Western Head
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Western Head clear sky chart from 2005-11-06 to 2024-12-09.

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	19% 9% 3 7% 5% 5% 5% 4 5% 7% 30%	102174
	Night	20% 10% 3 8% 5% 4 4 4 5% 6% 30%	97662
Transparency	Day	51% 8% 12% 18% 10% 1	105777
	Night	53% 7% 11% 18% 10% 1	102148
Seeing	Day	23% 10% 27% 29% 10% 1	17326
	Night	24% 10% 28% 28% 9% 1	24966

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	19% 10% 3 10% 6% 5% 5% 4 4 6% 30%	2526
	11th to 20th	Day	18% 9% 3 10% 7% 6% 7% 5% 9% 8% 20%	2756
	21st to end	Day	20% 9% 3 8% 5% 5% 4 5% 7% 7% 26%	3124
February	1st to 10th	Day	19% 13% 4 8% 5% 5% 6% 5% 6% 8% 21%	1710
	11th to 20th	Day	18% 9% 3 8% 7% 7% 6% 4 6% 7% 26%	1663
	21st to end	Day	14% 9% 4 7% 6% 5% 6% 5% 6% 8% 31%	1462
March	1st to 10th	Day	26% 12% 3 7% 5% 4 3 3 4 5% 28%	3430
	11th to 20th	Day	16% 10% 3 7% 5% 4 5% 4 7% 9% 30%	3480
	21st to end	Day	30% 9% 3 8% 5% 5% 4 3 4 5% 24%	3816
April	1st to 10th	Day	22% 12% 3 8% 5% 4 4 3 4 6% 29%	2236
	11th to 20th	Day	20% 9% 3 5% 4 3 4 3 6% 7% 35%	2344
	21st to end	Day	21% 7% 3 7% 5% 4 4 4 5% 7% 34%	2470
May	1st to 10th	Day	21% 10% 4 8% 5% 5% 5% 4 6% 8% 25%	4106
	11th to 20th	Day	24% 12% 4 8% 4 4 3 3 4 5% 29%	4362
	21st to end	Day	18% 9% 3 7% 4 4 5% 4 6% 8% 32%	4836
June	1st to 10th	Day	24% 10% 2 6% 5% 5% 4 3 4 8% 28%	2660
	11th to 20th	Day	19% 9% 3 7% 4 4 4 4 5% 6% 34%	2726
	21st to end	Day	25% 10% 4 7% 5% 5% 5% 4 4 6% 26%	2850
July	1st to 10th	Day	18% 9% 4 8% 6% 5% 5% 4 6% 8% 27%	4602
	11th to 20th	Day	12% 9% 4 10% 7% 7% 6% 4 6% 10% 27%	4440
	21st to end	Day	20% 10% 3 7% 5% 4 4 4 6% 8% 29%	4505
August	1st to 10th	Day	20% 10% 4 9% 6% 5% 6% 3 5% 8% 25%	4105
	11th to 20th	Day	15% 9% 3 8% 5% 6% 5% 5% 6% 8% 30%	4045
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 5% 8% 49%	4380
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 3 5% 7% 44%	2280
	11th to 20th	Day	18% 7% 2 5% 3 3 4 4 5% 7% 43%	2157
	21st to end	Day	18% 7% 2 5% 5% 3 4 3 4 6% 42%	2060
October	1st to 10th	Day	19% 5% 2 6% 5% 4 4 4 5% 8% 40%	1900
	11th to 20th	Day	18% 7% 2 5% 4 4 5% 4 5% 6% 39%	1900
	21st to end	Day	21% 7% 2 6% 5% 5% 5% 3 6% 7% 33%	2090
November	1st to 10th	Day	19% 9% 3 6% 5% 5% 3 3 5% 6% 34%	1680
	11th to 20th	Day	21% 9% 3 6% 5% 5% 6% 4 6% 6% 30%	1600
	21st to end	Day	20% 9% 3 8% 6% 4 5% 4 5% 7% 27%	1600
December	1st to 10th	Day	24% 12% 3 8% 5% 6% 5% 4 6% 6% 22%	1584
	11th to 20th	Day	30% 11% 3 6% 4 5% 5% 5% 6% 6% 19%	1906
	21st to end	Day	22% 10% 5% 9% 5% 4 4 4 5% 7% 26%	2783
January	1st to 10th	Night	16% 11% 4 12% 7% 6% 5% 4 5% 6% 24%	4429
	11th to 20th	Night	17% 10% 4 11% 7% 6% 6% 5% 6% 7% 21%	4203
	21st to end	Night	18% 12% 4 11% 6% 5% 5% 4 6% 7% 21%	4532
February	1st to 10th	Night	20% 11% 3 9% 7% 4 5% 5% 6% 7% 24%	2470
	11th to 20th	Night	18% 9% 3 8% 6% 5% 5% 5% 7% 7% 25%	2403
