Murphy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Murphy clear sky chart from 2005-11-06 to 2025-04-26.

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	14% 7% 3 6% 5% 5% 5% 4 6% 7% 39%	113952
	Night	14% 7% 3 6% 4 4 4 4 5% 7% 41%	114684
Transparency	Day	24% 43% 6% 13% 11% 3	117771
	Night	24% 42% 7% 13% 11% 3	119003
Seeing	Day	19% 11% 21% 22% 17% 10%	15441
	Night	18% 8% 19% 31% 20% 4	25561

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	17% 11% 4 5% 3 3 3 3 4 5% 42%	4056
	11th to 20th	Day	16% 6% 6% 7% 3 3 3 2 3 4 46%	4060
	21st to end	Day	21% 10% 2 5% 3 4 4 3 4 6% 38%	4511
February	1st to 10th	Day	17% 10% 3 7% 4 4 3 3 5% 6% 37%	2000
	11th to 20th	Day	23% 9% 2 6% 5% 4 4 2 5% 5% 34%	1948
	21st to end	Day	22% 8% 2 6% 5% 3 4 3 4 5% 38%	1650
March	1st to 10th	Day	19% 9% 3 6% 4 5% 5% 3 5% 6% 35%	4636
	11th to 20th	Day	12% 6% 2 5% 3 3 4 2 5% 7% 50%	4980
	21st to end	Day	16% 7% 2 7% 4 4 4 3 5% 5% 43%	5465
April	1st to 10th	Day	13% 7% 2 6% 4 5% 4 5% 7% 7% 41%	2254
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 5% 6% 43%	2374
	21st to end	Day	13% 6% 2 7% 4 5% 5% 4 5% 7% 41%	2535
May	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 5% 6% 7% 35%	4082
	11th to 20th	Day	17% 9% 3 7% 5% 5% 5% 4 6% 7% 30%	4081
	21st to end	Day	9% 6% 2 7% 5% 6% 6% 5% 7% 10% 38%	4476
June	1st to 10th	Day	11% 7% 3 7% 6% 5% 6% 5% 9% 9% 33%	2470
	11th to 20th	Day	6% 5% 2 6% 6% 6% 7% 5% 9% 10% 37%	2470
	21st to end	Day	9% 5% 2 7% 6% 5% 7% 5% 8% 10% 36%	2470
July	1st to 10th	Day	7% 5% 3 8% 7% 7% 7% 6% 9% 12% 31%	4120
	11th to 20th	Day	9% 6% 3 7% 6% 6% 7% 6% 7% 10% 32%	4120
	21st to end	Day	14% 10% 4 10% 8% 8% 8% 6% 7% 7% 17%	4466
August	1st to 10th	Day	6% 5% 2 8% 5% 6% 7% 5% 9% 11% 35%	4104
	11th to 20th	Day	8% 5% 3 6% 4 5% 5% 6% 9% 12% 36%	3898
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 6% 8% 46%	4180
September	1st to 10th	Day	10% 6% 3 8% 6% 6% 5% 5% 7% 8% 38%	2096
	11th to 20th	Day	13% 7% 3 7% 5% 5% 4 4 6% 8% 37%	2090
	21st to end	Day	14% 4 2 6% 4 4 5% 4 6% 8% 42%	2090
October	1st to 10th	Day	9% 5% 2 6% 4 4 4 3 6% 5% 52%	2090
	11th to 20th	Day	12% 4 2 5% 3 3 4 3 4 7% 53%	1957
	21st to end	Day	12% 7% 1 4 3 3 3 3 4 6% 52%	2090
November	1st to 10th	Day	11% 6% 1 4 3 3 3 4 4 5% 55%	1764
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 5% 7% 49%	1800
	21st to end	Day	15% 7% 3 5% 4 4 5% 3 4 6% 44%	1800
December	1st to 10th	Day	19% 7% 2 5% 3 3 3 3 4 6% 46%	2930
	11th to 20th	Day	22% 10% 3 6% 4 5% 4 3 5% 5% 32%	3373
	21st to end	Day	19% 10% 5% 6% 3 3 3 3 5% 7% 36%	4466
January	1st to 10th	Night	16% 10% 3 6% 3 3 3 2 5% 6% 41%	5889
	11th to 20th	Night	19% 7% 3 7% 4 3 3 2 4 5% 43%	5900
	21st to end	Night	19% 10% 2 5% 4 3 3 2 5% 6% 41%	6430
February	1st to 10th	Night	17% 7% 4 6% 4 4 4 3 5% 6% 40%	2400
	11th to 20th	Night	23% 9% 3 7% 4 4 4 2 4 5% 36%	2338
