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 2024-01-13.

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	12% 7% 3 6% 5% 3 5% 5% 5% 8% 42%	74741
	Night	13% 7% 3 6% 5% 3 4 4 5% 7% 44%	75004
Transparency	Day	40% 6% 12% 24% 16% 3	74451
	Night	40% 6% 11% 24% 17% 3	74816
Seeing	Day	16% 8% 25% 27% 18% 6%	14452
	Night	16% 8% 28% 32% 14% 1	24393

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	10% 12% 4 7% 6% 3 4 5% 4 7% 36%	1517
	11th to 20th	Day	15% 8% 5% 8% 7% 2 4 4 6% 7% 32%	1582
	21st to end	Day	13% 11% 4 7% 6% 3 4 4 4 6% 38%	1782
February	1st to 10th	Day	16% 9% 5% 9% 5% 2 5% 5% 5% 5% 34%	1620
	11th to 20th	Day	15% 9% 4 6% 6% 3 5% 4 6% 6% 36%	1730
	21st to end	Day	15% 10% 3 7% 5% 3 4 4 6% 6% 38%	1480
March	1st to 10th	Day	14% 9% 3 7% 6% 3 4 4 4 6% 41%	1828
	11th to 20th	Day	19% 11% 3 6% 6% 3 4 4 4 5% 35%	1980
	21st to end	Day	20% 10% 5% 8% 6% 3 5% 5% 5% 6% 29%	2289
April	1st to 10th	Day	10% 5% 3 5% 6% 3 6% 5% 7% 7% 43%	2160
	11th to 20th	Day	16% 8% 3 6% 5% 2 5% 5% 4 6% 40%	2134
	21st to end	Day	18% 7% 3 5% 6% 3 6% 4 4 6% 37%	2160
May	1st to 10th	Day	17% 6% 3 5% 6% 4 6% 6% 6% 7% 36%	2200
	11th to 20th	Day	16% 5% 2 5% 5% 3 5% 4 6% 8% 40%	2447
	21st to end	Day	10% 5% 2 7% 6% 4 6% 7% 6% 10% 37%	2725
June	1st to 10th	Day	8% 5% 2 5% 5% 3 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	7% 4 1 5% 4 3 5% 6% 6% 10% 49%	2520
	21st to end	Day	4 3 2 5% 6% 4 5% 7% 7% 11% 47%	2520
July	1st to 10th	Day	9% 4 2 4 5% 3 6% 6% 8% 10% 43%	2520
	11th to 20th	Day	4 3 1 4 4 4 6% 5% 6% 11% 51%	2520
	21st to end	Day	8% 5% 2 5% 5% 3 6% 5% 6% 9% 45%	2598
August	1st to 10th	Day	7% 5% 2 5% 5% 4 6% 7% 8% 10% 42%	2320
	11th to 20th	Day	9% 4 2 6% 6% 4 6% 6% 7% 10% 40%	2125
	21st to end	Day	8% 4 2 5% 5% 2 4 5% 5% 9% 50%	2376
September	1st to 10th	Day	14% 5% 2 4 4 3 4 4 5% 7% 48%	2160
	11th to 20th	Day	9% 5% 2 5% 4 3 4 4 6% 9% 49%	2138
	21st to end	Day	6% 4 2 5% 5% 2 5% 4 5% 7% 55%	1973
October	1st to 10th	Day	9% 5% 2 4 5% 3 4 3 5% 6% 54%	1800
	11th to 20th	Day	14% 6% 2 4 4 3 3 4 4 6% 51%	1800
	21st to end	Day	17% 8% 2 4 5% 3 4 2 4 5% 46%	1970
November	1st to 10th	Day	10% 4 2 4 4 3 4 3 5% 6% 55%	1672
	11th to 20th	Day	14% 5% 3 5% 5% 2 4 4 4 7% 47%	1710
	21st to end	Day	15% 10% 3 5% 5% 3 4 4 3 6% 41%	1644
December	1st to 10th	Day	13% 10% 3 6% 4 3 5% 4 5% 8% 39%	1520
	11th to 20th	Day	13% 10% 5% 6% 6% 3 4 4 5% 6% 38%	1918
	21st to end	Day	19% 13% 5% 8% 6% 4 4 4 4 6% 27%	2783
January	1st to 10th	Night	13% 8% 4 7% 6% 4 4 5% 4 6% 39%	2648
	11th to 20th	Night	16% 9% 4 8% 6% 3 5% 4 4 5% 36%	2420
	21st to end	Night	12% 10% 5% 8% 6% 3 4 5% 5% 6% 38%	2574
February	1st to 10th	Night	17% 10% 4 8% 5% 3 4 4 5% 5% 34%	2340
	11th to 20th	Night	15% 7% 4 7% 5% 3 4 4 4 6% 41%	2113
	21st to end	Night	17% 9% 3 8% 6% 3 4 3 3 6% 38%	1776