	21st to end	Night	13% 9% 4 8% 6% 5% 5% 5% 6% 7% 33%	1989
March	1st to 10th	Night	24% 11% 3 7% 6% 5% 4 3 4 5% 28%	3410
	11th to 20th	Night	16% 10% 4 10% 5% 5% 5% 4 7% 8% 27%	3479
	21st to end	Night	32% 10% 3 8% 4 3 3 3 3 5% 28%	3816
April	1st to 10th	Night	25% 11% 3 7% 5% 3 3 3 4 5% 31%	1943
	11th to 20th	Night	24% 7% 3 5% 5% 3 4 2 5% 7% 34%	1783
	21st to end	Night	23% 9% 3 6% 4 4 4 3 5% 6% 33%	1710
May	1st to 10th	Night	20% 12% 3 9% 5% 5% 4 3 4 6% 27%	2834
	11th to 20th	Night	26% 11% 3 8% 4 4 4 3 4 5% 27%	2538
	21st to end	Night	19% 12% 4 8% 5% 4 3 4 5% 6% 32%	2749
June	1st to 10th	Night	26% 9% 3 6% 3 4 4 3 5% 7% 30%	1520
	11th to 20th	Night	21% 9% 2 6% 4 5% 4 3 4 6% 35%	1463
	21st to end	Night	27% 10% 3 8% 5% 3 5% 3 5% 5% 26%	1330
July	1st to 10th	Night	20% 12% 4 10% 5% 4 5% 3 6% 7% 24%	2328
	11th to 20th	Night	14% 10% 4 13% 8% 6% 6% 5% 5% 5% 24%	2530
	21st to end	Night	21% 10% 3 8% 4 4 4 3 5% 7% 30%	3046
August	1st to 10th	Night	17% 9% 5% 11% 6% 4 3 2 4 6% 33%	2825
	11th to 20th	Night	15% 10% 4 8% 4 4 5% 4 5% 8% 33%	2782
	21st to end	Night	10% 5% 2 5% 3 4 4 3 5% 8% 51%	3274
September	1st to 10th	Night	14% 7% 2 6% 5% 4 4 4 6% 7% 42%	1900
	11th to 20th	Night	17% 7% 2 6% 3 3 3 3 5% 5% 45%	2020
	21st to end	Night	20% 8% 2 6% 5% 4 4 2 5% 6% 39%	2118
October	1st to 10th	Night	20% 6% 2 5% 3 4 3 3 4 7% 42%	2280
	11th to 20th	Night	18% 7% 3 5% 3 4 4 4 5% 7% 41%	2280
	21st to end	Night	23% 8% 1 5% 4 4 4 3 5% 7% 36%	2508
November	1st to 10th	Night	18% 8% 3 7% 4 3 4 3 6% 7% 37%	2614
	11th to 20th	Night	19% 8% 2 8% 5% 5% 5% 5% 7% 7% 29%	2800
	21st to end	Night	21% 9% 3 6% 5% 5% 5% 4 6% 7% 30%	2800
December	1st to 10th	Night	22% 11% 4 10% 6% 5% 5% 4 5% 7% 23%	2779
	11th to 20th	Night	29% 11% 3 8% 4 4 4 4 6% 6% 22%	3293
	21st to end	Night	24% 9% 3 7% 5% 4 4 3 5% 5% 28%	4884

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	56% 7% 15% 16% 5%	2527
	11th to 20th	Day	57% 10% 14% 14% 4	2756
	21st to end	Day	56% 8% 12% 18% 7%	3124
February	1st to 10th	Day	60% 8% 13% 12% 7% 1	1710
	11th to 20th	Day	57% 8% 12% 16% 7% 1	1671
	21st to end	Day	49% 8% 13% 19% 9% 2	1462
March	1st to 10th	Day	58% 6% 10% 16% 8% 2	3434
	11th to 20th	Day	47% 11% 16% 16% 9% 1	3480
	21st to end	Day	62% 4 7% 15% 9% 2	3816
April	1st to 10th	Day	55% 6% 9% 16% 13% 2	2236
	11th to 20th	Day	48% 5% 13% 20% 13% 1	2344
	21st to end	Day	49% 6% 12% 18% 13% 2	2470
May	1st to 10th	Day	54% 9% 16% 15% 5%	4120
	11th to 20th	Day	54% 8% 11% 17% 9% 1	4366
	21st to end	Day	46% 13% 14% 15% 11% 1	4836
June	1st to 10th	Day	55% 7% 11% 18% 10%	2660
	11th to 20th	Day	50% 7% 11% 18% 12% 2	2726
	21st to end	Day	60% 8% 9% 13% 9% 1	2850
July	1st to 10th	Day	56% 9% 10% 12% 12% 2	4531
	11th to 20th	Day	53% 10% 11% 17% 8% 1	4364
	21st to end	Day	52% 9% 11% 18% 9% 1	4361
August	1st to 10th	Day	58% 8% 9% 15% 9% 1	4092