	21st to end	Night	22% 9% 3 7% 4 4 4 3 5% 5% 35%	1980
March	1st to 10th	Night	20% 10% 3 7% 5% 4 5% 4 5% 6% 33%	5217
	11th to 20th	Night	12% 6% 2 4 3 3 4 4 6% 8% 50%	4980
	21st to end	Night	15% 7% 2 6% 4 5% 4 4 4 6% 42%	5467
April	1st to 10th	Night	14% 5% 2 5% 4 3 4 4 6% 7% 46%	2162
	11th to 20th	Night	12% 6% 2 6% 5% 3 3 3 4 7% 49%	1974
	21st to end	Night	11% 5% 3 5% 4 4 4 4 6% 7% 47%	1761
May	1st to 10th	Night	13% 8% 3 7% 6% 4 5% 4 6% 9% 36%	2813
	11th to 20th	Night	18% 7% 2 7% 6% 4 4 4 5% 8% 34%	2812
	21st to end	Night	6% 6% 2 6% 5% 5% 5% 4 8% 12% 39%	3079
June	1st to 10th	Night	8% 6% 3 7% 5% 5% 6% 5% 8% 9% 36%	1710
	11th to 20th	Night	4 5% 2 5% 4 5% 6% 5% 8% 12% 45%	1710
	21st to end	Night	7% 5% 2 5% 5% 5% 6% 4 7% 11% 43%	1710
July	1st to 10th	Night	8% 6% 3 8% 6% 6% 6% 6% 8% 11% 31%	2840
	11th to 20th	Night	8% 5% 2 6% 4 5% 6% 5% 8% 11% 40%	2840
	21st to end	Night	14% 10% 4 10% 6% 6% 6% 5% 7% 10% 22%	3087
August	1st to 10th	Night	6% 5% 2 7% 5% 6% 6% 4 8% 12% 38%	2825
	11th to 20th	Night	11% 5% 2 6% 5% 4 4 4 6% 9% 43%	2927
	21st to end	Night	7% 4 2 6% 4 4 5% 5% 7% 9% 47%	3476
September	1st to 10th	Night	9% 6% 3 7% 6% 5% 5% 4 6% 8% 41%	2063
	11th to 20th	Night	11% 6% 3 6% 6% 4 5% 5% 7% 9% 38%	2090
	21st to end	Night	11% 6% 2 6% 4 3 4 3 6% 8% 47%	2090
October	1st to 10th	Night	12% 5% 2 4 3 3 3 2 4 6% 56%	2090
	11th to 20th	Night	12% 5% 2 4 4 4 3 3 5% 6% 51%	2223
	21st to end	Night	12% 5% 2 5% 3 3 3 2 4 6% 54%	2508
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 4 6% 52%	2531
	11th to 20th	Night	14% 6% 2 6% 3 3 3 3 4 7% 48%	2600
	21st to end	Night	16% 7% 2 5% 4 3 4 4 5% 6% 44%	2600
December	1st to 10th	Night	19% 8% 3 6% 3 3 3 3 5% 6% 42%	4250
	11th to 20th	Night	23% 9% 3 7% 4 4 3 3 4 5% 34%	4822
	21st to end	Night	19% 9% 4 7% 4 4 4 3 5% 7% 33%	6490

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	32% 27% 4 14% 22% 2	4057
	11th to 20th	Day	29% 27% 2 11% 27% 4	4060
	21st to end	Day	34% 29% 4 12% 15% 5%	4511
February	1st to 10th	Day	19% 61% 3 9% 7% 1	2000
	11th to 20th	Day	23% 61% 1 6% 7% 2	1958
	21st to end	Day	19% 62% 2 5% 10% 2	1650
March	1st to 10th	Day	37% 31% 4 9% 13% 6%	4636
	11th to 20th	Day	21% 29% 3 13% 19% 15%	4980
	21st to end	Day	30% 29% 4 22% 12% 3	5465
April	1st to 10th	Day	18% 63% 4 7% 7% 1	2254
	11th to 20th	Day	18% 63% 4 8% 6% 1	2374
	21st to end	Day	15% 64% 4 10% 6% 1	2535
May	1st to 10th	Day	28% 43% 6% 14% 8% 1	4120
	11th to 20th	Day	32% 43% 5% 16% 3	4085
	21st to end	Day	24% 43% 8% 13% 11%	4489
June	1st to 10th	Day	16% 67% 6% 8% 3 1	2470
	11th to 20th	Day	14% 67% 8% 7% 4	2470
	21st to end	Day	15% 66% 7% 8% 3	2470
July	1st to 10th	Day	22% 46% 15% 13% 4	4055
	11th to 20th	Day	25% 42% 17% 13% 2	4051
	21st to end	Day	46% 40% 7% 5% 2	4324
August	1st to 10th	Day	22% 42% 13% 17% 5%	4091
