% 9% 34%	4173
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 4 7% 7% 37%	4045
	21st to end	Day	12% 5% 2 5% 4 4 4 3 5% 8% 46%	4482
September	1st to 10th	Day	17% 6% 2 6% 4 5% 4 3 6% 8% 40%	2280
	11th to 20th	Day	19% 5% 2 5% 4 4 4 3 4 6% 44%	2187
	21st to end	Day	19% 6% 2 6% 4 4 5% 3 5% 5% 40%	2046
October	1st to 10th	Day	16% 7% 2 6% 4 5% 4 3 5% 7% 40%	1900
	11th to 20th	Day	20% 10% 2 6% 4 4 4 4 4 7% 34%	1900
	21st to end	Day	22% 9% 3 7% 4 3 4 4 6% 7% 31%	1957
November	1st to 10th	Day	19% 8% 3 5% 5% 5% 5% 4 6% 7% 33%	1565
	11th to 20th	Day	21% 9% 3 7% 5% 5% 5% 4 5% 5% 31%	1600
	21st to end	Day	20% 12% 4 8% 5% 5% 5% 3 5% 6% 28%	1600
December	1st to 10th	Day	19% 12% 3 8% 4 5% 5% 3 5% 5% 31%	1489
	11th to 20th	Day	17% 12% 3 10% 6% 6% 5% 3 4 5% 29%	1668
	21st to end	Day	16% 11% 4 9% 5% 3 4 3 4 5% 36%	2431
January	1st to 10th	Night	9% 12% 4 10% 6% 6% 6% 4 6% 8% 29%	4748
	11th to 20th	Night	16% 10% 3 7% 5% 5% 5% 4 6% 7% 32%	4760
	21st to end	Night	7% 10% 3 7% 4 4 4 4 6% 6% 45%	4776
February	1st to 10th	Night	9% 13% 5% 9% 5% 5% 4 4 6% 5% 37%	2470
	11th to 20th	Night	13% 13% 4 9% 7% 5% 5% 3 5% 4 33%	2403
	21st to end	Night	12% 11% 5% 7% 6% 5% 4 4 5% 6% 34%	2041
March	1st to 10th	Night	11% 12% 4 9% 7% 6% 5% 4 5% 6% 31%	3493
	11th to 20th	Night	21% 18% 5% 10% 5% 5% 4 3 4 4 21%	3479
	21st to end	Night	26% 11% 4 7% 4 3 3 2 4 6% 30%	3816
April	1st to 10th	Night	22% 11% 3 8% 6% 3 4 2 5% 5% 31%	1910
	11th to 20th	Night	19% 9% 3 8% 4 3 4 3 6% 7% 35%	1693
	21st to end	Night	24% 10% 3 6% 4 3 3 2 4 5% 36%	1710
May	1st to 10th	Night	23% 10% 4 9% 5% 4 4 3 4 5% 30%	2597
	11th to 20th	Night	13% 8% 3 6% 4 4 4 3 6% 7% 42%	2506
	21st to end	Night	18% 10% 3 8% 6% 5% 5% 4 5% 8% 28%	2564
June	1st to 10th	Night	24% 8% 3 6% 4 4 3 4 6% 6% 32%	1330
	11th to 20th	Night	19% 6% 2 6% 4 5% 4 3 6% 7% 37%	1330
	21st to end	Night	26% 7% 3 6% 5% 4 4 5% 5% 5% 30%	1330
July	1st to 10th	Night	14% 7% 2 6% 4 4 5% 3 5% 8% 41%	2210
	11th to 20th	Night	14% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	2210
	21st to end	Night	11% 6% 2 6% 3 4 4 4 6% 6% 48%	2559
August	1st to 10th	Night	15% 7% 3 8% 5% 5% 5% 4 5% 7% 35%	2756
	11th to 20th	Night	14% 6% 3 7% 4 5% 5% 3 6% 7% 41%	2782
	21st to end	Night	13% 5% 2 4 4 4 3 3 5% 7% 49%	3174
September	1st to 10th	Night	18% 7% 2 4 4 3 4 2 4 6% 45%	1900
	11th to 20th	Night	17% 5% 2 4 3 4 3 3 5% 5% 48%	1990
	21st to end	Night	17% 6% 2 5% 3 4 3 3 5% 6% 46%	2133