	11th to 20th	Day	48% 8% 16% 20% 7%	4084
	21st to end	Day	32% 7% 12% 28% 20% 1	4380
September	1st to 10th	Day	40% 6% 11% 24% 17% 2	2280
	11th to 20th	Day	42% 6% 10% 23% 16% 2	2157
	21st to end	Day	43% 7% 8% 23% 17% 1	2060
October	1st to 10th	Day	42% 6% 13% 26% 12% 1	3160
	11th to 20th	Day	35% 6% 11% 23% 24% 1	3140
	21st to end	Day	42% 5% 14% 23% 11% 4	3428
November	1st to 10th	Day	50% 6% 11% 22% 9% 1	1680
	11th to 20th	Day	54% 9% 12% 17% 8% 1	1600
	21st to end	Day	56% 7% 14% 17% 5% 1	1600
December	1st to 10th	Day	63% 7% 12% 13% 4	1584
	11th to 20th	Day	65% 8% 9% 11% 6%	1905
	21st to end	Day	58% 9% 14% 12% 5% 2	2783
January	1st to 10th	Night	60% 9% 12% 15% 4 1	4429
	11th to 20th	Night	59% 11% 12% 12% 5%	4203
	21st to end	Night	61% 10% 12% 13% 5%	4532
February	1st to 10th	Night	60% 9% 11% 13% 7% 1	2470
	11th to 20th	Night	56% 9% 12% 14% 8% 1	2406
	21st to end	Night	50% 8% 14% 17% 9% 1	1989
March	1st to 10th	Night	60% 5% 9% 14% 11% 1	3419
	11th to 20th	Night	54% 9% 14% 14% 8% 1	3480
	21st to end	Night	61% 4 8% 16% 10% 2	3816
April	1st to 10th	Night	55% 5% 9% 14% 12% 3	1943
	11th to 20th	Night	50% 5% 11% 19% 13% 2	1783
	21st to end	Night	51% 4 10% 19% 13% 3	1710
May	1st to 10th	Night	57% 8% 11% 17% 7% 1	2840
	11th to 20th	Night	56% 8% 9% 19% 7% 1	2539
	21st to end	Night	53% 9% 11% 20% 8%	2750
June	1st to 10th	Night	56% 5% 10% 20% 8%	1520
	11th to 20th	Night	51% 5% 13% 18% 12% 1	1463
	21st to end	Night	61% 6% 10% 11% 11% 1	1330
July	1st to 10th	Night	61% 7% 9% 12% 10% 1	2290
	11th to 20th	Night	62% 9% 6% 13% 9% 2	2482
	21st to end	Night	53% 7% 9% 19% 10% 1	2950
August	1st to 10th	Night	55% 6% 9% 20% 9%	2813
	11th to 20th	Night	48% 8% 16% 21% 7%	2809
	21st to end	Night	32% 6% 13% 27% 21%	3273
September	1st to 10th	Night	41% 6% 10% 26% 16% 2	1900
	11th to 20th	Night	41% 5% 8% 26% 17% 2	2020
	21st to end	Night	48% 6% 8% 22% 15% 1	2118
October	1st to 10th	Night	45% 6% 12% 24% 11% 1	3800
	11th to 20th	Night	32% 5% 13% 27% 22%	3779
	21st to end	Night	41% 5% 10% 26% 18% 1	4120
November	1st to 10th	Night	48% 7% 13% 20% 10% 1	2614
	11th to 20th	Night	54% 8% 13% 17% 8%	2800
	21st to end	Night	55% 9% 14% 15% 5%	2800
December	1st to 10th	Night	62% 8% 11% 15% 4	2779
	11th to 20th	Night	66% 7% 8% 13% 5% 1	3295
	21st to end	Night	58% 7% 13% 16% 5%	4884

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	28% 17% 32% 19% 4	370
	11th to 20th	Day	28% 16% 34% 17% 4	370
	21st to end	Day	20% 16% 34% 26% 4	407
February	1st to 10th	Day	26% 15% 34% 21% 4	370
	11th to 20th	Day	24% 21% 34% 19% 1	366
	21st to end	Day	17% 16% 38% 24% 4	329
March	1st to 10th	Day	24% 16% 37% 20% 4	460
	11th to 20th	Day	20% 18% 33% 23% 6% 1	460
	21st to end	Day	25% 13% 33% 21% 7% 1	506
April	1st to 10th	Day	30% 14% 31% 20% 5%	460
	11th to 20th	Day	23% 9% 36% 27% 4	452
