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 2024-03-01.

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% 3 5% 5% 6% 8% 38%	78857
	Night	15% 7% 3 5% 5% 3 4 4 5% 8% 41%	80568
Transparency	Day	44% 7% 11% 18% 16% 4	78580
	Night	42% 7% 11% 19% 17% 4	80364
Seeing	Day	19% 11% 20% 22% 18% 10%	13890
	Night	18% 8% 18% 30% 21% 4	24041

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% 10% 4 5% 4 3 3 4 5% 6% 36%	2836
	11th to 20th	Day	18% 7% 5% 9% 5% 3 3 3 4 5% 38%	2840
	21st to end	Day	24% 11% 3 5% 3 2 3 4 4 4 37%	3155
February	1st to 10th	Day	18% 10% 4 6% 5% 3 4 4 4 6% 36%	1900
	11th to 20th	Day	23% 8% 3 6% 5% 3 3 3 4 6% 35%	1848
	21st to end	Day	23% 8% 3 6% 5% 2 4 4 4 5% 36%	1570
March	1st to 10th	Day	18% 6% 3 5% 4 3 4 4 6% 7% 40%	1858
	11th to 20th	Day	19% 8% 3 6% 4 3 5% 4 5% 7% 36%	1980
	21st to end	Day	16% 9% 2 7% 4 3 5% 5% 6% 7% 36%	2178
April	1st to 10th	Day	13% 6% 2 4 5% 4 5% 6% 6% 7% 42%	2028
	11th to 20th	Day	14% 7% 3 5% 5% 3 5% 4 5% 6% 43%	2134
	21st to end	Day	13% 5% 3 6% 5% 4 5% 5% 5% 8% 42%	2340
May	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 6% 6% 7% 41%	2340
	11th to 20th	Day	14% 8% 3 6% 6% 3 7% 6% 6% 8% 34%	2301
	21st to end	Day	10% 6% 2 6% 6% 5% 7% 7% 7% 9% 36%	2531
June	1st to 10th	Day	11% 6% 3 6% 7% 4 6% 6% 8% 9% 34%	2340
	11th to 20th	Day	6% 5% 3 5% 7% 4 7% 6% 9% 11% 38%	2340
	21st to end	Day	9% 5% 2 6% 7% 4 7% 7% 8% 11% 35%	2340
July	1st to 10th	Day	10% 6% 3 8% 8% 5% 8% 7% 8% 10% 28%	2340
	11th to 20th	Day	10% 6% 3 6% 8% 5% 8% 9% 8% 11% 26%	2340
	21st to end	Day	9% 6% 3 6% 7% 5% 9% 9% 9% 9% 28%	2547
August	1st to 10th	Day	9% 6% 3 7% 7% 5% 7% 7% 9% 11% 30%	2327
	11th to 20th	Day	11% 6% 3 7% 7% 4 6% 7% 8% 9% 31%	2227
	21st to end	Day	13% 6% 3 7% 8% 5% 7% 7% 7% 8% 30%	2376
September	1st to 10th	Day	10% 6% 3 7% 6% 4 5% 5% 6% 8% 37%	1986
	11th to 20th	Day	14% 7% 3 5% 6% 4 5% 5% 6% 8% 38%	1980
	21st to end	Day	13% 4 2 5% 6% 3 5% 5% 6% 8% 43%	1980
October	1st to 10th	Day	10% 5% 2 5% 4 3 4 4 5% 6% 52%	1980
	11th to 20th	Day	13% 4 3 4 4 3 4 4 5% 6% 52%	1854
	21st to end	Day	13% 7% 2 4 3 2 3 4 4 6% 52%	1980
November	1st to 10th	Day	11% 6% 2 3 3 2 3 4 4 5% 57%	1674
	11th to 20th	Day	13% 5% 2 4 4 2 4 4 5% 7% 50%	1710
	21st to end	Day	16% 7% 3 4 4 2 5% 4 4 6% 44%	1710
December	1st to 10th	Day	23% 8% 3 6% 5% 3 5% 4 5% 6% 34%	1710
	11th to 20th	Day	16% 9% 4 5% 4 3 5% 4 5% 6% 39%	2153
	21st to end	Day	18% 11% 6% 6% 5% 3 4 4 4 7% 32%	3124
January	1st to 10th	Night	19% 10% 3 5% 5% 3 4 3 5% 7% 37%	4109
	11th to 20th	Night	21% 8% 3 6% 5% 2 3 4 5% 5% 38%	4120
	21st to end	Night	25% 13% 3 5% 4 2 3 3 4 5% 34%	4500