	11th to 20th	Day	17% 43% 17% 13% 9% 1	3937
	21st to end	Day	14% 41% 8% 27% 9%	4179
September	1st to 10th	Day	15% 62% 6% 8% 8% 1	2096
	11th to 20th	Day	16% 62% 6% 9% 7%	2090
	21st to end	Day	16% 62% 7% 8% 7% 1	2090
October	1st to 10th	Day	13% 40% 5% 11% 23% 8%	3480
	11th to 20th	Day	10% 37% 3 12% 20% 19%	3236
	21st to end	Day	16% 38% 4 17% 16% 9%	3428
November	1st to 10th	Day	18% 57% 3 7% 11% 3	1764
	11th to 20th	Day	15% 57% 2 10% 12% 4	1800
	21st to end	Day	17% 58% 3 9% 12% 1	1800
December	1st to 10th	Day	25% 36% 3 12% 19% 5%	2930
	11th to 20th	Day	36% 34% 4 11% 13% 3	3370
	21st to end	Day	36% 28% 7% 21% 8% 1	4466
January	1st to 10th	Night	32% 26% 5% 13% 21% 3	5889
	11th to 20th	Night	29% 29% 3 13% 19% 7%	5900
	21st to end	Night	32% 28% 4 14% 17% 5%	6430
February	1st to 10th	Night	18% 62% 3 9% 6% 2	2400
	11th to 20th	Night	23% 61% 2 7% 6% 2	2339
	21st to end	Night	18% 62% 3 7% 7% 3	1980
March	1st to 10th	Night	40% 30% 4 10% 14% 2	5217
	11th to 20th	Night	20% 29% 6% 14% 18% 13%	4980
	21st to end	Night	31% 30% 5% 18% 12% 4	5467
April	1st to 10th	Night	15% 63% 5% 8% 7% 2	2162
	11th to 20th	Night	17% 63% 5% 9% 5% 2	1974
	21st to end	Night	13% 65% 5% 11% 6% 1	1761
May	1st to 10th	Night	27% 44% 9% 14% 5% 1	2840
	11th to 20th	Night	30% 42% 7% 14% 7%	2813
	21st to end	Night	19% 45% 11% 16% 9%	3087
June	1st to 10th	Night	13% 68% 7% 7% 3 1	1710
	11th to 20th	Night	9% 68% 10% 9% 4	1710
	21st to end	Night	12% 66% 8% 10% 3	1710
July	1st to 10th	Night	27% 45% 14% 13% 1	2795
	11th to 20th	Night	20% 43% 18% 17% 2 1	2786
	21st to end	Night	43% 41% 7% 6% 2	2988
August	1st to 10th	Night	22% 41% 18% 16% 3	2814
	11th to 20th	Night	20% 41% 16% 14% 9%	2954
	21st to end	Night	13% 42% 12% 24% 8% 1	3476
September	1st to 10th	Night	14% 63% 6% 8% 8% 1	2063
	11th to 20th	Night	14% 63% 6% 10% 7%	2090
	21st to end	Night	15% 62% 7% 9% 7%	2090
October	1st to 10th	Night	10% 41% 7% 14% 20% 8%	3480
	11th to 20th	Night	10% 37% 4 11% 25% 14%	3683
	21st to end	Night	13% 39% 5% 17% 18% 9%	4120
November	1st to 10th	Night	19% 56% 4 9% 9% 2	2531
	11th to 20th	Night	17% 57% 3 8% 10% 4	2600
	21st to end	Night	17% 57% 3 11% 10% 1	2600
December	1st to 10th	Night	28% 36% 4 11% 20% 3	4250
	11th to 20th	Night	34% 35% 4 10% 14% 3	4824
	21st to end	Night	36% 29% 9% 17% 9% 1	6490

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	34% 21% 32% 10% 3	300
	11th to 20th	Day	33% 23% 25% 13% 5%	300
	21st to end	Day	27% 29% 27% 14% 3	330
February	1st to 10th	Day	32% 16% 32% 18% 2	300
	11th to 20th	Day	42% 25% 24% 7% 2	300
	21st to end	Day	37% 20% 32% 8% 2	249
March	1st to 10th	Day	33% 14% 29% 15% 7% 1	365
	11th to 20th	Day	28% 17% 24% 25% 5% 1	500
	21st to end	Day	27% 18% 27% 21% 6% 1	550
April	1st to 10th	Day	26% 13% 27% 20% 13% 1	500
	11th to 20th	Day	17% 19% 25% 23% 13% 3	492
	21st to end	Day	21% 11% 24% 24% 16% 3	480