	21st to end	Day	22% 9% 29% 30% 10% 1	460
May	1st to 10th	Day	25% 8% 32% 27% 6% 1	463
	11th to 20th	Day	22% 7% 28% 32% 11% 1	651
	21st to end	Day	25% 7% 26% 32% 8% 1	735
June	1st to 10th	Day	27% 5% 22% 35% 9% 1	680
	11th to 20th	Day	22% 6% 21% 38% 13% 1	680
	21st to end	Day	30% 5% 19% 33% 11% 1	680
July	1st to 10th	Day	23% 5% 21% 36% 14% 1	670
	11th to 20th	Day	24% 5% 15% 40% 16% 1	668
	21st to end	Day	22% 5% 17% 37% 17% 1	557
August	1st to 10th	Day	18% 7% 17% 37% 19% 2	486
	11th to 20th	Day	20% 7% 19% 30% 21% 4	479
	21st to end	Day	16% 4 22% 34% 21% 4	539
September	1st to 10th	Day	18% 3 20% 39% 18% 2	490
	11th to 20th	Day	22% 7% 21% 29% 17% 5%	490
	21st to end	Day	21% 6% 23% 31% 15% 3	473
October	1st to 10th	Day	20% 5% 26% 30% 17% 2	390
	11th to 20th	Day	18% 12% 28% 26% 13% 3	390
	21st to end	Day	24% 11% 29% 26% 9%	429
November	1st to 10th	Day	20% 13% 29% 27% 11%	395
	11th to 20th	Day	25% 20% 28% 22% 6% 1	400
	21st to end	Day	26% 15% 32% 23% 5%	400
December	1st to 10th	Day	31% 13% 31% 21% 4	394
	11th to 20th	Day	31% 23% 28% 16% 2	370
	21st to end	Day	24% 19% 34% 20% 4 1	407
January	1st to 10th	Night	25% 17% 33% 21% 4	850
	11th to 20th	Night	25% 15% 34% 22% 4	781
	21st to end	Night	21% 15% 37% 21% 5%	836
February	1st to 10th	Night	28% 16% 32% 21% 3	760
	11th to 20th	Night	23% 18% 37% 20% 2	743
	21st to end	Night	17% 12% 40% 24% 6%	628
March	1st to 10th	Night	25% 13% 37% 22% 3	760
	11th to 20th	Night	22% 11% 31% 28% 7%	760
	21st to end	Night	23% 12% 32% 25% 6%	836
April	1st to 10th	Night	33% 7% 29% 25% 6%	613
	11th to 20th	Night	27% 5% 34% 26% 7% 1	564
	21st to end	Night	27% 5% 26% 30% 10% 2	570
May	1st to 10th	Night	29% 4 25% 31% 8% 2	570
	11th to 20th	Night	27% 4 24% 32% 11% 2	562
	21st to end	Night	24% 4 23% 37% 11% 1	616
June	1st to 10th	Night	30% 5% 19% 32% 13% 1	570
	11th to 20th	Night	26% 4 19% 39% 12%	513
	21st to end	Night	30% 4 16% 33% 16% 1	380
July	1st to 10th	Night	24% 4 14% 41% 16% 1	433
	11th to 20th	Night	20% 6% 16% 43% 15% 1	552
	21st to end	Night	23% 6% 12% 41% 18%	623
August	1st to 10th	Night	17% 3 16% 39% 22% 3	568
	11th to 20th	Night	19% 3 18% 36% 22% 2	562
	21st to end	Night	17% 3 18% 36% 21% 4	627
September	1st to 10th	Night	17% 5% 19% 37% 19% 2	570
	11th to 20th	Night	21% 4 21% 31% 19% 4	690
	21st to end	Night	23% 6% 23% 30% 14% 4	760
October	1st to 10th	Night	24% 5% 25% 32% 13% 2	760
	11th to 20th	Night	20% 10% 30% 26% 13% 2	760
	21st to end	Night	26% 11% 29% 27% 6%	836
November	1st to 10th	Night	21% 11% 30% 29% 9% 1	835
	11th to 20th	Night	25% 17% 27% 24% 7%	900
	21st to end	Night	25% 17% 31% 20% 7% 1	900
December	1st to 10th	Night	28% 13% 32% 21% 5% 1	893
	11th to 20th	Night	27% 21% 32% 16% 3	850
	21st to end	Night	26% 16% 34% 19% 5%	935

Page generated at 2024-12-06 04:54:48. Version ac07

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