February	1st to 10th	Night	17% 6% 4 5% 5% 3 4 4 4 6% 40%	2280
	11th to 20th	Night	22% 8% 3 6% 4 2 5% 3 4 5% 37%	2218
	21st to end	Night	23% 9% 3 6% 5% 3 4 4 5% 5% 34%	1884
March	1st to 10th	Night	15% 6% 2 5% 6% 3 5% 4 4 7% 43%	2109
	11th to 20th	Night	17% 7% 4 5% 6% 3 4 5% 5% 7% 38%	1980
	21st to end	Night	15% 7% 3 6% 6% 3 5% 4 5% 6% 39%	2178
April	1st to 10th	Night	14% 4 2 4 4 2 4 5% 5% 8% 48%	1946
	11th to 20th	Night	12% 6% 2 5% 5% 2 4 4 4 7% 49%	1775
	21st to end	Night	11% 4 3 5% 4 3 5% 4 5% 7% 49%	1620
May	1st to 10th	Night	9% 5% 2 5% 6% 3 5% 5% 6% 9% 44%	1620
	11th to 20th	Night	11% 5% 3 6% 6% 3 5% 6% 6% 9% 40%	1592
	21st to end	Night	7% 6% 2 5% 6% 4 5% 6% 8% 12% 39%	1744
June	1st to 10th	Night	8% 5% 3 6% 6% 4 7% 6% 8% 10% 37%	1620
	11th to 20th	Night	4 4 2 4 4 4 6% 5% 8% 13% 45%	1620
	21st to end	Night	7% 5% 2 4 5% 4 6% 5% 7% 12% 44%	1620
July	1st to 10th	Night	9% 5% 3 6% 7% 4 7% 7% 7% 11% 34%	1620
	11th to 20th	Night	9% 5% 2 5% 5% 3 6% 7% 9% 13% 37%	1620
	21st to end	Night	6% 5% 3 6% 5% 4 7% 7% 8% 14% 35%	1771
August	1st to 10th	Night	8% 5% 2 6% 5% 4 7% 5% 7% 12% 39%	1611
	11th to 20th	Night	9% 5% 2 6% 7% 4 6% 5% 7% 10% 39%	1670
	21st to end	Night	11% 5% 3 6% 6% 3 5% 7% 7% 9% 36%	1980
September	1st to 10th	Night	9% 6% 3 6% 6% 4 5% 6% 6% 8% 41%	1954
	11th to 20th	Night	11% 6% 2 5% 7% 3 5% 6% 7% 9% 40%	1980
	21st to end	Night	9% 6% 2 5% 4 2 4 5% 5% 8% 48%	1980
October	1st to 10th	Night	13% 4 2 4 3 2 3 3 3 6% 57%	1980
	11th to 20th	Night	13% 4 2 4 5% 4 3 4 5% 6% 50%	2106
	21st to end	Night	13% 5% 2 4 4 2 3 3 4 6% 54%	2376
November	1st to 10th	Night	12% 5% 2 4 3 2 4 4 4 6% 54%	2401
	11th to 20th	Night	13% 6% 3 5% 4 3 3 3 4 7% 49%	2470
	21st to end	Night	17% 6% 2 4 5% 2 4 5% 5% 6% 44%	2470
December	1st to 10th	Night	21% 8% 4 6% 5% 3 4 5% 5% 7% 33%	2470
	11th to 20th	Night	17% 8% 4 7% 4 3 3 4 4 6% 41%	3042
	21st to end	Night	20% 10% 4 7% 5% 3 5% 5% 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	48% 4 5% 16% 24% 4	2837
	11th to 20th	Day	50% 5% 5% 14% 24% 3	2840
	21st to end	Day	50% 4 6% 17% 21% 3	3155
February	1st to 10th	Day	51% 3 6% 18% 18% 4	1900
	11th to 20th	Day	52% 4 6% 16% 18% 5%	1858
	21st to end	Day	51% 4 7% 13% 19% 6%	1570
March	1st to 10th	Day	43% 6% 9% 15% 21% 7%	1858
	11th to 20th	Day	48% 6% 11% 15% 15% 4	1980
	21st to end	Day	47% 6% 11% 21% 13% 2	2178
April	1st to 10th	Day	39% 7% 11% 22% 18% 3	2028
	11th to 20th	Day	42% 6% 9% 17% 22% 4	2134
	21st to end	Day	40% 6% 10% 26% 14% 2	2340
May	1st to 10th	Day	41% 7% 14% 22% 14% 3	2340
	11th to 20th	Day	48% 9% 12% 20% 11% 1	2305
