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 2024-10-25.

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 7% 5% 5% 5% 4 6% 8% 38%	100911
	Night	14% 7% 3 6% 4 4 4 4 6% 8% 40%	97870
Transparency	Day	23% 50% 6% 11% 8% 2	100723
	Night	22% 50% 6% 11% 8% 2	97727
Seeing	Day	19% 11% 20% 22% 18% 10%	14839
	Night	18% 8% 18% 31% 21% 4	24848

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	18% 11% 4 6% 3 3 4 3 6% 6% 36%	2836
	11th to 20th	Day	18% 7% 5% 9% 5% 4 3 2 4 5% 38%	2840
	21st to end	Day	24% 12% 3 5% 3 3 3 3 4 4 37%	3155
February	1st to 10th	Day	18% 11% 3 7% 4 3 3 3 4 6% 36%	1900
	11th to 20th	Day	23% 9% 2 6% 5% 4 4 2 4 6% 35%	1848
	21st to end	Day	23% 9% 2 7% 5% 3 4 3 4 5% 36%	1570
March	1st to 10th	Day	24% 9% 3 5% 3 3 4 3 5% 6% 34%	3234
	11th to 20th	Day	14% 6% 2 5% 3 3 4 2 4 6% 50%	3480
	21st to end	Day	17% 8% 2 7% 4 4 4 3 6% 6% 39%	3815
April	1st to 10th	Day	12% 7% 2 5% 4 5% 4 5% 7% 7% 41%	2141
	11th to 20th	Day	14% 7% 2 7% 4 4 4 4 5% 6% 42%	2254
	21st to end	Day	13% 6% 2 7% 4 5% 5% 4 5% 7% 42%	2470
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% 53%	2027
November	1st to 10th	Day	11% 6% 1 4 3 3 3 4 4 5% 56%	1674
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 5% 7% 50%	1710
	21st to end	Day	16% 7% 3 5% 4 3 5% 3 4 6% 44%	1710
December	1st to 10th	Day	22% 8% 3 7% 4 4 4 4 5% 6% 33%	1710
	11th to 20th	Day	16% 9% 4 6% 4 4 4 3 5% 6% 39%	2153
	21st to end	Day	18% 11% 6% 7% 4 4 4 3 5% 7% 32%	3124
January	1st to 10th	Night	19% 11% 3 6% 4 4 4 2 5% 6% 37%	4109
	11th to 20th	Night	21% 8% 3 7% 4 3 3 3 5% 5% 38%	4120
	21st to end	Night	25% 13% 3 5% 3 3 3 2 4 5% 34%	4500
February	1st to 10th	Night	16% 7% 4 6% 4 4 4 3 5% 6% 40%	2280
	11th to 20th	Night	22% 9% 3 6% 4 4 4 2 4 5% 37%	2218
	21st to end	Night	23% 10% 3 7% 4 4 4 3 5% 4 34%	1884
March	1st to 10th	Night	22% 10% 3 7% 5% 4 5% 4 4 6% 30%	3619
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 6% 8% 47%	3480
	21st to end	Night	16% 7% 3 6% 5% 5% 4 4 5% 6% 40%	3817
April	1st to 10th	Night	14% 5% 2 5% 4 3 4 4 5% 7% 46%	2054
	11th to 20th	Night	13% 6% 2 5% 5% 3 3 3 4 7% 48%	1874
	21st to end	Night	11% 5% 3 5% 4 4 4 4 6% 7% 48%	1710
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 3 6% 55%	2435
November	1st to 10th	Night	12% 5% 2 4 3 3 3 3 4 6% 53%	2401
	11th to 20th	Night	13% 6% 2 6% 3 3 3 3 4 7% 49%	2470
	21st to end	Night	17% 7% 2 5% 4 3 3 4 5% 6% 44%	2470
December	1st to 10th	Night	20% 8% 3 7% 4 4 4 4 6% 6% 33%	2470
	11th to 20th	Night	16% 9% 4 7% 4 4 3 3 4 5% 41%	3042
	21st to end	Night	19% 11% 4 8% 4 5% 5% 4 6% 7% 28%	4532