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 4 6% 41%	2280
	11th to 20th	Night	20% 8% 2 6% 4 4 3 3 5% 5% 37%	2280
	21st to end	Night	23% 8% 2 6% 4 4 4 3 5% 5% 37%	2640
November	1st to 10th	Night	20% 8% 3 7% 5% 4 4 3 5% 5% 36%	2733
	11th to 20th	Night	21% 10% 3 7% 4 4 4 3 5% 6% 32%	2800
	21st to end	Night	22% 12% 3 7% 4 5% 4 4 5% 6% 28%	2800
December	1st to 10th	Night	20% 13% 3 7% 5% 4 4 4 4 5% 31%	2803
	11th to 20th	Night	23% 12% 4 8% 5% 4 4 3 5% 4 28%	3531
	21st to end	Night	17% 11% 4 10% 5% 4 4 3 5% 5% 31%	5236

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	53% 2 9% 21% 14%	2208
	11th to 20th	Day	48% 3 11% 24% 14%	2210
	21st to end	Day	40% 3 13% 27% 16% 1	2880
February	1st to 10th	Day	52% 3 11% 21% 11% 2	1710
	11th to 20th	Day	54% 3 10% 21% 11% 1	1671
	21st to end	Day	46% 4 9% 24% 13% 3	1413
March	1st to 10th	Day	51% 2 15% 22% 9% 1	3339
	11th to 20th	Day	62% 2 9% 17% 8% 2	3480
	21st to end	Day	56% 2 7% 22% 10% 2	3816
April	1st to 10th	Day	52% 3 8% 20% 15% 2	2269
	11th to 20th	Day	48% 4 10% 24% 13% 1	2432
	21st to end	Day	53% 2 11% 18% 13% 3	2470
May	1st to 10th	Day	56% 3 10% 22% 8%	4365
	11th to 20th	Day	49% 2 15% 25% 8% 1	4402
	21st to end	Day	55% 3 10% 22% 9% 1	5049
June	1st to 10th	Day	55% 3 12% 21% 9% 1	2850
	11th to 20th	Day	46% 5% 13% 25% 10% 1	2850
	21st to end	Day	56% 5% 13% 18% 8%	2850
July	1st to 10th	Day	42% 6% 19% 22% 11%	4685
	11th to 20th	Day	42% 6% 21% 24% 7%	4679
	21st to end	Day	35% 6% 24% 25% 10%	4815
August	1st to 10th	Day	43% 6% 22% 21% 8%	4159
	11th to 20th	Day	42% 6% 20% 23% 8% 1	4084
	21st to end	Day	34% 5% 19% 26% 15%	4482
September	1st to 10th	Day	41% 5% 16% 27% 11%	2280
	11th to 20th	Day	41% 3 14% 29% 12% 1	2187
	21st to end	Day	43% 4 12% 28% 12% 1	2046
October	1st to 10th	Day	43% 4 17% 26% 9% 1	3160
	11th to 20th	Day	49% 4 13% 26% 6% 1	3140
	21st to end	Day	42% 4 17% 23% 13% 1	3200
November	1st to 10th	Day	49% 4 15% 20% 11% 1	1565
	11th to 20th	Day	55% 4 13% 18% 9% 1	1600
	21st to end	Day	59% 4 13% 15% 9%	1600
December	1st to 10th	Day	56% 4 12% 20% 7%	1489
	11th to 20th	Day	59% 3 10% 19% 9%	1668
	21st to end	Day	54% 2 13% 19% 9% 3	2431
January	1st to 10th	Night	55% 3 14% 23% 6%	4748
	11th to 20th	Night	54% 3 10% 21% 12% 1	4760
	21st to end	Night	46% 3 13% 24% 14% 1	4776
February	1st to 10th	Night	50% 3 10% 19% 15% 3	2470
	11th to 20th	Night	55% 3 9% 20% 11% 1	2406