	21st to end	Day	42% 10% 14% 21% 13% 1	2531
June	1st to 10th	Day	44% 10% 17% 21% 8% 1	2340
	11th to 20th	Day	39% 10% 18% 21% 10% 2	2340
	21st to end	Day	40% 11% 17% 18% 11% 2	2340
July	1st to 10th	Day	46% 13% 17% 16% 6% 1	2275
	11th to 20th	Day	48% 13% 17% 11% 9% 2	2271
	21st to end	Day	47% 12% 16% 17% 7%	2405
August	1st to 10th	Day	45% 14% 17% 19% 5% 1	2314
	11th to 20th	Day	46% 11% 17% 15% 10% 1	2227
	21st to end	Day	50% 10% 15% 14% 9% 2	2376
September	1st to 10th	Day	43% 8% 13% 17% 15% 3	1986
	11th to 20th	Day	44% 7% 11% 18% 18% 2	1980
	21st to end	Day	39% 6% 12% 18% 19% 6%	1980
October	1st to 10th	Day	33% 7% 9% 18% 26% 6%	1980
	11th to 20th	Day	34% 5% 9% 21% 21% 9%	1854
	21st to end	Day	34% 4 7% 22% 25% 9%	1980
November	1st to 10th	Day	31% 4 6% 17% 31% 10%	1674
	11th to 20th	Day	34% 5% 6% 21% 26% 9%	1710
	21st to end	Day	42% 4 6% 19% 24% 6%	1710
December	1st to 10th	Day	51% 6% 5% 18% 16% 4	1710
	11th to 20th	Day	45% 5% 7% 14% 23% 5%	2150
	21st to end	Day	52% 5% 6% 21% 14% 2	3124
January	1st to 10th	Night	49% 3 6% 16% 23% 4	4109
	11th to 20th	Night	46% 7% 6% 17% 16% 8%	4120
	21st to end	Night	54% 3 5% 13% 20% 4	4500
February	1st to 10th	Night	46% 4 9% 19% 19% 4	2280
	11th to 20th	Night	52% 3 6% 18% 17% 5%	2219
	21st to end	Night	54% 4 8% 15% 16% 5%	1884
March	1st to 10th	Night	43% 5% 8% 17% 20% 7%	2109
	11th to 20th	Night	46% 6% 11% 19% 16% 3	1980
	21st to end	Night	46% 5% 11% 21% 15% 2	2178
April	1st to 10th	Night	36% 4 13% 23% 21% 3	1946
	11th to 20th	Night	36% 4 11% 21% 21% 6%	1775
	21st to end	Night	35% 6% 13% 29% 15% 1	1620
May	1st to 10th	Night	37% 7% 16% 23% 16% 2	1620
	11th to 20th	Night	40% 11% 17% 21% 11% 1	1593
	21st to end	Night	35% 11% 16% 26% 9% 2	1745
June	1st to 10th	Night	39% 12% 19% 21% 9% 1	1620
	11th to 20th	Night	29% 11% 24% 26% 8% 2	1620
	21st to end	Night	33% 11% 20% 22% 11% 3	1620
July	1st to 10th	Night	41% 12% 18% 19% 8% 1	1575
	11th to 20th	Night	36% 13% 25% 15% 7% 3	1566
	21st to end	Night	35% 15% 22% 20% 7% 1	1672
August	1st to 10th	Night	37% 13% 21% 23% 6%	1600
	11th to 20th	Night	39% 13% 16% 18% 12% 1	1670
	21st to end	Night	41% 10% 18% 21% 9% 2	1980
September	1st to 10th	Night	37% 10% 15% 19% 14% 4	1954
	11th to 20th	Night	39% 10% 14% 19% 18% 1	1980
	21st to end	Night	34% 8% 12% 21% 20% 6%	1980
October	1st to 10th	Night	30% 6% 11% 20% 29% 5%	1980
	11th to 20th	Night	35% 5% 10% 22% 21% 7%	2106
	21st to end	Night	34% 4 5% 23% 27% 8%	2376
November	1st to 10th	Night	33% 4 6% 22% 25% 9%	2401
	11th to 20th	Night	36% 4 6% 20% 24% 10%	2470
	21st to end	Night	41% 5% 6% 22% 22% 5%	2470