March	1st to 10th	Night	15% 9% 3 6% 5% 3 4 3 3 5% 43%	2146
	11th to 20th	Night	20% 7% 3 6% 5% 3 5% 4 5% 5% 37%	1980
	21st to end	Night	19% 10% 3 7% 5% 4 5% 4 5% 5% 32%	2066
April	1st to 10th	Night	11% 6% 3 5% 5% 3 4 5% 5% 7% 48%	1800
	11th to 20th	Night	13% 6% 3 6% 6% 3 4 4 6% 7% 44%	1775
	21st to end	Night	20% 7% 3 5% 4 2 3 3 4 7% 41%	1800
May	1st to 10th	Night	15% 7% 3 5% 4 2 5% 4 5% 7% 43%	1758
	11th to 20th	Night	15% 7% 2 5% 4 3 3 5% 5% 8% 44%	1445
	21st to end	Night	8% 6% 3 6% 5% 4 6% 5% 6% 9% 42%	1551
June	1st to 10th	Night	8% 4 2 5% 5% 3 5% 4 6% 10% 49%	1440
	11th to 20th	Night	6% 4 2 3 4 3 4 5% 5% 9% 56%	1440
	21st to end	Night	4 3 1 3 4 3 4 5% 6% 9% 55%	1440
July	1st to 10th	Night	9% 3 2 4 4 3 4 5% 6% 10% 50%	1440
	11th to 20th	Night	5% 5% 2 5% 3 3 4 4 5% 11% 54%	1440
	21st to end	Night	6% 4 2 5% 5% 3 5% 5% 6% 10% 50%	1716
August	1st to 10th	Night	6% 3 2 4 5% 3 4 5% 7% 9% 52%	1619
	11th to 20th	Night	5% 5% 2 5% 5% 3 5% 5% 6% 9% 50%	1776
	21st to end	Night	5% 4 2 3 4 3 4 4 5% 8% 56%	1980
September	1st to 10th	Night	12% 4 1 5% 4 2 4 4 4 6% 53%	1800
	11th to 20th	Night	8% 4 2 4 5% 2 5% 4 5% 7% 53%	1803
	21st to end	Night	8% 4 2 4 4 2 4 4 5% 7% 56%	1984
October	1st to 10th	Night	8% 4 2 4 4 2 3 4 4 8% 57%	2160
	11th to 20th	Night	13% 6% 2 4 3 3 2 4 4 7% 52%	2160
	21st to end	Night	18% 7% 2 4 3 2 3 4 4 4 47%	2384
November	1st to 10th	Night	11% 5% 1 4 4 2 3 3 5% 5% 57%	2406
	11th to 20th	Night	15% 5% 2 4 5% 3 4 3 4 6% 49%	2470
	21st to end	Night	18% 8% 3 5% 4 2 3 4 4 6% 44%	2531
December	1st to 10th	Night	15% 11% 4 6% 5% 2 4 5% 5% 7% 37%	2660
	11th to 20th	Night	16% 8% 4 6% 5% 4 5% 3 4 5% 41%	3279
	21st to end	Night	17% 17% 5% 9% 7% 3 4 5% 5% 5% 23%	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	47% 6% 12% 21% 12% 2	1518
	11th to 20th	Day	50% 6% 12% 23% 9% 1	1582
	21st to end	Day	46% 5% 13% 23% 11% 2	1782
February	1st to 10th	Day	50% 5% 11% 22% 10% 1	1620
	11th to 20th	Day	48% 5% 11% 20% 13% 4	1740
	21st to end	Day	47% 5% 9% 23% 12% 4	1480
March	1st to 10th	Day	45% 4 10% 22% 16% 3	1828
	11th to 20th	Day	52% 4 10% 18% 14% 2	1980
	21st to end	Day	56% 6% 12% 16% 9% 1	2289
April	1st to 10th	Day	37% 6% 12% 26% 18% 1	2160
	11th to 20th	Day	44% 5% 10% 23% 14% 4	2134
	21st to end	Day	47% 6% 10% 23% 13% 1	2160
May	1st to 10th	Day	46% 9% 12% 23% 10% 1	2200
	11th to 20th	Day	41% 8% 12% 23% 14% 2	2451
	21st to end	Day	40% 9% 15% 21% 13% 2	2725
June	1st to 10th	Day	34% 8% 13% 26% 18% 2	2520
	11th to 20th	Day	29% 8% 13% 25% 22% 3	2520
	21st to end	Day	28% 10% 18% 24% 15% 6%	2520
July	1st to 10th	Day	32% 8% 17% 25% 13% 4	2451
	11th to 20th	Day	25% 9% 15% 26% 20% 3	2445
	21st to end	Day	33% 8% 13% 28% 15% 2	2454
August	1st to 10th	Day	33% 10% 14% 27% 16% 1	2306
	11th to 20th	Day	37% 8% 13% 27% 14% 1	2125