	21st to end	Night	51% 4 7% 21% 15% 2	2041
March	1st to 10th	Night	55% 3 9% 23% 9% 1	3502
	11th to 20th	Night	69% 2 6% 15% 7% 1	3480
	21st to end	Night	58% 1 7% 18% 13% 2	3816
April	1st to 10th	Night	57% 3 9% 15% 14% 2	1910
	11th to 20th	Night	50% 3 8% 24% 13% 2	1693
	21st to end	Night	54% 2 8% 18% 16% 2	1710
May	1st to 10th	Night	60% 2 8% 19% 10% 1	2602
	11th to 20th	Night	44% 4 12% 31% 8% 1	2507
	21st to end	Night	55% 4 11% 21% 8% 1	2565
June	1st to 10th	Night	54% 3 12% 21% 10%	1330
	11th to 20th	Night	46% 5% 14% 21% 12% 2	1330
	21st to end	Night	55% 5% 15% 16% 8% 1	1330
July	1st to 10th	Night	42% 6% 19% 19% 13%	2175
	11th to 20th	Night	43% 6% 16% 29% 5%	2168
	21st to end	Night	36% 8% 23% 23% 10%	2478
August	1st to 10th	Night	50% 7% 16% 20% 7%	2745
	11th to 20th	Night	41% 6% 19% 25% 8%	2809
	21st to end	Night	34% 6% 19% 28% 13%	3173
September	1st to 10th	Night	42% 4 14% 30% 9% 1	1900
	11th to 20th	Night	39% 4 15% 29% 13% 1	1990
	21st to end	Night	41% 4 13% 27% 14% 1	2133
October	1st to 10th	Night	48% 4 12% 27% 8% 1	3800
	11th to 20th	Night	43% 3 12% 30% 12%	3779
	21st to end	Night	45% 6% 16% 22% 11%	4350
November	1st to 10th	Night	50% 4 15% 21% 9% 2	2733
	11th to 20th	Night	55% 3 11% 21% 9% 1	2800
	21st to end	Night	60% 4 13% 15% 8%	2800
December	1st to 10th	Night	57% 3 13% 19% 7%	2803
	11th to 20th	Night	63% 2 8% 18% 8% 1	3532
	21st to end	Night	58% 2 14% 19% 7%	5236

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	27% 6% 19% 34% 11% 3	180
	11th to 20th	Day	27% 4 24% 27% 12% 4	180
	21st to end	Day	13% 4 29% 34% 16% 5%	321
February	1st to 10th	Day	20% 5% 26% 34% 11% 4	370
	11th to 20th	Day	16% 2 30% 36% 14% 2	366
	21st to end	Day	16% 2 24% 36% 19% 3	307
March	1st to 10th	Day	20% 5% 20% 38% 14% 3	451
	11th to 20th	Day	18% 4 23% 28% 20% 7%	460
	21st to end	Day	24% 4 21% 33% 15% 3	506
April	1st to 10th	Day	27% 5% 19% 32% 15% 1	460
	11th to 20th	Day	23% 4 18% 35% 16% 4	452
	21st to end	Day	25% 5% 17% 30% 19% 5%	460
May	1st to 10th	Day	27% 3 11% 34% 20% 5%	604
	11th to 20th	Day	22% 4 14% 29% 25% 6%	674
	21st to end	Day	24% 3 15% 39% 16% 3	735
June	1st to 10th	Day	30% 3 12% 31% 21% 4	680
	11th to 20th	Day	20% 2 13% 36% 24% 5%	680
	21st to end	Day	27% 3 9% 35% 22% 5%	680
July	1st to 10th	Day	19% 2 11% 38% 25% 5%	670
	11th to 20th	Day	14% 2 9% 40% 32% 3	668
	21st to end	Day	19% 2 9% 34% 28% 8%	740
August	1st to 10th	Day	13% 2 9% 33% 34% 9%	528