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	31% 37% 3 8% 18% 3	2837
	11th to 20th	Day	31% 38% 3 8% 18% 2	2840
	21st to end	Day	32% 40% 3 9% 14% 1	3155
February	1st to 10th	Day	19% 64% 2 7% 7% 1	1900
	11th to 20th	Day	21% 64% 1 6% 7% 2	1858
	21st to end	Day	19% 65% 2 5% 7% 2	1570
March	1st to 10th	Day	34% 41% 4 9% 6% 6%	3234
	11th to 20th	Day	18% 40% 3 15% 16% 8%	3480
	21st to end	Day	27% 41% 4 16% 9% 3	3815
April	1st to 10th	Day	17% 65% 3 6% 7% 1	2141
	11th to 20th	Day	18% 66% 4 6% 5% 1	2254
	21st to end	Day	14% 66% 4 10% 6% 1	2470
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	15% 62% 4 9% 9% 2	2090
	11th to 20th	Day	12% 60% 4 9% 9% 6%	1957
	21st to end	Day	14% 60% 2 9% 11% 4	2027
November	1st to 10th	Day	17% 59% 2 6% 12% 3	1674
	11th to 20th	Day	14% 60% 2 9% 11% 4	1710
	21st to end	Day	17% 60% 3 8% 11% 2	1710
December	1st to 10th	Day	24% 60% 2 8% 5% 2	1710
	11th to 20th	Day	22% 49% 2 6% 17% 4	2150
	21st to end	Day	34% 38% 3 15% 9% 1	3124
January	1st to 10th	Night	33% 36% 3 9% 17% 3	4109
	11th to 20th	Night	27% 40% 3 11% 11% 7%	4120
	21st to end	Night	36% 39% 3 6% 14% 2	4500
February	1st to 10th	Night	16% 65% 3 8% 6% 2	2280
	11th to 20th	Night	21% 64% 1 6% 5% 2	2219
	21st to end	Night	19% 65% 3 6% 5% 3	1884
March	1st to 10th	Night	37% 43% 5% 7% 6% 2	3619
	11th to 20th	Night	17% 40% 6% 15% 14% 8%	3480
	21st to end	Night	27% 42% 4 13% 11% 3	3817
April	1st to 10th	Night	14% 65% 5% 7% 7% 2	2054
	11th to 20th	Night	16% 66% 5% 7% 4 2	1874
	21st to end	Night	12% 66% 5% 11% 6% 1	1710
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	12% 61% 6% 9% 10% 2	2090
	11th to 20th	Night	13% 60% 5% 8% 9% 4	2223
	21st to end	Night	12% 60% 2 9% 12% 5%	2435
November	1st to 10th	Night	18% 59% 3 8% 9% 2	2401
	11th to 20th	Night	16% 60% 3 7% 9% 5%	2470
	21st to end	Night	17% 60% 3 9% 10% 1	2470
December	1st to 10th	Night	24% 60% 3 6% 5% 2	2470
	11th to 20th	Night	20% 50% 3 8% 16% 3	3044
	21st to end	Night	37% 37% 5% 12% 8% 1	4532

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	33% 20% 33% 11% 4	270
	11th to 20th	Day	33% 22% 26% 14% 6%	270
	21st to end	Day	27% 28% 28% 13% 4	297
February	1st to 10th	Day	34% 16% 31% 17% 1	270
	11th to 20th	Day	40% 24% 26% 7% 2	270
	21st to end	Day	40% 20% 31% 8% 1	225
March	1st to 10th	Day	33% 13% 30% 16% 8% 1	332
	11th to 20th	Day	27% 17% 25% 25% 5% 1	460
	21st to end	Day	26% 18% 27% 22% 7% 1	506
April	1st to 10th	Day	25% 13% 27% 20% 13% 2	460
	11th to 20th	Day	17% 20% 24% 23% 14% 3	452
	21st to end	Day	21% 11% 24% 24% 16% 3	460
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	18% 12% 19% 29% 18% 4	514
November	1st to 10th	Day	18% 12% 31% 24% 12% 4	272
	11th to 20th	Day	18% 19% 32% 23% 8%	270
	21st to end	Day	18% 16% 36% 21% 8% 2	270
December	1st to 10th	Day	34% 19% 22% 20% 5% 1	270
	11th to 20th	Day	29% 14% 27% 19% 8% 2	270
	21st to end	Day	31% 19% 28% 16% 6%	297
January	1st to 10th	Night	27% 14% 28% 24% 6%	760
	11th to 20th	Night	29% 14% 26% 26% 6%	760
	21st to end	Night	23% 15% 30% 30% 3	836
February	1st to 10th	Night	22% 12% 27% 34% 5%	760
	11th to 20th	Night	30% 13% 28% 26% 2	743
	21st to end	Night	31% 15% 28% 22% 3	628
March	1st to 10th	Night	20% 15% 30% 30% 5%	760
	11th to 20th	Night	20% 16% 26% 29% 8% 1	760
	21st to end	Night	21% 12% 28% 31% 8%	836
April	1st to 10th	Night	19% 13% 25% 33% 9% 1	724
	11th to 20th	Night	17% 11% 22% 35% 13% 1	563
	21st to end	Night	13% 7% 22% 38% 18% 2	570
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	812
November	1st to 10th	Night	16% 7% 17% 37% 19% 3	740
	11th to 20th	Night	17% 12% 22% 35% 12% 2	760
	21st to end	Night	21% 11% 22% 32% 13% 1	760
December	1st to 10th	Night	28% 11% 23% 29% 8% 1	760
	11th to 20th	Night	23% 11% 24% 33% 8% 1	760
	21st to end	Night	29% 10% 21% 34% 5%	836

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