	21st to end	Day	31% 7% 15% 24% 18% 5%	2376
September	1st to 10th	Day	34% 6% 11% 26% 18% 5%	2160
	11th to 20th	Day	32% 6% 10% 26% 24% 2	2138
	21st to end	Day	28% 6% 10% 28% 25% 3	1973
October	1st to 10th	Day	31% 5% 10% 25% 25% 4	1800
	11th to 20th	Day	34% 4 10% 24% 21% 6%	1800
	21st to end	Day	41% 3 8% 27% 17% 4	1970
November	1st to 10th	Day	31% 4 13% 26% 20% 6%	1672
	11th to 20th	Day	37% 5% 9% 23% 21% 5%	1710
	21st to end	Day	44% 4 9% 26% 15%	1644
December	1st to 10th	Day	44% 5% 12% 26% 12% 1	1520
	11th to 20th	Day	47% 5% 10% 22% 15% 2	1915
	21st to end	Day	58% 6% 10% 15% 9% 1	2783
January	1st to 10th	Night	46% 5% 10% 23% 15% 1	2648
	11th to 20th	Night	51% 4 9% 24% 12% 1	2420
	21st to end	Night	46% 5% 13% 22% 12% 1	2574
February	1st to 10th	Night	52% 5% 9% 21% 11% 1	2340
	11th to 20th	Night	45% 5% 10% 21% 17% 3	2114
	21st to end	Night	48% 4 11% 20% 12% 4	1776
March	1st to 10th	Night	45% 4 8% 23% 16% 3	2146
	11th to 20th	Night	48% 6% 9% 21% 13% 3	1980
	21st to end	Night	53% 7% 11% 19% 9% 1	2066
April	1st to 10th	Night	35% 6% 11% 27% 18% 3	1800
	11th to 20th	Night	40% 5% 10% 24% 17% 4	1775
	21st to end	Night	45% 5% 8% 24% 16% 2	1800
May	1st to 10th	Night	40% 7% 12% 23% 16% 2	1758
	11th to 20th	Night	39% 7% 13% 24% 16% 2	1446
	21st to end	Night	37% 9% 15% 20% 16% 3	1552
June	1st to 10th	Night	30% 7% 15% 27% 18% 3	1440
	11th to 20th	Night	25% 7% 13% 28% 25% 4	1440
	21st to end	Night	24% 7% 15% 29% 18% 7%	1440
July	1st to 10th	Night	30% 7% 15% 28% 15% 5%	1400
	11th to 20th	Night	25% 7% 16% 27% 21% 4	1392
	21st to end	Night	28% 7% 14% 30% 19% 2	1621
August	1st to 10th	Night	27% 9% 16% 32% 15% 2	1609
	11th to 20th	Night	29% 7% 15% 26% 21% 2	1776
	21st to end	Night	26% 6% 15% 25% 23% 5%	1980
September	1st to 10th	Night	33% 5% 10% 25% 21% 6%	1800
	11th to 20th	Night	30% 6% 10% 25% 26% 4	1803
	21st to end	Night	28% 6% 9% 24% 28% 4	1984
October	1st to 10th	Night	27% 4 11% 26% 27% 5%	2160
	11th to 20th	Night	33% 4 7% 27% 21% 7%	2160
	21st to end	Night	40% 4 9% 20% 21% 4	2384
November	1st to 10th	Night	30% 4 12% 25% 23% 6%	2406
	11th to 20th	Night	37% 4 8% 24% 23% 4	2470
	21st to end	Night	42% 4 10% 24% 18% 2	2531
December	1st to 10th	Night	46% 6% 10% 24% 12% 1	2660
	11th to 20th	Night	46% 4 10% 23% 16% 1	3281
	21st to end	Night	60% 6% 10% 15% 8% 1	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	23% 17% 33% 20% 7% 1	270
	11th to 20th	Day	28% 13% 40% 17% 2	246
	21st to end	Day	19% 20% 41% 17% 4	264
February	1st to 10th	Day	25% 18% 40% 14% 4	240
	11th to 20th	Day	24% 22% 31% 16% 6%	240
	21st to end	Day	26% 17% 37% 18% 3	198
March	1st to 10th	Day	18% 17% 48% 13% 4	240
	11th to 20th	Day	33% 13% 34% 14% 5% 1	240
	21st to end	Day	29% 16% 30% 19% 6%	375
April	1st to 10th	Day	18% 12% 39% 21% 10%	420
	11th to 20th	Day	21% 13% 32% 21% 12%	412