December	1st to 10th	Night	51% 6% 8% 16% 15% 4	2470
	11th to 20th	Night	45% 5% 7% 15% 24% 5%	3044
	21st to end	Night	54% 4 9% 18% 13% 2	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% 32% 8% 1	225
March	1st to 10th	Day	30% 13% 33% 17% 7%	298
	11th to 20th	Day	29% 17% 23% 25% 5% 1	420
	21st to end	Day	26% 18% 26% 22% 7% 1	462
April	1st to 10th	Day	24% 13% 25% 22% 15% 2	420
	11th to 20th	Day	17% 19% 23% 23% 14% 3	412
	21st to end	Day	21% 11% 23% 23% 18% 3	420
May	1st to 10th	Day	17% 18% 23% 21% 14% 6%	423
	11th to 20th	Day	17% 6% 22% 26% 18% 11%	447
	21st to end	Day	11% 7% 17% 28% 22% 15%	485
June	1st to 10th	Day	13% 5% 16% 29% 23% 15%	450
	11th to 20th	Day	8% 6% 13% 26% 25% 22%	450
	21st to end	Day	12% 4 21% 24% 22% 18%	450
July	1st to 10th	Day	11% 3 9% 24% 28% 24%	445
	11th to 20th	Day	9% 5% 8% 23% 30% 25%	444
	21st to end	Day	10% 2 9% 24% 29% 26%	488
August	1st to 10th	Day	15% 4 13% 21% 22% 24%	446
	11th to 20th	Day	10% 4 12% 23% 31% 21%	439
	21st to end	Day	16% 2 9% 19% 29% 24%	495
September	1st to 10th	Day	10% 4 11% 22% 34% 19%	450
	11th to 20th	Day	14% 4 14% 22% 28% 18%	450
	21st to end	Day	12% 5% 13% 30% 30% 10%	450
October	1st to 10th	Day	16% 6% 18% 24% 27% 9%	450
	11th to 20th	Day	17% 10% 23% 25% 20% 4	450
	21st to end	Day	18% 13% 19% 29% 17% 4	495
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	32% 15% 28% 22% 3	628
March	1st to 10th	Night	20% 15% 31% 30% 5%	723
	11th to 20th	Night	21% 15% 26% 28% 8% 1	720
	21st to end	Night	22% 11% 28% 31% 9%	792
April	1st to 10th	Night	18% 13% 24% 34% 9% 1	686
	11th to 20th	Night	17% 11% 22% 34% 14% 2	533
	21st to end	Night	13% 7% 22% 38% 18% 2	540
May	1st to 10th	Night	12% 9% 21% 36% 20% 2	540
	11th to 20th	Night	15% 4 14% 36% 27% 4	531
	21st to end	Night	11% 3 11% 32% 36% 7%	584
June	1st to 10th	Night	11% 3 8% 34% 38% 6%	540
	11th to 20th	Night	7% 1 9% 32% 37% 13%	540
	21st to end	Night	9% 1 6% 32% 42% 9%	540
July	1st to 10th	Night	10% 2 6% 24% 48% 11%	525
	11th to 20th	Night	11% 3 5% 22% 43% 17%	522
	21st to end	Night	8% 1 6% 21% 49% 14%	591
August	1st to 10th	Night	10% 2 6% 23% 46% 13%	537
	11th to 20th	Night	11% 1 7% 29% 42% 9%	534
	21st to end	Night	14% 2 6% 22% 46% 11%	594
September	1st to 10th	Night	12% 2 8% 26% 43% 10%	694
	11th to 20th	Night	13% 2 9% 29% 41% 5%	720
	21st to end	Night	13% 3 12% 33% 35% 4	720
October	1st to 10th	Night	15% 6% 14% 29% 29% 7%	720
	11th to 20th	Night	14% 8% 19% 35% 20% 3	720
	21st to end	Night	17% 9% 19% 37% 16% 2	792
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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