May	1st to 10th	Day	18% 18% 23% 21% 14% 6%	463
	11th to 20th	Day	18% 6% 23% 25% 18% 10%	487
	21st to end	Day	11% 7% 20% 28% 21% 14%	529
June	1st to 10th	Day	12% 7% 17% 29% 22% 13%	490
	11th to 20th	Day	7% 6% 13% 28% 26% 20%	490
	21st to end	Day	12% 4 21% 24% 22% 17%	490
July	1st to 10th	Day	11% 3 10% 25% 27% 24%	485
	11th to 20th	Day	9% 6% 8% 24% 29% 25%	484
	21st to end	Day	11% 4 9% 25% 28% 24%	532
August	1st to 10th	Day	14% 4 15% 23% 21% 23%	486
	11th to 20th	Day	9% 5% 14% 24% 29% 19%	479
	21st to end	Day	15% 2 9% 20% 29% 25%	539
September	1st to 10th	Day	10% 4 11% 24% 33% 18%	490
	11th to 20th	Day	14% 4 16% 21% 27% 17%	490
	21st to end	Day	15% 5% 13% 29% 29% 10%	490
October	1st to 10th	Day	14% 6% 18% 26% 28% 8%	490
	11th to 20th	Day	16% 11% 23% 26% 21% 4	490
	21st to end	Day	17% 12% 19% 29% 18% 4	539
November	1st to 10th	Day	18% 13% 31% 23% 12% 3	302
	11th to 20th	Day	20% 17% 33% 22% 8%	300
	21st to end	Day	18% 18% 34% 20% 7% 2	300
December	1st to 10th	Day	33% 19% 23% 19% 4 1	300
	11th to 20th	Day	31% 14% 28% 18% 8% 2	300
	21st to end	Day	31% 18% 27% 17% 7%	330
January	1st to 10th	Night	27% 14% 29% 24% 5%	800
	11th to 20th	Night	28% 13% 27% 26% 6%	800
	21st to end	Night	22% 15% 32% 29% 3	880
February	1st to 10th	Night	22% 12% 27% 34% 5%	800
	11th to 20th	Night	31% 13% 28% 25% 2	783
	21st to end	Night	30% 15% 29% 23% 3	660
March	1st to 10th	Night	20% 15% 31% 29% 5%	800
	11th to 20th	Night	21% 16% 26% 30% 8% 1	800
	21st to end	Night	21% 11% 29% 31% 8%	880
April	1st to 10th	Night	19% 14% 25% 33% 9% 1	762
	11th to 20th	Night	17% 11% 23% 35% 13% 1	593
	21st to end	Night	13% 7% 22% 38% 18% 2	587
May	1st to 10th	Night	13% 9% 21% 36% 20% 2	570
	11th to 20th	Night	16% 4 14% 36% 26% 4	561
	21st to end	Night	11% 4 11% 33% 35% 7%	617
June	1st to 10th	Night	11% 3 9% 35% 37% 6%	570
	11th to 20th	Night	7% 1 9% 34% 37% 12%	570
	21st to end	Night	9% 1 7% 32% 42% 8%	570
July	1st to 10th	Night	10% 2 6% 24% 47% 10%	555
	11th to 20th	Night	11% 3 5% 22% 44% 16%	552
	21st to end	Night	10% 1 7% 21% 48% 13%	624
August	1st to 10th	Night	10% 2 5% 25% 45% 13%	567
	11th to 20th	Night	11% 2 7% 31% 40% 9%	564
	21st to end	Night	13% 2 6% 22% 46% 11%	627
September	1st to 10th	Night	12% 2 8% 27% 41% 9%	733
	11th to 20th	Night	13% 3 10% 29% 40% 5%	760
	21st to end	Night	14% 3 12% 33% 34% 3	760
October	1st to 10th	Night	14% 6% 14% 31% 28% 6%	760
	11th to 20th	Night	14% 8% 19% 37% 20% 3	760
	21st to end	Night	16% 8% 18% 38% 17% 2	836
November	1st to 10th	Night	16% 7% 19% 37% 18% 3	780
	11th to 20th	Night	18% 11% 22% 35% 12% 2	800
	21st to end	Night	21% 11% 23% 32% 12% 1	800
December	1st to 10th	Night	28% 11% 24% 29% 8% 1	800
	11th to 20th	Night	24% 11% 24% 32% 8% 1	800
	21st to end	Night	29% 10% 21% 34% 5%	880

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