	21st to end	Day	24% 11% 35% 21% 9%	420
May	1st to 10th	Day	19% 12% 29% 28% 10% 1	423
	11th to 20th	Day	19% 7% 29% 24% 16% 4	593
	21st to end	Day	12% 4 29% 32% 16% 8%	679
June	1st to 10th	Day	11% 4 18% 31% 28% 8%	630
	11th to 20th	Day	9% 3 20% 39% 22% 8%	630
	21st to end	Day	5% 5% 26% 35% 22% 7%	630
July	1st to 10th	Day	10% 1 12% 26% 32% 18%	621
	11th to 20th	Day	6% 2 16% 37% 30% 9%	618
	21st to end	Day	9% 1 15% 35% 31% 8%	684
August	1st to 10th	Day	10% 2 13% 35% 31% 10%	618
	11th to 20th	Day	11% 3 13% 27% 35% 11%	439
	21st to end	Day	9% 2 12% 27% 36% 13%	495
September	1st to 10th	Day	15% 3 14% 27% 31% 11%	450
	11th to 20th	Day	8% 2 12% 31% 32% 15%	450
	21st to end	Day	8% 8% 19% 31% 23% 11%	443
October	1st to 10th	Day	14% 7% 23% 37% 14% 4	270
	11th to 20th	Day	17% 14% 34% 24% 11%	270
	21st to end	Day	31% 16% 24% 21% 7%	297
November	1st to 10th	Day	13% 9% 32% 29% 13% 4	270
	11th to 20th	Day	18% 18% 30% 20% 12% 2	270
	21st to end	Day	25% 14% 29% 21% 10% 1	270
December	1st to 10th	Day	16% 17% 38% 18% 7% 4	270
	11th to 20th	Day	23% 13% 35% 23% 4 1	270
	21st to end	Day	28% 18% 36% 14% 3 1	297
January	1st to 10th	Night	19% 13% 39% 24% 5%	950
	11th to 20th	Night	22% 15% 35% 23% 5%	911
	21st to end	Night	18% 13% 40% 26% 2	990
February	1st to 10th	Night	23% 13% 37% 25% 3	900
	11th to 20th	Night	20% 14% 41% 25% 1	718
	21st to end	Night	21% 14% 39% 24% 2	592
March	1st to 10th	Night	21% 12% 37% 25% 4	706
	11th to 20th	Night	22% 10% 36% 26% 5%	540
	21st to end	Night	26% 9% 32% 28% 5%	594
April	1st to 10th	Night	16% 11% 38% 29% 6%	540
	11th to 20th	Night	17% 9% 35% 28% 11%	533
	21st to end	Night	22% 6% 38% 27% 7%	540
May	1st to 10th	Night	18% 6% 30% 35% 10% 1	540
	11th to 20th	Night	19% 4 24% 36% 16% 1	531
	21st to end	Night	11% 4 22% 40% 21% 3	584
June	1st to 10th	Night	8% 3 17% 43% 27% 1	540
	11th to 20th	Night	7% 3 18% 49% 23% 1	540
	21st to end	Night	5% 2 23% 44% 24% 2	540
July	1st to 10th	Night	10% 1 8% 38% 35% 8%	525
	11th to 20th	Night	6% 2 12% 44% 33% 3	522
	21st to end	Night	7% 2 13% 42% 33% 3	591
August	1st to 10th	Night	7% 1 9% 43% 36% 3	537
	11th to 20th	Night	7% 2 10% 40% 37% 4	534
	21st to end	Night	6% 2 9% 38% 40% 5%	594
September	1st to 10th	Night	14% 2 11% 37% 30% 6%	540
	11th to 20th	Night	9% 3 13% 33% 36% 5%	543
	21st to end	Night	10% 5% 21% 32% 28% 4	720
October	1st to 10th	Night	9% 4 26% 33% 25% 4	720
	11th to 20th	Night	17% 8% 31% 31% 11% 1	720
	21st to end	Night	24% 9% 31% 29% 7% 1	792
November	1st to 10th	Night	13% 7% 35% 33% 11% 1	740
	11th to 20th	Night	17% 13% 31% 30% 9%	760
	21st to end	Night	23% 9% 34% 28% 6% 1	821
December	1st to 10th	Night	22% 10% 34% 29% 5% 1	950
	11th to 20th	Night	23% 9% 29% 33% 6%	950
	21st to end	Night	25% 13% 34% 25% 3	1045

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