	11th to 20th	Day	16% 2 6% 37% 30% 9%	479
	21st to end	Day	14% 2 12% 35% 28% 9%	539
September	1st to 10th	Day	18% 2 16% 39% 21% 5%	490
	11th to 20th	Day	22% 3 17% 34% 18% 6%	490
	21st to end	Day	20% 4 21% 32% 17% 6%	466
October	1st to 10th	Day	16% 3 22% 36% 20% 3	390
	11th to 20th	Day	26% 4 23% 27% 15% 5%	390
	21st to end	Day	26% 4 27% 31% 11% 2	429
November	1st to 10th	Day	25% 6% 27% 29% 11% 2	395
	11th to 20th	Day	29% 7% 27% 25% 10% 3	400
	21st to end	Day	26% 10% 31% 26% 7% 1	400
December	1st to 10th	Day	24% 6% 26% 32% 11% 2	314
	11th to 20th	Day	23% 6% 37% 24% 8% 2	180
	21st to end	Day	19% 11% 30% 26% 11% 3	198
January	1st to 10th	Night	25% 5% 35% 26% 9% 1	850
	11th to 20th	Night	23% 7% 32% 29% 9% 1	850
	21st to end	Night	17% 5% 34% 29% 13% 2	861
February	1st to 10th	Night	18% 5% 34% 32% 10% 2	760
	11th to 20th	Night	22% 3 29% 34% 10% 2	743
	21st to end	Night	18% 4 25% 35% 15% 2	628
March	1st to 10th	Night	18% 4 29% 35% 12% 1	760
	11th to 20th	Night	21% 4 28% 31% 13% 2	760
	21st to end	Night	23% 6% 26% 33% 11% 2	836
April	1st to 10th	Night	31% 3 23% 32% 10% 1	580
	11th to 20th	Night	24% 5% 23% 31% 17% 2	564
	21st to end	Night	29% 3 17% 33% 14% 4	570
May	1st to 10th	Night	28% 4 12% 34% 20% 3	570
	11th to 20th	Night	22% 4 11% 33% 24% 6%	562
	21st to end	Night	20% 3 21% 40% 16% 2	509
June	1st to 10th	Night	29% 3 10% 32% 24% 1	380
	11th to 20th	Night	21% 4 8% 37% 24% 6%	380
	21st to end	Night	28% 3 7% 37% 22% 3	380
July	1st to 10th	Night	19% 2 9% 38% 27% 5%	370
	11th to 20th	Night	17% 2 11% 37% 29% 4	368
	21st to end	Night	20% 2 7% 38% 30% 4	510
August	1st to 10th	Night	15% 2 8% 38% 32% 5%	568
	11th to 20th	Night	18% 2 8% 37% 29% 6%	562
	21st to end	Night	16% 3 10% 37% 28% 6%	627
September	1st to 10th	Night	21% 4 19% 35% 17% 3	570
	11th to 20th	Night	20% 3 19% 34% 22% 2	660
	21st to end	Night	19% 4 25% 33% 17% 2	760
October	1st to 10th	Night	21% 4 26% 32% 15% 1	760
	11th to 20th	Night	24% 7% 23% 31% 13% 2	760
	21st to end	Night	27% 5% 31% 26% 11% 1	859
November	1st to 10th	Night	25% 7% 31% 27% 8% 1	880
	11th to 20th	Night	26% 11% 28% 25% 9% 2	900
	21st to end	Night	29% 8% 30% 27% 7% 1	900
December	1st to 10th	Night	27% 8% 32% 24% 8% 1	878
	11th to 20th	Night	26% 12% 36% 21% 5% 1	850
	21st to end	Night	26% 8% 34% 23% 8% 1	935

Page generated at 2024-12-03 06:45:11. Version ac07

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